TECHNICAL FIELD

The technical field generally relates to the solution-processed design of nanoparticles and/or seeds, and more specifically concerns the solution-phase synthesis of nanoparticles and/or seeds having at least an inorganic or a metal -based portion, such as an inorganic or a metal core.

BACKGROUND

Solution-phase syntheses of inorganic nanoparticles (NPs) generally require capping agents to maintain the NPs as discrete colloids. However, these capping agents influence the formation of the NPs and are relatively difficult to displace. The association between the synthesis of NPs and the use of capping agents limits the range of NPs that may be obtained using existing approaches.

Challenges still exist in the field of solution-phase syntheses of NPs.

SUMMARY

In accordance with an aspect, there is provided a method for preparing nanoparticles, the method comprising: providing a seed solution, the seed solution comprising nanoparticle’s seeds; adding the seed solution to a growth solution to obtain the nanoparticles from the nanoparticle’s seeds, each nanoparticle having, in the growth solution: an inorganic core; and a transitory ligand transiently adsorbed to the inorganic core; and substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core.

In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic core according to a periodic sequence, an aperiodic sequence or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent. In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is comprised in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule.

In some embodiments, the transitory ligand is acetone.

In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether.

In some embodiments, the transitory ligand is a non-ionic compound.

In some embodiments, the transitory ligand has a denticity lower or equal than 2.

In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, substituting the transitory ligand comprises removing the transitory ligand, said removing the transitory ligand comprising drop-casting the nanoparticles on a substrate to evaporate the transitory ligand.

In some embodiments, said substituting the transitory ligand comprises quantitively displacing the transitory ligand, the capping agent being chemically compatible with the inorganic core.

In some embodiments, the nanoparticle’s seeds and the nanoparticles each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure.

In some embodiments, the nanoparticle’s seeds and the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped

In some embodiments, the nanoparticle’s seeds and the nanoparticles are metallic.

In some embodiments, the nanoparticle’s seeds and the nanoparticles comprise Au.

In some embodiments, the nanoparticle’s seeds and the nanoparticles comprise Au and Pd. In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the seed solution is an aqueous seed solution.

In some embodiments, the growth solution is an aqueous growth solution.

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®.

In some embodiments, the seed solution comprises acetone, a solvent, a metal precursor, and a reducing agent.

In some embodiments, the seed solution comprises at least acetone, Nal, water, HAuCU and NaBH .

In some embodiments, the seed solution comprises at least acetone, NaBr, water, H A11CI4 and NaBH ₄ .

In some embodiments, the seed solution comprises at least HA11CI4. trisodium citrate, water and NaBH ₄ .

In some embodiments, the growth solution comprises acetone, a solvent, a metal precursor, and a reducing agent.

In some embodiments, the growth solution comprises at least one of acetone, Nal, water, HA11CI4. HC1 and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HA11CI4. HC1 and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HA11CI4. NaOH and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HA11CI4. HC1, AgNOs and HQ.

In some embodiments, the growth solution comprises at least acetone, water and HQ.

In some embodiments, the growth solution comprises at least acetone, water, HA11CI4. K^PdCU and HA11CI4.

In some embodiments, the growth solution comprises at least acetone, water, K^PdCB, HQ and HA11CI4. In some embodiments, the growth solution comprises at least acetone water, AgNOs, HA, HAiiCU and K ₂ PdCl ₄ .

In some embodiments, the capping agent is provided in a capping agent solution.

In some embodiments, the capping agent solution is an aqueous solution.

In some embodiments, the capping agent solution is an organic-solvent solution

In some embodiments, the capping agent solution is a THF-based solution.

In some embodiments, the capping agent solution is a DMSO-based solution.

In some embodiments, the method further comprises adding the growth solution to the capping agent solution.

In some embodiments, said adding the growth solution to the capping agent solution is carried out at room temperature.

In accordance with an aspect, there is provided a method for preparing nanoparticle’s seeds, the method comprising: mixing a seed solution with a transitory ligand solution, the seed solution comprising the nanoparticle’s seeds, each nanoparticle’s seed having an inorganic core, the transitory ligand solution comprising a transitory ligand, the transitory ligand being transiently adsorbed to the inorganic core in the seed solution; and substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core according to a periodic sequence, an aperiodic sequence or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent.

In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is comprised in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule. In some embodiments, the transitory ligand is acetone.

In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether.

In some embodiments, the transitory ligand is a non-ionic compound.

In some embodiments, the transitory ligand has a denticity lower or equal than 2.

In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, said substituting the transitory ligand comprises removing the transitory ligand, said removing the transitory ligand comprising drop-casting the nanoparticle’s seeds on a substrate to evaporate the transitory ligand.

In some embodiments, said substituting the transitory ligand comprises quantitively displacing the transitory ligand, the capping agent being chemically compatible with the inorganic core.

In some embodiments, the nanoparticle’s seeds each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure.

In some embodiments, the nanoparticle’s seeds are spherical, icosahedral, octahedral, rod shaped, or star shaped.

In some embodiments, the nanoparticle’s seeds are metallic.

In some embodiments, the nanoparticle’s seeds comprise Au.

In some embodiments, the nanoparticle’s seeds comprise Au and Pd.

In some embodiments, the seed solution is an aqueous seed solution.

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®. In some embodiments, the seed solution comprises acetone, a solvent, a metal precursor, and a reducing agent.

In some embodiments, the seed solution comprises at least acetone, Nal, water, HAuCU and NaBH ₄ .

In some embodiments, the seed solution comprises at least acetone, NaBr, water, H AuCI ₄ and NaBH ₄ .

In some embodiments, the seed solution comprises at least HA11CI4. trisodium citrate, water and NaBH ₄ .

In some embodiments, the capping agent is provided in a capping agent solution.

In some embodiments, the capping agent solution is an aqueous solution.

In some embodiments, the capping agent solution is an organic-solvent solution.

In some embodiments, the capping agent solution is a THF-based solution.

In some embodiments, the capping agent solution is a DMSO-based solution.

In accordance with an aspect, there is provided a method for preparing nanoparticles, the method comprising: mixing a growth solution with a transitory ligand solution, the growth solution comprising the nanoparticles, each nanoparticle having an inorganic core, the transitory ligand solution comprising a transitory ligand, the transitory ligand being transiently adsorbed to the inorganic core in the growth solution; and substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core.

In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic core according to a periodic sequence, an aperiodic sequence or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent.

In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is comprised in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule. In some embodiments, the transitory ligand is acetone.

In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether.

In some embodiments, the transitory ligand is a non-ionic compound.

In some embodiments, the transitory ligand has a denticity lower or equal than 2.

In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, said substituting the transitory ligand comprises removing the transitory ligand, said removing the transitory ligand comprising drop-casting the nanoparticles on a substrate to evaporate the transitory ligand.

In some embodiments, substituting the transitory ligand comprises quantitively displacing the transitory ligand, the capping agent being chemically compatible with the inorganic core.

In some embodiments, the nanoparticles each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure.

In some embodiments, the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped.

In some embodiments, the nanoparticles are metallic.

In some embodiments, the nanoparticles comprise Au.

In some embodiments, the nanoparticles comprise Au and Pd.

In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the growth solution is an aqueous growth solution.

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®.

In some embodiments, the growth solution comprises acetone, a solvent, a metal precursor, and a reducing agent.

In some embodiments, the growth solution comprises at least one of acetone, Nal, water, HAuCU. HC1 and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HAuCU. HC1 and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HA11CI4. NaOH and HQ.

In some embodiments, the growth solution comprises at least acetone, NaBr, water, HAuCU, HC1, AgNOs and HQ.

In some embodiments, the growth solution comprises at least acetone, water and HQ.

In some embodiments, the growth solution comprises at least acetone, water, HAuCU. K^PdCU and HAuCU.

In some embodiments, the growth solution comprises at least acetone, water, K^PdCB, HQ and HAuCU.

In some embodiments, the growth solution comprises at least acetone water, AgNOs, HA, HAuCU. and K ₂ PdCl ₄ .

In some embodiments, the capping agent is provided in a capping agent solution.

In some embodiments, the capping agent solution is an aqueous solution.

In some embodiments, the capping agent solution is an organic-solvent solution.

In some embodiments, the capping agent solution is a THF-based solution.

In some embodiments, the capping agent solution is a DMSO-based solution.

In some embodiments, further comprises adding the growth solution to the capping agent solution.

In some embodiments, said adding the growth solution to the capping agent solution is carried out at room temperature. In accordance with an aspect, there is provided a method for growing nanoparticle’s seeds or nanoparticles, the method comprising: mixing a first solution with a second solution, the first solution comprising at least one of the nanoparticle’s seeds or the nanoparticles, the second solution comprising a transitory ligand, the transitory ligand being transiently adsorbed to an inorganic portion of said at least one of the nanoparticle’s seeds and the nanoparticles when the first solution is mixed with the second solution; and substituting the transitory ligand with a capping agent.

In some embodiments, the inorganic portion is an inorganic core of the nanoparticle’s seeds or the nanoparticles.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic portion.

In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic portion according to a periodic sequence, an aperiodic sequence or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent.

In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is comprised in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule.

In some embodiments, the transitory ligand is acetone.

In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether.

In some embodiments, the transitory ligand is a non-ionic compound.

In some embodiments, the transitory ligand has a denticity lower or equal than 2.

In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol. In some embodiments, said substituting the transitory ligand comprises removing the transitory ligand, said removing the transitory ligand comprising drop-casting the nanoparticles on a substrate to evaporate the transitory ligand.

