Dispensable silver / silver chloride compositions, sensor electrodes, sensors and sensor strips using the same and methods of manufacture thereof

Abstract

In some embodiments, a dispensable suspension composition can include a liquid carrier, silver (Ag) particles, silver chloride (AgCl) particles, and cellulose nanofibers. The dispensable suspension composition can be used to effectively fabricate electrodes via microdispensing. Such Ag / AgCl electrodes can be used as a reference electrode or an indicating electrode in electrochemical sensing systems. Accordingly, Ag / AgCl electrodes formed from the dispensable suspension and sensors using the same are provided, as well as methods of fabricating Ag / AgCl electrodes using the dispensable suspension. Other aspects including the dispensable Ag / AgCl suspension composition are disclosed.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 592,309, filed October 23, 2023, pursuant to 35 USC § 119(e). The entire contents of the aforementioned patent application are expressly incorporated herein by reference.

[0002] field This disclosure relates to dispensable silver / silver chloride compositions, sensor electrodes, sensors and sensor assemblies made using such compositions, and methods of manufacturing such sensor electrodes.

[0003] background Electrochemical sensing systems are used in the biomedical, food, and agricultural industries due to their relatively low cost, variability in measurable signals (voltage, current, conductivity), and relatively low theoretical detection limits. In particular, these electrochemical sensing systems are used in point-of-care diagnostics, where the diagnostic instruments are small, portable, and allow healthcare professionals to test blood at the patient's bedside. Their use can increase testing speed, which can help improve treatment. Electrochemical sensing systems may include reference electrodes. Reference electrodes provide a stable and repeatable potential to the indicator electrode as a reference point for operation. Among the many types of reference electrodes available, silver (Ag) coated with its insoluble salt (i.e., silver chloride (AgCl)) is commonly used in commercial applications due to its suitability for miniaturization and low toxicity. Although Ag / AgCl electrodes are typically immersed in an electrolyte with a known chloride concentration (used to stabilize the potential), bare Ag / AgCl (pseudo-reference electrodes) have also been used, particularly in micro and / or disposable systems.

[0004] These Ag / AgCl electrodes are not only used as reference electrodes, but they have also been successfully used as indicator electrodes. For example, Ag / AgCl is used in ion-selective electrode sensors, which are typically covered by a polymer film that is selective for the desired ions.

[0005] Ag / AgCl electrodes are typically made by chlorinating bulk silver via chemical or electrochemical treatment (via anodizing in the presence of chloride ions). However, such chlorination methods require post-washing, can involve complex setups, and are generally unsuitable for continuous manufacturing.

[0006] With this in mind, screen printing techniques utilizing commercial Ag / AgCl pastes have been developed. Some manufacturers offer inkjet-printable formulations with different Ag:AgCl ratios. Nevertheless, in most cases, Ag / AgCl electrodes are obtained by printing with Ag ink followed by chemical chlorination via bleach or FeCl3. The inks used in these methods are typically prepared by dispersing silver and silver chloride particles in a solvent-based polymer (binder) solution.

[0007] Although several methods for preparing Ag / AgCl electrodes are available, continuous fabrication of micro-dispensing electrodes remains highly challenging. Typically, in continuous micro-dispensing fabrication, it is desirable for the ink to be mechanically stable for many hours. This means that the quality of the dispensed ink and, consequently, the properties of the electrode formed from it, should not change significantly.

[0008] Overview In some embodiments, a dispensable silver / silver chloride (Ag / AgCl) composition is provided. This dispensable suspension composition comprises a liquid carrier (e.g., a solvent), silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. Such dispensable suspensions can be used to form electrodes via microdispensing methods. This composition exhibits excellent shelf-life stability, i.e., excellent anti-sedimentation properties, and can be microprinted with very small droplet sizes.

[0009] In other embodiments, a conductive electrode is provided. This conductive electrode comprises a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized.

[0010] In a further embodiment, a method for manufacturing a conductive electrode is provided. The method includes microdistributing a dispensable suspension onto a substrate of a host, said dispensable suspension comprising: a liquid carrier, silver particles, silver chloride particles, and cellulose nanofibers. The method further includes drying the droplets of said suspension.

