SELF-WICKING ASSAY DEVICES BACKGROUND [0001] Self-wicking assay devices can be used to detect the presence of a target analyte in a sample fluid, for example. These devices can be simple and can often be used typically without specialized training by the user. In some examples, self-wicking assay devices can be widely used for medical diagnostic testing, environmental sample testing, and/or in laboratories, to name a few. BRIEF DESCRIPTION OF THE DRAWINGS [0002] FIG.1 graphically illustrates an example self-wicking assay device in accordance with the present disclosure; [0003] FIG.2 graphically illustrates an example self-wicking assay device in use in accordance with the present disclosure; [0004] FIG.3 graphically illustrates an example system for manufacturing a self-wicking assay device in accordance with the present disclosure; [0005] FIG.4 graphically illustrates an alternative example system for manufacturing a self-wicking assay device in accordance with the present disclosure; and [0006] FIG. is a flow diagram illustrating an example method of manufacturing a self-wicking assay device in accordance with the present disclosure. DETAILED DESCRIPTION [0007] Self-wicking assay devices can permit the detection of a target analyte from a sample fluid. These devices can incorporate a hydrophilic porous substrate so that a sample fluid can sequentially run along the hydrophilic porous substrate via capillary flow. When a target analyte is present in the sample fluid, the target analyte can interact with the hydrophilic porous substrate differently in different regions of the device. An example of a self- wicking assay device is a lateral flow device, such as those devices commonly used for pregnancy testing. There are, however, many other applications of lateral flow devices. [0008] Lateral flow devices typically include multiple functional regions, and as such the substrates in the various regions are typically comprised of different types of material, and those various substrates can be joined or laminated together at junctures, such as by lamination or other joining techniques. In accordance with the present disclosure, however, a hydrophilic porous substrate can be used at multiple regions, provided a region where antigen testing occurs is modified to receive fluids for application of the test and control lines are used to detect and validate the presence of an analyte(s). For example, the application of fluids can be to apply biomolecules to form test and control lines. Benefits that can be achieved may include enhancements in reproducibility, reduction in fabrication complexity related to joining and/or overlapping of substrates, and/or more customization at the user level, e.g., selection of test and control compounds and/or placement of test and control compounds. [0009] In accordance with an example of the present disclosure, a self- wicking assay device (“device”) can include a hydrophilic porous substrate for sequential sample fluid flow from a complexing region to a detecting region thereof. The complexing region can include an analyte-complexing compound on the hydrophilic porous substrate. The detecting region can be positioned downstream from the complexing region along the hydrophilic porous substrate. The detecting region in this example includes a binding promoter applied to the detecting region of the hydrophilic porous substrate, an immobilized testing compound applied to the binding promoter at a first discrete location of the detecting region, and an immobilized control compound applied to the binding promoter at a second discrete location of the detecting region. In one example, a fluid receiving region can also be included that is at or upstream from the complexing region to receive a sample fluid so that an analyte in the sample fluid while at the complexing region is available to potentially interact (or not interact) with analyte-complexing compound. In another example, the hydrophilic porous substrate can be a non-woven substrate including fibers or particles that are hydrophilic or surface-treated with hydrophilic moieties, the fibers or particles including glass, cellulose, polyester, rayon, or a combination thereof. [0010] The binding promoter can be covalently attached to a surface of the hydrophilic porous substrate at the detecting region and the binding promoter can include moieties to immobilize the binding compound and the control compound via covalent bonding, electrostatic interaction, hydrogen bonding, hydrophobic interaction, physical entrapment, or a combination thereof. Alternatively, the binding promoter can have an affinity with the hydrophilic porous substrate at the detecting region but without covalent bonding, e.g., cationic polymer, hydrophobic compound, etc., and the binding promoter can include moieties to immobilize the binding compound and control compound via covalent bonding, electrostatic interaction, hydrogen bonding, hydrophobic interaction, physical entrapment, or a combination thereof. The hydrophilic porous substrate in another specific example can be a polyester, and the binding promoter can include a surface of the polyester that is plasma- treated to break ester bonds and increase a number of negative charge centers. In another example, the immobilized testing compound can include a molecule to bind an analyte that is complexed with the analyte-complexing compound (e.g., occurring in the complexing region). The immobilized