In some embodiments, said substituting the transitory ligand comprises quantitively displacing the transitory ligand, the capping agent being chemically compatible with the inorganic portion.

In some embodiments, the nanoparticle’s seeds and the nanoparticles each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure.

In some embodiments, the nanoparticle’s seeds and the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped

In some embodiments, the nanoparticle’s seeds and the nanoparticles are metallic.

In some embodiments, the nanoparticle’s seeds or the nanoparticles comprise Au.

In some embodiments, the nanoparticle’s seeds or the nanoparticles comprise Au and Pd.

In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the first solution is an aqueous solution.

In some embodiments, the second solution is an aqueous solution.

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®.

In some embodiments, the first solution comprises acetone, a solvent, a metal precursor, and a reducing agent.

In some embodiments, the capping agent is provided in a third solution.

In some embodiments, the third solution is an aqueous solution. In some embodiments, the third solution is an organic-solvent solution

In some embodiments, the method comprises further adding the third solution to the first solution and the solution.

In some embodiments, said adding the third solution is carried out at room temperature.

In accordance with an aspect, there is provided a nanoparticle’s seed or a nanoparticle produced according to the techniques herein described.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures la and lb are schematic illustrations of the experimental workflow (a) and reaction pathway for transitory synthesis, which spatiotemporally separates capping from nucleation and growth (b). A transitory ligand, such as acetone, adsorbs weakly and transiently to NP surfaces to facilitate synthesis. After growth completion, the colloidal NPs are added to a solution of any chemically compatible capping agent, which quantitatively displaces the transitory ligand, a process termed transitory exchange. NPs grown via this pathway can be separately added to different capping agents to efficiently construct large NP libraries. NPs can also be drop-cast onto a substrate before transitory ligand removal, including by evaporation, for molecularly bare NPs. Transitory synthesis enables for modular, pick-and-choose capabilities between the NP size, shape, and elemental composition and then the final surface features via capping.

Figure 2 shows a comparison of the capabilities of transitory synthesis with those of conventional pathways in the synthesis of colloidal metal NCs.

Figures 3ato 3e are snapshots ofMD simulations ofthe adsorption interactions of acetone with (a) Au(l 11), (b) Au(100), (c) Au(110), and (d) Au(210). (e) DFT-calculated binding energies of acetone and water to various Au facets. NB, non-binding.

Figures 4a to h present a transitory synthesis of a library of colloidal Au NPs with various capping agents. Model, SE-STEM image, HAADF-STEM image, and low-magnification STEM images of Au NPs with (a) spherical, (c) icosahedral, (e) octahedral, and (g) star shapes. These NPs were each capped with 1 in (i) for transitory exchange. Structural characterization ofthe (b) spherical, (d) icosahedral, (f) octahedral, and (h) star Au NPs after transitory exchange with the (i) library of organic capping agents, which includes sodium citrate 1, PVP 2, CTAB 3, PLA 4, SDS 5, MUTAB 6, Pluronic F127 7, PS-thiol 8, and Tween 80 9. The size and shape measurements are shown to the right of the respective plot. The open circles in various colors represent raw data, while black filled circles and bars represent the mean ± SD. (j) ATR-IR characterization of the quantitative transitory exchange of acetone with capping agents 3 and 6 on representative Au NPs. Au foil was used as a substrate to show the quantitative desorption of acetone after evaporation (gold curve). Representations of acetone as (k) neat molecules and (1) adsorbed in the r|l(O) orientation as determined via their C=O stretching modes.

Figures 5a to 5o present a transitory synthesis of colloidal heterostructured AuPd NPs with various capping agents. SE-STEM image, HAADF-STEM image, and EDX elemental maps of a single NP and low- magnification STEM images for (a-c) conformal core/shell AuPd icosahedra, (d-f) AuPd icosahedra with divots, (g-i) grain-separated AuPdAu NPs, (j-1) island-shell PdAu NPs, and (m-o) dough-shell PdAu NPs. The elemental intensity profiles were taken from the dashed boxed area shown in the respective EDX map and represent the relative intensity for Au and Pd, separately. These NPs were each capped with sodium citrate (1 in Figure le) for transitory exchange. The arrows in (d) denote twin planes.

Figure 6a to 6j present a transitory synthesis of colloidal heterostructured AuPdAg NPs with various capping agents, (a) SE- and HAADF-STEM images, (b) overlay EDX elemental map, (c) unary and binary XPS elemental maps, (d) low-magnification HAADF-STEM image, (e) BF-TEM image, (f) single-particle SAED pattern, and (g,h) HRTEM images of the green and pink boxed areas shown in (e) and their (i,j) FFT patterns for AuPdAg NPs composed of a hollow, porous Au frame, intermediate Pd layer, and protruding Ag crystallites. The elemental intensity profiles were taken from the dashed boxed area shown in the EDX map and represent the relative intensity for Au, Pd, and Ag, separately. These NPs were capped with sodium citrate (1 in Figure le) for transitory exchange. UV exposure slightly etched the Ag crystallites to expose the intermediate Pd layer for the NP shown in (a-d). A pristine AuPdAg NP is shown in (e). For SAED and FFT indexing, the color text represents elements: red (Pd), gold (Au), Ag (blue) and Au or Ag undefined (white).

Figure 7 is an image of vials filled with various Au NPs grown through the transitory synthesis pathway and capped with citrate.

Figures 8A-E show the reagent roles in the transitory growth formulation. The synthesis formulation was used without various components to show the role of each component, (a) No nucleation or growth in the absence of seed, (b) No growth in the absence of the reducing agent, hydroquinone (HQ), (c) No growth in the absence of the metal precursor, HAuC14. (d) In the absence of acetone, spontaneous nucleation occurs immediately, including in the absence of seed, (e) With all components of the growth formulation and added HC1, nanoplasmonic color development is observed for the growth of colloidal Au NCs.

Figures 9A-B show the inhibition of NC nucleation in the presence of acetone in the growth formulation, (a) Relationship between the time of autonucleation, defined as the appearance of nanoplasmonic color, in the absence of seed in the growth formulation and the concentration of acetone (N = 3 independent replicates for each concentration). Autonucleation with 0% v/v acetone in the growth formulation is shown in Figure 8d. (b) The influence of acetone on the oxidation peak potential of hydroquinone (HQ), the reducing agent in our growth formulation, in linear sweep voltammetry (N = 3 independent replicates for each concentration). The data from each plot had an exponential relationship with % acetone (v/v), and the Pearson correlation coefficient (r) and P-value for regression are shown (P < 0.05, statistically significance).

Figure 10 illustrates the NPs stability after transitory exchange. Au nanospheres were synthesized via transitory synthesis and underwent transitory exchange with various capping agents. The original sample was left in the leftmost vial and, since it was not added to any capping agent, the NPs are no longer stable, as observed through the presence of no nanoplasmonic color and macroscopic NP aggregates.

Figures 11 A-C show AuPd core-shell icosahedral NPs with thick Pd shell, (a) SE-STEM (left), HAADF- STEM (center), and BF-STEM (right) images of a Au icosahedral NP coated with a Pd shell, grown in the presence of Br. The NPs were capped with citrate. The molar ratio of Au and Pd precursor added is 1 and 2, respectively, leading to a thicker Pd shell than the NPs in Figure 4a. Scale bar, 10 nm. (b) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (a), (c) Large-area SE-STEM (left), HAADF- STEM (center) and BF-STEM (right) images of AuPd core-shell icosahedral NPs that have been capped with citrate. Scale bar, 50 nm.

Figures 12A-B show AuPd NPs with a bumpy Pd shell on Au icosahedral core, (a) SE-STEM (left), HAADF-STEM (center), and BF-STEM (right) images of a Au icosahedral NP coated with Pd, which was grown in the absence of Br. The molar ratio of Au and Pd added are 1 and 1, respectively. Scale bar, 5 nm. (b) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the AuPd NPs. Scale bar, 50 nm. These NPs were capped with citrate. The Pd layer is bumpier than when it is grown with Br.

Figures 13A-C are micrographs of golf-ball-like AuPd NPs. (a) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPd icosahedra with divots. These NPs were capped with citrate during transitory exchange. The NP has developed slight carbon contamination during imaging. Scale bar, 10 nm. (b) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of two AuPd icosahedra with divots capped with citrate. The NPs have developed slight carbon contamination during imaging. Scale bar, 10 nm. (c) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPd icosahedra with divots that have been capped with citrate. Scale bar, 200 nm.

Figures 14A-B show AuPdAu NPs with a conformal PdAu shell on Au icosahedral core, grown with Br. (a) SE-STEM (left), HAADF-STEM (center), and BF-STEM (right) images of a Au icosahedral NP coated with a smooth, conformal PdAu shell, which was grown in the presence of Br. The molar ratio of Au, Pd and Au precursors added are 1, 1 and 1, respectively. Scale bar, 10 nm. (b) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the AuPdAu NPs. Scale bar, 50 nm. The NPs were capped with citrate.

Figures 15A-E show AuPdAu NPs with a grainy PdAu shell on Au icosahedral core, (a) SE-STEM (left), HAADF-STEM (center), and BF-STEM (right) images of a Au icosahedral NP coated with Pd and Au grains. The molar ratio of Au, Pd and Au added are 1, 1 and 1, respectively. Scale bar, 10 nm. (b) EDX maps of Au, Pd and an overlay of the elements for another AuPdAu NP from the sample shown in (a), (c) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPdAu NPs. Scale bar, 200 nm. (d) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images taken at higher resolution at the areas depicted by the color boxes in (c). Scale bar, 50 nm. (e) SE-STEM (left), HAADF- STEM (center) and BF-STEM (right) images of a single layer of AuPdAu NPs. Scale bar, 50 nm. These NPs were capped with citrate.

