WO2022081133A1

WO2022081133A1 - Modified porous wicking membranes

Info

Publication number: WO2022081133A1
Application number: PCT/US2020/055304
Authority: WO
Inventors: Rajasekar Vaidyanathan; Benjamin Abelovski; Beverly CHOU; Anita Rogacs
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-10-13
Filing date: 2020-10-13
Publication date: 2022-04-21

Abstract

The present disclosure describes methods of modifying porous wicking membranes. In one example, a method of modifying a porous wicking membrane can include applying a flow modifier composition to a porous wicking membrane. The porous wicking membrane can have an initial capillary flow time (CFT) before the flow modifier composition is applied and a modified CFT after the flow modifier composition is applied. The modified CFT can be finite and different from the initial CFT. The CFT can be defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane. The flow modifier composition can include an aqueous liquid vehicle and a flow modifying material that includes wax nanoparticles to increase the CFT or a surfactant to decrease the CFT.

Description

MODIFIED POROUS WICKING MEMBRANES

BACKGROUND

[0001] Porous wicking membranes are used in a variety of applications. For example, certain types of chemical testing utilize a porous wicking membrane material through which a sample fluid flows by capillary action. As a specific example, lateral flow assays are a type of test in which a sample fluid flows along a porous material such as a porous nitrocellulose pad. Lateral flow assays often include a test line and a control line. The test line can include a suitable test reactant that is reactive with a target molecule in the sample fluid. In some cases, the target molecule can bind with a colored conjugate tag as the sample fluid flows through the membrane. The target molecules can then bind with test reactants at the test line, which can produce a visible color change at the test line due to the accumulation of conjugate tags at the test line. The sensitivity and selectivity of lateral flow assays often depends somewhat on the flow rate of the sample fluid through the membrane. Lateral flow assay tests are often designed to operate at a particular flow rate in order to provide sufficient time for target molecules to react with test reactants and to bind with conjugate tags.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a flowchart illustration of an example method of modifying a porous wicking membrane in accordance with examples of the present disclosure;

[0003] FIGs. 2A and 2B show an example porous wicking membrane in accordance with the present disclosure; [0004] FIG. 3 shows another example porous wicking membrane in accordance with the present disclosure;

[0005] FIG. 4 shows yet another example porous wicking membrane in accordance with the present disclosure;

[0006] FIG 5 shows another example porous wicking membrane in accordance with the present disclosure;

[0007] FIG 6 shows yet another example porous wicking membrane in accordance with the present disclosure;

[0008] FIG 7 shows still another example porous wicking membrane in accordance with the present disclosure;

[0009] FIG. 8 shows another example porous wicking membrane in accordance with the present disclosure;

[0010] FIG. 9 shows another example porous wicking membrane in accordance with the present disclosure;

[0011] FIG. 10 shows yet another porous wicking membrane in accordance with the present disclosure;

[0012] FIG. 11 is a schematic illustration of an example fluid ejection device in accordance with the present disclosure; and

[0013] FIG. 12 is a graph showing the distance traveled by a water front in 21 seconds and in 60 seconds across porous wicking membranes that were treated with different concentrations of wax nanoparticles.

DETAILED DESCRIPTION

[0014] The present disclosure describes methods of modifying porous wicking membranes. In one example, a method of modifying a porous wicking membrane includes applying a flow modifier composition to the porous wicking membrane. The porous wicking membrane has an initial capillary flow time (CFT) before the flow modifier composition is applied and a modified CFT after the flow modifier composition is applied. The modified CFT is finite and different from the initial CFT. CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane. The flow modifier composition includes an aqueous liquid vehicle and a flow modifying material that includes wax nanoparticles to increase the CFT or a surfactant to decrease the CFT. In some examples, the porous wicking membrane can include nitrocellulose, cellulose, polyvinylidene fluoride, nylon, polyethersulfone, paper, glass fiber, cotton, polycarbonate, polystyrene, polypropylene, polyester, polyethylene, or a combination thereof. In certain examples, applying the flow modifier composition to the porous wicking membrane can include applying the flow modifier over an entire surface area of the porous wicking membrane to provide a uniform CFT across the entire porous wicking membrane. In other examples, applying the flow modifier composition to the porous wicking membrane can include applying the flow modifier composition to a first portion of the surface of the porous wicking membrane to modify the CFT in the first portion of the porous wicking membrane. Further examples can include applying a second flow modifier composition to a second portion of the porous wicking membrane to provide a CFT in the second portion that is different from the CFT in the first portion. In various specific examples, the flow modifier composition and the second flow modifier composition can include different flow modifying materials, or the flow modifier composition and the second flow modifier composition can include the flow modifying material in different concentrations, or the flow modifier composition and the second flow modifier composition can be applied in different amounts to provide different amounts of the flow modifying material to the surface of the porous wicking membrane. In certain examples, the first portion of the surface of the porous wicking membrane can have a two-dimensional pattern shape that increases mixing of fluid wicking through the porous wicking membrane. In still further examples, the method can include forming a test line including a test reactant on the porous wicking membrane, wherein the first portion of the surface of the porous wicking membrane is before or after the test line, with respect to the wicking direction of a fluid wicking through the porous wicking membrane. In some examples, the wax nanoparticles can have an average particle size of less than 1 pm which is less than an average pore diameter of the porous wicking membrane.

[0015] The present disclosure also describes lateral flow membranes. In one example, a lateral flow membrane includes a porous wicking membrane having an initial capillary flow time (CFT), and a flow modifying material applied to the porous wicking membrane. The flow modifying material modifies the initial CFT to a modified CFT that is finite and different from the initial CFT. CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane. The flow modifying material includes wax nanoparticles to increase the CFT or a surfactant to decrease the CFT. In some examples, the porous wicking membrane can include nitrocellulose, cellulose, polyvinylidene fluoride, nylon, polyethersulfone, paper, glass fiber, cotton, polycarbonate, polystyrene, polypropylene, polyester, polyethylene, or a combination thereof. Other examples can also include a test line including a test reactant on the porous wicking membrane.

[0016] The present disclosure also describes fluid ejection devices. In one example, a fluid ejection device includes a membrane support to receive a porous wicking membrane and a fluidic actuator to receive a flow modifier composition and positioned to jet the flow modifier composition onto an area of a surface of the porous wicking membrane. The flow modifier composition includes an aqueous liquid vehicle and a flow modifying material that includes wax nanoparticles or a surfactant. The fluid ejection device also includes a processor in communication with the fluidic actuator to control an amount of the flow modifier composition applied to the porous wicking membrane such that the flow modifier composition modifies a capillary flow time (CFT) of the porous wicking membrane from an initial CFT to a modified CFT that is finite and different from the initial CFT. CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane. In some examples, the processor can adjust the amount of the flow modifier composition applied to multiple portions of the surface of the porous wicking to provide different CFTs in the multiple portions of the surface of the porous wicking membrane. In further examples, the flow modifier composition can include the wax nanoparticles, and the device can also include a second fluidic actuator to receive a second flow modifier composition and positioned to jet the second flow modifier composition onto an area of the surface of the porous wicking membrane. The second flow modifier composition can include an aqueous liquid vehicle and a surfactant.

[0017] In addition to the examples described above, the methods and devices will be described in greater detail below. It is also noted that when discussing the methods of modifying porous wicking membranes, the lateral flow membranes, and the fluid ejection devices described herein, these relative discussions can be considered applicable to the other examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing a flow modifier composition in the context of a method of modifying a porous wicking membrane, this description can also apply to flow modifier compositions used with the fluid ejection devices and the flow modifier composition used to make lateral flow membranes, and vice versa.

