Background

[0001] Lateral flow assays can be relatively simple matrix-based devices intended to detect the presence of a target analyte in a liquid sample without the need for specialized and costly equipment, though many lab-based applications exist that are supported by reading equipment. These tests can run a liquid through a pad with reactive molecules that show a visual positive or negative result. Typically, these tests are used for medical diagnostics for home testing, point of care testing, or laboratory use. Adapting these tests to particular target analytes can include performing a plurality of tests utilizing different variables, which can utilize a large quantity of analytes and/or testing materials.

Brief Description of the Drawings

[0002] Figure 1 illustrates an example system including a controller and a dispense device for fluid dispenser frequencies consistent with the present disclosure. [0003] Figure 2 illustrates an example of a memory resource for fluid dispenser frequencies, in accordance with the present disclosure.

[0004] Figure 3 illustrates an example system including a controller and a dispense device for fluid dispenser frequencies consistent with the present disclosure. [0005] Figure 4 illustrates an example of a side view and a top view of a matrix utilized for fluid dispenser frequencies, in accordance with the present disclosure. [0006] Figure 5 illustrates an example of a top view of a matrix utilized for a fluid dispenser frequencies, in accordance with the present disclosure. [0007] Figure 6 illustrates an example of a method for fluid dispenser frequencies, in accordance with the present disclosure.

Detailed Description

[0008] A lateral flow assay (LFA) can include a matrix (e.g., paper-based platform, nitrocellulose, etc.) that can be utilized for the detection and/or quantification of analytes in a mixture (e.g., sample, reagent sample, etc.). In some examples, the sample can be placed on a test device and the results can be displayed in a relatively short period of time (e.g., 5-30 minutes, etc.). In some examples, LFAs can include a relatively long shelf life and may not need refrigeration, which can allow LFAs to be utilized in areas with relatively lower resources (e.g., disaster zone, developing countries, etc.).

[0009] In some examples, LFAs can have a relatively labor-intensive development process. That is, an LFA can be relatively difficult to optimize for different applications (e.g., testing different types of samples, utilizing different types of matrices, etc.). For example, a first matrix can include a first porosity that will allow a particular fluid to pass through the matrix at a first speed (e.g., capillary flow time (CFT), leading edge progression as a function of time, etc.). In this example, a second matrix can include a second porosity that will allow the particular fluid to pass through the second matrix at a second speed. In these examples, the speed or capillary flow time (CFT), a local porosity, and/or the bed volume of the first matrix and the second matrix can affect a test performance of a particular test. In some examples, the CFT, porosity, and/or bed volume of a matrix can provide different interaction times between a particular fluid or sample (e.g., combination of reagents deposited on to a matrix, etc.) and a test line of the matrix.

[0010] As used herein, a test line can include antigens, reagents, or other elements to interact with a fluid or sample deposited on the matrix. In this way, the qualities or performance of the matrix (e.g., CFT, porosity, bed volume, local porosities, etc.) can affect the interaction time, which can affect a test performance. For example, a relatively low interaction time may result in a fluid deposited on the matrix not interacting with the test line for a long enough period and a relatively high interaction time may result in a fluid or sample deposited on the matrix to cause relatively high non-specific interactions causing relatively high background noise. Thus, a fluid composition to be utilized with a particular matrix can be adjusted based on a performance (e.g., CFT, local porosity, bed volume, etc.) of the particular matrix to increase a test performance of a test utilizing the particular matrix by optimizing the interaction time between the fluid and the test line of the particular matrix.

[0011] The present disclosure relates to determining matrix performance for a

LFA or similar device by utilizing a controller coupled to a droplet dispenser (e.g., an inkjet printhead, digital microfluidic system, etc.) to deposit a fluid on a matrix at a particular frequency to control the fluid input to the matrix. As used herein, a matrix performance can include an advancing capillary fluid front location as a function of time for a particular fluid, a capillary flow speed for a particular fluid, capillary flow time for a particular fluid, flow rate as a function of time provided by a dispense device, porosity of a particular matrix, and/or bed volume of a particular matrix. As used herein, the term reservoir refers to a container capable of including a fluid or reagent within the container.

[0012] A controller can be utilized to align a droplet dispenser with a particular portion or particular area of the matrix and deposit the fluid or reagent from a coupled reservoir on to the matrix. As used herein, the term matrix refers to a material that can form a structure suitable for the transfer and/or separation of molecules. For example, a matrix can be a nitrocellulose membrane that can be compatible with a variety of detection methods. Although LFA devices utilizing nitrocellulose membranes are used as specific examples, examples of the present disclosure are not so limited.

[0013] By controlling the fluid input to the matrix, an image sensor (e.g., imaging device, image capturing device, camera, video camera, etc.) can be utilized to monitor a location of advancing capillary fluid front (e.g., front portion of a moving fluid, etc.) of the fluid. In this way, a capillary flow speed (CFS) and/or CFT of the fluid within the matrix can be determined based on the fluid provided to the matrix as a function of time and/or the monitored advancing capillary fluid front of the fluid within the matrix. In some examples, the quantity of the fluid deposited by the dispense head can be monitored over time and utilized to determine a porosity or local porosity of the matrix. Thus, the present disclosure can be utilized to determine the matrix performance.

[0014] Figure 1 illustrates an example system 100 including a controller 104 and a dispense device 102 for fluid dispenser frequencies consistent with the present disclosure. In some examples, the dispense device 102 (e.g., droplet dispenser, digital microfluidic system, etc.) can include a reservoir 108 that can be utilized to store a fluid. As used herein, the term fluid refers to a substance that can be deposited by a droplet dispenser such as the dispense device 102.