Figures 16A-D show bumpy Pd NPs with progressively grown Au islands, (a) SE-STEM (top) and HAADF- STEM (bottom) images of bumpy Pd NP. Scale bar, 10 nm. (b) SE-STEM (top) and HAADF-STEM (bottom) images of bumpy Pd core with Au grown on its surface (elemental ratio of Pd and Au added, 1 to 0.01). (c) SE-STEM (top) and HAADF-STEM (bottom) images of bumpy Pd core with Au grown on its surface (elemental ratio of Pd and Au added, 1 to 0.02). (d) SE-STEM (top) and HAADF-STEM (bottom) images of bumpy Pd core with Au grown on its surface (elemental ratio of Pd and Au added, 1 to 0.1). (e) Large-area SE-STEM (top) and HAADF-STEM (bottom) images of the NPs shown in (a). Scale bar, 50 nm. (f) Large-area SE-STEM (top) and HAADF-STEM (bottom) images of the NPs shown in (b). (g) Large- area SE-STEM (top) and HAADF-STEM (bottom) images of the NPs shown in (c). (h) Large-area SE- STEM (top) and HAADF-STEM (bottom) images of the NPs shown in (d). The NPs were all capped with citrate.

Figures 17A-B are large-area micrographs Pd NPs (elemental ratio, 1 to 0.1) with Au islands, (a) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the Pd NPs coated with a shell of Au islands. The molar ratio of Pd and Au added is 1 and 0.1, respectively. Scale bar, 200 nm. (b) SE- STEM (left), HAADF-STEM (center) and BF-STEM (right) images taken at higher resolution at the areas depicted by the color boxes in (a). Scale bar, 50 nm. These NPs were capped with citrate.

Figures 18A-E are micrographs of PdAu NPs (elemental ratio, 1 to 0.5) with granular Au shell, (a) SE- STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a Pd NP coated with a shell of Au grains. The molar ratio of Pd and Au added is 1 and 0.5, respectively. Scale bar, 10 nm. (b) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (a), (c) Large-area SE-STEM (left), HAADF- STEM (center) and BF-STEM (right) images of the PdAu NPs. Scale bar, 200 nm. (d) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images taken at higher resolution at the areas depicted by the color boxes in (c). Scale bar, 50 nm. These NPs were capped with citrate, (e) SE-STEM (left), HAADF- STEM (center) and BF-STEM (right) images of the PdAu NPs at another area on the grid, in which many of the NPs form a single layer and facilitate inspection in HAADF- and BF-STEM. Scale bar, 50 nm.

Figures 19A-D are large-area micrographs of PdAu NPs (elemental ratio, 1 to 1) with dough-like Au shell.

(a) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of additional Pd NPs coated with dough-like Au shell The molar ratio of Pd and Au added is 1 and 1, respectively. NPs grown using this formulation primarily have elongated valleys in the Au shell (yellow arrows). Some NPs present holes in the Au shell (blue arrow). Scale bar, 20 nm. (b) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the PdAu NPs. Scale bar, 50 nm. (c)Large-area high-contrast (hc)-SE-STEM image of the PdAu NPs. Scale bar, 200 nm. (d) hc-SE-STEM (left) and SE-STEM images taken at higher resolution at the area depicted by the color box in (C). The he micrographs are used to better resolve the elongated valleys of the Au shells. Scale bar, 50 nm. These NPs were capped in citrate.

Figures 20A-G are micrographs of PdAu NPs (elemental ratio, 1 to 1.25) with a filled Au shell, (a) SE- STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a Pd NP coated with a Au shell and capped with citrate. The molar ratio of Pd and Au added is 1 and 1.25, respectively. Further reduction of Au on the PdAu NPs shown in fig. SJ fills the elongated valleys, developing towards a conformal Au shell. The green arrow points at Au that has filled in a valley on the shell. Scale bar, 10 nm. (b) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (a), (c) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of another PdAu NP from the same sample as the NP shown in (a). Scale bar, 10 nm. (d) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (c). (e) Large-area SE- STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the PdAu NPs. Scale bar, 0.5 pm. (f) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images taken at higher resolution at the areas depicted by the color boxes in (E). Scale bar, 50 nm. (g) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a single-layer of PdAu NPs. Scale bar, 50 nm.

Figures 21A-G show AuAg NPs with a hollow, porous Au shell and Ag crystallite extrusions, (a) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a AuAg NP, which consist of a hollow Au frame and extruding Ag crystallites. Equivalent molar amounts of Ag and Au were used. Scale bar, 40 nm.

(b) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (a), (c) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a AuAg NP without UV exposure from the sample as was imaged in (a). Scale bar, 40 nm. (d) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (c). (e) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the AuAg NP shown in (c) after extensive UV exposure. The green arrow points at a visible region on the Au frame, which has been revealed after the removal of the Ag crystallites. The Au frame is hollow and appears to be porous in some areas on the structures. Scale bar, 40 nm. (f) EDX maps of Au, Pd and an overlay of the elements for the NP shown in (e). (g) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of the AuAg NPs. The image was taken near the Cu mesh on the TEM grid, leading to white and black areas in the upper-half portion of the HAADF- and BF-STEM images, respectively. The micrographs were acquired at low magnification, such that the spot size is observable in the bottom of the BF-STEM image. Scale bar, 200 nm. These NPs were capped with citrate.

Figures 22A-B are large-area micrographs of AuPdAg NPs with a hollow Au frame, intermediate Pd layer and protruding Ag crystallites, (a) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPdAg NPs, which consist of a Au frame, Pd layer and then Ag protrusions. The molar ratios of Ag, Au and Pd used are 1.5, 1.5 and 1, respectively. They are also taken at a low magnification, such that the spot size is observable in the BF-STEM image. Scale bar, 0.5 pm. (b) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPdAg NPs taken at higher resolution at the areas depicted by the color boxes in (A). Scale bar, 200 nm. These NPs were capped with citrate.

Figures 23A-E are AuPdAg NPs with a hollow Au frame, thick intermediate Pd layer, and Ag crystallite extrusions, (a) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of a AuPdAg NP, which consists of a Au frame, Pd frame that is thicker than the NP shown in Fig. SM and then Ag protrusions. The molar ratios of Ag, Au and Pd used are 1.5, 1.5 and 2, respectively. The red arrow points at the grainy intermediate Pd layer, which has been exposed by UV treating the sample. Scale bar, 40 nm. (b) EDX maps of Au, Pd, Ag, an overlay of Au and Pd and an overlay of Pd and Ag of the NP shown in (a). Ag protrusions coat an intermediate Pd shell, which covers the underlying Au frame, (c) EDX overlay map of the trimetallic NP shown in (a), (d) Large-area SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images the AuPdAg NPs. The green arrow points at an artifact in the grid. Scale bar, 0.5 pm. (e) SE-STEM (left), HAADF-STEM (center) and BF-STEM (right) images of AuPdAg NPs at another section on the grid. Scale bar, 200 nm. The NPs were capped with citrate.

Figure 24 illustrates a table compiling characteristics of various capping agents.

DETAILED DESCRIPTION

In the following description, similar features in the drawings have been given similar reference numerals. In order to not unduly encumber the figures, some elements may not be indicated on some figures if they were already mentioned in preceding figures. It should also be understood herein that the elements of the drawings are not necessarily drawn to scale and that the emphasis is instead being placed upon clearly illustrating the elements and structures of the present embodiments. The terms “a”, “an” and “one” are defined herein to mean “at least one”, that is, these terms do not exclude a plural number of items, unless stated otherwise.

Terms such as “substantially”, “generally” and “about”, that modify a value, condition or characteristic of a feature of an exemplary embodiment, should be understood to mean that the value, condition or characteristic is defined within tolerances that are acceptable for the proper operation of this exemplary embodiment for its intended application.

Unless stated otherwise, the terms “connected” and “coupled”, and derivatives and variants thereof, refer herein to any structural or functional connection or coupling, either direct or indirect, between two or more elements. For example, the connection or coupling between the elements may be mechanical, optical, electrical, logical, or any combination thereof.

The technology and its advantages will become more apparent from the detailed description and examples that follow, which describe the various embodiments of the technology.

Broadly described, the techniques that will be described herein relates to a transitory synthesis pathway. The transitory synthesis pathway relies on transitory ligands to spatiotemporally separate the NP synthesis (z.e., the seed stage and the growth stage of the NP synthesis) from the capping (i.e., the stage at which capping agents are introduced). The transitory ligands, which may for example be embodied by acetone, adsorb relatively weakly and transiently on colloidal NPs to facilitate controlled nucleation and growth but, afterwards, can be quantitatively removed by evaporation, or alternatively be quantitatively displaced by any chemically compatible capping agent(s). The present techniques allow developing relatively large NP libraries and experimentally demonstrate >100 different metal or metal -based NPs, including, for example and without being limitative, heterostructured multimetallic, ligand-free, and other previously unattainable NPs. The technology presented herein uses relatively simple and standard benchtop chemistry to enable pick-and-choose capabilities between the size, shape, and elemental composition and the surface features of NPs. The techniques that will now be described can be seen as a facile or universal approach that can achieve a large number of NP designs.