Methods of Modifying Porous Wicking Membranes

[0018] The methods described herein can be used to modify the capillary flow time (CFT) of porous wicking membranes. Porous wicking membrane materials are used in a variety of applications, such as lateral flow assays, vertical flow assays, dot blot assays, western blots, catalytic substrates, enzymatic substrates, filtration media, separation media, and others. The membranes can have the ability to conduct a flow of water or aqueous fluid through pores in the membranes by capillary action. The CFT of a porous wicking membrane material can be defined as the amount of time for a water front to traverse a distance of 4 cm across the membrane when flowing by capillary action. For example, if a strip of membrane material is wetted at one end, the water can move across the membrane by capillary action. The water front is the boundary between dry membrane material and wetted membrane material in which water is flowing through the pores. The amount of time taken for the water front to move a distance of 4 cm along the membrane material is the CFT of the material. The CFT can depend on several factors, such as the pore size, pore distribution, and surface energy of the membrane material. [0019] As mentioned above, porous wicking membranes are often used in chemical detection tests such as lateral flow assays. These tests are often designed to operate with a particular CFT. In the case of a lateral flow assay, the membrane may include a test line where a test reactant can be positioned. A sample fluid can be applied to the membrane and the sample fluid can flow to the test line. The test may produce the best results when the sample fluid flows at a particular, ideal flow rate that is selected to give the particular reactants involved the best opportunity to react, while minimizing undesired side reactions such as nonspecific binding of target molecules on the membrane. Therefore, the tests may be most accurate when the porous wicking membrane has a particular CFT for which the test was designed. However, commercially available membrane materials often have inconsistent properties, including CFT. Therefore, it can sometimes be difficult to obtain membrane material with the appropriate CFT for a particular lateral flow assay design. Other applications of porous wicking membrane materials can also rely on consistency in the CFT. Therefore, inconsistencies in the CFT of the membrane materials can prevent other processes and devices involving porous wicking membranes from performing to their fullest extent.

[0020] The methods described herein provide a way to modify the CFT of porous wicking membrane materials. The methods can include applying a flow modifier composition to the porous wicking membrane. The flow modifier composition can change the CFT of the membrane material from an initial CFT to a modified CFT. The modified CFT can be different from the initial CFT. The modified CFT can also be finite, meaning that water can flow through the material by capillary action at a non~zero flow rate (a flow rate of zero would indicate an infinite CFT). The flow modifier composition can include an aqueous liquid vehicle and wax nanoparticles or a surfactant, depending on whether the CFT is to be increased or reduced. Wax particles can make the membrane more hydrophobic, which can make water wet the membrane slower and thereby increase the CFT. A surfactant can make water wet the membrane faster and thereby decrease the CFT. When wax nanoparticles are used, the wax nanoparticles can slow the flow of water through the membrane without completely preventing the flow of water through the membrane. This can be accomplished, in some examples, by limiting the concentration of wax nanoparticles in the membrane to a concentration that allows water to flow through. However, in some examples, a higher concentration of wax may be applied to certain areas of the membrane to form flow barriers, while other areas can allow water to flow through.

[0021] In some examples, the methods described herein can be used to correct inconsistencies in porous wicking membrane materials. For example, a batch of commercially available membrane material may be found to have a CFT that is different from the desired CFT for a particular application, such as a lateral flow assay. A flow modifier composition can be applied uniformly to the entire membrane to adjust the CFT of the membrane to be the desired CFT or closer to the desired CFT. If the initial CFT of the membrane material is too low, then the flow modifier composition can include wax nanoparticles to increase the CFT. If the initial CFT is too high, then the flow modifier composition can include a surfactant to reduce the CFT. This method can be used to correct inconsistencies in CFT between different batches of membrane material.

[0022] In other examples, the methods described herein can provide an easy way to produce membranes having different CFT values across a range. For example, if a new lateral flow assay test is being developed, it can be useful to perform experiments with multiple membranes having different CFT values. Such a process may be used to determine the best CFT value to use for the particular lateral flow assay test. In a particular example of the methods described herein, flow modifier compositions can be applied to multiple membranes to produce membranes with a range of different CFT values. Therefore, a single type of commercially available membrane can be obtained and then modified to have multiple different CFT values. This can be much more cost effective than obtaining multiple commercially available membranes having different initial CFT values.

[0023] In further examples, the methods described herein can be used to locally modify the CFT of a porous wicking membrane in a particular region of the membrane to make a membrane having multiple different CFT values in different areas of the membrane. Manipulating the CFT in discrete areas of the membrane can allow for a variety of useful effects that may not be possible with a membrane having a single, uniform CFT across the entire membrane. In certain examples, a membrane can be formed having multiple channels formed in the membrane, with different CFT in the individual channels. Flow channels can be formed in the membrane by forming flow barriers to separate the flow channels, for example. As an example, a lateral flow immunoassay can test for a particular disease by screening for a biomarker of the disease. If the disease has multiple biomarkers that can be detected, then a lateral flow assay can be made having multiple flow channels on the membrane, where the individual flow channels include test reactants for detecting the individual biomarkers of the disease. The tests for the different biomarkers may operate best when the membrane has different CFT values. Therefore, the flow channels of the lateral flow assay can be locally modified to have different CFT values so that the individual biomarkers can be detected as accurately as possible. In some examples, a lateral flow assay that tests for multiple biomarkers in this way can be significantly more accurate compared to tests that test for a single biomarker.

[0024] In other examples, it can be useful to locally modify the CFT in particular portions of the membrane when testing for a single target molecule. Tests that use a porous wicking membrane having a uniform CFT can often involve a trade-off between signal intensity and background noise. For example, in a lateral flow assay, a target molecule may be bonded to a conjugate, and the target molecule and conjugate can flow along the membrane with the sample fluid. After flowing across the membrane, the sample fluid can meet a test line when a test reactant is positioned to capture the target molecule and conjugate. The amount of target molecules that are captured by the test reactant corresponds to the signal intensity. However, target molecules in the sample fluid may also non-specifically bind to the membrane in the region before the test line as the sample fluid flows along the membrane. This non-specific binding is background noise that can make it more difficult to detect the signal at the test line. When such a test incorporates a membrane with a low CFT, the sample fluid flows quickly. This allows less time for the target molecule to non-specifically bind to the membrane, which reduces the background noise. However, the target molecules also have less time to react with the test reactant at the test line, which decreases the signal intensity. Conversely, membranes with a high CFT can cause the sample fluid to flow slowly. This allows more time for the target molecule to react with the test reactant, thereby increasing the signal intensity. However, the target molecules also have more time to non-specifically bind to the membrane, which increases the background noise. The methods described herein can be used to increase the signal intensity while simultaneously decreasing background noise by modifying the CFT in specific portions of the membrane. In one example, a flow modifier composition including wax nanoparticles can be applied to an area of the membrane immediately before the test line. In this example, the sample fluid can flow quickly across the membrane until it reaches the area modified with wax nanoparticles. The sample fluid can then slow down as the sample fluid crosses the test line. This can allow more time for target molecules to react with the test reactant, while also letting the sample fluid flow quickly across the membrane to reduce non-specific binding of the target molecule to the membrane.

[0025] In another specific example, a flow modifier composition including wax nanoparticles can be applied to an area of the membrane just after the test line. In this example, the sample fluid can flow quickly across the membrane to the test line, but the area with the wax nanoparticles can slow the flow and cause a “back-up” of fluid in the area of the test line. This can allow for more target molecules to react with the test reactant.

[0026] In further examples, flow modifier compositions can be applied in certain areas of the membrane in a pattern to create a variety of microfluidic effects, such as changing the direction of flow. In a particular example, a two-dimensional pattern of areas having modified CFT can create a flow pattern in the sample fluid that increases mixing of the sample fluid as the sample fluid flows along the membrane. Mixing the sample fluid can be useful in some cases, such as when the sample fluid is mixed with a conjugate reactant to encourage the conjugate reactant to react with the target molecule before the sample fluid reaches the test line.

[0027] With this description in mind, FIG. 1 is a flowchart illustrating an example method 100 of modifying a porous wicking membrane. The method includes applying 110 a flow modifier composition to a porous wicking membrane, wherein the porous wicking membrane has an initial capillary flow time (CFT) before the flow modifier composition is applied and a modified CFT after the flow modifier composition is applied, wherein the modified CFT is finite and different from the initial CFT, wherein CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane, and wherein the flow modifier composition includes an aqueous liquid vehicle, and a flow modifying material that includes wax nanoparticles to increase the CFT or a surfactant to decrease the CFT.