[0011] In another embodiment, a sensor is provided. The sensor includes an insulator, a substrate formed on the insulator, and a conductive electrode formed on the substrate, the conductive electrode having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

[0012] In a further embodiment, a strip assembly is provided. The strip assembly includes an insulator, a plurality of spacer substrates formed on the insulator, and a conductive electrode formed on each of the plurality of spacer substrates, each conductive electrode having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

[0013] Numerous other aspects are provided under this disclosure. Other features and aspects of this disclosure will become fully apparent from the following detailed description, the claims, and the accompanying drawings. Brief description of the attached diagram Figure 1 This is a schematic diagram of a sensor according to an embodiment of the present disclosure, which includes an Ag / AgCl-based electrode disposed on a conductive substrate.

[0015] Figure 2A This is a partial cross-sectional side view of a manufacturing assembly for microfabrication of Ag / AgCl electrodes (such as indicator electrodes or reference electrodes) according to an embodiment of this disclosure.

[0016] Figure 2B This is a side view schematic diagram illustrating exemplary particles (e.g., silver particles and silver chloride particles) that are part of the chemical composition of a material that can be used to form an Ag / AgCl electrode according to an embodiment of this disclosure.

[0017] Figure 2C This is a side view schematic diagram of cellulose nanofibers as part of the chemical composition of a substance, which provides improved stability of silver and silver chloride particles in a composition (e.g., a suspension) according to an embodiment of the present disclosure.

[0018] Figure 2D It is a graphical depiction of a three-dimensional network formed by cellulose nanofibers, silver particles and silver chloride particles according to an embodiment of the present disclosure.

[0019] Figure 3 This is a flowchart depicting a method for manufacturing an electrode according to an embodiment of the present disclosure.

[0020] Detailed Explanation Regardless of the use of grammatical terms, individuals with male or female gender identities are included in this term.

[0021] In diagnostic analyzers, such as blood gas analyzers, sensors including sensor electrodes are used to provide measurements of certain components in biological samples, such as the quantification or presence of components (e.g., analytes, such as glucose, BUN (blood urea nitrogen), etc.) and / or the measurement of conditions (e.g., pH) of the biological sample. Such sensor assemblies may include conductive electrodes. For example, as is known in the art, a reference electrode provides a stable and repeatable voltage potential to the indicator electrode as a reference point for the detection system.

[0022] In one embodiment, this disclosure relates to a conductive composition comprising conductive silver (Ag) particles, silver chloride (AgCl) particles, cellulose nanofibers, and a liquid carrier (e.g., a solvent). These Ag / AgCl compositions can be used (e.g., via microdispensing manufacturing methods) to form Ag / AgCl electrodes (e.g., Ag / AgCl microelectrodes) on a conductive substrate. These formed microelectrodes can be used as reference or indicator electrodes in electrochemical sensing systems. This conductive Ag / AgCl composition is particularly suitable for continuous microdispensing methods because very small droplet sizes can be achieved. For example, due to the relatively high stability of this material composition (e.g., an Ag / AgCl suspension composition), the microfabrication of the electrode can begin from a single untouched ink container and continue for at least 24 hours. Furthermore, advantageously, the printed electrode does not require curing above room temperature. As used herein, microdispensing is defined as the formation of a composition by dispensing particles having a size less than 1,000 µm.

[0023] Commercially available Ag / AgCl-based inks are typically fluids with relatively high viscosity. These prior art inks are suitable for dispensing larger droplet sizes (e.g., approximately 2.54 mm or larger in diameter). Smaller droplet diameters can be attempted by diluting the ink with organic solvents, but this results in significant mechanical instability of the suspension. In particular, a density gradient of particles forms within the ink volume over a short period. This makes these diluted inks unsuitable for continuous micro-dispensing manufacturing applications. Once deposited, such inks may still require post-processing chlorination.

[0024] In view of the above-mentioned problems and concerns, a dispensable suspension is provided in a first embodiment. Specifically, the dispensable suspension comprises a liquid carrier, silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. The dispensable suspension composition may be substantially free of polymer binders (except for the cellulose nanofibers). "Substantially free of polymer binders" means that the dispensable suspension composition contains less than 0.5% by weight of polymer binders (unlike cellulose nanofibers) of the total dry components. However, the dispensable suspension composition may contain up to 5% by weight of polymer binders (unlike cellulose nanofibers) of the total dry components, but it is advantageous that the composition is substantially free of polymer binders (unlike cellulose nanofibers). The silver particles and silver chloride particles are stabilized in the suspension (e.g., an aqueous suspension) by comprising a novel binder containing cellulose fibers, particularly cellulose nanofibers 223. These cellulose nanofibers form a three-dimensional network (e.g., Figure 2D(Illustrated in the diagram) to retain silver and silver chloride particles in situ for an extended period in the dispensable suspension 225, thereby improving the shelf life and stability of the dispensable suspension 225. This contributes to improving the anti-settling and printability properties of the dispensable suspension 225. The addition of cellulose nanofibers 223 provides a stable, low-viscosity suspension of silver and silver chloride particles, which is desirable for microdispensing manufacturing.