control compound can include a different molecule to bind analyte-complexing compound that has not bound to analyte (e.g., also received from the complexing region). [0011] In another example, a system for manufacturing a self-wicking device (“system”) can include a first fluidjet ejector to eject a binding agent including a binding promoter from a first reservoir when loaded therein, a second fluidjet ejector to eject a testing agent including a testing compound from a second reservoir when loaded therein, and a third fluidjet ejector to eject a control agent including a control compound from a third reservoir when loaded therein. The system can also include a hardware controller to generate a command to apply binding agent onto a detecting region of a hydrophilic porous substrate, apply testing agent to immobilize the testing compound at a first discrete region of the detecting region after application of the binding agent, and apply control agent to immobilize the control compound at a second discrete region of the detecting region after application of the binding agent. In one example, the system further includes a fourth fluidjet ejector to eject a second testing agent from a fourth reservoir when loaded therein. In another example, the system can include the binding agent, the testing agent, and the control agent as part of the system components. In another example, the hydrophilic porous substrate can also be included as part of the system components. [0012] In another example, a method of manufacturing a self-wicking assay device (“method”) can include applying binding agent including a binding promoter to a hydrophilic porous substrate to leave the binding promoter at a detecting region of the hydrophilic porous substrate. The binding promoter in this example is not applied to a separate complexing region that is positioned upstream along the hydrophilic porous substrate relative to the detecting region. The method can further include applying a testing agent including a testing compound to the binding compound at a first discrete location of the detecting region to provide an immobilized testing compound at the first discrete location, and applying a control agent including a control compound to the binding compound at a second discrete location of the detecting region to provide an immobilized control compound at the second discrete location. In one example, applying the binding agent can be via a first fluidjet ejector, applying the testing agent can be via a second fluidjet ejector, applying the control agent can be via a third fluidjet ejector, or a combination thereof. The method can further include applying a complexing agent including an analyte-complexing compound to the complexing region. In another example, the method can include applying a second testing agent including a second testing compound to the binding compound at a third discrete location of the detecting region to provide a second immobilized testing compound at the third discrete location, wherein the immobilized testing compound includes a molecule to bind an analyte that is complexed with the analyte-complexing compound, wherein the immobilized second testing compound includes a second molecule to bind a second analyte that is complexed with the analyte-complexing compound or a second analyte- complexing compound, and wherein the immobilized control compound includes a third molecule to bind the analyte-complexing compound or another compound that is not bound to the analyte. [0013] When discussing the self-wicking assay device, the system of manufacturing the self-wicking assay device, and/or the method of manufacturing the self-wicking assay device, such discussions can be considered applicable to one another whether or not they are explicitly discussed in the context of that example. Thus, for example, when discussing a complexing region in a self-wicking assay devices, such disclosure is also relevant to and directly supported in the context of the systems and/or methods, and vice versa. Furthermore, in accordance with the definitions and examples herein, FIGS 1-5 depict various self-wicking assay devices, systems, and methods. These various examples can include various common features. Thus, the reference numerals used to refer to features depicted in FIGS.1-4 in particular may be the same throughout to avoid redundancy. [0014] Terms used herein will be interpreted as the ordinary meaning in the relevant technical field unless specified otherwise. In some instances, there are terms defined more specifically throughout or included at the end of the present disclosure, and thus, these terms are supplemented as having a meaning described herein. Self-wicking Assay Devices [0015] A self-wicking assay device 100, as illustrated in FIG.1, can include a fluid flow pathway for fluid to pass or wick through a hydrophilic porous substrate 110 as well as for sequential fluid flow through multiple regions thereof. Notably, when referring to the hydrophilic porous substrate that includes multiple region, the hydrophilic porous substrate is a single substrate in that the multiple regions use a common hydrophilic porous substrate. This is made possible because one (or more) of the regions along the substrate can be modified to alter properties of the hydrophilic porous substrate, e.g., increased hydrophobicity, modified electrostatic properties, or modified hydrogen bonding properties. For example, the multiple