Overview

Metal NPs or metal-based NPs present physicochemical, electrical, magnetic, and optical properties that can be more desirable or even unavailable in bulk metals. ^1-6 The properties of the NPs typically depend on the design of the NPs. Properties of interest for NPs may include, for example and without being limitative, their size, shape, crystal structure, surface features, and elemental composition. ^6-11 A relatively precise control over the design of NPs is therefore crucial for optimizing their performance having regard to their intended use or application. Nonlimitative examples of use or application include next-generation additive manufacturing, ^{12 14} wearable electronics, ¹⁵ chemical and biological sensing, ^{16 18} imaging, ¹⁹ - ²⁰ medical therapies, ²¹ - ²² metamaterials, ³ - ²³ environmental remediation, ²⁴ - ²⁵ water desalination, ²⁶ - ²⁷ and chemical processing. ²⁸ - ²⁹ The fields of chemistry, materials science, and nanoscience have been active in developing approaches allowing relatively precise design capabilities of NPs.

The synthesis of colloidal NPs includes two fundamental steps or processes: nucleation and growth. Nucleation here refers to the initial formation of condensed phases from monomeric units, whereas growth here comprises the integration of monomers into already nucleated clusters. ³⁰ While nucleation and growth can occur concurrently (i.e., in “parallel”) in crystallization reactions, ³¹ - ³² seed-mediated syntheses spatiotemporally separate nucleation reactions from growth reactions and can therefore yield greater control over NP uniformity, size, shape, and elemental composition. ^33-35 However, inorganic NPs are intrinsically unstable thermodynamic products, and the solution-phase syntheses of the same conventionally use organic capping agents, such as small molecules, surfactants, or macromolecules, that bind to the NP surface to inhibit coalescence, dissolution, and other undesirable processes during and after synthesis. ³⁶ - ³⁷ Although a small number of capping agent-free syntheses have been demonstrated, such as for Au nanospheres or Au nanostars, these procedures are confined to produce a strictly defined selection of NP shapes and elemental compositions. ^38-40 Thus, for the broader synthesis of colloidal NPs, there is generally no spatiotemporal separation of capping from nucleation or growth. ³⁶ - ³⁷

While one of the functions of capping agents is to facilitate the controlled synthesis of discrete colloidal NPs, they also interact with monomers or surface facets to influence NP formation and then remain bound after synthesis completion. ³⁴ - ³⁵ These interactions can selectively direct growth to produce desired structures, but this also means that capping agents limit the range of NP designs that are achievable by a synthesis method, especially for elemental composition, shape, and surface features. ^34-37 - ^41-44 Because the capping agents remain bound to the surface and typically resist desorption, ³⁷ - ⁴⁵ - ⁴⁶ the capping agents used during synthesis also affect the local NP environment after synthesis, constraining accessible surface properties and interfacial interactions. For instance, capping agents can affect, and can sometimes negatively impact, the carrier dynamics of electrons and holes, ⁴⁷ optical properties, ⁴ catalytic environment, ⁴⁸ - ⁴⁹ and biological interactions ⁵⁰ - ⁵¹ of NPs. As such, achieving desired properties often requires post-synthesis surface modification via ligand exchange. ⁴ - ^52-56 These reactions, however, can induce structural transformations, especially for small NPs, ⁵⁷ - ⁵⁸ can require up to days for higher exchange yields, ⁵⁹ and do not go to completion in the case of direct ligand exchange. ⁴⁵ - ⁵⁹ - ⁶⁰ For quantitative ligand exchange, NPs must be immobilized on a substrate or undergo multistep processes that include the deposition of a sacrificial layer of metal or additional ligand exchange reactions. ⁴⁸ - ⁴⁹ - ⁶¹ ■ ⁶² Moreover, ligand exchange reactions require case-by-case considerations of the underlying NP, chemical environment, and interplay between the initial and displacing ligands. ⁵³ - ⁵⁹ - ^63-65 That is, there is no general method or reaction that in a facile manner enables for an initial capping agent used during synthesis to be exchanged with a broad range of capping agents post-synthesis on the surface of the NPs. In summary, capping agents facilitate the controlled solution-phase synthesis of NPs but also limit design capabilities, as well as properties of the NPs after their synthesis. In other words, conventional approaches that associate capping with synthesis are generally incompatible with quantitative, modular NP design. ³⁶ - ³⁷

Method for preparing nanoparticles

The present technology is generally directed towards techniques, including a method, which may sometimes be referred to a “transitory synthesis pathway” for preparing inorganic, metal or metal-based nanoparticles. The techniques that will now be described uses transitory ligands to spatiotemporally separate synthesis from capping for colloidal NPs, an example of which is illustrated in Figure 1. Transitory ligands accomplish at least one of the functions of conventional capping agents during synthesis, such as, for example, facilitating controlled nucleation and growth. However, the transitory ligands differ from conventional capping agents at least because they form relatively weak, labile, and transient interactions that generally do not maintain the NPs as discrete colloids significantly beyond the time of synthesis. These interactions enable for the transitory ligands to be quantitatively displaced by any chemically compatible capping agent after synthesis. The transitory ligands can be quantitatively removed by simply depositing the NPs on a substrate and applying reduced pressure, yielding ligand-free NPs. Thus, the techniques that will be described avoid many of the limitations of conventional methods and expands the design capabilities, as illustrated in the table provided in Figure 2. At least 100 different metal NPs may be produced according to the techniques described herein, including ones with polyelemental compositions as well as those that morphologically resemble golf balls, dough balls, leukocytes, and other distinctive forms, to demonstrate the quantitative, modular design capabilities of transitory synthesis.

In some embodiments, the many different NPs can be all produced in a single day by a single person using relatively simple, green and standard benchtop chemistry. Of note, unlike conventional synthesis pathways, which require relatively complex, case-by-case ligand exchange reactions, the modularity of the techniques described herein means that it is compatible with many self-driven Al systems for NP investigation. ^79-81 In addition, the principles of transitory synthesis, and the characteristics of a transitory ligand, are generalizable beyond metal NPs. The techniques presented herein may enable for the development of similar transitory synthesis protocols for other types of NPs, including quantum dots and perovskites. Moreover, as demonstrated in this study, such pathways open ligand-tailored or ligand-free NPs to be rapidly prepared. Because any chemically compatible capping agent can be chosen independent of the underlying NP grown, transitory synthesis enables for an unrestricted number of NP designs to be achieved. There is provided a method for preparing nanoparticles. In accordance with one broad aspect, the method includes mixing a first solution with a second solution. The first solution includes at least one of the nanoparticle’s seeds or the nanoparticles, i.e., the first solution may include nanoparticle’s seeds and/or nanoparticles at different stages of nucleation or growth. The second solution includes a transitory ligand. The transitory ligand is transiently adsorbed to an inorganic portion of said at least one of the nanoparticle’s seeds and the nanoparticles when the first solution is mixed with the second solution. In the context of the current disclosure, the expression “transiently adsorbed” refers to the fact the transitory ligand is relatively weakly and temporarily attached or adsorbed to the inorganic portion of the seeds and/or nanoparticles. More specifically, the transitory ligand may be sequentially adsorbed and desorbed from the inorganic portion. In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic portion according to a periodic sequence, an aperiodic sequence, or a random sequence. The method further includes substituting the transitory ligand with a capping agent. The inorganic portion may be embodied by an inorganic core of the nanoparticle’s seeds or the nanoparticles.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent. In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is included in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

Now turning to the nature, chemical composition and other properties of the transitory ligand may be an organic molecule. In some embodiments, the transitory ligand may be acetone. In other embodiments, the transitory ligand may be s selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether. Now turning to the properties of the transitory ligand, the transitory ligand may be a non-ionic compound. In some embodiments, the transitory ligand has a denticity lower or equal than 2. In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, the step of substituting the transitory ligand includes removing the transitory ligand. This step of removing the transitory ligand may include, for example, drop-casting the nanoparticles on a substrate to evaporate the transitory ligand. In other embodiments, the step of substituting the transitory ligand includes quantitively displacing the transitory ligand. The capping agent may be chemically compatible with the inorganic portion of the seeds or the nanoparticles.

In some embodiments, the nanoparticle’s seeds and the nanoparticles each have an initial crystallographic structure and a final crystallographic structure. In some embodiments, the initial crystallographic structure is similar to the final crystallographic structure, i. e. , the structure is not affected by the presence and then the removal of the transitory ligand.

In some embodiments, the nanoparticle’s seeds and the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped. In some embodiments, the nanoparticle’s seeds and the nanoparticles are metallic. In some embodiments, the nanoparticle’s seeds or the nanoparticles include Au. In some embodiments, the nanoparticle’s seeds or the nanoparticles include Au and Pd. In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the first solution is an aqueous solution. In some embodiments, the second solution is an aqueous solution. In some embodiments, the first solution may include acetone, a solvent, a metal precursor, and a reducing agent.

The capping agent may be selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (1 l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®. In some embodiments, the capping agent is provided in a third solution, which may be an aqueous solution. In some embodiments, the third solution is an organic-solvent solution.

In some embodiments, the method includes adding the third solution to the first solution and the solution. This step may be carried out at room temperature.

Three implementations of that general method will now be described in greater detail.

According to a first implementation, the method includes a seeding or nucleation step and a growth step. In this implementation, the method incudes providing a seed solution, which includes nanoparticle’s seeds. The method also includes adding the seed solution to a growth solution to obtain the nanoparticles from the nanoparticle’s seeds. Each nanoparticle has an inorganic core and a transitory ligand transiently adsorbed to the inorganic core. The method according to this implementation also includes substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core. In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic core according to a periodic sequence, an aperiodic sequence or a random sequence. In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent. In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is included in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule. In some embodiments, the transitory ligand is acetone. In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether. In some embodiments, the transitory ligand is a non-ionic compound. In some embodiments, the transitory ligand has a denticity lower or equal than 2. In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, the step of substituting the transitory ligand may include removing the transitory ligand. The step of removing the transitory ligand may include drop-casting the nanoparticles on a substrate to evaporate the transitory ligand. In other embodiments, the step of substituting the transitory ligand includes quantitively displacing the transitory ligand. The capping agent is chemically compatible with the inorganic core.