[0025] An aqueous suspension of Ag and AgCl particles and potentially oxidized cellulose nanofibers is stable from a sedimentation perspective over long manufacturing cycles, such as greater than 12 hours or greater than 1 day. Furthermore, this dispensable suspension is chemically stable at room temperature for extended periods, such as one month or longer, i.e., without significant reactions between solution components. Therefore, this dispensable suspension provides a useful shelf life. Additionally, this dispensable suspension exhibits relatively low viscosity, enabling efficient microdispensing and microprinting. For example, when using microVisc-m available from RheoSense, Inc. of San Ramon, CA... TM When measured with a viscometer at 20°C and a shear rate of 1992 1 / s, this dispensable suspension can have a dynamic viscosity of less than approximately 20 mPa∙s. Generally, if the viscosity is too low, the shelf life will be insufficient, but if the viscosity is too high, it will not be effective for microprinting.

[0026] In another embodiment of this disclosure, a conductive electrode is provided. The electrode, which may be specifically a reference electrode or an indicator electrode, comprises a micro-distribution body of silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. As used herein, micro-distribution refers to a method of distributing one or more droplets 240 of a suspension onto a conductive substrate, wherein each droplet 240 has a droplet volume of 20 nanoliters or less. In this embodiment, the micro-distribution body is a collective mass of the silver particles, silver chloride particles, and cellulose nanofibers that constitute the composition of the conductive electrode.

[0027] The Ag / AgCl electrode can be micro-dispensed from an amber-colored container (e.g., to protect the suspension from UV light) that can be equipped with, for example, a precision dispensing head. The dispensing head can have a small inner diameter of 100 µm to 150 µm. Air pressure can be used to generate the main driving pressure, which propels droplets 240 of the Ag / AgCl / cellulose nanofiber suspension through the dispensing head to achieve precise fluid micro-dispensing and deposition on the substrate 105. The size of the droplets 240 is controlled by the dispensing time and air pressure.

[0028] Droplets 240 can be dispensed in a predetermined area, such as in a hole 242 of the body 103 containing substrate 105, such as at the center of substrate 105. Substrate 105 can be disposed in the bottom surface of hole 242 and completely or partially cover the bottom surface of hole 242. Droplets 240 may have a maximum size (e.g., diameter) of less than 150 µm. Dispensed droplets 240 may completely or partially cover substrate 105. Dispensed droplets 240 may have an electrode diameter size De greater than or equal to 200 µm after drying. For example, in some embodiments, electrode 106 may have an electrode diameter size De of approximately 300 µm to approximately 600 µm in the dried state. Other suitable electrode diameters De may be used. Therefore, it should be appreciated that, as Figure 1 The sensor 100 shown may include, for example, an electrode 106. The sensor 100 may include an insulator 103, a substrate 105 formed on the insulator 103, and a conductive electrode 106 formed on the substrate 105. The conductive electrode 106 may have a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers, wherein the cellulose nanofibers may be oxidized. The dispensed Ag / AgCl electrode 106 advantageously eliminates the need for any post-printing or post-dispensing chemical processing, such as chlorination, thereby simplifying electrode production.

[0029] In another embodiment of this disclosure, a method for manufacturing a conductive electrode 106 is provided. The method includes microdistributing a dispensable suspension (e.g., dispensable suspension 225) onto a substrate (e.g., substrate 105) of a host (e.g., host 103), the dispensable suspension (e.g., dispensable suspension 225) further comprising: a liquid carrier, silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. The substrate (e.g., substrate 105) may comprise a thin gold film formed on an insulator (e.g., host 103) by any suitable method (e.g., chemical vapor deposition).

[0030] The dispensable suspension composition of the present invention can be micro-dispensed and printed using an inkjet method to create the Ag / AgCl electrode 106. The dispensed Ag / AgCl electrode does not require post-forming chlorination or any other post-forming chemical or electrochemical treatment. The droplets of the dispensed Ag / AgCl / cellulose nanofiber composition can be dried by evaporation at room temperature, or optionally by slight heating.