regions can include a complexing region 120 with an analyte-complexing compound 142 applied thereto that may have a functional group for binding with an analyte introduced with a sample fluid (not shown but shown at FIG.2). The detecting region 150 in this example includes the same hydrophilic porous substrate as is present at the complexing region, but in this example, the detecting region is modified with a binding promoter 162. The binding promoter can interact with the hydrophilic porous substrate in a manner so that the detecting region has suitable conditions to receive and immobilize a testing compound and also receive and immobilize a control compound. The testing compound in FIG.1 is shown as an immobilized testing compound 172 at a first discrete location and the control compound is shown as an immobilized control compound 182 at a second discrete location. In this example, the immobilized control compound is positioned downstream from the immobilized testing compound, but this may or may not be the arrangement in every circumstance. The two discrete regions (or lines in this example) can intersect, for example, or can be elsewhere within the detecting region. [0016] The term “discrete location” means a discrete location relative to the detecting region, e.g., having a smaller footprint than the detecting region, but does not infer that the immobilized testing compound and the immobilized control compound are necessarily completely discrete relative to one another. For example, the immobilized testing compound may be applied in a line that partially overlaps with the immobilized control compound, e.g., two lines may intersect to form a “plus” pattern. [0017] The term “immobilized” includes any material that can be applied and will not wick away, at least for long enough for analyte testing to occur, when a sample fluid is passed through the self-wicking device. Thus, the immobilized testing compound or the immobilized control compound may be held in place by covalent attachment, hydrophobic attraction, electrostatic attraction, hydrogen bonding, physical trapping, or the like. [0018] In further detail, the complexing region 120 can be loaded, e.g., adsorbed or impregnated with, an analyte-complexing compound 142 having a functional group that can bind with an analyte in a sample fluid to form an analyte complex. The complexing region can release the analyte-complexing compound having the functional group to bind with the analyte in the sample upon application and movement of a sample fluid therethrough. The analyte- complexing compound identity may vary based on the analyte and the purpose of the self-wicking assay device. In some examples, the analyte-complexing compound can include a colloidal gold, a colored latex particle, a fluorescent latex particle, a paramagnetic latex particle, a cellulose nanobead, a florescent tag, or a combination thereof. The analyte-complexing compound can include, for example, a detection moiety that can be detected by the immobilized control compound also in the detecting region, thereby indicating that a sample fluid has passed through the self-wicking assay device. This is one way of determining that the test has run its course if the results are negative, e.g., the immobilized testing compound did not detect an analyte complex. [0019] Notably, as shown in FIG.1, there are two additional regions shown, namely an upstream region 112 and a downstream region 114. These regions may be of a different substrate material joined with the hydrophilic porous substrate or may be of the same substrate material extended into regions 112 and/or 114 beyond what is specifically shown at reference numeral 110. Example functions that may occur at upstream region 112 may include receiving sample fluid to a sample pad, fluid processing prior to reaching the complexing region 120, etc. Example functions that may occur at downstream region 114 may include fluid absorption to an absorbent pad. Notably, there may also be intervening regions between the complexing region and the detecting region 150, such as concentrating regions or other fluid processing regions. [0020] Referring now to FIG.2, the same self-wicking assay device 100 is presented as is shown in FIG.1, including features such as the hydrophilic porous substrate 110, the complexing region 120 including the analyte- complexing compound 142, and the detecting region 150 including the binding promoter 162 applied at the hydrophilic porous substrate, the immobilized testing compound 172, and the immobilized control compound 182. However, in this example, the device is shown in the context of a system coupled with sample fluid 130 that contains an analyte 132 to be tested using the self-wicking assay device. As mentioned, the analyte should be capable of binding with the analyte-complexing compound in the complexing region and allowed to pass therethrough to be received at the detecting region positioned downstream relative to the complexing region. [0021] An example method detecting the presence of an analyte 132 in a sample fluid 130 using the self-wicking device 100 shown in FIG.2 may be carried out as follows. In one example, a method may include flowing the sample fluid through a complexing region 120 of a hydrophilic porous substrate 110 of the self-wicking assay device. The complexing region in this example can include a complexing compound 142 to bind with the analyte (or not if the analyte is not