[0015] Some examples of fluids that can be contained in the reservoir 108 include a reagent fluid, an antibody fluid, a fluidic barrier, a washing buffer, a stain (e.g., a generic visualization stain), water, etc. For example, the dispense device 102 can include multiple antibody fluids, a hydrophobic fluid for a fluidic barrier, hydrophobic fluid for an evaporation barrier layer, different concentrations of antibody fluids, reagents, stains, and combinations thereof. The dispense device 102 can include a dispense head 110 that can be utilized to deposit a fluid as a droplet 112. The dispense head 110 can deposit the droplet 112 from a reservoir 108 onto the matrix 114 positioned on a stage 116.

[0016] As used herein, “communicatively coupled” refers to various wired and/or wireless connections between devices such that data and/or signals may be transferred in various directions between the devices. The controller 104 can transmit control signals to the dispense device 102 and/or the stage 116 related to an operation of the stage 116. The controller 104 can receive information from the stage 116 or the matrix 114 (e.g., image sensor, imaging device, optical device, humidity information, temperature information, etc.).

[0017] The controller 104 can control the movement and operation of the stage 116, the dispense head 110, or both. The stage 116 can be communicatively coupled to the controller 104 to support the matrix 114 of the LFA or similar matrix, where the stage 116 is moveable to align the matrix 114 with the dispense head 110. The controller 104 can be a component of a computing device such as a processor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a metal- programmable cell array (MPCA), or other combination of circuitry and/or logic to orchestrate execution of instructions. In other examples, the controller 104 can be a computing device that can include instructions stored on a machine-readable medium (e.g., memory resource, non-transitory computer-readable medium, etc.) and executable by a processing resource.

[0018] The dispense head 110 can be a modified inkjet printhead. In some examples, the dispense head 110 can include a mechanically actuated device or micro- mechanically actuated device (e.g., continuous inkjet (CIJ), etc.). In some examples, a modified inkjet printhead can be a thermal inkjet (TIJ) which uses a heating resistor to form an ejection bubble to propel a liquid droplet 112. In another example, the dispense head 110 (e.g., the modified inkjet printhead) is a piezoelectric inkjet (PIJ) which uses a piezoelectric actuator to eject the droplet 112. Although specific examples of a modified inkjet printhead are provided, the disclosure is not limited to these specific examples.

[0019] The dispense head 110 can alter the droplet 112 to a particular volume to be deposited onto the matrix 114 when instructed by the controller 104. For example, the droplet 112 can be customized by the dispense head 110 to deposit a precise volume at a particular frequency (e.g., drop frequency, quantity of drops per unit of time, volume/weight per drop, etc.). In some examples, droplets 112 can utilize relatively small volumes (e.g., pico, nano, and/or micro liters) of reagents and/or fluid. In some examples, the controller 104 can be communicatively coupled to a humidity and temperature control 118. In these examples, the humidity and temperature control 118 can be a system that can alter a humidity and/or temperature of the dispense device 102. For example, the humidity and temperature control 118 can be utilized to maintain a temperature and/or humidity of the area around the matrix 114 within a particular range to ensure the operation of the matrix 114.

[0020] The controller 104 can move the dispense head 110 to an area that is aligned with an access point or particular location of the matrix 114. In some examples, a user of the dispense device 102 can be prompted to place the matrix 114 in a predetermined position and/or orientation relative to the stage 116. For example, the predetermined position can be prompted to the user by utilizing pre-placed markings on the stage 116 which can direct the user to position the matrix 114 on the stage 116. In another example, instead of or in addition to the pre-placed markings on the stage 116, a physical protrusion and/or indentation on the stage 116 can prevent incorrect placement of the matrix 114 on to the stage 116.

[0021] In some examples, the dispense device 102 can include a slide 115. In some examples, the slide 115 can be a transparent slide to allow light to pass through the slide 115 to the matrix 114. For example, the slide 115 can be a glass material or polymer material that can allow light to pass through. That is, in some examples, the slide 115 can be transparent or substantially transparent to allow for images to be captured through the slide 115. In some examples, the dispense device 102 can include a first image sensor 120-1. As used herein, an image sensor, such as the first image sensor 120-1, can include a device that can capture images (e.g., visual images, etc.). For example, the first image sensor 120-1 can be a camera that can capture still images and/or video images. In this way, the first image sensor 120-1 can be utilized to capture images of a flow of a fluid through the matrix 114. In some examples, the slide 115 can be transparent or substantially transparent to allow the first image sensor 120-1 to capture images of the matrix 114 and/or the flow of a fluid through the matrix 114. In this way the first image sensor 120-1 can be utilized to capture images of a front edge of the liquid progressing through the matrix 114. In some examples, the captured images can be utilized to determine a capillary flow speed and/or capillary flow time of the fluid within the matrix 114.

[0022] The dispense device 102 illustrates the first image sensor 120-1 below the matrix 114. In these examples, a slide 115 can be utilized to allow the first image sensor 120-1 to capture images of the matrix 114 and/or the fluid moving through the matrix. In some examples, dyes or other compounds can be added to the fluid to allow the first image sensor 120-1 to more easily capture images of the fluid within the matrix 114. In some examples, the first image sensor 120-1 can be positioned below the matrix 114 when the matrix 114 includes an evaporation barrier layer (e.g., evaporation layer, evaporation barrier, etc.) that is non-transparent or substantially non-transparent. As used herein, non-transparent or substantially non-transparent can include an element that prevents a portion of light from passing through the element. For example, a nontransparent or substantially non-transparent evaporation barrier layer on a top surface of the matrix 114 can prevent an imaging device, such as the first imaging sensor 120- 1 , from capturing images of the fluid within the matrix 114.