[0028] In certain examples, a flow modifier composition can be applied uniformly across an entire porous wicking membrane. This can provide a uniform CFT across the porous wicking membrane. In some cases, the entire porous wicking membrane can be modified in this way when the porous wicking membrane is off-specification, having a CFT that is different from the desired CFT. The method can include measuring the CFT of the porous wicking membrane in some examples. If the measured CFT is different from the desired CFT, then an appropriate flow modifier composition can be applied to the porous wicking membrane to achieve the desired CFT. In certain examples, the flow modifier composition can be applied evenly to a large sheet of membrane material or a batch of membrane material. The membrane material can then be cut into smaller pieces, such as strips, to use in individual devices, such as lateral flow assays. Similarly, a smaller piece of membrane material, such as a strip that has been cut from a larger sheet, can be modified by applying a flow modifier composition uniformly across the smaller piece of membrane material. Accordingly, in these examples, a “porous wicking membrane” can refer to a batch of membrane material, a large sheet of membrane material, a smaller piece that has been cut from a larger sheet, and any other form of membrane material. [0029] As mentioned above, modifying a porous wicking membrane to have a uniform CFT across the entire membrane area can be useful in applications where experiments are performed with membranes having multiple different CFT values. For example, when developing a lateral flow assay test to detect a particular target molecule, experiments can be performed with multiple sample membranes that have different CFT values in order to determine the best CFT value or range of CFT values that can provide the best test results. Experiments using multiple membranes with different CFT values can also be useful in a variety of other situations. In some examples of the methods described herein, a series of multiple porous wicking membranes can be modified to have different CFT values. In further detail, the individual membranes may have a uniform CFT across the surface area of the individual membranes, but the CFT of one membrane can differ from the next membrane. In this way, any number of membranes having different CFT values can be prepared. In certain examples, a sheet of porous wicking membrane material can be cut into individual strips or other smaller pieces and then the individual pieces can be modified to have different CFT values.

[0030] When modifying porous membranes to have different CFT values, in some examples a different flow modifier composition can be applied. The different flow modifier compositions can differ in type of ingredients and/or concentration of ingredients. In certain examples, a first flow modifier composition can be designed to decrease the CFT of the membrane, and the first flow modifier can include a surfactant. In further examples, a second flow modifier composition can be designed to increase the CFT of the membrane, and the second flow modifier composition can include wax nanoparticles. In alternative examples, the first and second flow modifier compositions can both include a surfactant, or the compositions can both include wax nanoparticles. The compositions can include two different surfactants, or the same surfactant at two different concentrations, in some examples. In other examples, the compositions can include two different types of wax nanoparticles, or the same wax nanoparticles at different concentrations. In still further examples, different CFT values can be achieved using a single flow modifier composition, by simply applying different amounts of the flow modifier composition to different porous wicking membranes.

[0031] In certain examples, the method can include selecting a series of different desired CFT values. The method can then include modifying a series of porous wicking membranes by applying a flow modifier composition or multiple flow modifier compositions to the membranes to impart the desired CFT values to the membranes.

[0032] FIG. 2A is a top-down schematic view of a porous wicking membrane 200. This porous wicking membrane is unmodified. The membrane has an initial CFT before being modified. As described above, a flow modifier composition can be applied to change the CFT to a modified CFT. FIG. 2B shows the porous wicking membrane 200 with the flow modifier composition 210 applied across the surface area of the porous wicking membrane. In this example, it is applied across the entire surface area of the porous wicking membrane. Accordingly, the entire area of the porous wicking membrane has a modified CFT due to the flow modifier composition.

[0033] In other examples, a flow modifier composition can be applied in localized portions of the porous wicking membrane instead of across the entire surface area of the porous wicking membrane. In certain examples, a flow modifier composition can be applied to a first portion of the membrane to modify the CFT in the first portion of the porous wicking membrane. A second portion of the porous wicking membrane can be left unmodified. The resulting membrane can have a region of modified CFT in the first portion and a region having the initial CFT in the second portion. FIG. 3 shows such an example membrane 200. This membrane has a flow modifier composition 210 applied at a first portion 220 of the membrane. A second portion 222 of the membrane remains unmodified.

[0034] Different CFT values can also be achieved in different portions of a single membrane by applying multiple flow modifier compositions in different areas. For example, a first flow modifier composition can be applied on a first portion of a membrane, and a second flow modifier composition can be applied on a second portion of the membrane. The first and second portions of the membrane can have different CFT values after being modified. The membrane may also include a third portion that has no flow modifier composition applied thereon, and which retains the initial CFT of the membrane. In further examples, any number of additional flow modifier compositions can be applied to different portions of the membrane to make areas having different CFT values.

[0035] FIG. 4 shows another example porous wicking membrane 200 that includes a first portion 220 having a first flow modifier composition 210 applied thereon. The membrane also includes a second portion 222 that has a second flow modifier composition 212 applied thereon. The first portion of the second portion of the membrane can have different CFT values. The first flow modifier composition and the second flow modifier composition can include different flow modifying materials, or the same flow modifying materials in different concentrations. The first flow modifier composition and the second flow modifier composition can also be a single composition or identical compositions, in some examples, and the different CFT values can be achieved by applying different amounts of the flow modifier composition on the first and second portions of the membrane.

[0036] The methods described herein can also be used to form patterns of areas having different CFT values on a porous wicking membrane. The patterns can be designed to provide useful flow characteristics, such as encouraging a fluid flowing across the membrane to be better mixed. FIG. 5 shows one example porous wicking membrane 200 that includes a two-dimensional pattern of areas on which flow modifier composition 210 has been applied. In this example, the pattern is a series of stripes across the membrane. As fluid flows along the membrane, the fluid will pass through the areas having a modified CFT. The flow rate of the fluid can repeatedly change as the fluid flows through the areas with modified CFT and the areas with unmodified CFT. This repeated change in flow rate can help the fluid become better mixed.

[0037] FIG. 6 shows another example porous wicking membrane 200. In this example, a flow modifier composition 210 is applied in a two-dimensional pattern that has a checkerboard shape. When a fluid flows through along this membrane, the areas having modified CFT and the areas having unmodified CFT can encourage the fluid to flow in multiple different directions due to the differences in flow rate in the different areas. Thus, this pattern can generate some amount of cross flow with respect to the overall direction of flow of the fluid along the membrane. This can help the fluid become better mixed.

[0038] FIG. 7 shows yet another example porous wicking membrane 200 having a flow modifier composition 210 applied in certain areas in a two dimensional pattern. In this pattern, the flow modifier composition is applied in multiple triangle-shaped areas. These triangular areas of modified CFT can encourage fluid flowing along the membrane to flow in angled directions around the triangular areas. This can also help the fluid to become better mixed.

[0039] In various examples, the methods described herein can also include forming a test line of a test reactant on the porous wicking membrane. For example, a test reactant can be applied to an area of the membrane to form a test line. The test reactant can be a compound that reacts in some way with a target molecule that may be in a sample fluid flowing through the membrane. In some examples, the test reactant can bind to the target compound through covalent bonding or other types of binding. As an example, in a lateral flow immunoassay, the test reactant can be an antibody that can bind to a target compound. The antibody can be immobilized on the membrane in an area of the membrane to form a test line. When a sample fluid flows across the test line, target molecules in the sample fluid can bind to the antibodies and accumulate at the test line. In many cases, the target molecule can already be bound to a conjugate that has a visible color so that the accumulation of the target molecules and conjugates at the test line can result in a visible color change. In various examples, the conjugate can be mixed with the sample fluid before the sample is applied to the membrane, or the sample fluid can flowthrough a conjugate pad and pick up the conjugate before the sample flows through the porous wicking membrane, or the conjugate can be applied to an area of the porous wicking membrane ahead of the test line.