present) of the sample fluid to form an analyte complex, shown at 144. The method may further include flowing the sample fluid, including the analyte complex formed in the complexing region, into a detecting region 150 that includes an assay component, which in this case includes a test line in the form of an immobilized testing compound 172 and a control line in the form of an immobilized control compound 182. The immobilized testing compound and the immobilized control compound would not normally be able to bind effectively with the hydrophilic porous substrate but can bind in this example because of the presence of a binding promoter 162 that was pre-applied to the detecting region. [0022] The hydrophilic porous substrates in these and other examples can include, for example, a non-woven substrate including fibers or particles that are hydrophilic or surface-treated with hydrophilic moieties. The fibers or particles can include glass fibers, glass particles, cellulose fibers, cellulose particles, polyester, and/or rayon, for example. The term “hydrophilic” is used here to describe a surface wettable by aqueous fluids that do not typically bind strongly with biomolecules or other analytes, and thus, is a relative term in relation to analyte material that may be introduced thereto. The analyte should be capable of binding with the analyte-complexing compound and allowed to pass therethrough to be received at the detecting region positioned downstream relative to the complexing region. Pores of the hydrophilic porous substrate can have an average pore size ranging from about 500 nm to about 10 μm, from about 1 μm to about 10 μm, from about 5 μm to about 10 μm, from about 500 nm to about 5 μm, or from about 2 μm to about 8 μm. A thickness of the hydrophilic porous substrate can range from about 0.1 mm to about 2 mm, from about 0.5 mm to about 1 mm, or from about 0.2 mm to about 0.8 mm. A length of the hydrophilic porous substrate can range from about 1 mm to about 200 mm, from about 1 mm to about 100 mm, from about 1 mm to about 50 mm, from about 1 mm to about 10 mm, from about 5 mm to about 10 mm, from about 1 mm to about 5 mm, or from about 2 mm to about 8 mm. A width of the hydrophilic porous substrate can range from about 1 mm to about 50 mm, from about 1 mm to about 20 mm, from about 5 mm to about 15 mm, or from about 8 mm to about 16 mm. [0023] The self-wicking assay devices can be positioned in some instances in a housing (not shown) with a fluid flow channel therein. In some examples, the fluid flow channel can include a negative space that can be etched, molded, or engraved from a material of a housing and may surround the hydrophilic porous substrate of a self-wicking assay device. The housing can be a casing that the hydrophilic porous substrate may be disposed within. In some examples, the housing may further include a viewing window over the detecting region. The viewing window may be an opening in the housing or may include an optically transparent material in the area of the detecting region to allow a user to view the results of a self-wicking test. [0024] The fluid flow channel through the housing can have a channel size perpendicular to fluid flow through the channel that can range from about 5 μm to about 15 mm. In yet other examples, the fluid flow channel can have a size that can range from about 5 μm to about 15 mm, from about 5 μm to about 2 mm, from about 1 mm to about 15 mm, from about 100 μm to about 500 μm, from about 500 μm to about 1 mm, or from about 5 mm to about 10 mm, etc. The fluid flow channel may include a pathway. The pathway may be a linear pathway, a curved path, a pathway with turns, a branched pathway, a serpentine pathway, or any other pathway configuration. In some examples, the pathway may be linear and/or branched. The hydrophilic porous substrate may be present in a portion of or throughout the entire length of the fluid flow channel. [0025] In some examples, the self-wicking assay device may further include other components. For example, the device may include a fluid input port. The fluid input port may be used to access the complexing region so that a sample fluid, an elution fluid, or a combination thereof may be applied through the fluid flow channel and onto the hydrophilic porous substrate. The self- wicking assay device may also include an elution fluid input port. The elution fluid input port may be positioned at or upstream of the concentrating region. The elution fluid input port may also be used to add other charge-modifying fluids into the self-wicking assay device. [0026] In some examples, the self-wicking assay device can further include a backing. The backing can support the hydrophilic porous substrate. In some examples, the backing can include polyphenylene ether, polyester, polytetrafluoroethylene, glass, glass fiber, cellulose, nitrocellulose, or a combination thereof. The backing can be used to provide stability to the hydrophilic porous substrate. [0027] In some examples, the self-wicking assay device can further include a flow controlling agent. The flow controlling agent may be impregnated within the hydrophilic porous substrate and may include buffer salts, proteins, surfactants, and the like. The flow controlling agent may increase or decrease a fluid flow rate of the sample fluid through the hydrophilic porous substrate. [0028] These specific examples are provided to illustrate how the self- wicking assay device may be