[0023] In other examples, the matrix 114 can include a transparent or substantially transparent evaporation barrier layer that can allow an image sensor, such as the first image sensor 120-1 , to capture images from a top surface or above the matrix 114. In these examples, the first image sensor 120-1 can be positioned above the matrix 114 to capture the flow of the fluid within the matrix 114. However, in some examples, a substantially transparent evaporation barrier layer can be utilized when the first image sensor 120-1 is positioned below the matrix 114 as illustrated in Figure 1. In some examples, the first image sensor 120-1 can be utilized to determine a speed of the fluid within the matrix 114. In some examples, the first image sensor 120-1 can capture images or video of the progression of the fluid within the matrix 114 for a time period. In some examples, the progression of a front edge of the fluid within the matrix 114 can be utilized as a function of time to determine a capillary flow speed. In addition, the capillary flow speed can be utilized with a distance traveled to determine a capillary flow time. Thus, the first image sensor 120-1 can be utilized to determine a flow distance of the fluid through the matrix 114 as a function of time, which can be utilized to determine a rate or speed of the fluid through the matrix 114.

[0024] As described further herein, the flow rate of a particular fluid can be utilized to determine the porosity of the matrix 114 even when the matrix 114 includes a heterogeneous porosity. As used herein, a matrix, such as matrix 114, with a heterogeneous porosity can include a matrix with different porosities within different areas of the matrix. For example, the matrix 114 can include a first portion with a first porosity and a second portion with a second porosity. In this example, the first porosity can have a first flow rate and the second porosity can have a second flow rate for the same fluid. In this way, the dispense device 102 can be utilized to determine a local porosity for the matrix 114. As used herein, a local porosity can include a porosity for a specific portion of a matrix.

[0025] In some examples, the dispense device 102 can include a second image sensor 120-2. In some examples, the second image sensor 120-2 can be a similar device as the first image sensor 120-1. For example, the second image sensor 120-2 can be utilized to capture images such as, but not limited to: still images, video images, infrared images, one dimensional (1D) images (e.g., profile of the accumulation droplet 113 height via a laser and linear photo-detector), etc. In some examples, the second image sensor 120-2 can be directed at an accumulation droplet 113 (e.g., sample, droplet, etc.) positioned on the matrix 114. As described further herein, the accumulation droplet 113 can be positioned at an access port of an evaporation barrier layer positioned on a surface of the matrix 114. As used herein, an evaporation barrier layer can include a barrier solution that is deposited on a surface of the matrix 114 to prevent a fluid from evaporating out of the matrix 114. In some examples, the access port of the evaporation barrier layer can be an aperture of the evaporation barrier layer that allows fluid of the accumulation droplet 113 to enter the matrix 114. In some examples, the access port can prevent the fluid of the accumulation droplet 113 from entering the matrix 114 at other areas of the matrix 114 other than the access port. In some examples, the size of the access port can be adjusted based on the fluid utilized.

[0026] In some examples, the second image sensor 120-2 can be utilized to capture images of the accumulation droplet 113 to determine a volume of the accumulation droplet 113 based on a height and/or diameter of the accumulation droplet 113. In this way, the second image sensor 120-2 can be utilized to ensure that the volume of the accumulation droplet 113 is maintained within a particular volume range. For example, the volume of the accumulation droplet 113 can be maintained at or below an upper threshold volume and/or at or above a lower threshold volume. In these examples, the volume of the accumulation droplet 113 can be utilized to alter a frequency of the droplet 112 dispensed by the dispense head 110. That is, the accumulation droplet 113 can be maintained through a feedback loop with the controller 104. For example, the dispense head 110 can dispense the droplet 112 at a first frequency. In this example, the accumulation droplet 113 can exceed the upper threshold volume. In this example, the controller 104 can instruct the dispense head 110 to alter the first frequency to a second frequency that is lower than the first frequency in response to determining the accumulation droplet has exceeded the upper threshold volume. In this way, the volume of the accumulation droplet 113 can be lowered without allowing the volume of the accumulation droplet 113 to fall below the lower threshold volume.

[0027] In some examples, the second image sensor 120-2 can be utilized with a light source 122 and/or a filter 124. In some examples the light source and filter 124 can be utilized to highlight the accumulation droplet 113 such that the second image sensor 120-2 can capture images of the accumulation droplet that are relatively clearer, which can result in more precise analysis of the quantity of fluid within the accumulation droplet 113. In some examples, the light source 122 can be a light emitting diode (LED), an array of LEDs, a laser diode, an array of laser diodes, a vertical-extemal-cavity surface-emitting-laser (VECSEL), and/or an array of VECSELs. As used herein, an array of LEDs can include a plurality of LEDs arranged to emit light. In some examples, the filter 124 can be a diffuser. As used herein, a diffuser can include a material that scatters light. In some examples, the diffuser can scatter light to “soften” the light transmitted by the light source 122. In some examples, the filter 124 can include a material such as glass with an unpolished surface, Teflon, opal glass, among other types of material that are capable of scattering light from the light source 122. In some examples, the light source 122 and filter 124 can be positioned on a first side of the stage 116 and the second image sensor 120-2 can be positioned on a second side of the stage 116. In some examples, the first side and the second side of the stage 116 can be opposite sides of the stage 116.

[0028] In some examples, the controller 104 can include instructions 126, 128, 130, 132. In some examples, the controller 104 can be a computing device that include a memory resource to store the instructions 126, 128, 130, 132 and the instructions 126, 128, 130, 132 can be executed by a processing resource (e.g., central processing unit (CPU), processor, etc.) to instruct the dispense device 102 to perform particular functions.