[0040] A test line can be added to any of the example porous wicking membranes described above. For example, porous wicking membranes that had a flow modifier composition applied uniformly across the entire membrane can be used as a flow assay membrane and a test line can be formed by applying a test reactant to the membrane. In other examples, a porous wicking membrane can have two or more regions with different CFT values, as described above, and a test line can be formed in such membranes in the same way.

[0041] In a particular example, a porous wicking membrane having two or more different regions with different CFT values can be used to make a flow assay membrane that can perform multiple different flow assay tests simultaneously. For example, the membrane can be divided into multiple flow channels by forming flow barriers separating the flow channels. Flow barriers can be formed in a variety of ways, such as by applying hydrophobic material to the membrane to block flow of aqueous fluids across the barriers. In certain examples, a flow modifier composition including wax nanoparticles, as described herein, can be used to form flow barriers if a sufficient amount of wax nanoparticles are applied to block flow of aqueous fluids. Accordingly, the membrane may be divided into multiple flow channels. The flow channels can be treated with a flow modifier composition or multiple different flow modifier compositions to impart different CFT values to the individual flow channels. This may be done because different flow assay tests are designed to operate at different CFT values. A test line, or multiple test lines, can also be formed on this membrane. In one example, different test lines made with different test reactants can be formed in the individual flow channels. Thus, several different test reactants can interact with a sample fluid that is flowing through the flow channels.

[0042] FIG. 8 shows another example porous wicking membrane 200. This example includes flow barriers 230 separating the membrane into multiple flow channels. A first flow modifier composition 210 is applied on one flow channel, and a second flow modifier composition 212 is applied on a second flow channel, and a third flow modifier composition 214 is applied on a third flow channel. A first test line 240, second test line 242, and third test line 244 are formed in the flow channels. These test lines can include different test reactants that can be designed to operate best with the different CFT values in the different flow channels.

[0043] In further examples, a flow modifier composition can be applied to a porous wicking membrane before or after a test line to help increase the signal intensity of target molecules detected at the test line while also limiting the background noise caused by non-specific binding of the target molecule on the membrane. As mentioned above, in some examples this can be accomplished by applying a flow modifier composition with wax nanoparticles to slow down flow of the sample fluid just before or just after the test line. FIG. 9 shows an example porous wicking membrane 200 that includes a test line 240 after an area where a flow modifier composition 210 has been applied. The flow modifier composition can increase the CFT of the membrane so that the flow of sample fluid is slower in the area where the flow modifier composition is applied. After the sample fluid flows through the area where the flow modifier composition is applied, the flow can remain at a slower rate while the fluid flows across the test line. In some examples, a fast-wicking membrane material can be used so that the sample fluid flows quickly across the membrane to reduce non-specific binding of target molecules to the membrane. The sample fluid can then be slowed by the flow modifying material before the test line as described above.

[0044] FIG. 10 shows yet another example porous wicking membrane 200 that includes a test line 240 before an area where a flow modifier composition 210 has been applied. The CFT may be in the area where the flow modifier composition can be longer so that a sample fluid may flow more slowly through this area. Because the sample fluid is constrained by the slower flow in the area where the flow modifier composition was applied, the sample fluid can also flow slowly in the area where the test line is located. This can allow more time for target molecules in the sample fluid to react with test reactants at the test line.

[0045] Any of the example porous wicking membranes described above can be made using the methods of modifying porous wicking membranes described herein. In particular, methods can include applying a flow modifier composition or multiple flow modifier compositions to a porous wicking membrane in any of the ways described above. Methods can also include applying test reactants to form test lines in any of the ways described above. Specific types of porous wicking membranes and ingredients that can be included in the flow modifier compositions are described in more detail below.

[0046] Additionally, in some examples, wax nanoparticles in the flow modifier composition can be cured after the flow modifier composition is applied to the porous wicking membrane. Curing can include heating the wax nanoparticles to a curing temperature. In some examples, the curing temperature can be from about 50 °C to about 150 °C. However, in other examples, the wax nanoparticles can be applied without any additional curing operation. In certain examples, the wax nanoparticles can effectively modify the CFT of the membrane at room temperature. In other examples, flow barriers can also be formed by applying a higher concentration of wax nanoparticles, with or without curing.

Lateral Flow Membranes

[0047] Methods of modifying porous wicking membranes are described above. The present disclosure also describes lateral flow membranes that can be made using the methods described above. In one example, a lateral flow membrane can include a porous wicking membrane that has an initial capillary flow time (CFT). The lateral flow membrane can also include a flow modifying material applied to the porous wicking membrane. The flow modifying material can modify the initial CFT to a modified CFT that is finite and different from the initial CFT. The CFT can be defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane. The flow modifying material can include wax nanoparticles to increase the CFT or a surfactant to decrease the CFT.

[0048] In certain examples, the initial CFT of the porous wicking membrane can be from 75 seconds to 500 seconds. In further examples, the initial CFT can be from 100 seconds to 400 seconds or from 200 seconds to 400 seconds. The modified CFT can also be in the same ranges. However, the modified CFT can be different from the initial CFT. [0049] In various examples, lateral flow membranes can include any of the arrangements of regions where flow modifier compositions are applied as shown in the figures and described in the examples above. As used herein, “flow modifying material” can refer to an ingredient present in a flow modifier composition that is left in the porous wicking membrane after the flow modifier composition has been applied and dried. In particular examples, the flow modifying material can include wax nanoparticles or a surfactant. In certain examples, wax nanoparticles and a surfactant can both be included. Lateral flow membranes can also include a test line including a test reactant, in any of the arrangements described above. In further examples, lateral flow membranes can include additional components such as flow barriers that can block fluid flow or channel fluid flow into specific flow channels, control lines that include control reactants, conjugate reactants to react with target molecules before the test reactants, and others.

[0050] Lateral flow membranes can be incorporated into devices such as lateral flow assays. In one example, a lateral flow assay can include a porous wicking membrane that has been modified using any of the methods described herein. A test line and a control line can be formed on the membrane. In certain examples, the membrane can be assembled with other components such as a housing, a sample pad, a conjugate pad, an absorbent pad, conjugate molecules, flow barriers, additional test lines, back materials, test line viewing windows, and others.

Fluid Ejection Devices

[0051] In some examples, the flow modifier compositions can be applied to porous wicking membranes using a fluid ejection device. FIG. 11 shows one example fluid ejection device 300 that can be used. This fluid ejection device includes a membrane support 350 to receive a porous wicking membrane and a fluidic actuator 360 to receive a flow modifier composition and positioned to jet the flow modifier composition onto an area of a surface of the porous wicking membrane. The flow modifier composition can include an aqueous liquid vehicle and a flow modifying material that includes wax nanoparticles or a surfactant. The fluid ejection device also includes a processor 370 in communication with the fluidic actuator to control an amount of the flow modifier composition applied to the porous wicking membrane such that the flow modifier composition modifies a capillary flow time (CFT) of the porous wicking membrane from an initial CFT to a modified CFT that is finite and different from the initial CFT. The CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane.

[0052] The processor of the fluid ejection device can be a processing unit that has been programmed to control the fluidic actuator to apply a flow modifier composition onto a porous wicking membrane as described above. The processor can be more specifically programmed to perform any of the methods described above and to form any of the example porous wicking membranes described above and shown in the figures. In some examples, the processor can be programmed to move the fluid actuator to specific areas of the porous wicking membrane to apply a flow modifier composition in discrete areas. In further examples, the fluid ejection device can include multiple fluid actuators that can eject multiple different flow modifier compositions. In such examples, the processor can be programmed to use the multiple fluid actuators to apply the multiple different flow modifier compositions to the porous wicking membrane. In a specific example, the fluid ejection device can include a first fluidic actuator that ejects a first flow modifier composition including wax nanoparticles, and a second fluidic actuator that ejects a second flow modifier composition including a surfactant. The processor can be programmed to eject the first flow modifier composition in areas where the CFT is to be increased and the second flow modifier composition in areas where the CFT is to be decreased. The processor can include a processing unit of a general purpose computer such as a personal computer, workstation computer, laptop, and so on. In other examples, the processor can be a processor integrated in the fluid ejection device, such as a raster image processor.