In some embodiments, the nanoparticle’s seeds and the nanoparticles each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure.

In some embodiments, the nanoparticle’s seeds and the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped. In some embodiments, the nanoparticle’s seeds and the nanoparticles are metallic. In some embodiments, the nanoparticle’s seeds and the nanoparticles include Au. In some embodiments, the nanoparticle’s seeds and the nanoparticles include Au and Pd. In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the seed solution is an aqueous seed solution. In some embodiments, the seed solution includes acetone, a solvent, a metal precursor, and a reducing agent. In some embodiments, the seed solution includes at least acetone, Nal, water, HAiiCT and NaBH ₄ . In some embodiments, the seed solution includes at least acetone, NaBr, water, HAiiCfiand NaBH ₄ . In some embodiments, the seed solution includes at least HAuC’U trisodium citrate, water and NaBH ₄ . In some embodiments, the growth solution includes acetone, a solvent, a metal precursor, and a reducing agent. In some embodiments, the growth solution is an aqueous growth solution.

In some embodiments, the capping agent may be selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®.

In some embodiments, the growth solution includes at least one of acetone, Nal, water, HAuCU. HC1 and HQ. In some embodiments, the growth solution includes at least acetone, NaBr, water, HAuCU, HC1 and HQ. In some embodiments, the growth solution includes at least acetone, NaBr, water, HAiiCF. NaOH and HQ. In some embodiments, the growth solution includes at least acetone, NaBr, water, HA11CI4. HC1, AgNOs and HQ. In some embodiments, the growth solution includes at least acetone, water and HQ. In some embodiments, the growth solution includes at least acetone, water, HA11CI4. K^PdCU and HA11CI4. In some embodiments, the growth solution includes at least acetone, water, K^PdCU, HQ and H A11CI4. In some embodiments, the growth solution includes at least acetone water, AgNOs, HA, HA11CI4. and K^PdCU

In some embodiments, the capping agent is provided in a capping agent solution. In some embodiments, the capping agent solution is an aqueous solution. In some embodiments, the capping agent solution is an organic-solvent solution. In some embodiments, the capping agent solution is a THF-based solution. In some embodiments, the capping agent solution is a DMSO-based solution.

In some embodiments, the method includes adding the growth solution to the capping agent solution. In some embodiments, this step is carried out at room temperature.

According to a second implementation, the method includes a seeding or nucleation step during which a transitory ligand is used. The method according to this implementation includes mixing a seed solution with a transitory ligand solution. The seed solution includes the nanoparticle’s seeds and each nanoparticle’s seed has an inorganic core. The transitory ligand solution includes a transitory ligand, which is transiently adsorbed to the inorganic core in the seed solution. The method also includes substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core. In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core according to a periodic sequence, an aperiodic sequence, or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent. In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is included in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule. In some embodiments, the transitory ligand is acetone. In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether. In some embodiments, the transitory ligand is a non-ionic compound. In some embodiments, the transitory ligand has a denticity lower or equal than 2. In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, the step of substituting the transitory ligand includes removing the transitory ligand. The step of removing the transitory ligand includes drop-casting the nanoparticle’s seeds on a substrate to evaporate the transitory ligand. In other embodiments, the step of substituting the transitory ligand includes quantitively displacing the transitory ligand. The capping agent is chemically compatible with the inorganic core.

In some embodiments, the nanoparticle’s seeds each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure. In some embodiments, the nanoparticle’s seeds are spherical, icosahedral, octahedral, rod shaped, or star shaped. In some embodiments, the nanoparticle’s seeds are metallic. In some embodiments, the nanoparticle’s seeds include Au. In some embodiments, the nanoparticle’s seeds include Au and Pd.

In some embodiments, the seed solution is an aqueous seed solution. In some embodiments, the seed solution includes acetone, a solvent, a metal precursor, and a reducing agent. In some embodiments, the seed solution includes at least acetone, Nal, water, HAuC’U and NaBH ₄ . In some embodiments, the seed solution includes at least acetone, NaBr, water, HAuCUand NaBH ₄ . In some embodiments, the seed solution includes at least HAiiC’U. trisodium citrate, water and NaBH ₄ .

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®.

In some embodiments, the capping agent is provided in a capping agent solution. In some embodiments, the capping agent solution is an aqueous solution. In some embodiments, the capping agent solution is an organic-solvent solution. In some embodiments, the capping agent solution is a THF-based solution. In some embodiments, the capping agent solution is a DMSO-based solution. According to a third implementation, the method includes a growth step. The method according to this implementation includes mixing a growth solution with a transitory ligand solution. The growth solution includes the nanoparticles, each nanoparticle having an inorganic core. The transitory ligand solution includes a transitory ligand. The transitory ligand is transiently adsorbed to the inorganic core in the growth solution. The method also includes substituting the transitory ligand attached with the inorganic core with a capping agent.

In some embodiments, the transitory ligand is sequentially adsorbed and desorbed from the inorganic core. In some embodiments, the transitory ligand is sequentially attached and unattached from the inorganic core according to a periodic sequence, an aperiodic sequence or a random sequence.

In some embodiments, a binding energy of the transitory ligand is smaller than a binding energy of the capping agent. In some embodiments, a difference between the binding energy of the transitory ligand and the binding energy of the capping agent is included in a range extending from about 0 eV to about 3 eV per adsorbed moiety.

In some embodiments, the transitory ligand is an organic molecule. In some embodiments, the transitory ligand is acetone. In some embodiments, the transitory ligand is selected from the group consisting of: ethanol, methylene chloride, carbon monoxide, hydrogen peroxide, methanol, acetic acid, 2-butanone, diethyl ether, ethylene glycol, chloroform and methyl /-butyl ether. In some embodiments, the transitory ligand is a non-ionic compound. In some embodiments, the transitory ligand has a denticity lower or equal than 2. In some embodiments, the transitory ligand has a molecular weight comprised in a range lower or equal to 200 g/mol.

In some embodiments, the step of substituting the transitory ligand includes removing the transitory ligand. The step of removing the transitory ligand includes drop-casting the nanoparticles on a substrate to evaporate the transitory ligand.

In some embodiments, the step of substituting the transitory ligand includes quantitively displacing the transitory ligand, the capping agent being chemically compatible with the inorganic core.

In some embodiments, the nanoparticles each have an initial crystallographic structure and a final crystallographic structure, the initial crystallographic structure being similar to the final crystallographic structure. In some embodiments, the nanoparticles are spherical, icosahedral, octahedral, rod shaped, or star shaped. In some embodiments, the nanoparticles are metallic. In some embodiments, the nanoparticles include Au. In some embodiments, the nanoparticles include Au and Pd. In some embodiments, the nanoparticles are AuPd-based nanoparticles, conformal core-shell AuPd icosahedra, AuPd icosahedra with divots, grain-separated AuPdAu nanoparticles, island-shell PdAu nanoparticles or dough-shell PdAu nanoparticles.

In some embodiments, the growth solution is an aqueous growth solution. In some embodiments, the growth solution includes acetone, a solvent, a metal precursor, and a reducing agent. In some embodiments, the growth solution includes at least one of acetone, Nal, water, HAtiCU HC1 and HQ. In some embodiments, the growth solution includes at least acetone, NaBr, water, HAuCL, HC1 and HQ. HQ or weak reducing agents or L-ascorbic acid. In some embodiments, the growth solution includes at least acetone, NaBr, water, HAuCh, NaOH and HQ. In some embodiments, the growth solution includes at least acetone, NaBr, water, HA11CI4. HC1, AgNOs and HQ. In some embodiments, the growth solution includes at least acetone, water and HQ. In some embodiments, the growth solution includes at least acetone, water, HA11CI4. K^PdCU and HA11CI4. In some embodiments, the growth solution includes at least acetone, water, K^PdCU, HQ and HA11CI4. In some embodiments, the growth solution includes at least acetone water, AgNOs, HA, HA11CI4. and K2PdC14.

In some embodiments, the capping agent is selected from the group consisting of: sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (l l-mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80®. In some embodiments, the capping agent is provided in a capping agent solution. In some embodiments, the capping agent solution is an aqueous solution. In some embodiments, the capping agent solution is an organic-solvent solution. In some embodiments, the capping agent solution is a THF -based solution. In some embodiments, the capping agent solution is a DMSO-based solution.

In some embodiments, the method includes adding the growth solution to the capping agent solution. In some embodiments, adding the growth solution to the capping agent solution is carried out at room temperature.

With reference to Figures 9A-B, the role of acetone has been investigated. It has been found that acetone can facilitate seed-mediated growth as a chemically simple capping agent, as this small molecule typically forms weak, labile interactions with fee metals. Acetone, in a concentration-dependent manner indeed inhibited nucleation in the absence of seed in our formulation. Because nucleation occurs above a critical supersaturation, which is reached via the reduction of Au precursor to monomer, acetone can inhibit nucleation in one of two ways: by hindering the ability of HQ to reduce Au precursor or by interacting with Au precursor to limit its reduction. Linear sweep voltammetry demonstrated that acetone decreases the reduction potential of HQ, while density functional theory (DFT) calculations showed that acetone does not bind more strongly to Au precursor (E_bind=-0.37 eV) than water (E_bind=-0.53 eV), briefly supporting the former way.