[0029] In some examples, the controller 104 can include instructions 126 to cause the dispense head 110 to deposit the fluid at a particular position on the matrix 114 at a first frequency. In some examples, the particular position on the matrix 114 can be a position that corresponds to an access port on the matrix 114. For example, a barrier solution can be deposited on a surface of the matrix 114 such that a plurality of apertures are positioned through the barrier solution to generate the plurality of access ports. In these examples, the plurality of access ports can allow the accumulation droplet 113 to enter into the matrix 114 at the particular position on the matrix 114. In some examples, the access ports can prevent an accumulation droplet 113 from entering the matrix 114 through the barrier solution outside of the access port.

[0030] In this way, the flow of the accumulation droplet 113 into the matrix 114 can be controlled by the frequency and/or volume of the droplets 112 as well as by the an area or size of the access port. For example, a diameter or area of the access port can be altered to allow a greater quantity of fluid from the accumulation droplet 113 into the matrix 114 or to allow a lower quantity of fluid from the accumulation droplet 113.

For example, a relatively smaller access port can slow the fluid from the accumulation droplet 113 entering the matrix 114 compared to the same fluid from the accumulation droplet 113 entering the matrix 114 through a relatively larger access port.

[0031] As described herein, the dispense head 110 can receive instructions from the controller 104 to deposit droplets 112 at a particular volume and/or a particular frequency. In some examples, the first frequency can be an initial frequency and volume to generate the accumulation droplet 113 with a particular volume. For example, the dispense head 110 can deposit a first plurality of droplets 112 with a first volume at the first frequency to generate an accumulation droplet 113 on the matrix 114 or evaporation barrier layer (e.g., barrier solution deposited on a surface of the matrix 114 to prevent evaporation of a fluid within the matrix 114, etc.) that is above a lower threshold volume. In some examples, the lower threshold volume can be a volume of the accumulation droplet 113 to provide flow of fluid into the matrix 114.

[0032] In some examples, the controller 104 can include instructions 128 to determine an accumulation volume of the fluid (e.g., accumulation droplet 113, etc.) at the particular position on the matrix 114. As used herein, the accumulation volume of the fluid includes a volume of an accumulation droplet 113 on the matrix 114. As described herein, the accumulation volume of the fluid can be determined utilizing the second image sensor 120-2, light source 122, and/or the filter 124. In some examples, the controller 104 can utilize the second image sensor 120-2 to determine a height and/or diameter of the accumulation droplet 113. In these examples, the controller 104 can utilize the height and/or diameter of the accumulation droplet 113 to determine the accumulation volume of the accumulation droplet 113. As described herein, the accumulation volume can be maintained between a lower threshold volume and an upper threshold volume. In some examples, the lower threshold volume can correspond to a minimum quantity of fluid to provide a constant flow of fluid through the matrix 114. In other examples, the upper threshold volume can correspond to a maximum quantity of fluid before the quantity of fluid alters a test performance associated with the flow of fluid through the matrix 114.

[0033] In some examples, the controller 104 can include instructions 130 to alter the first frequency to a second frequency based on the accumulation volume. As described herein, the controller 104 can alter the frequency of the droplets 112 based on or in response to the accumulation volume of the accumulation droplet 113. In some examples, the first frequency can be greater than the second frequency. For example, the accumulation volume can be at or exceeding an upper threshold volume. In this example, the controller 104 can lower the frequency of the droplets 112 by altering the frequency from the first frequency to the second frequency when the first frequency is greater than the second frequency. As described herein, the first frequency can be utilized to generate the accumulation droplet 113 with a particular accumulation volume before altering to the second frequency. In a different example, the second frequency can be greater than the first frequency. In this example, the accumulation volume of the accumulation droplet 113 can be at or exceeding a lower threshold and the controller may alter the frequency to the second frequency to increase the accumulation volume of the accumulation droplet 113.

[0034] In some examples, the controller 104 can include instructions 132 to determine a speed of lateral flow of the fluid through the matrix 114 while utilizing the second frequency. In some examples, the controller 104 can be utilized to determine the speed of lateral flow of the fluid. For example, the first image sensor 120-1 can capture images of the fluid within the matrix 114 at different times with corresponding different positions. In some examples, the controller 104 can determine when the second frequency is initiated, which can trigger the acquisition and time-stamps for the acquisition of the images from the first image sensor 120-1 to determine the speed of the flow. For example, the controller 104 can determine when the frequency of the droplets 112 provides a volume of the accumulation droplet 113 that is between an upper threshold and a lower threshold volume. In this example, the first image sensor 120-1 can capture images necessary to determine a starting position and a stopping position for the fluid over a period of time and/or capture images of the fluid traveling from the starting position to the stopping position. In some examples, the starting position and the stopping position can be positioned between an access port and a vent port of an evaporation barrier layer. In this way, the speed of lateral flow may not be affected by dynamics of an entry point or ending point of a lateral flow path of the fluid through the matrix 114.

[0035] As used herein, a speed of lateral flow can include a distance traveled in a particular direction over a period of time. In these examples, the speed of lateral flow can be calculated by the controller 104 based on a time stamp associated with a starting position and a time stamp associated with a stopping position. In some examples, the matrix 114 can be a three-dimensional matrix that can allow the fluid to move in a radial direction or move in a three-dimensional direction. In these examples, the speed of lateral flow can include the movement of the fluid in a lateral direction with respect to the matrix 114. In some examples, the dispense device 102 can be utilized to deposit a fluidic barrier to define a lateral flow path for the fluid to travel through the matrix 114. In this way, the fluid can be restricted to move in a lateral direction within the matrix 114. As described herein, a starting position and a stopping position can be identified by the controller 104 utilizing the captured images from the first image sensor 120-1 to determine the speed of lateral flow of the fluid within the matrix 114. In some examples, the starting position can be positioned between an access port and a center of a lateral flow path and the stopping position can be positioned between a vent port and the center of the lateral flow path.