used, but it is noted that there are many other similar uses, particularly as these devices relate to different types of lateral flow devices, for example. The self-wicking assay devices can be used for competitive assays, sandwich assays, quantitative assays, or the like. Example sample fluids that may be tested can include urine, blood, saliva, sweat, serum, or other biological samples regardless of origin or application, e.g., environmental, disease, clinical, laboratory, hospitals, physicians, veterinary, chemical analysis, toxins, pregnancy, etc. [0029] The sample fluid may be a fluid that can include an analyte to be detected or can exclude the analyte to be detected by the self-wicking assay device. When the sample fluid includes the analyte, a positive result may be generated by the device. When the sample fluid excludes the analyte, a negative result may be generated by the device. The analyte in the sample fluid may be selected from amino acids, peptide strands, glycans, polypeptides, antibodies, proteins, or a combination thereof. In one example, the analyte can include a protein. The analyte may be at least ten residues long. A single strand of the analyte may have a weight average molecular weight ranging from about 1,500 Daltons to about 250 KD, about 5,000 Daltons to about 200 KD, or from about 50 KD to about 250 KD. Systems for Manufacturing Self-Wicking Assay Devices [0030] Systems for manufacturing a self-wicking assay device are show by way of Example in FIGS.3 and 4. In FIG.3, the system is shown in the context of an example where various fluids or “agents” can be digitally controlled by ejection from fluidjet printheads, for example. In this example, a binding agent 160 can be applied to a detecting region 150 of hydrophilic porous substrate 110, followed by application of a testing agent 170 to a first discrete location of the detecting region as well as a control agent 180 to a second discrete location of the detecting region. Application (A) can occur before application (B) and application (C) which may be applied together or in either order. In one example, a first fluidjet ejector 164 can be used to eject the binding agent including a binding promoter from a first reservoir 166 when loaded therein, a second fluidjet ejector 174 can be used to eject a testing agent 170 including a testing compound from a second reservoir 176 when loaded therein, and a third fluidjet ejector 184 can be used to eject a control agent 180 including a control compound from a third reservoir 186 when loaded therein. The system can also include a hardware controller 190 to generate a command to apply binding agent onto a detecting region of a hydrophilic porous substrate, apply testing agent to immobilize the testing compound at a first discrete region of the detecting region after application of the binding agent, and apply control agent to immobilize the control compound at a second discrete region of the detecting region after application of the binding agent. In one example, the system further includes a fourth fluidjet ejector (not shown) to eject a second testing agent from a fourth reservoir when loaded therein. In another example, the system can include the binding agent, the testing agent, and the control agent as part of the system components. In another example, the hydrophilic porous substrate can also be included as part of the system components. Notably, the hydrophilic porous substrate in this example is shown as being supported by a platform 102 that can have any configuration suitable for holding the hydrophilic porous substrate in place for application of the various fluid agents. [0031] As shown in FIG.4, an alternative system is shown that can include the same features as that shown in FIG.3, as shown by common reference numerals outlined above, except that in this example, the analyte- complexing compound 146 can likewise be applied using a complexing agent 140 loaded in a complexing agent reservoir 146 and ejected from a complexing agent fluidjet ejector 144. In this instance, since it is the analyte-complexing compound that is being applied, it may be applied to the complexing region rather than the detecting region. Though the analyte-complexing compound is shown as being applied by a fluidjet ejector, it can likewise be applied by other methodologies, such as by the use of a pipette, blotting, soaking, dipping, spraying, etc., at the time of use or by bulk treating the hydrophilic porous substrate 110. Methods for Manufacturing Self-Wicking Assay Devices [0032] A method 300 of manufacturing a self-wicking assay device can include applying 310 binding agent including a binding promoter to a hydrophilic porous substrate to leave the binding promoter at a detecting region of the hydrophilic porous substrate. The binding promoter in this example is not applied to a separate complexing region that is positioned upstream along the hydrophilic porous substrate relative to the detecting region. The method can further include applying 320 a testing agent including a testing compound to the binding compound at a first discrete location of the detecting region to provide an immobilized testing compound at the first discrete location, and applying 330 a control agent including a control compound to the binding compound at a second discrete location of the detecting region to provide an immobilized control compound at the second discrete location. In one example, applying