Examples of results

The following section provides examples of results related to embodiments of the technology such as described above . It will be readily understood that these examples of results should not be taken as limitative to the scope of protection

The transitory synthesis pathway

Conventional or existing solution-phase syntheses of NPs typically require at least three reagents: a metal salt precursor, a capping agent, and a reducing agent. In the present disclosure, the conventional formulation of the capping agent is replaced with the transitory ligand. The transitory ligands are adapted to facilitate or modulate nucleation and growth steps of the synthesis, based on the strength of the reducing agent, i.e., the transitory ligands enable the NPs nucleation upon addition of a strong reducing agent (e.g., NaBH ) and at the same time inhibit NPs nucleation upon the addition of weak reducing agent (e.g., L-ascorbic acid or hydroquinone) in seed-mediated growth. ³⁵ The transitory ligands are displaceable by any chemically compatible capping agent(s) after synthesis completion, without inducing significant structural transformations of the NPs. Based on the observations that strongly binding ligands preferentially displace weakly binding ones ⁶⁶ and that, under mild conditions, ligand exchange does not significantly alter NP structure ^{59, 67} , the transitory ligands are embodied by organic molecules that form relatively weak, labile interactions with both the monomer and NPs. Hence, transitory synthesis is unlikely to maintain the NPs as discrete colloids for long periods of time beyond synthesis completion. In doing so, the transitory synthesis spatiotemporally separates nucleation and growth from capping.

In some embodiments, the transitory ligand in the aqueous synthesis of colloidal metal NPs is acetone. Acetone generally forms relatively weak, labile interactions with metals ^{68, 69} and has a small molecular size, which limits intermolecular interactions that help to resist desorption ^{45, 46} as well as minimizes the impact of steric crowding at the NP surface on ligand exchange. ^{36, 59} Moreover, acetone is a volatile solvent that, at typical temperatures and pressures, forms a non-azeotrope with water; ^{70, 71} As such, acetone exhibits a thermodynamic preference to be separated from the NP surface and aqueous formulation, especially in the presence of displacing capping agents that bind more strongly to the NPs, via evaporation. These hypotheses were tested using Au and acetone as a model system for proof-of-concept studies. DFT molecular dynamics simulations showed that acetone indeed adsorbs weakly and transiently to metals like Au, as illustrated in Figures 3a-e. Acetone was drop-casted onto pristine Au foil and the resulting samples were placed under hood ventilation. Attenuated total reflectance infrared spectroscopy (ATR-IR) showed that acetone indeed desorbs molecularly and quantitatively from Au via evaporation, as demonstrated by the disappearance of the C=O stretching mode (Figure 4j).

With reference to Figures 3a-e, there are illustrated examples of a transient and relatively weak adsorption of acetone on Au facets. Snapshots of MD simulations of the adsorption interactions of acetone with (a) Au(l 11), (b) Au(100), (c) Au(l 10), and (d) Au(210) are illustrated. Figure 3e shows DFT-calculated binding energies of acetone and water to various Au facets.

The ability of acetone to facilitate the seed-mediated synthesis of colloidal NPs was investigated. Au salt (HA11CI4) and then weak (e.g., L-ascorbic acid (L-AA) or hydroquinone (HQ) were added to an aqueous mixture with different concentration of acetone. This minimal formulation excludes seed that should resist nucleation in seed-mediated growth reactions. In the absence of acetone, the addition of weak reducing agent rapidly induced nucleation, likely via disproportionation because neither L-AA nor HQ are strong enough reducing agents to directly reduce Au ³⁺ to Au°. By contrast, acetone inhibited nucleation in a concentration-dependent manner in this formulation, for which 40% v/v of acetone tended to inhibit autonucleation for >15 min. Concentrations of acetone up to 40% v/v also enabled for the controlled nucleation of Au seed upon the addition of strong reducing agent, NaBH . As expected of a transitory ligand, acetone does not maintain the NPs as discrete colloids for extended periods of time, as observed by timedependent NP coalescence as early as 5 minutes after synthesis completion. NPs prepared via transitory synthesis still require capping to remain as discrete, stable, and precisely formed colloids. Thus, the NPs should be added to the desired capping agent for transitory exchange soon after synthesis completion and acetone allowed to evaporate off. Taken together, these results provided initial support for acetone as a transitory ligand for the general transitory synthesis of colloidal metal NPs.

Au NPs

To investigate the ability of transitory synthesis to produce a broad range of Au NPs, seed-mediated synthesis procedures using 40% v/v acetone (Methods) for four well-defined NP shapes were developed: spheres (Figure 4a), icosahedra (Figure 4c), octahedra (Figure 4e), and stars (Figure 4g). Moreover, since transitory exchange of acetone should be compatible with any chemical compatible displacing capping agent (Figure 1), each of these Au NPs were prepared via transitory exchange and added separately them to different capping agents, including sodium citrate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), poly(lactic acid) (PLA), sodium dodecyl sulfate (SDS), (11- mercaptoundecyl)trimethylammonium bromide (MUTAB), Pluronic® F-127, monothiolated polystyrene (PS-thiol), and Tween 80® (Figure 4i). This library of capping agents is diverse, spanning small molecules, surfactants, polymers, different charges, and different hydrophilicities (Figure 24). The NPs shown in the secondary electron scanning transmission electron microscopy (SE-STEM) and high-angle annular darkfield (HAADF)-STEM images in Figure 4 were capped with citrate. As depicted in Figure la, the color of the NPs was consistent between the completion of the growth reaction and after capping regardless of the capping agent, suggesting that transitory exchange has a minimal influence on the metal structure of the NP. Structural characterization of the size and shape of these Au NPs across the library of capping agent provided further, quantitative support that transitory exchange has this minimal influence, especially for larger NPs (Figure 4b,d,f,h). The observed variation in final NP structure occurred more due to batch variation than variation from transitory exchange.

With reference to Figures 4a-l, there is illustrated a transitory synthesis of a library of colloidal Au NPs with various capping agents. Figures 4a to4h show a model, SE-STEM image, HAADF-STEM image, and low- magnification STEM images of Au NPs with (a) spherical, (c) icosahedral, (e) octahedral, and (g) star shapes. These NPs were each capped with sodium citrate (annotated as 1 in (i)) for transitory exchange. Structural characterization of the (b) spherical, (d) icosahedral, (f) octahedral, and (h) star Au NPs after transitory exchange with the (i) library of organic capping agents, which includes sodium citrate (annotated as 1), PVP (annotated as 2), CTAB (annotated as 3), PLA (annotated as 4), SDS (annotated as 5), MUTAB (annotated as 6), Pluronic® F-127 (annotated as 7), PS-thiol (annotated as 8), and Tween 80 (annotated as 9). The size and shape measurements are shown to the right of the respective plot. The open circles in various colors represent raw data, while black filled circles and bars represent the mean ± SD. (j) ATR-IR characterization of the quantitative transitory exchange of acetone with capping agents 3 and 6 on representative Au NPs. Au foil was used as a substrate to show the quantitative desorption of acetone after evaporation (gold curve). Representations of acetone as (k) neat molecules and (1) adsorbed in the // ¹ (O) orientation as determined via their C=O stretching modes. While the C=O stretching mode of acetone typically exhibits an IR peak of -1709 cm' ¹ (Figure 4j,k), ATR-IR showed that acetone on Au NPs had the peak at -1625 cm' ¹ (Figure 4j), consistent with a peak shift due to acetone adsorbing on metals in the h O) orientation (Figure 41). ⁶⁹ This binding orientation facilitates acetone to desorb molecularly from metal surfaces. ⁶⁹ To assess the ability of capping agents to displace acetone in transitory exchange, the molecular composition of the Au NPs after transitory exchange with CTAB and MUTAB was characterized. As can be seen, the capping agents in the library lack the C=O functional group. Of note, these capping agents span interaction strengths with Au, as CTAB binds through weaker interactions mediated by Br whereas MUTAB forms the stronger Au-S bond. ^{72, 73} ATR-IR showed that neither CTAB- nor MUTAB-capped NPs showed any C=O stretching mode but did show the stretching modes around 2852 cm' ¹ and 2919 cm' ¹ associated with these aliphatic compounds (Figure 4j). ⁶¹ These results indicated that acetone is indeed quantitatively displaced by both weakly and strongly binding capping agents during transitory exchange on colloidal NPs. Heterostructured binary AuPd NPs

Because heterostructured multimetallic NPs can exhibit superior or emergent properties, including for heterogeneous catalysis, ^{74, 75} the question of whether the transitory synthesis could produce well-defined heterostructured AuPd NPs across the library of capping agents or not was assessed. Using the presented pathway, Au icosahedra was prepared, as shown in Figure 4c, in the presence of Br and excess reducing agent but, after reaction completion, added Pd salt precursor (lUPdCU. 1 molar equivalent [equiv] relative to Au precursor added); the Pd deposited as a uniform, conformal shell to form heterostructured AuPd icosahedra (Figures 5a-c). The thickness of the conformal Pd shell was modulated by simply altering the concentration of Pd precursor added. When these AuPd icosahedra were grown in the absence of Br, the Pd instead formed a bumpy shell, indicating that Br facilitates uniform shell formation. The influence of adding Pd (0.1 equiv) before the completion of Au growth was also assessed. These NPs grew to form AuPd icosahedra with well-defined divots, morphologically resembling golf balls (Figure 5d-f), whereas the conformal core/shell AuPd icosahedra had a separate Pd layer over the Au icosahedra (Figure 5c), the simultaneous deposition of Au and Pd lead to AuPd golfballs with Au and Pd interspersed along the exterior of these NPs (Figure 5f).