[0036] As described herein, the system 100 (e.g., controller 104, etc.) can be utilized to determine a speed of lateral flow, a CFT, a bed volume, and/or a porosity of a matrix 114 for an LFA test for a particular use (e.g., combination of reagents, types of reagents, concentration of reagents, depth of the reagents positioned in the matrix 114, time of interaction between reagents and a test line, and/or other features that can affect a performance of the matrix 114).

[0037] Figure 2 illustrates an example of a memory resource 240 for fluid dispense frequencies, in accordance with the present disclosure. In some examples, the memory resource 240 can be a part of a computing device or controller that can be communicatively coupled to a dispense device. For example, the memory resource 240 can be part of a controller 104 as referenced in Figure 1 and communicatively coupled to a dispense device 102 as referenced in Figure 1. In some examples, the memory resource 240 can be communicatively coupled to a processing resource 242 that can execute instructions 246, 248, 250, 252, 254 stored on the memory resource 240. For example, the memory resource 240 can be communicatively coupled to the memory resource 240 through a communication path 244. As used herein, a communication path 244 can include a wired or wireless connection that can allow communication between devices.

[0038] The memory resource 240 may be electronic, magnetic, optical, or other physical storage device that stores executable instructions. Thus, non-transitory machine readable medium (e.g., a memory resource 240) may be, for example, a non- transitory MRM comprising Random Access Memory (RAM), an Electrically-Erasable Programmable ROM (EEPROM), a storage drive, an optical disc, and the like. The non- transitory machine readable medium (e.g., a memory resource 240) may be disposed within a controller and/or computing device. In this example, the executable instructions 246, 248, 250, 252, 254 can be “installed" on the device. Additionally, and/or alternatively, the non-transitory machine readable medium (e.g., a memory resource 684) can be a portable, external or remote storage medium, for example, that allows the system 680 to download the instructions 246, 248, 250, 252, 254 from the portable/extemal/remote storage medium. In this situation, the executable instructions may be part of an “installation package”. As described herein, the non-transitory machine readable medium (e.g., a memory resource 240) can be encoded with executable instructions for array droplet manipulations.

[0039] The instructions 246, when executed by a processing resource such as the processing resource 242, can include instructions to cause a dispense head to deposit a first barrier solution to separate a matrix (e.g., matrix 114 as referenced in Figure 1, etc.) into a plurality of portions (e.g., lateral flow paths, etc.). In some examples, the first barrier solution can be deposited to separate the matrix 114 into a plurality of lateral flow paths. As used herein, the lateral flow paths or portions of the matrix 114 can include a sided barrier to force a fluid to flow in a lateral direction or linear direction. For example, a portion or lateral flow path can include a barrier solution that is deposited on each side of the portion or lateral flow path. In some examples, the size of the portion or lateral flow path can be based on a distance the fluid will be traveling through the matrix to allow a controller to determine a speed of lateral flow for a fluid utilizing a starting position of the fluid, a stopping position of the fluid, and a quantity of time the fluid took to move from the starting position to the stopping position. The plurality of portions and/or lateral flow paths are described further herein with reference to Figure 5.

[0040] The instructions 248, when executed by a processing resource such as the processing resource 242, can include instructions to cause a dispense head to deposit a second barrier solution on a surface of a matrix to generate an evaporation barrier layer on a top of the plurality of portions, wherein the evaporation barrier layer includes an access port and a vent port for each of the plurality of portions. In some examples, the second barrier solution can be deposited across a top surface of the matrix (e.g., matrix 114 as referenced in Figure 1 , etc.) to prevent a fluid passing through the matrix from moving out of a top surface of the matrix. In some examples, the evaporation barrier layer can prevent the fluid from evaporating through a top surface of the matrix, which can alter results of a calculated speed of lateral flow and/or porosity of the matrix.

[0041] In some examples, the evaporation barrier layer can include an access port to allow the fluid to enter the matrix at a first end of the portion and/or lateral flow path and a vent port to allow air to exit the matrix as the fluid travels through the matrix. In some examples, the vent port can prevent the fluid from stopping due to a pressure build up within the matrix when the evaporation barrier layer prevents gasses from evaporating the matrix. In some examples, the access port can be an aperture through the evaporation barrier layer to allow fluid to enter into the matrix when a droplet is deposited at the location of the access port. In some examples, the size of the aperture of the access port can be based on a predicted entry speed (e.g., speed at which the fluid enters the matrix) and/or a predicted lateral flow speed of the fluid. In some examples, the frequency of the droplets being provided to the access port can be altered to allow a particular quantity of fluid to enter the matrix through the access port. [0042] The instructions 250, when executed by a processing resource such as the processing resource 242, can include instructions to cause a dispense head to deposit a fluid at the access port of the evaporation barrier layer. As described herein, a dispense head can receive instructions to deposit the fluid at the access port of the evaporation barrier layer at a particular frequency and/or quantity to allow a flow of fluid into the matrix and through the portion or lateral flow path.

[0043] The instructions 252, when executed by a processing resource such as the processing resource 242, can include instructions to monitor a speed of lateral flow for the plurality of portions. As described herein, the speed of lateral flow can be determined or calculated by determining a distance traveled over a period of time in a lateral or linear direction. In some examples, the speed of lateral flow can be calculated utilizing an image sensor that monitors a distance traveled by the fluid over a period of time. The speed of lateral flow can be calculated for a matrix with a heterogenous porosity. As used herein, a heterogenous porosity matrix can include a matrix that includes a plurality of different porosities across the matrix. In some examples a matrix can have different porosities that surround different test lines. In this way, the matrix can be utilized to alter a speed of lateral flow as the fluid passes a particular test line within the matrix. As described herein, the CFT or speed of lateral flow can affect how a reagent within the matrix interacts with components of the test line. In this way, the same fluid with reagents may interact with a first test line for a first quantity of time and interact with a second test line for a second quantity of time.