[0031] References will be provided here. Figure 1-3 These and other embodiments of this disclosure are described.

[0032] Refer again Figure 1This illustrates one embodiment of sensor 100. Sensor 100 may be a reference sensor comprised of a body 103 containing an insulator. Body 103 may include a base 103B, a top layer 103T, and possibly an intermediate layer 103I. At least base 103B includes an insulating layer. Base 103B may be made of any suitable insulating material, such as plastic. Furthermore, as is conventional, all three of base 103B, intermediate layer 103I, and top layer 103T may be made of an insulating material sandwiched together and adhered together. Base 103B, intermediate layer 103I, and top layer 103T may cooperate to form a channel 120 in body 103. In operation, channel 120 receives a flow of sample 122 (e.g., biological fluid), for example, in the direction indicated by the arrow. Other suitable configurations of sensor 100 may be used.

[0033] Refer again Figure 1 Sensor 100 includes a substrate 105 on which electrodes 106 are formed. Substrate 105 may be a thin conductive metal layer, such as a gold layer. Optionally, substrate 105 may be any suitable conductive layer, such as platinum, tungsten, or possibly iridium. For example, substrate 105 may have a thickness Ts of approximately 0.25 µm to approximately 5 µm. Other suitable thicknesses and / or suitable conductive materials may be used for substrate 105. Substrate 105 may be a layer deposited, for example, by vapor deposition or other suitable layer-forming methods. Electrical conductors, such as conductive traces, including electrical contacts 110, may be formed. Electrical contacts 110 are electrically connected to substrate 105 in any suitable manner. Furthermore, electrical contacts 110 are configured to engage with similar bonding electrical contacts 112 (which may be, for example, part of a diagnostic analyzer). As shown, bonding electrical contacts 112 may interconnect with detection system 114. Any suitable configuration or process for forming conductive traces or electrical contacts 110 may be used.

[0034] The detection system 114 may include connectivity to one or more other sensors 115, which may be, for example, various ISE (ion-selective electrode) sensors. These other sensors and sensor 100 may be specifically part of a sensor cassette, card, diagnostic analyzer, etc. The detection system 114 may include suitable electronics configured to read and measure the difference in potential (or current) between the one or more other sensors 115 and the reference sensor 100; such electronics are known to those skilled in the art. In the case of a potential difference, the detection system 114 may include a potential meter. In the case of a current difference, the detection system 114 may include a galvanometer.

[0035] More specifically, the sensor 100, including the electrode 106 manufactured using the disclosed Ag / AgCl dispensable composition (Ag / AgCl ink), may comprise a membrane 116. In some embodiments, the membrane 116 may be a heterogeneous membrane, such as the heterogeneous membrane disclosed in US20040231984A1. The membrane 116 may act as a salt bridge providing ionic conductivity but preventing the internal electrolyte from mixing with the sample 122. The membrane 116 may improve robustness to interferences (such as halides) present in blood or plasma samples.

[0036] In some embodiments, membrane 116 may be, for example, an ion-selective membrane (ISM) or a protective membrane. Membrane 116 may be formed of a semi-permeable material, such as a polymer material. For example, the polymer material may be inert polytetrafluoroethylene (PTFE), PVC, polyurethane, etc.

[0037] In some embodiments, the walls of body 103 and membrane 116 may form a reservoir 117. Membrane 116 may be formed as a thin polymer sheet selective for certain cations. In short, membrane 116 is used to allow selective cations to pass through membrane 116 while disallowing other unselected cations from passing through membrane 116.

[0038] It should be understood that the sensor 100, including the membrane 116, may or may not be used with an internal electrolyte 118. For example, the reference sensor 100 may contain a dry internal electrolyte. It may comprise a chloride-based salt embedded in a polymer matrix, such as polyvinyl alcohol (PVA) or cellulose ester, such as Methocel®, available from Sigma Aldrich of Saint Louis, MO. However, in some embodiments, the sensor comprising a reference electrode 106 based on the disclosed Ag / AgCl dispensable composition may be membrane-free.

[0039] In some further embodiments, electrode 106 may be formed and operated as an indicator electrode based on an Ag / AgCl dispensable composition and may be directly coated or contacted with an ion-selective membrane, i.e., based on polyvinyl chloride (PVC) having an ion carrier to provide selectivity for the desired ions, wherein such conventional ion-selective membranes are known to those skilled in the art.