the binding agent can be via a first fluidjet ejector, applying the testing agent can be via a second fluidjet ejector, applying the control agent can be via a third fluidjet ejector, or a combination thereof. The method can further include applying a complexing agent including an analyte-complexing compound to the complexing region. In another example, the method can include applying a second testing agent including a second testing compound to the binding compound at a third discrete location of the detecting region to provide a second immobilized testing compound at the third discrete location, wherein the immobilized testing compound includes a molecule to bind an analyte that is complexed with the analyte-complexing compound, the immobilized second testing compound includes a second molecule to bind a second analyte that is complexed with the analyte-complexing compound or a second analyte-complexing compound, and wherein the immobilized control compound includes a third molecule to bind the analyte-complexing compound or another compound that is not bound to the analyte. Binding Promoters [0033] There are several different methods and compositions that can be used to modify hydrophilic porous substrates at the detecting region in accordance with examples herein, including the fluidjet application described in one example herein. However, it is noted that the self-wicking assay device can be prepared with binding promoter using other methodologies, followed by fluidjet application of the testing agent and the control agent to form the immobilized testing compound and the immobilized control compound at discrete locations on the binding promoter. Binding promoter can be in the form of covalently attached compounds, non-covalently attached compounds, or surface modified regions from plasma treatment, in situ polymerization that results in covalent attachment or non-covalent attraction with the hydrophilic porous substrate etc. [0034] In one example, such as when the hydrophilic porous substrate includes surface hydroxyl groups, silylation, e.g., the attachment of silane- coupling compounds with functional groups suitable to interact with analyte complexes or interact with other compounds other than the analyte complexes, occurs. Suitable chemistry for interaction between the analyte complex (or other compound or complex) and the functional group at the immobilized testing compound and/or the immobilized control compound can include, for example, groups reactive with a free amine or thiol that can be activated to amino acids with diamide and then linked to amine or thiol. For example, a protein can be activated by mixing with EDC/NHS and then it can be applied to the hydrophilic porous substrate. Protein activation chemistries, as well as diamide chemistries, can be used, for example. On the other hand, proteins may have free amine groups, so in those instances, they may not benefit from further activation if using carboxylic acids on the silane groups. [0035] As an example, a binding promoter agent can include binding promoter components for attachment to surface hydroxyl groups of the hydrophilic porous substrate, e.g., glass fiber mat. Formula I provides an example of the chemistry that can be used, as follows: R In Formula I above, R can include, for example: O * _{( )} ^{NH2 * SH} * _{( )} H . he thiol group, and the R groups with acid group can be formed in situ after oxidation using an oxidizing compound. For example, to oxidize an R group to form the carboxylic acid shown in the third structure above, the carboxylic acid can be made by oxidizing a surface of the hydrophilic porous substrate having one of the following precursor structures as the initial R group present, as follows: . in the presence of potassium permanganate (KMnO4) or other oxidizing compounds, e.g., potassium dichromate, chromic acid, etc. Again, these precursor structures may likewise be prepared where n is from about 1 to about 10. [0036] Furthermore, in some more specific examples, to increase the number of surface hydroxyl groups that are available for coupling with the organosilanes, a formulation including nitric acid, an admixture of 70:30 (w/w) water and hydrogen peroxide, ammonium hydroxide, may be applied in some instances. In another example, it is also noted that there can be other R groups other than those set forth above. For example, a biomolecule, an oligomer, or a polymer can be attached similarly by silylation. A binding promoter can be applied from a binding agent from a fluidjet ejector that includes silane-based chemical components with a modifiable functional portion having an affinity for proteins that may be applied as the testing compound and/or the control compound. [0037] In a more specific example, a glass fiber as the hydrophilic porous substrate may be functionalized by sol-gel deposition of organosilanes after treating the substrate to enhance (increase) the surface density of surface hydroxyls and ultimately of the reactive silanol groups. For example, selected organosilane reagents can be selected to undergo subsequent condensation with desired molecules, e.g., carboxyl/amine-PEG, proteins, polymers, etc. Nucleophilic condensations partners such as amines or thiols may be incorporated directly, for example. Electrophilic condensation partners may be generated post-functionalization. For example, carboxylic acids may be generated from the oxidation of alcohols or aldehydes, or