[0044] In some examples, the memory resource 240 can include instructions to monitor a volume of fluid dispensed at the access port. As described herein, a dispense device can deposit a particular volume of fluid at a particular frequency. In addition, the particular frequency can be altered based on a feedback loop associated with a volume of an accumulation droplet. In this way, the volume or quantity of fluid that is deposited by the dispense device can be altered over a period of time. In these examples, a controller or sensor can be utilized to monitor the volume or quantity of fluid deposited by the dispense device as a function of time. In these examples, the monitored volume or quantity of fluid deposited as a function of time can be utilized to calculate or determine a porosity of the matrix.

[0045] The instructions 254, when executed by a processing resource such as the processing resource 242, can include instructions to determine a porosity of the matrix based on the speed of lateral flow and volume of fluid dispensed as a function of time. In some examples, the matrix porosity can be calculated based on a geometry of the matrix (e.g., volume of the matrix, width x length x height of the matrix etc.), advancing capillary fluid front location on the matrix as a function of time, and/or a volume flow rate as a function of time (e.g., volume of fluid deposited on the matrix over time, etc.). In some examples, the instructions 254 can include instructions to determine a local porosity for the matrix. As used herein, a local porosity of the matrix includes a porosity of a particular portion of the matrix. As described herein, a matrix can include a plurality of portions that each utilize a corresponding porosity to either increase or decrease a speed of a fluid passing a test line.

[0046] In some examples, the memory resource 240 can include instructions to monitor a volume of a droplet of the fluid on the access port of the evaporation barrier layer as a function of time. As described herein, the frequency and/or volume of each droplet dispensed by a dispense device can be altered utilizing a feedback loop. As such, the frequency of droplets and/or the volume of droplets can be altered over a period of time. In these examples, the droplet frequency and/or the droplet volume can be monitored to determine the volume of fluid that is deposited on the access port over a period of time. In some examples, the quantity of fluid deposited by the dispense device as a function of time can be utilized as a rate of fluid deposition or flow rate of the dispense head. As described further herein, the rate of fluid deposition or flow rate of the dispense head can be utilized with the flow front of the fluid in the matrix as function of time and/or the matrix geometry to determine a porosity or local porosity of the matrix. [0047] As such, a plurality of local porosities can be calculated or determined based on the speed of lateral flow of the fluid through the corresponding portion of the matrix. In some examples, the memory resource can include instructions to determine a bed volume for the matrix based on drop volume, a frequency of drops deposited at the access port, and/or a monitoring time (e.g., time it takes for the fluid to move from a starting location to a stopping location, etc.). As used herein, a bed volume can include a volume of fluid that can occupy a portion of the matrix.

[0048] Figure 3 illustrates an example system 300 including a controller 304 and a dispense device 302 (e.g., digital microfluidic array, etc.) for fluid dispense frequencies consistent with the present disclosure. In some examples, the system 300 can include the same or similar elements as system 100 as referenced in Figure 1. For example, the system 300 can include a dispense device 302 communicatively coupled to a controller 304 via communication path 306.

[0049] As described herein, the system 300 can include a stage 316 that can be utilized to position a slide 315 (e.g., transparent slide, etc.) that can hold a matrix 314. As described herein, the controller 304 can be utilized to provide instructions to the dispense device 302 to provide a fluid from a reservoir 308 to a dispense head 310 such that the dispense head 310 can deposit droplets 312 on to the matrix 314. In some examples, the dispense head 310 can dispense the droplets 312 at a particular volume and/or frequency to generate an accumulation droplet 313 such that the accumulation droplet 313 includes a volume that is within a threshold range of volumes. In some examples, the dispense device 302 can include a plurality of devices such as a humidity and temperature control 318, a first image sensor 320-1, a second image sensor 320-2, a light source 322, and/or a filter 324. As described herein, the humidity and temperature control can be utilized to maintain an operating temperature and operating humidity for the dispense device 302. As used herein, an operating temperature can include a temperature or temperature range that promotes a fluid moving through the matrix 314 and an operating humidity can include a humidity or humidity range that promotes a fluid moving through the matrix 314.

[0050] In some examples, the system 300 can include a first image sensor 320-1 positioned to capture a first image of a capillary flow of the fluid moving through the matrix 314. In some examples, the first image sensor 320-1 can be positioned below a surface of the stage 316 and/or below a surface of the matrix 314. In these examples, the stage 316 can include an aperture or transparent surface to allow the first image sensor 320-1 to capture images of a fluid moving through the matrix 314. In these examples, the slide 315 can be made of a transparent or substantially transparent material to allow the first image sensor 320-1 to capture images of the fluid moving through the matrix 314 from a position below the slide 315. That is, the first image sensor 320-1 can be directed to capture images through the stage 316 and through the slide 315.

[0051] In some examples, the first image sensor 320-1 can be positioned above the matrix 314. In these examples, a transparent or substantially transparent evaporation barrier layer can be generated on the surface of the matrix 314. As described herein, an evaporation barrier layer can be a barrier solution that is deposited over a portion of the matrix 314 to prevent a fluid from exiting or evaporating out of the matrix 314, which can alter a test performance of the fluid (e.g., capillary flow time (CFT), speed of lateral flow, etc.). In these examples, the first image sensor 320-1 can be positioned above the matrix 314 to determine a speed of lateral flow for the fluid. In these examples, the slide 315 can be removed from the dispense device 302 and/or the dispense device 302 can utilize a non-transparent material for the slide 315. As described herein, the first image of a capillary flow can include a still image, video image, or other type of image that can be utilized to monitor a change in location of the fluid within the matrix 314 over time.