[0040] In other embodiments, the indicator electrode based on the disclosed Ag / AgCl dispensable composition may be separated from the membrane by an electrolyte-containing reservoir 117, thereby potentially improving the stability of the measurable signal. The internal electrolyte 118 may be in any suitable form (e.g., a chloride-based salt (e.g., KCl or NaCl) bound in a polymer matrix in dry or wet form).

[0041] The membrane 116 can be attached to the host 103 by any suitable means, such as different types of adhesion, bonding, compression, and sealing using a sealing ring, or other suitable mechanical or chemical attachment means for sealing the membrane-host interface. The electrode 106 based on the disclosed Ag / AgCl composition can be placed in a hole 242 formed in the insulator 103. Such holes can improve dispensing quality and aid in sealing the membrane 116.

[0042] The conductive electrode 106 of this disclosure contains silver particles 219. Figure 2B ), silver chloride particles 221 ( Figure 2B ) and cellulose nanofibers 223 ( Figure 2C The material (mass) can be substantially homogeneous. In some embodiments, the cellulose nanofibers 223 can be oxidized cellulose nanofibers. Figure 2B The illustrative particles shown are for reference only, as actual particles may not be perfectly spherical, but may be elliptical or other shapes. As described herein, the material of silver particles 219, silver chloride particles 221, and cellulose nanofibers 223 (which may be oxidized) is suitable for microdistribution.

[0043] The manufacturing method and materials used to construct electrode 106 will now be described in detail. Figure 2A As shown, a dispensable suspension 225 comprising at least a liquid carrier (e.g., solvent), silver particles 219 (e.g., silver nanoparticles), silver chloride particles 221 (e.g., silver chloride nanoparticles), and cellulose nanofibers 223 (which may be oxidized) can be provided in a supply container 230 of the microdispensing device 200. For example, the supply container 230 may include a reservoir of sufficient volume to allow production to run for, for example, at least several hours or longer (e.g., 12 hours or longer). In some embodiments, the supply container 230 can be replenished without interrupting the microprinting process. A dispensing portion 235 may be disposed at the lower end or otherwise attached thereto, configured to print droplets 240 of the dispensable suspension 225 onto a substrate (e.g., substrate 105). The microdispensing device 200 can operate continuously as a production line for producing electrode 106 for at least 12 hours or longer.

[0044] In some embodiments, the dispensing portion 235 can be configured as a printhead and can dispense individual droplets 240 of the dispensable suspension 225 onto the substrate 105. The droplets 240 can be dispensed in predetermined regions containing the previously deposited or molded substrate 105 formed in the body 103 through holes 242, such as at the center of the substrate 105. The dispensed droplets 240 can have a droplet diameter of less than 150 µm. After dispensing onto each substrate 105, the droplets 240 will spread out on the surface of the substrate 105. For example, the droplets 240 can be as follows: Figure 2A The electrode 106 is laid out as shown and formed after drying. In the dry state, the electrode 106 may have a maximum electrode diameter De of, for example, about 300 µm to about 600 µm, and an electrode thickness Te of, for example, about 2 µm to about 50 µm. Other suitable electrode diameters De and electrode thicknesses Te may be used. Therefore, it should be appreciated that the sensor 100 may include an insulator 103, a substrate 105 formed on the insulator 103, and a conductive electrode 106 formed on the substrate 105, the conductive electrode 106 having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers (which may be oxidized).

[0045] Regarding cellulose nanofibers 223, when they are mixed into a dispersible suspension 225, the cellulose nanofibers (which may be oxidized cellulose nanofibers) form as... Figure 2D The schematic diagram shows a three-dimensional network 226 of nanofibrated cellulose. This three-dimensional network 226 helps prevent the sedimentation of silver particles 219 and silver chloride particles 221 without significantly increasing the viscosity of the dispersible suspension 225.

[0046] Silver particles As shown in Table 1 below, when in a dry state, silver particles 219 can be provided in the dispensable suspension 225 at approximately 60% to approximately 95% by weight of the total components. The silver particles 219 in the dispensable suspension 225 can have an average lateral size (referred to herein as "average particle size D") of less than or equal to 300 nm. For example, as... Figure 2B As shown, the average particle size D can be from about 5 nm to about 300 nm, or even from about 5 nm to about 150 nm.