[0053] In certain examples, the processor can include modules for performing operations in the methods described above. For example, the processor can include a jetting module for positioning the fluidic actuator in a desired position over the porous wicking membrane and jetting a desired volume of flow modifier composition onto the porous wicking membrane. The processor can also include a heating module to control a heat source such as a heated platen or optical irradiation source. In examples that utilize a curing operation, the controller can include a curing module to cure wax nanoparticles from a flow modifier composition.

[0054] In some examples, the fluid ejection device can include a membrane support to receive a porous substrate. The porous wicking membrane can be any of the types of porous wicking membrane described herein. The membrane support can be any size and shape designed to be compatible with the porous wicking membrane. In some examples, the membrane support can be a platform or platen for holding a porous wicking membrane while the flow modifier is jetted onto the porous substrate. In certain examples, the membrane support can include heaters for controlling the temperature of the porous wicking membrane. For example, the membrane support can be a heated platen as described above. In other examples, the membrane support can include rollers or other mechanical features for moving the porous wicking membrane through the device as the flow modifier composition is jetted onto the porous wicking membrane.

[0055] In some examples, the fluid ejection device can include a reservoir of the flow modifier composition. In other examples, the fluid ejection device can include a connection for connecting to a reservoir of flow modifier composition that may be provided separately. The fluidic actuator can be connectable to the reservoir of flow modifier composition so that the fluidic actuator can jet the flow modifier composition onto the porous wicking membrane.

[0056] Some of the functional units described in the fluid ejection device have been labeled as modules in order to more particularly emphasize their implementation independence. For example, a module can be implemented as a hardware circuit including custom very-large-scale integration (VLSI) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module can also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0057] Modules can also be implemented in machine-readable software for execution by various types of processors. An identified module of executable code can, for instance, include block(s) of computer instructions, which can be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but can include disparate instructions stored in different locations which include the module and achieve the stated purpose for the module when joined logically together.

[0058] Indeed, a module of executable code can be a single instruction, or many instructions, and can even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data can be identified and illustrated herein within modules, and can be in a suitable form and organized within a suitable type of data structure. The operational data can be collected as a single data set, or can be distributed over different locations including over different storage devices. The modules can be passive or active, including agents operable to perform desired functions.

[0059] The modules described here can also be stored on a computer readable storage medium that includes volatile and non-volatile, removable and non-removable media implemented with a disclosure for the storage of information such as computer readable instructions, data structures, program modules, or other data. Computer readable storage media can include, but are not limited to, RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory or other memory disclosure, compact disc read-only memory (CD-ROM), digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or other computer storage medium which can be used to store the desired information.

[0060] In some examples the processor can include some or all of the modules described above as hardware components. In other examples, the processor can be capable of executing the modules described above as software modules. In some examples, a combination of hardware and software modules can be used.

Flow Modifier Compositions

[0061] The flow modifier compositions used in the methods described above can include an aqueous liquid vehicle and a flow modifying material. The flow modifying material can include wax nanoparticles to increase the CFT of the porous wicking membrane, or a surfactant to decrease the CFT.

[0062] As used herein, “aqueous liquid vehicle” refers to a solvent system that includes water and which may include additional solvents, such as organic solvents. In some examples, the aqueous liquid vehicle can be water. In other examples, the aqueous liquid vehicle can include water and an organic solvent. Water used in the aqueous liquid vehicle can include deionized water, distilled water, purified water, filtered water, or other water. In certain examples, the flow modifier composition can include the aqueous liquid vehicle in an amount from about 1 wt% to about 99 wt% based on the total weight of the flow modifier composition. In further examples, the flow modifier composition can include wax nanoparticles in an amount from about 0.1 wt% to about 20 wt%. In other examples, the flow modifier composition can include a surfactant in an amount from about 0.1 wt% to about 20 wt%. In certain examples, the flow modifier composition can consist of the aqueous liquid vehicle and wax nanoparticles or a surfactant. In a particular example, the flow modifier composition can consist of water and wax nanoparticles. In another example, a dispersant can be included to disperse the wax nanoparticles. In other examples, the flow modifier composition can include other ingredients such as, biocides, anti-kogation agents, and other additives.

[0063] In further examples, the flow modifier composition can include the aqueous liquid vehicle in an amount of from about 1 wt% to about 99 wt%, dispersed wax nanoparticles in an amount of from about 1 wt% to about 20 wt%, and a dispersant in an amount of from about 0.05 wt% to about 5 wt%. In certain examples, these flow modifier compositions can also include a surfactant in an amount from about 0.1 wt% to about 10 wt%. In some further examples, the flow modifier composition can include water in an amount of from about 1 wt% to about 90 wt%, an organic co-solvent in an amount of from about 1 wt% to about 20 wt%, wax nanoparticles in an amount of from about 1 wt% to about 20 wt%, a dispersant in an amount of from about 0.05 wt% to about 5 wt%, and a surfactant in an amount of from about 0.1 wt% to about 10 wt%. In some examples, the flow modifier composition can consist of the water, co-solvent, dispersed wax nanoparticles, dispersant, and surfactant as described above.

[0064] In other examples, the flow modifier composition can include the aqueous liquid vehicle in an amount of from about 1 wt% to about 99 wt% and a surfactant in an amount from about 1 wt% to about 20 wt%. In some examples, the flow modifier composition can include water in an amount of from about 1 wt% to about 90 wt%, an organic co-solvent in an amount of from about 1 wt% to about 20 wt%, and a surfactant in an amount from about 1 wt% to about 20 wt%. In some examples, the flow modifier composition can consist of the water, co-solvent, and surfactant as described above

[0065] In some examples, the aqueous liquid vehicle can be included in the flow modifier composition in an amount greater than about 50 wt%. In further examples, the aqueous liquid vehicle can be included in an amount of from about 50 wt% to about 99 wt%, or from about 60 wt% to about 97.4 wt%, or from about 70 wt% to about 90.4 wt%, or from about 70 wt% to about 87.6 wt%, or from about 70 wt% to about 97.4 wt%.

[0066] As mentioned above, the aqueous liquid vehicle can include an organic co-solvent in some examples. In certain examples, a co-solvent can be included in the flow modifier composition in an amount of from about 1 wt% to about 20 wt%, based on the total weight of the flow modifier composition. In further examples, the co-solvent can be present in an amount of from about 3 wt% to about 12 wt%, or from about 5 wt% to about 10 wt%, or from about 5 wt% to about 7 wt%. Including an organic co-solvent can help to make the flow modifier composition jettable from a fluid actuator such as a thermal inkjet printhead. Non-limiting examples of suitable co-solvents can include aliphatic alcohols, aromatic alcohols, diols, triols, glycol ethers, poly (glycol) ethers, lactams, formamides, acetamides, long chain alcohols, ethylene glycol, propylene glycol, diethylene glycols, triethylene glycols, glycerine, dipropylene glycols, glycol butyl ethers, polyethylene glycols, polypropylene glycols, amides, ethers, carboxylic acids, esters, organosulfides, organosulfoxides, sulfones, alcohol derivatives, carbitol, butyl carbitol, cellosolve, ether derivatives, amino alcohols, and ketones. For example, co-solvents can include primary aliphatic alcohols of 30 carbons or less, primary aromatic alcohols of 30 carbons or less, secondary aliphatic alcohols of 30 carbons or less, secondary aromatic alcohols of 30 carbons or less, 1 ,2-diols of 30 carbons or less, 1 ,3-diols of 30 carbons or less, 1 ,5-diols of 30 carbons or less, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, poly(ethyiene glycol) alkyl ethers, higher homologs of polyethylene glycol) alkyl ethers, polypropylene glycol) alkyl ethers, higher homologs of polypropylene glycol) alkyl ethers, lactams, substituted formamides, unsubstituted formamides, substituted acetamides, and unsubstituted acetamides.