[0052] In some examples, the system 300 can include a second image sensor 320-2 positioned to capture a second image of a droplet of fluid to determine a volume of the droplet. In some examples, the second image sensor 320-2 can positioned or directed at a top surface of the matrix 314 such that the second image sensor 320-2 can capture images of an accumulation droplet 313 that is positioned on a surface of the matrix 314. In some examples, the controller 304 can utilize the second image sensor 320-2 to determine a height of the accumulation droplet 313 and calculate the volume of the accumulation droplet 313 based on the determined height of the accumulation droplet 313. In some examples, the second image sensor 320-2 can include a light array and an image capturing device positioned parallel to a top surface of the matrix 314. For example, the second image sensor 320-2 can be a camera (e.g., image capturing device) that utilizes a light source 322 and a filter 324 to more precisely calculate the volume of the accumulation droplet 313. In some examples, the location of the second image sensor 320-2 can be on a first end of the matrix 314 and the light source 322 and filter 324 can be on a second end of the matrix 314.

[0053] In some examples, the controller 304 can include instructions 356. In some examples, the controller 304 can be a computing device that include a memory resource to store the instructions 356 and the instructions 356 can be executed by a processing resource (e.g., central processing unit (CPU), processor, etc.) to instruct the dispense device 302 to perform particular functions.

[0054] In some examples, the controller 304 can include instructions 356 to to cause a dispense head dispense the fluid on to an access port of the matrix at a particular frequency and volume based on the volume of the droplet. As described herein, the volume of the accumulation droplet 313 can be adjusted such that the volume is within a range of volumes that promote the flow of a fluid through the matrix 314. In some examples, the frequency of the droplets 312 can be altered to dynamically adjust the volume of the accumulation droplet 313 such that the volume of the accumulation droplet is less than an upper threshold volume and more than a lower threshold volume. In this way, the speed of lateral flow for the fluid within the matrix 314 can be determined without adjusting for an effect of the accumulation droplet 313 being greater than the upper threshold volume or being less than the lower threshold volume. [0055] Figure 4 illustrates an example of a side view and a top view of a matrix 414 utilized for fluid dispenser frequencies, in accordance with the present disclosure. Figure 4 illustrates a side view on the left and a top view on the right. The side view on the left illustrates a matrix 414 with an evaporation barrier layer 462 positioned on a top surface. As described herein, the evaporation barrier layer 462 can be a barrier solution that is deposited on a surface of the matrix 414. In some examples, the evaporation barrier layer 462 does not penetrate into the matrix 414. That is, the evaporation barrier layer 462 may not alter or prevent a flow of the fluid within the matrix 414. In contrast, the evaporation barrier layer 462 can prevent the fluid from evaporating through a surface or evaporating out of the matrix 414. In some examples, the evaporation barrier layer 462 can include a vent 466 to allow the fluid to move in a lateral direction within the matrix 414 under the evaporation barrier layer 462.

[0056] In some examples, the side view of the matrix 414 can illustrate an accumulation droplet 413 positioned over an access port 460 of the evaporation barrier layer 462. As described herein, the access port 460 can include an aperture through the evaporation barrier layer 462 to allow fluid of the accumulation droplet 413 to enter the matrix 414 through a surface of the matrix 414. When the fluid has entered the matrix 414, the fluid can move in a lateral direction as illustrated by arrow 464. In some examples, the fluid within the matrix can move in the direction of arrow 464 when the vent port 466. In some examples, the fluid can move through the matrix 414 in a lateral flow path that is defined by a barrier solution. For example, a path can be separated or defined utilizing a barrier solution that is penetrated through the matrix 414 to prevent the fluid from diverting from the lateral flow path. In some examples, a lateral flow path can include parallel sides defined by the barrier solution and/or parallel ends that are defined by the barrier solution. In this way, the fluid of the accumulation droplet 413 can be forced in a lateral or linear direction through the matrix 414.

[0057] In some examples, the top view of the matrix can illustrate the evaporation barrier layer 462 covering the lateral flow path of the matrix 414. The top view of the matrix also illustrates an access port 460 positioned on a first end of the lateral flow path and a vent port 466 positioned on a second end of the lateral flow path. As described herein, the accumulation droplet 413 can be positioned over the access port 460 to allow the fluid of the accumulation droplet 413 to enter the matrix 414. In some examples, the vent port 466 can allow air to escape the matrix 414 as the fluid moves in the direction of arrow 464.

[0058] In some examples, the access port 460 and/or vent port 466 can be apertures with particular shapes. For example, the access port 406 can be a circular or oval aperture to allow the fluid of the accumulation droplet 413 to enter the matrix 414 at a particular location across a width of the lateral flow path. In this example, the access port 406 can be positioned between a first edge and a second edge of the lateral flow path. In other examples, the access port 406 can be positioned closer to a first edge than a second edge of the lateral flow path. In some examples, the access port 406 and/or vent port 466 can extend from a first edge of the lateral flow path to a second edge of the lateral flow path. For example, the access port 406 and/or vent port 466 can extend from a left edge of the lateral flow path to a right edge of the lateral flow path as illustrated by Figure 4. In these examples, the access port and/or vent port 466 can be rectangular or square shaped to allow for more fluid to enter the lateral flow path or allow for more air to escape the lateral flow path.

[0059] Figure 5 illustrates an example of a top view of a matrix 514-1 , 514-2 utilized for a fluid dispenser frequencies, in accordance with the present disclosure. Figure 5 illustrates a top view of a first matrix 514-1 and a second matrix 514-2. In some examples, the first matrix 514-1 can illustrate a top view after a deposit of a first barrier solution and the second matrix 514-2 can illustrate a top view after a deposit of a second barrier solution.