[0047] Silver particles 219 can be provided in powder or fluid form. In some embodiments, they may include a dispersant, such as a water-soluble polymer, such as polyvinylpyrrolidone (PVP). Furthermore, in some embodiments, silver particles 219 may contain a hydrophobic coating, such as a dodecyl mercaptan functional group.

[0048] Silver chloride (AgCl) particles The silver chloride (AgCl) particles 221 in the dispensable suspension 225 can be provided at approximately 5% to approximately 30% by weight of the total dry components. Furthermore, the silver chloride particles 221 can have an average lateral size (average particle size D) of less than or equal to 500 nm. For example, the average particle size D can be from approximately 50 nm to approximately 500 nm. The silver chloride particles 221 can be provided in powder form or as an aqueous suspension. An exemplary aqueous suspension form of the silver chloride particles 221 is available from Cerion Nanomaterials of Rochester, NY, and may also contain gelatin or other types of stabilizers. The AgCl particles 221 can be formed from silver (Ag) particles by treatment with chlorine bleach or KCl followed by washing and drying.

[0049] Cellulose nanofibers The composition comprises cellulose nanofibers 223, such as oxidized cellulose nanofibers. The cellulose nanofibers 223 of the dispensable suspension 225 may be provided at 1% to 5% by weight of the total dry components.

[0050] Cellulose nanofibers 223 can be oxidized chemically, enzymatically, or via a chemo-enzymatic approach. Chemical oxidation of cellulose nanofibers 223 can be carried out in the presence of a catalyst, such as through TEMPO (2,2,6,6-tetramethylpiperidin-1-oxy radical)-mediated oxidation, while undergoing subsequent mild mechanical disintegration in water. This method can introduce carboxyl groups onto the surface of the cellulose microfibers. Cellulose nanofibers 223 may include carbonyl functional groups.

[0051] Therefore, oxidized cellulose nanofibers 223 may contain carboxyl and / or carbonyl functional groups, which can provide relatively strong repulsive forces between nanofibers 223, thereby improving the stability of nanofibers 223 in aqueous suspensions.

[0052] Cellulose nanofibers 223 can have the following properties: Figure 2C The end-to-end lengths shown (hereinafter referred to as "length L") are significantly larger than their maximum widths (W), for example, L ≥ 50 * W. In some embodiments, the aspect ratio (L / W) of length L to width W can be greater than or equal to 25, or even greater than or equal to 100, or larger. In some embodiments, the aspect ratio (L / W) of length L to width W can be from 25 to 1,600.

[0053] In some embodiments, the length (L) of the cellulose nanofibers 223 may be 0.2 µm or greater, 0.2 µm to 5 µm, or even 0.2 µm to 80 µm. The width W of the cellulose nanofibers 223 may be 50 nm or less. For example, the width W may be 2 nm to 50 nm in some embodiments, and 5 nm to 50 nm in other embodiments.

[0054] In some embodiments, the cellulose nanofibers have a width (W) of 5 nm to 50 nm and a length (L) of 0.2 µm to 80 µm. For example... Figure 2C The width W and length L of the cellulose nanofiber 223 are shown in the figure.

[0055] Liquid carrier The liquid carrier can be water. In particular, the liquid carrier can be free of organic solvents (e.g., it can be substantially free of alcohols). The absence of organic solvents is desirable, not only because of lower toxicity but also because of slower evaporation, which has been found to extend the shelf life of the composition and thus improve its overall stability. As shown below, the weight percentage (wt%) of the liquid carrier (e.g., water) can be from 80 wt% to 97 wt% of the total weight of the dry components (WDI) plus the weight of the liquid carrier (WLV): Wt% LV = [WLV / (WDI +WLV)] * 100 As described in this article, "organic solvent-free" means that the liquid carrier may contain less than 10% by weight of organic solvents of the total weight of the liquid carrier.

[0056] Other ingredients In some embodiments, the dispensable suspension 225 may optionally contain one or more chloride-based salts, such as potassium chloride (KCl), sodium chloride (NaCl), and calcium chloride (CaCl2). The chloride-based salts can enhance robustness to disturbances present in blood and plasma and / or further stabilize electrode potentials within the dispensable suspension 225. The chloride-based salts may be provided in the dispensable suspension 225 at less than 1.0% of the total dry composition.