[0067] Certain specific examples of co-solvents can include hydantoin glycol (such as, e.g., 1 ,3-bis-(2-hydroxyethyl)-5,5-dimethylhydantoin),

1 -(2-hydroxyethyl)-2-pyrrolidinone, 1 -(2-hydroxyethyl)-2-imidazolidinone, tetratethylene glycol, 1 ,2,6-hexanetriol, glycerol, glycerol propoxylate, 1 ,5-pentanediol, LIPONIC® ethoxylated glycerol 1 (LEG-1) or LIPONIC® ethoxylated glycerol 7 (LEG-7) from Vantage Specialty Chemicals (USA), 2-methyl-2,4-pentanediol,

2-methyl-1 ,3-propanediol, 2-ethyl-2-hydroxymethyl-1 ,3-propanediol, diethylene glycol,

3-methoxybutanol, propylene glycol monobutyl ether, 1,3-dimethyl-2-imidazolidinone, or combinations thereof.

[0068] The wax nanoparticles in the flow modifier composition can include a variety of waxes. In some examples the wax can be selected from a group consisting of a paraffin wax, a polyethylene wax, a fluorothermoplastic, and combinations thereof. The wax can be a wax emulsion. Wax emulsions are commercially available from a number of vendors, for example Keim-Additec (Germany), Lubrizol (USA), Michelman (USA), and BYK Chemie (Germany). Specific examples of wax emulsions include: Lubrizol: LIQUILUBE™ 488 (melting point (mp) 85^OC), LIQUILUBE™ 443 (mp 80°C), LIQUILUBE™ 405; Michelman: ME48040 (mp 85°C), ME98040M1 (mp 98°C), ML160 (mp 85°C); Keim~Additec: ULTRALUBE® E-7093 (mp 84°C), ULTRALUBE® 7095/1 (mp 80°C), BYK: AQUACER® 2650 (mp 85°C), AQUACER® 533 (mp 95°C), and AQUASLIP™ 942 (mp 83°C).

[0069] In some examples, the wax can include a paraffin wax or modified paraffin wax with a relatively low melting point. Specific examples of a paraffin wax or modified paraffin wax with a relatively low melting point include BYK AQUACER® A494 with a melting point of about 60 °C, BYK AQUACER® A497 with a melting point of about 60 °C, BYK AQUACER® 8330 with a melting point of about 60 °C, BYK AQUACER® 8333 with a melting point of about 60 °C, and BYK AQUACER® 8335 with a melting point of about 58 °C. Other examples of paraffin wax can include BYK AQUACER® 494, BYK AQUACER® 533, BYK AQUACER® 539, BYK AQUACER® 1039, BYK AQUACER® 565, BYK AQUACER® 581 , BYK AQUACER® 2650, BYK AQUACER® 8603, and BYK AQUACER® 8669 (available from BYK, Germany).

[0070] In various examples, the wax nanoparticles can be included in the flow modifier composition in an amount of from about 0.1 wt% to about 20 wt%. In other examples, the amount can be from about 0.1 wt% to about 10 wt%, or from about 0.1 wt% to about 5 wt%, or from about 0.1 wt% to about 3 wt%, or from about 1 wt% to about 5 wt%, or from about 2 wt% to about 5 wt%.

[0071] The wax nanoparticles can have an average particle size that can allow the particles to flow through the pores in the porous substrate. In some examples, the wax nanoparticles can have an average particle size of from about 10 nm to about 1 ,000 nm. In further examples, the average particle size can be from about 100 nm to about 1 ,000 nm or from about 100 nm to about 300 nm.

[0072] The wax nanoparticles can be dispersed in the aqueous liquid vehicle by a dispersant. In certain examples, the dispersant can include an alcohol ethoxylate dispersant. In a particular example, the dispersant can include UNITHOX™ 750 (Baker Hughes, USA), which is an alcohol ethoxylate dispersant with a molecular weight of 1400 g/mol, with a 50% ethylene oxide content by weight. [0073] As mentioned above, in some examples, the flow modifier composition can include a surfactant. The surfactant can include non-ionic, cationic, or anionic surfactants. In some examples, the surfactant can be present in an amount of from about 0.1 wt% to about 20 wt% with respect to the total weight of the flow modifier composition. In further examples, the surfactant can be included in an amount of from about 0.1 wt% to about 10 wt% or from about 0.1 wt% to about 5 wt%.

[0074] In certain examples, the surfactant can include an ethoxylated alcohol such as those from the TERGITOL® series (e.g., TERGITOL® 15S30, or TERGITOL® 15S9), manufactured by The Dow Chemical Company (USA); surfactants from the SURFYNOL® series (e.g., SURFYNOL® 104, SURFYNOL® 440 and SURFYNOL® 465), and DYNOL™ series (e.g. , DYNOL™ 360, DYNOL™ 604, and DYNOL™ 607) manufactured by Air Products and Chemicals, Inc. (USA). In other examples, the surfactant can include a polysorbate surfactant. Examples of polysorbate surfactants can include Polysorbate 20 (or polyoxyethylene 20 sorbitan monolaurate), Polysorbate 40 (or polyoxyethylene 20 sorbitan monopalmitate), Polysorbate 60 (or polyoxyethylene 20 sorbitan monostearate), Polysorbate 80 (or polyoxyethylene 20 sorbitan monooleate), or the like. Other polysorbates can likewise be used, including Polysorbate 85, or TWEEN® 85, which is polyethylene glycol sorbitan trioleate; or Polysorbate 81 , TWEEN® 81 , which is a polyoxyethylene (5) sorbitan monooleate, or TWEEN® 20 which is a polyoxyethylenesorbitan monolaurate (available from Croda, United Kingdom). Polyoxyethylene sorbitan dioleate can also be used. In other examples, the surfactant can include a polyoxyethylene glycol ether. Examples of such surfactants that can be used include BRU® S, BRU® O, BRU® C, and BRU® L type surfactants (available from Croda, United Kingdom). SYNPERONIC® surfactants can also be used (available from Croda, United Kingdom). Specific examples include BRU® S10, BRU® S5, BRU®, S15, BRU® S20, BRU® S2/93, BRU® S7, BRU® 98/020, BRU® 010, BRU® 35, BRU® 02, BRIJ®, 03, BRU® 05, BRU® C2, BRU® C7, BRU® C10, BRU®, C20, BRU® L4/30, BRIJ® L9, BRU® L15, SYNPERONIC® 91-2.5, SYNPERONIC® 91-2.5, SYNPERONIC® 91-10, or mixtures thereof (available from Croda, United Kingdom). In some examples, the surfactant can be TRITON ™ X100, which is a polyethylene glycol tert-octylphenyl ether surfactant manufactured by Air Products and Chemicals, Inc. (USA).

[0075] In certain examples, the flow modifier composition can be free of certain ingredients. In one example, the flow modifier composition can be acid-free. For example, the flow modifier composition can be free of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, sulphamic acid, tartaric acid, phytic acid, boric acid, succinic acid, suberic acid, and/or benzoic acid. In further examples, the flow modifier composition can be colorant-free. The flow modifier composition can be free of colorants such as pigments and dyes, which are often used in marking agents such as inks. However, the flow modifier compositions described herein can, in some examples, be applied using similar devices to those used in inkjet printers. In particular, a thermal fluid jet similar to a thermal inkjet printhead can be used to jet the flow modifier composition. However, the flow modifier composition is not an ink and therefore, in some examples, the flow modifier composition can be free of colorants. In further examples, the flow modifier composition can be free of binders. Binders can include additional polymers besides the wax nanoparticles. In certain examples, binders can include polyurethane polymers. Accordingly, in some examples, the flow modifier composition can be free of these binders.

[0076] In other examples, the flow modifier composition can include an acid, or a colorant, or a binder, but in a relatively small amount. In certain examples, the flow modifier composition can include an acid, a colorant, or a binder in an amount of less than about 5 wt%, or less than about 3 wt%, or less than about 1 wt%, or less than about 0.1 wt%.