the ozonolysis of alkenes followed by oxidation. For multiplexing applications, silanes can be selected or designed with varying functional groups to enable bioorthogonal chemistries to immobilize biomolecules. [0038] As another example, activation of carboxylic acids for nucleophilic condensation can be used as well. For example, carbodiimides can be used as coupling reagents for solid phase peptide synthesis and the immobilization of biological molecules (proteins, peptides, etc.) to other materials (surfaces, other proteins, etc.). Carbodiimides can increase the reactivity of carboxylic acids to nucleophiles; like primary amines, thiols, etc. The result of the coupling reaction can be a new covalent bond between two species and a urea biproduct. Some examples of include dicyclohexylcarbodiimide (DCC), N,N'- diisopropylcarbodiimide (DIC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), or 1-cyclohexyl-(2-morpholinoethyl)carbodiimide metho-p-toluene (CMC). [0039] As a specific example, a carboxylate compound can be reacted with EDC to form an unstable reactive acylisourea ester, which can be reacted with a sulfo-N-hydroxysuccinimide to form an amine-reactive N- hydroxysuccinimide-ester, which can be reacted by compound with an amino group to form a stable amide bond linking the interactive portion of the testing compound or the control compound to the hydrophilic porous substrate via silylation. [0040] Notably, in these and other examples, the binding promoter that is applied can be covalently attached to the hydrophilic porous substrate, and furthermore, the testing compound and/or the control compound can be applied to covalently attach thereto or alternatively can be applied to interact by electrostatic attraction, hydrogen bonding, hydrophobic interaction, or the like, without covalent attachment. [0041] In still another example, depending on the chemistry of the hydrophilic porous substrate, the binding promoter may be a surface chemistry modification of the substrate. Modification of the surface chemistry can be by any methodology, but in one example, surface chemistry modification can occur by plasma treatment. Polyester in particular is a material that can be treated with plasma to break ester bonds to generate a surface with a more negative charge. Thus, even though a binding promoter is not applied as a chemical per se, the plasma changes the nature of the surface, so this example can be considered to be a substrate with covalently bonded binding promoter, even though these groups may be small or short, e.g., small molecule modification. This is because the surface is changed to have anionic groups thereon that are not native to the substrate, and thus, there are new groups thereon that are covalently bonded to the hydrophilic porous substrate. [0042] In other examples, the binding promoter that is applied to the hydrophilic porous substrate can have an affinity therewith, but may not be covalently bonded thereto, e.g., adsorption, electrostatic attraction, hydrogen bonding, etc. With this more non-specific binding or affinity, binding promoter can be any material that has an affinity for the hydrophilic porous substrate when applied, but also has the ability to prevent or significantly ameliorate the testing compound and/or the control compound from wicking away. Though a covalent bond may provide immobilization, in many instances, a non-specific interaction, e.g., enhanced hydrophobicity, electrostatic attraction, or hydrogen bonding, may be enough. [0043] To provide a more specific example of non-covalent bonding that can be used to provide location stability to the testing compound and/or control compound used to form the test and control lines of a lateral flow device, the binding promoter applied may be a cationic polymer, or in some instances, a dual functional polymer having a portion with an affinity with the hydrophilic porous substrate and another portion with an affinity with a biomolecule(s) used as the testing compound and/or the control compound. For example, if the hydrophilic porous substrate has a minority of moieties that give the substrate some degree of hydrophobicity (enough to receive and cling to a hydrophobic portion of a polymer), but is still too hydrophilic to prevent wicking away of the testing compound and/or control compound, then a polymer with this type of dual functionality may be useable. Definitions [0044] 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. [0045] 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 presentation in a common group without indications to the contrary. [0046] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. A 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, and also to include 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 numeric range that ranges from about 10 to about 500 should be interpreted to include the explicitly recited sub-range of about 10 to about 500 as well as sub-ranges thereof such as about 50 and about 300, as well as sub- ranges such as from about 100 to about 400, from about 150 to about 450, from about 25 to about 250, etc. [0047] The terms, descriptions, and figures used herein are set forth by way of illustration and are not meant as limitations. Many variations are possible within the disclosure, which is intended to be defined by the following claims and their equivalents in which all terms are meant in the broadest reasonable sense unless otherwise indicated.