With reference to Figure 5, there is illustrated a transitory synthesis of colloidal heterostructured AuPd NPs with various capping agents. SE-STEM image, HAADF-STEM image, and EDX elemental maps of a single NP and low-magnification STEM images for (a-c) conformal core/shell AuPd icosahedra, (d-f) AuPd icosahedra with divots, (g-i) grain-separated AuPdAu NPs, (j-1) island-shell PdAu NPs, and (m-o) doughshell PdAu NPs. The elemental intensity profiles were taken from the dashed boxed area shown in the respective EDX map and represent the relative intensity for Au and Pd, separately. These NPs were each capped with sodium citrate (1 in Figure le) for transitory exchange. The arrows in (d) denote twin planes.

The transitory synthesis was then used to prepare AuPdAu NPs, which had three sequential metal layers. In the presence of Br and excess reducing agent, the conformal core/shell AuPd icosahedra was synthetized, as shown in Figure 5a-c, and, upon reaction completion, then again added Au precursor (1 equiv). Since Br remained in the reaction, the Au deposited as another conformal shell for uniform AuPdAu icosahedra. If this reaction is conducted in the absence of Br, the outer layer of the AuPdAu icosahedra is composed of distinct Au and Pd grains (Figure 5g— i), due to the codeposition of Au and Pd. ⁷⁶ These results further supported that Br facilitates the formation of uniform shells, whereas the absence of Br in these reactions leads to metals that deposit as islands (Figure 5h).

Up until this point, the AuPd NPs have been synthesized with an Au core. To replace the Au core with a Pd core, Pd NPs were synthetized. These Pd NPs were grown using an Au seed and in the absence of Br, leading to a bumpy surface. After synthesis completion for these NPs, an Au precursor was added, which deposited on the top of the Pd bumps. With higher concentration of Au precursor added, the Au further deposited on top of the existing Au islands (Figures 5j— 1). As past reports have shown, such heterostructure growth is facilitated by the lattice mismatch between Au (lattice parameter, 4.078 A) and Pd (3.891 A) at the nanoscale. ⁷⁴ ’ ⁷⁷ As even more Au is deposited, the Au islands grow upwards and outwards, eventually coalescing and then resulting in a shell that morphologically resembles a ball of dough (Figures 5m-o, until enough shell coalescence occurs that a conformal Au shell results. Notably, using transitory exchange, each NP shown in Figure 5a-o was capped with the full library of capping agents (Figure 4i). Similar to the monometallic Au NPs, these AuPd NPs and PdAu NPs showed quantitative displacement of acetone, and transitory exchange had a minimal influence on the underlying NP structure. Taken together, these findings demonstrate transitory synthesis as a robust pathway to prepare heterostructured bimetallic NPs.

Heterostructured ternary AuPdAg NPs

To further assess the design capabilities of transitory synthesis, the pathway was used to synthesize ternary heterostructured NPs. A growth formulation for Ag NPs was developed. After synthesis completion for these Ag NPs, Au precursor was added, which induced galvanic replacement, the etching of the underlying Ag core during Au deposition. ⁷⁸ Moreover, because this growth formulation had excess reducing agent, the dissolved Ag then redeposited, leading to the formation of hollow, porous Au frames with exterior Ag crystallites. To turn this binary heterostructured NP into a ternary heterostructured one, the Ag NPs were synthetized, and an Au precursor as described above was added, before adding a Pd precursor. This formulation produced the porous, hollow Au frame, like above, but now led to the deposition of an intermediate Pd layer before the redeposition of Ag and extruding crystallites (Figures 6a-j). As these NPs were grown in the absence of Br, the intermediate Pd layer deposited as a grainy shell on top of the underlying hollow Au frame (Figures 6a-j). In contrast to the AuAg NPs, for the AuPdAg NPs, the presence of the intermediate Pd layer facilitates the growth of distinct, isolated Ag crystallites during the redeposition process (Figures 6a-l). Both the intermediate grainy Pd layer and Ag crystallites showed high index {311} facets (Figures 6f-j). As has been consistent throughout this study, transitory exchange on these AuPdAg NPs occurred quantitatively, and these NPs had minimal structural transformations across the full library of capping agents (Figure 4i).

Other experimental results are illustrated in Figures 7 to 24.

Experimental section

Some experimental details will now be presented. It will be noted that these details serve illustrative purposes only and should not be considered limitative. Chemicals and materials

Acetone (99.9%), gold (III) chloride hydrate (HAuCU xtfeO, x ~ 3, 99.995%), potassium tetrachloropalladate(II) (K^PdCU, 99.99%), silver nitrate (AgNOs, 99.999%), copper(II) nitrate hydrate (CU(NO ₃ ) ₂ XH ₂ O, x ~ 3, 99.999%), iron(III) nitrate nonahydrate (Fe(NC>3)3 9H ₂ O, 99.999%), cobalt(II) nitrate hexahydrate (Co(NC>3) ₂ 6H ₂ O, 99.999%), nickel(II) nitrate hexahydrate (Ni(NC>3) ₂ 6H ₂ O, 99.999%), hydrochloric acid (HC1, 37%), nitric acid (HNOs, 70%), hydroquinone (HQ, 99.5%), L-ascorbic acid (L- AA, 99.0%), sodium borohydride (NaBH . 99.99%), trisodium citrate dihydrate (>99.0%), polyvinylpyrrolidone (PVP, ~55 kDa), cetyltrimethylammonium bromide (CTAB, >99%), cetyltrimethylammonium chloride (CTAC, >98%), poly(lactic acid) (PLA, ~40 kDa), sodium dodecyl sulfate (SDS, >99.0%), (1 l-mercaptoundecyl)-N,N,N -trimethylammonium bromide (MUTAB), Pluronic F- 127, monothiolated polystyrene (PS-thiol, 5 kDa, polydispersion index < 1.1), Tween 80, dimethyl sulfoxide (DMSO, >99.9%), tetrahydrofuran (THF, 99.9%), toluene (99.8%), sodium hydroxide (NaOH, >95%), potassium hydroxide (KOH, >85%), and Si wafers (no dopant) were purchased from Sigma-Aldrich (Oakville, ON, Canada). TEM grids were purchased from Ted Pella (Redding, CA, USA). Solutions were prepared with MilliQ water (18.2 MW- cm) unless otherwise noted. Glassware and stir bars were cleaned with NaOH (12 M) and aqua regia (3: 1, HCl/HNOs), respectively, and rinsed with copious amounts of MilliQ water before use. Chemicals were used without further purification.

Transitory synthesis of NPs

Seed-mediated NP syntheses were conducted by adding a series of reagents at specific timepoints. For all NPs except Au stars, the seed and growth reactions were conducted side-by-side, according to the times described, where t = 0 s denotes the initial time point. The reagents, amounts, concentrations, and addition times are described for each seed formulation and NP growth formulation below. The colorimetric progression of growth reactions was monitored by taking photographs every 30 s, and the reaction was considered completed when the color change was completed.

Seed A

Acetone (0.9 ml) and Nal (0.1 ml, 10 mM) were added to 16.82 ml of MilliQ water. This solution was kept at room temperature and placed under magnetic stirring (900 rpm). HA11CI4 (180 pl, 25 mM; 0 s) and NaBFU (90 pl, 0.1 M; 60 s) were then added to the solution to form the seeds. The seed solution was extracted via pipette at 90 s and used immediately for NP synthesis. Seed B

Acetone (0.9 ml) and NaBr (0.25 ml, 25 mM) were added to 16.67 ml of MilliQ water. This solution was placed in an oil bath (80 °C) with magnetic stirring (900 rpm). HAuCb (180 pl, 25 mM; 0 s) and NaBH (90 pl, 0.1 M; 60 s) were then added to the solution to form the seeds. The seed solution was extracted via pipette at 90 s and used immediately for NP synthesis.

Seed C

HAuCfi (191 pl, 25mM) and trisodium citrate (1 ml, 2 mM) were added to MilliQ water (18.812 ml). While maintaining this solution at ambient temperature and magnetic stirring (2000 rpm), NaBPU (60 pl, 0.1 M) was added rapidly. After stirring the solution for one minute, the stir bar was removed and stored at ambient temperature overnight, protected from light. The solution was filtered through a 0.2 pm syringe filter the next morning and left at 4°C until use. The seed was equilibrated to ambient temperature and analyzed by UV-Vis spectrometry prior to addition to the growth solution to ensure the maximum wavelength lies between 514-516 nm with an optical density between 0.55-0.62.

Au spheres

Acetone (7.2 ml) and NaI (300 pl, 10 mM) were added to MilliQ water (10.37 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCfi (180 pl, 25 mM) and HC1 (50 pl, 1 M) were added at 30 s, followed by the addition of HQ (90 pl, 0.1 M; added dropwise) and seed A (200 pl; added rapidly) at 90 s. The growth solution was stirred until the completion of the growth reaction.

Au icosahedra

Acetone (7.2 ml) and NaBr (250 pl, 25 mM) were added to MilliQ water (10.37 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCfi (180 pl, 25 mM) and HC1 (50 pl, 1 M) were added at 30 s, followed by the sequential addition of HQ (90 pl, 0.1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. The growth solution was stirred until the completion of the reaction.