[0077] In still further examples, the flow modifier composition can be free of photccurable or ultraviolet (UV) curable materials. These materials can include monomers or polymers that can be polymerized and/or cross-linked upon exposure to ultra-violet radiation. In some examples, the flow modifier compositions can be used without application of UV light. The hydrophobic material particles in the flow modifier composition can form hydrophobic barriers without the use of UV light for curing. In certain examples, the flow modifier composition can be free of UV curable monomers. In further examples, the flow modifier composition can be free of photoinitiators.

[0078]The flow modifier compositions can also include additional additives. Additives can include anti-kogation agents, pH adjusters, antimicrobial agents, sequestering agents, viscosity modifiers, humectants, penetrants, wetting agents, preservatives, jettability additives, and mixtures thereof.

[0079] Kogation refers to the deposit of residue on a heating element of a thermal inkjet printhead. An anti-kogation agent can be included to assist in preventing the buildup of kogation. Anti-kogation agents can include an anionic surfactant, a nonionic surfactant, a zwitterionic surfactant, an amphoteric surfactant, or mixtures thereof. A list of surfactants is given above. In some examples, the anti-kogation agents can include oleth-3-phosphate (commercially available as CRODAFOS® O3A or CRODAFOS® N-3 acid, from Croda, United Kingdom) or dextran 500k. The anti-kogation agent can be present in the flow modifier composition in an amount ranging from about 0.1 wt% to about 3.0 wt% of the total weight of the flow modifier composition.

[0080]A pH adjuster can also be added to the flow modifier compositions in some examples. A pH adjuster can include sodium hydroxide, potassium hydroxide, ammonia, hydrochloric acid, nitric acid, sulfuric acid, and (poly)alkanolamines such as triethanolamine and 2-amino-2~methyl-1-propaniol, phosphate, Tris, HEPES (4-(2-hydroxyethyl)-1 -piperazineethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid), or mixtures thereof. In some examples, the pH adjuster can provide a buffered solution to control the pH of the flow modifier composition within a range based on the biomolecules that may be used on the porous substrate.

[0081] In some examples, the flow modifier composition can also include an antimicrobial agent. Suitable antimicrobial agents include biocides and fungicides. Examples of antimicrobial agents include ACTICIDE® M20 (i.e., active ingredient is 2-methyl-4-isothiazolin-3-one), ACTICIDE® B20 (/.e_, active ingredient is

1 .2-benzisothiazolin-3-one) (available from Thor, United Kingdom), AMP (i.e., amino-tris-(methylene phosphonate), TRIS (i.e., tris(hydroxymethyl)nitromethane), and mixtures thereof. Other examples of antimicrobial agent include NUOSEPT® (Ashland Inc., USA), UCARCIDE™ or KORDEK™ (The Dow Chemical Co., USA), and PROXEL® (Arch Chemicals, USA) series, and combinations thereof.

[0082] In some examples, sequestering agents can be added to the flow modifier compositions. These sequestering agents can be useful to impart increased stability characteristics to the flow modifier composition and can include an alkali metal, an alkaline earth metal, and an ammonium salt of a linear aliphatic substituted glycine compound. The term linear aliphatic substituted glycine designates glycine compounds in which the amino group of glycine has been substituted with linear aliphatic groups. In some examples, the sequestering agents can include the alkali metal (e.g., sodium), alkaline earth metal (e.g., calcium) and ammonium salts of ethylene diamine tetraacetic acid, nitrilo triacetic acid, diethylene triamine pentaacetic acid, hydroxyethylene diamine triacetic acid, dihydroxyethyl glycine, iminodiacetic acid and ethanol diglycine. Similar salts of other linear aliphatic substituted glycine compounds can also be used.

[0083] In some examples, viscosity modifiers can be added to the flow modifier compositions. Examples of viscosity modifiers include aliphatic ketones, stearone, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 4-nitrobenzyl alcohol, 4-hydroxy-3~methoxy benzyl alcohol, 3-methoxy-4-nitrobenzyl alcohol,

2-amino-5-chlorobenzyl alcohol, 2-amino-5-methylbenzyl alcohol,

3-amino-2-methylbenzyl alcohol, 3-amino-4-methyl benzyl alcohol, 2(2“(aminomethyl)phenylthio)benzyl alcohol, 2, 4, 6-tri methylbenzyl alcohol,

2-amino-2~methyl-1 ,3-propanediol, 2-amino-1-phenyl-1 ,3-propanediol,

2.2-dimethyl-1-phenyl-1 ,3-propanediol, 2-bromo-2-nitro-1 ,3-propanediol,

3-tert-butylamino-1 ,2-propanediol, 1 , 1 -diphenyl-1 ,2-propanediol, 1 ,4-dibromo-2,3-butanediol, 2,3-dibromo-1 ,4-butanediol, 2,3-dibromo-2-butene-1 ,4-diol, 1 ,1 ,2-triphenyl-1 ,2-ethanediol, 2-naphthalenemethanol, 2-methoxy-1 -naphthalenemethanol, decafluoro benzhydrol, 2-methylbenzhydrol, 1-benzeneethanol, 4,4'-isopropylldene bis(2-(2,6-dibromo phenoxy)ethanol), 2 ,2^!-(1 ,4-phenylenedioxy)diethanol, 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, di(trimethylolpropane), 2-amino-3-phenyl-1 -propanol, tricyclohexyl methanol, tris(hydroxymethyl)aminomethane succinate, 4,4'-trimethylene bis(1 -piperidine ethanol), N-methyl glucamine, or mixtures thereof.

[0084] In some examples, the flow modifier compositions can also contain penetrants for accelerating penetration of the flow modifier composition into the porous wicking membrane. Suitable penetrants include polyhydric alcohol alkyl ethers (glycol ethers) and/or 1 ,2-alkyl diol s. Examples of suitable polyhydric alcohol alkyl ethers are ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1 -methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-isopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, or combinations thereof. Examples of 1 ,2-alkyldiols can include 1 ,2-pentanediol, 1 ,2-hexanediol, or combinations thereof. The penetrant can also be selected from straight-chain hydrocarbon diols, such as 1 ,3-propanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,7-heptanediol, 1 ,8-octanediol, and combinations thereof.

[0085] In some examples, the flow modifier compositions can include preservatives. Specific examples of preservatives can include dichlorophene, hexachlorophene, 1 , 2-benzothiazolin-3-one, 3,4-isothiazolin-3-one, or 4,4-dimethyl oxazolidine, alkyl isothiazolone, chloroalkyl isothiazolone, benzoisothiazolone, bromonitroalcohol, chloroxylenol, or mixtures thereof.

[0086] In various examples, the flow modifier composition can include a single additive from the additives described above, or a combination of multiple additives. In some examples, the additives can be included in a total amount from about 0.1 wt% to about 10 wt% based on the total weight of the fluid modifier composition.

Porous Wicking Membranes

[0087] The porous wicking membranes used with the present methods can include a variety of porous materials that can allow fluid flow within the pores of the material. In some examples, the porous wicking membrane can wick fluids through the membrane material by capillary action. The ability to wick fluids by capillary action can be utilized to allow sample fluids to flow through the porous wicking membrane when the porous wicking membrane is incorporated into a device such as a lateral flow assay.

[0088] In some examples, the porous wicking membrane can be hydrophilic.

Aqueous fluids can flow through hydrophilic membranes by capillary at a high flow rate. In other examples, the porous wicking membrane can include a hydrophobic material. In certain examples, hydrophobic porous wicking membranes can be treated with a detergent or other material to help aqueous fluids flow through the membrane. In further examples, the porous wicking membrane can include fibers. In various examples, the fibers can include hydrophilic fibers, hydrophobic fibers, or both. In further examples, the fibers can include natural fibers, synthetic fibers, or both. In other examples, the porous wicking membrane can be a sintered material having a porous network through which fluid can flow. In still other examples, the porous wicking membrane can be a microstructured material that includes a porous network formed by another suitable method. Non-limiting examples of porous wicking membrane materials that can be used include nitrocellulose, cellulose, polyvinylidene fluoride, nylon, polyethersulfone, paper, glass fiber, cotton, polycarbonate, polystyrene, polypropylene, polyester, polyethylene, and combinations thereof.