[0060] In some examples, the first matrix 514-1 can illustrate when the matrix 514-1 is separated into a plurality of lateral flow paths 572 utilizing a barrier solution. As described herein, the lateral flow paths 572 can be lateral paths that are defined utilizing a barrier solution that penetrates through the matrix 514-1. In some examples, each of the plurality of lateral flow paths 572 can be utilized to perform corresponding performance tests to determine a speed of lateral flow of a fluid.

[0061] In some examples, the second matrix 514-2 can illustrate when the matrix 514-2 is provided with an evaporation barrier layer that covers each of the plurality of lateral flow paths 572. In some examples, the evaporation barrier layer can include a barrier solution that is deposited on to a surface of the matrix 514-2 without penetrating the matrix 514-2. In this way, the evaporation barrier layer can be utilized to prevent a fluid moving through the plurality of lateral flow paths 572 from evaporating through a top surface of the matrix 514-2. In some examples, the evaporation barrier layer can be non-transparent, which may allow an image device or image sensor to capture images of the flow of the fluid through the lateral flow paths 572 from below the matrix 514-2. In other examples, the evaporation barrier layer can include a barrier solution that is transparent or substantially transparent to allow an image device or image sensor to capture images of the flow of the fluid through the lateral flow paths 572 from above the matrix 514-2 or below the matrix 514-2.

[0062] As described herein, the evaporation barrier layer can include an access port 560 positioned at a first end of the lateral flow paths 572 and a vent port 566 positioned at a second end of the lateral flow paths 572. In this way, a fluid can be deposited on to the location of the access ports 560 and the corresponding vent ports 566 can allow air to escape the lateral flow paths 572 as the fluid moves through the lateral flow paths 572.

[0063] Figure 6 illustrates an example of a method 680 for fluid dispenser frequencies, in accordance with the present disclosure. In some examples, the method 680 can be performed by a computing device and/or controller. For example, each part of the method 680 can represent instructions that can be stored on a memory resource and executed by a processing resource to instruct a dispense device to perform particular functions.

[0064] At 682, the method 680 can include inserting a substrate (e.g., matrix, etc.) and loading reservoirs (e.g., reservoir 108 as illustrated in Figure 1, reservoir 308 as illustrated in Figure 3, etc.) with fluid. As described herein, the matrix can be positioned at a particular location on a stage and/or slide that can be positioned on the stage. In some examples, the stage and/or slide can utilize markings to identify a particular location to position the matrix or substrate. In this way, a controller or computing device can identify a location to deposit the fluid on to the matrix.

[0065] At 684, the method 680 can include adjusting the sample into focus. In some examples, the sample can be the fluid deposited on to the matrix and/or evaporation barrier layer. For example, a sample can include an accumulation droplet (e.g., accumulation droplet 113 as illustrated in Figure 1, etc.). In some examples, the sample can include a fluid with known properties (e.g., known molecular weight, etc.). In some examples, adjusting the sample into focus can include altering a location of the accumulation drop to align with a view of an image sensor. As described herein, an image sensor can be utilized to determine a height and/or diameter of the sample. In some examples, the height and/or diameter of the sample can be utilized to determine a volume of the sample on the matrix. In this way, the image sensor or location of the sample can be altered to increase a clarity of an image of the sample, which can increase an accuracy of a calculated or determined volume of the sample.

[0066] At 686, the method 680 can include starting feedback controlled dispensing. As described herein, the dispense head of a dispense device can provide droplets onto the substrate or matrix at a particular volume and/or frequency. In some examples, the volume and/or frequency can be altered based on a determined volume of the sample or accumulation droplet. In this way, feedback of the volume can be provided to the controller and the controller can alter the volume or frequency of fluid provided by the dispense device. Thus, the volume of the sample or accumulation droplet can be controlled by feedback of the volume of the sample or accumulation droplet.

[0067] At 688, the method 680 can include monitoring a speed of a liquid flow boundary. As used herein, the liquid flow boundary can be a leading edge of the fluid as the fluid moves through the substrate or matrix. For example, the liquid flow boundary can be an edge of a fluid moving from the access port to the vent port of the lateral flow path within the matrix. In some examples, the leading edge of the fluid can be utilized to determine a distance traveled by the fluid over a period of time, which can be utilized to calculate the speed of the liquid flow.

[0068] At 690, the method 680 can include analyzing flow speed and bed volume relation with firing frequency. As described herein, the flow speed and bed volume can have a relationship that can be utilized to determine a porosity of the matrix or substrate. For example, the matrix porosity can be calculated based on a geometry of the matrix (e.g., width x length x height of the matrix etc.), advancing capillary fluid front location on the matrix as a function of time, and/or a volume flow rate as a function of time (e.g., volume of fluid deposited on the matrix overtime, etc.).

[0069] The figures herein follow a numbering convention in which the first digit corresponds to the drawing figure number and the remaining digits identify an element or component in the drawing. Elements shown in the various figures herein can be added, exchanged, and/or eliminated so as to provide a number of additional examples of the present disclosure. In addition, the proportion and the relative scale of the elements provided in the figures are intended to illustrate the examples of the present disclosure and should not be taken in a limiting sense. As used herein, the designator “N”, particularly with respect to reference numerals in the drawings, indicates that a number of the particular feature so designated can be included with examples of the present disclosure. It is also to be understood that the terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” can include both singular and plural referents, unless the context clearly dictates otherwise. The designators can represent the same or different numbers of the particular features. Further, as used herein, "a number of an element and/or feature can refer to one or more of such elements and/or features.

[0070] In the foregoing detailed description of the present disclosure, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration how examples of the disclosure may be practiced. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the examples of this disclosure, and it is to be understood that other examples may be utilized and that process, electrical, and/or structural changes may be made without departing from the scope of the present disclosure.