Au octahedra

Acetone (7.2 ml) and NaBr (50 pl, 25 mM) were added to MilliQ water (10.37 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), a pre-mixed solution of HAiiCfi (180 pl, 25 mM) and NaOH (28.37 pl, 1 M) was added at 30 s, followed by the sequential addition of HQ (90 pl, 0. 1 M; added dropwise) and seed B (25 pl; added rapidly) at 90 s. The growth solution was stirred until the completion of the reaction.

Au stars

Acetone (7.2 ml) and NaBr (4 ml, 25mM) were added to MilliQ water (6.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCft (180 pl, 25 mM), HC1 (18 pl, IM) and AgNOs (180 pl, 4mM) were added at 0 s. HQ (90 pl, 0.1 M; added dropwise) and seed C (100 pl; added rapidly) were then added at 60 s. The growth solution was stirred till the completion of the reaction.

AuPd core/conformal shell icosahedra

Acetone (7.2 ml) and NaBr (250 pl, 25 mM) were added to MilliQ water (10.37 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCft (180 pl, 25 mM) and HC1 (18 pl, 1 M) were added at 30 s, followed by the sequential addition of HQ (320 pl, 0.1 M; added dropwise) and seed B (150 pl) at 90 s. After this reaction was complete (colour saturation), K^PdCU (216 pl, 25 mM) was added. This solution was continued to be stirred until the completion of the growth reaction.

AuPd icosahedra with divots

Acetone (7.2 ml) was added to MilliQ water (10.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCft (180 pl, 25mM) was added at 30 s, followed by the sequential addition of HQ (90 pl, 0.1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. K^PdCU (18 pl, 25 mM) was then added at 120 s. The growth solution was stirred until the completion of the reaction.

AuPdAu core/shell/island icosahedra

Acetone (7.2 ml) was added to MilliQ water (10.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), HAuCft (180 pl, 25 mM) was added at 30 s, followed by the sequential addition of HQ (550 pl, 0. 1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. After this reaction was complete (colour saturation), K^PdCB (180 pl, 25 mM) was added, and the reaction was allowed to reach completion once again (colour saturation). At this point, HAiiCU (180 pl, 25 mM) was added. This solution was continued to be stirred until the completion of the growth reaction. PdAu core/island-shell NPs

Acetone (7.2 ml) was added to MilliQ water (10.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), K^PdCE (180 pl, 25 mM) was added at 30 s, followed by the sequential addition of HQ (90 pl, 0.1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. After this reaction was complete (colour saturation), HAuCft (18 pl, 25 mM) was added. The growth solution was continued to be stirred until the completion of the reaction.

PdAu core/dough-shell NPs

Acetone (7.2 ml) was added to MilliQ water (10.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), K^PdCft (180 pl, 25 mM) was added at 30 s, followed by the sequential addition of HQ (350 pl, 0. 1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. After this reaction was complete (colour saturation), HAuCft (180 pl, 25 mM) was added. The growth solution was continued to be stirred until the completion of the reaction.

AuPdAg NPs

Acetone (7.2 ml) was added to MilliQ water (10.62 ml) immediately prior to the start of synthesis. While maintaining this growth solution at ambient temperature with magnetic stirring (900 rpm), AgNOs (270 pl, 25 mM) was added at 30 s, followed by the sequential addition of HA (550 pl, 0. 1 M; added dropwise) and seed B (150 pl; added rapidly) at 90 s. After this reaction was complete (colour saturation), HAuCft (270 pl, 25 mM) was added, and the reaction was allowed to reach completion once again (colour saturation). At this point, K^PdCU (180 pl, 25 mM) was added. This solution was continued to be stirred until the completion of the growth reaction.

Preparation of capping agents

CTAB (4 mM), CTAC (4 mM), SDS (21 mM), Tween 80 (1 mM), trisodium citrate (6.66 mM), PVP (2.23% w/v), MUTAB (5 mM), and Pluronic F-127 (0.26% w/v) were each prepared in MilliQ water. Polystyrenethiol (0.55% w/v) was prepared in THF. Poly(lactic acid) (0.036 % w/v) was prepared in DMSO. The capping agent solutions were prepared and aliquoted into vials prior to the start of synthesis.

Transitory exchange

For transitory exchange of acetone with a capping agent other than PS-thiol, the NP solution was added dropwise immediately after completion of the synthesis reaction to a solution of the desired capping agent at a 1: 1 v/v ratio at ambient temperature and then mixed. Except for PS-thiol, these solutions were left uncapped in a fumehood overnight to facilitate acetone evaporation. The vials were capped the following day and stored in the dark at ambient temperature until further characterization. For transitory exchange of acetone with PS-thiol, a previously reported procedure was modified. ⁸² The 1: 1 v/v mixture of PS-thiol dissolved in THF (1.1 mM) and NPs after completion of the synthesis reaction was vortexed vigorously (3 min), became turbid, and then allowed to sit until the NPs precipitated out of the aqueous phase. These NPs were then extracted via pipette, avoiding aspiration of THF, and resuspended in toluene. This solution was centrifuged (15,000 ref, 15 min), the supernatant was removed, and the NPs were resuspended by sonication in toluene. The centrifugation and resuspension step was repeated twice.

Purification

For all capping agents other than PS-thiol, NPs that were capped via transitory exchange were sonicated for ~1 min and then transferred to microcentrifuge tubes. The NPs were purified by centrifugation (13,000 ref, 10 min), and resuspended by sonication in MilliQ water. The centrifugation and resuspension step was repeated once.

Electron microscopy

Low-resolution transmission electron microscopy (TEM) samples were prepared by drop casting sample on a C Type-B Cu grid and drying under hood ventilation. High-resolution transmission electron microscopy (HRTEM) samples were prepared by drop casting sample on an ultrathin C film on lacey C support Cu grid or a holey lacey C support Cu grid and drying under hood ventilation.

Scanning electron (SE)-STEM, high-angle annular darkfield (HAADF)-STEM, brightfield (BF)-STEM, and TEM images were acquired using a Hitachi HF-3300 Environmental TEM operating in vacuo with an acceleration voltage of 300 kV. For NPs without Ag, the sample grids were cleaned with ultraviolet light (5-10 min per side, Zone TEM sample cleaner, Hitachi High-Technologies Canada Inc, Etobicoke, ON, Canada) before imaging.

HAADF-STEM tomography series were acquired using a double -aberration corrected FEI Titan 80-300 HB operating with an electron acceleration voltage of 200 kV and a FEI single-tilt tomography holder. Tilt series were taken with the permissible tilt range for each NP at its location on the TEM grid with 2° intervals.

Sizing

Sizing of the NPs was performed manually on representative electron microscopy images using ImageJ. For each NP, both the size and shape were measured as shown in the schematic representation next to the respective plot to evaluate consistency across different capping agents (n > 20 individual NPs for every NP- capping agent combination). The formula for each shape factor (.S') was chosen based on key shape-specific features for each NP type.

Elemental analysis

Elemental composition was characterized via energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). For EDX, the Bruker EDX detector equipped on the HF-3300 STEM was used with an acceleration voltage of 300 kV. The La peaks of Au, Pd and Ag and the Ka peaks of Co, Ni, Cu and Fe were used for elemental mapping and composition quantification. EDX composition analysis has an inherent error <5% due to X-ray absorption and fluorescence.

Molecular analysis

Molecular composition was characterized via attenuated total reflection-infrared spectroscopy (ATR-IR). All ATR-IR measurements were done with a Nicolet iS50 FTIR equipped with an ATR accessory from Thermo Scientific. Data was collected with the OMNIC software with a wavelength range of 4000-400 cm' ¹ with a step size of 1-2 cm' ¹ and 32 scans per sample. Capped NPs were concentrated via centrifugation (15,000 ref, 15 min) and deposited on Al foil as the substrate for ATR-IR. ⁸³ For uncapped NPs, aliquots of the sample were added to Al foil and allowed to evaporate, and this was conducted >6 times to increase the amount of sample on the substrate.

Computational section

Density functional theory calculations

DFT molecular dynamics (MD) calculations were conducted through the CP2K package with Perdew- Burke-Emzerhof as the exchange correlation and conjugate gradients as the minimizes ⁸⁴ Molopt DZP was selected for the basis set along with Godecker-Teter-Hutter as the pseudopotentials. The grid cutoff value was set to 600 Ry. Au slab unit cells were set up with 64 atoms for Au(l l l), 72 atoms for Au(100), 96 atoms for Au(l 10), and 72 atoms for Au(210). For cell dimension, a 15 A vacuum space was set on the z- axis. Each slab was fully relaxed through cell optimization and geometry optimization to obtain the slab energy. The atoms were fixed during MD and enthalpy calculations except for the first Au slab layer, acetone molecule, and water molecule. The timestep used for MD was set at 1 fs. Acetone or water was relaxed with 15 A in all three dimensions. Binding energies were calculated as: bind A ~ E _l ~ E* — E _A (1) where E _{bind A} is the binding energy of A on Au surface, E, _A is the relaxed energy for A on relaxed Au surface, E _A is the relaxed energy of A in vacuum, and E, is the relaxed energy for Au slabs. Additional software

Schematic illustrations in Figure la-b were modified from Servier Medical Art by Servier, licensed under a Creative Commons Attribution 3.0 Unported License. NP models in Figure 4 were made in Blender (version 2.79b, Blender Foundation, Amsterdam, Netherlands) and Inkscape (version 1.2.1, https://gitlab.com/inkscape/inkscape) was used to compose the figures.

Several alternative embodiments and examples have been described and illustrated herein. The embodiments described above are intended to be exemplary only. A person skilled in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person skilled in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive. Accordingly, while specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the scope defined in the appended claims.

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