[0089] In many examples, the porous wicking membrane can have a thickness from about 50 micrometers to about 200 micrometers. The other dimensions (i.e. , length and width) can have a size suitable for the particular application that the porous wicking membrane is to be used for. In certain examples, a porous wicking membrane used in a chemical test such as a lateral flow assay can have a length and width from about 1 mm to about 10 cm, or from about 2 mm to about 5 cm, or from about 5 mm to about 2 cm.

[0090] In further examples, the porous wicking membrane can include pores that can allow fluids to flow through the porous wicking membrane. When flow modifier composition is applied to the porous wicking membrane, the flow modifying material such as wax nanoparticles or surfactant can pass through the pores in the membrane. Accordingly, in some examples, the pores can be larger than the wax nanoparticles. Additionally, other fluids such as sample fluids can flow through the pores of the porous substrate. In some examples, the porous substrate can have an average pore size from about 0.1 micrometer to about 30 micrometers. In further examples, the porous substrate can have an average pore size from about 0.2 micrometers to about 20 micrometers, or from about 1 micrometer to about 15 micrometers. In some examples, the average pore size can be measured using a standard measurement technique, such as mercury intrusion porosimetry, gas adsorption porosimetry, capillary flow porometry, and so on.

[0091] It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise.

[0092] As used herein, particle size with respect to the wax nanoparticles, or any other particles, can be based on volume of the particle size normalized to a spherical shape for diameter measurement, for example. Particle size can be collected using a Malvern ZETASIZER™ system (Malvern Panalytical, United Kingdom), for example. Particle size information can also be determined and/or verified using a scanning electron microscope (SEM).

[0093] As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above" or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable based on experience and the associated description herein.

[0094] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though individual members of the list are individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0095] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, but also all the individual numerical values or sub-ranges encompassed within that range as if individual numerical values and sub-ranges are explicitly recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of about 1 wt% and about 20 wt%, but also to include individual weights such as 2 wt%, 11 wt%, 14 wt%, and sub-ranges such as 10 wt% to 20 wt%, 5 wt% to 15 wt%, etc.

EXAMPLES

[0096] The following examples illustrate the technology of the present disclosure. However, it is to be understood that the following are illustrative of the application of the principles of the presented technology. Numerous modifications and alternatives may be devised without departing from the present disclosure. The appended claims are intended to cover such modifications and arrangements. Thus, while the disclosure has been provided with particularity, the following describes further detail in connection with what are presently deemed to be the acceptable examples.

Example 1 - Flow Modifier Compositions

[0097] A series of sample flow modifier compositions were prepared including water and LIQUILUBE™ 405 dispersed wax nanoparticles. The sample flow modifier compositions differed in the concentration of wax nanoparticles. Several strips of nitrocellulose membrane with polyester backing were prepared to use as porous wicking membranes. The porous wicking membranes were dipped into the individual flow modifier compositions and allowed to dry. The flow rate of water through the membrane strips was then tested by applying water to one end of the strips and then measuring the distance (in millimeters) traveled by the water front after 21 seconds and then again after 60 seconds. The results are shown in the graph of FIG. 12. The x-axis of the graph is the concentration of wax in the example flow modifier compositions in which the membrane strips were dipped. The graph shows that very low concentrations of wax allowed the water front to travel the farthest distance. The highest concentrations of wax resulted in zero flow of the water through the membrane. A region in between the two extremes appears to allow for the rate of flow to be controlled by adjusting the concentration of the wax.

[0098] While the present technology has been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the technology of this disclosure. It is intended, therefore, that the disclosure be limited by the scope of the following claims.

Claims

CLAIMS What is Claimed Is:

1. A method of modifying a porous wicking membrane, comprising: applying a flow modifier composition to a porous wicking membrane, wherein the porous wicking membrane has an initial capillary flow time (CFT) before the flow modifier composition is applied and a modified CFT after the flow modifier composition is applied, wherein the modified CFT is finite and different from the initial CFT, wherein CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane, and wherein the flow modifier composition comprises: an aqueous liquid vehicle, and a flow modifying material that includes wax nanoparticles to increase the CFT or a surfactant to decrease the CFT.

2. The method of claim 1 , wherein the porous wicking membrane comprises nitrocellulose, cellulose, polyvinylidene fluoride, nylon, polyethersulfone, paper, glass fiber, cotton, polycarbonate, polystyrene, polypropylene, polyester, polyethylene, or a combination thereof.

3. The method of claim 1 , wherein applying the flow modifier composition to the porous wicking membrane comprises applying the flow modifier over an entire surface area of the porous wicking membrane to provide a uniform CFT across the entire porous wicking membrane.

4. The method of claim 1 , wherein applying the flow modifier composition to the porous wicking membrane comprises applying the flow modifier composition to a first portion of the surface of the porous wicking membrane to modify the CFT in the first portion of the porous wicking membrane.

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5. The method of claim 4, further comprises applying a second flow modifier composition to a second portion of the porous wicking membrane to provide a CFT in the second portion that is different from the CFT in the first portion.

6. The method of claim 5, wherein the flow modifier composition and the second flow modifier composition include different flow modifying materials, or wherein the flow modifier composition and the second flow modifier composition include the flow modifying material in different concentrations, or wherein the flow modifier composition and the second flow modifier composition are applied in different amounts to provide different amounts of the flow modifying material to the surface of the porous wicking membrane.

7. The method of claim 4, wherein the first portion of the surface of the porous wicking membrane has a two-dimensional pattern shape that increases mixing of fluid wicking through the porous wicking membrane.

8. The method of claim 4, further comprising forming a test line comprising a test reactant on the porous wicking membrane, wherein the first portion of the surface of the porous wicking membrane is before or after the test line, with respect to the wicking direction of a fluid wicking through the porous wicking membrane.

9. The method of claim 1 , wherein the wax nanoparticles have an average particle size of less than 1 pm and which is less than an average pore diameter of the porous wicking membrane.

10. A lateral flow membrane, comprising: a porous wicking membrane having an initial capillary flow time (CFT): and a flow modifying material applied to the porous wicking membrane, wherein the

36 flow modifying material modifies the initial CFT to a modified CFT that is finite and different from the initial CFT, wherein CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane, and wherein the flow modifying material comprises wax nanoparticles to increase the CFT or a surfactant to decrease the CFT.

11 . The lateral flow membrane of claim 10, wherein the porous wicking membrane comprises nitrocellulose, cellulose, polyvinylidene fluoride, nylon, polyethersulfone, paper, glass fiber, cotton, polycarbonate, polystyrene, polypropylene, polyester, polyethylene, or a combination thereof.

12. The lateral flow membrane of claim 10, further comprising a test line comprising a test reactant on the porous wicking membrane.

13. A fluid ejection device, comprising: a membrane support to receive a porous wicking membrane; a fluidic actuator to receive a flow modifier composition and positioned to jet the flow modifier composition onto an area of a surface of the porous wicking membrane, wherein the flow modifier composition comprises an aqueous liquid vehicle and a flow modifying material that includes wax nanoparticles or a surfactant; and a processor in communication with the fluidic actuator to control an amount of the flow modifier composition applied to the porous wicking membrane such that the flow modifier composition modifies a capillary flow time (CFT) of the porous wicking membrane from an initial CFT to a modified CFT that is finite and different from the initial CFT, wherein CFT is defined as the time for a water front to traverse a distance of 4 cm across the porous wicking membrane.

14. The fluid ejection device of claim 13, wherein the processor adjusts the amount of the flow modifier composition applied to multiple portions of the surface of the porous wicking to provide different CFTs in the multiple portions of the surface of the porous wicking membrane.

15. The fluid ejection device of claim 13, wherein the flow modifier composition comprises the wax nanoparticles, and wherein the device further comprises a second fluidic actuator to receive a second flow modifier composition and positioned to jet the second flow modifier composition onto an area of the surface of the porous wicking membrane, wherein the second flow modifier composition comprises an aqueous liquid vehicle and a surfactant.