[0057] In some embodiments, the dispensable suspension 225 may optionally contain a nonionic surfactant, such as Tween®-20 or Triton, available from Sigma-Aldrich, Inc. of Saint Louis, MO. TM X-100. The surfactant in the dispersible suspension 225 serves to increase the dispersibility of the particles. The surfactant may be provided in the dispersible suspension 225 in an amount of less than 3.0% by weight of the total dry components.

[0058] In some embodiments, the dispensable suspension 225 may optionally contain an organosulfur compound. The organosulfur compound can enhance robustness against interferences present in blood and plasma within the dispensable suspension 225. Examples of organosulfur compounds include L-cysteine. The organosulfur compound may be provided in the dispensable suspension 225 in an amount less than 1.0% of the total dry components.

[0059] When referring to the weight percentage (wt%) of the components of the dispensable suspension 225, what is being referred to is the weight of the specific component in dry form divided by the weight of all components in dry form. It should be understood that some components are sold in an aqueous state. In this case, the weight of water is only included in the determination of the weight % of the liquid carrier in the dispensable suspension 225, and only the calculated dry weight of the specific component and the total components is used for the weight % calculation of that component. For example, the weight percentage (wt%) of a component is calculated as follows: The wt% of an ingredient = (weight of a specific dried ingredient / weight of all dried ingredients) * 100.

[0060] Table 1 – Exemplary Dispensable Suspension Compositions Components Wt% Average particle size (nm) Nanofiber length (µm) Nanofiber width (nm) silver 75.91% dry 20 to 150 na na silver chloride 18.98% dry 80 to 200 na na Oxidized cellulose nanofibers 3.8% dry na 500 to 80,000 6 to 50 Chloride salts or organic sulfur compounds 0.1 dry na na na surfactants 1.21% dry na na na Liquid carrier (water) 93.4% na na na

[0061] Manufacturing method The manufacturing method for forming electrode 106 can utilize dispensing and evaporation methods. (See now for reference.) Figure 2A and Figure 3 The document describes a method 300 for manufacturing a conductive electrode (e.g., electrode 106). Method 300 includes, in block 302, microdistributing a suspension (e.g., a dispensable suspension 225) onto a substrate (e.g., substrate 105) formed on a host (e.g., host 103). As described herein, the suspension (e.g., the dispensable suspension 225) further comprises: a liquid carrier, silver particles (e.g., silver particles 219), silver chloride particles (e.g., silver chloride particles 221), and cellulose nanofibers (e.g., oxidized cellulose nanofibers 223).

[0062] After the suspension (e.g., a dispensable suspension 225) is micro-dispensed onto the substrate 105, the droplets can be dried, for example, by passive evaporation. Thus, once dried, a conductive electrode 106 is formed comprising a micro-dispensed body containing silver particles, silver chloride particles, and cellulose nanofibers.

[0063] To fabricate additional conductive electrodes (e.g., electrode 106), method 300 may optionally further include, in block 304, advancing (e.g., in the direction of arrow 244) a body (e.g., body 103) to align a next substrate (e.g., next substrate 105N) with a dispensing portion (e.g., dispensing portion 235) of a microdispensing device (e.g., microdispensing device 200). This advancement can be performed by any suitable advancement mechanism. For example, a body 103 comprising a plurality of substrates 105, 105N may be provided on a reel, and each next substrate 105N may be advanced to the immediate vicinity of the dispensing portion 235 by a pull or push mechanism.

[0064] Next, in block 306, the dispensing portion (e.g., dispensing portion 235) dispenses the droplet (e.g., droplet 240) onto the next substrate (e.g., next substrate 105N).

[0065] Next, in block 308, blocks 304 and 306 are repeated to reach a predetermined time (e.g., in some embodiments, continuously reaching at least 12 hours or longer). In block 310, method 300 includes allowing any droplets of the suspension to dry.

[0066] After the required number of electrodes 106 have been formed on the substrates 105 and 105N, the body 103 of a certain length can be cut to form a strip assembly 245. This cutting can be achieved by any suitable cutting mechanism 246, such as a blade, saw, etc., to cut the body 103 at the desired location (e.g., along line segment 247) to form the strip assembly 245. Complete drying without airflow or heat assistance can be achieved before or after cutting.

[0067] Therefore, it should be recognized that a strip assembly 245 having a plurality of electrodes 106 formed thereon based on the disclosed dispensable composition can be manufactured. For example, the strip assembly 245 may include 10 or more electrodes formed thereon. Thus, the strip assembly 245 includes an insulator 103, a plurality of spacer substrates 105, 105N formed on the insulator 103, and conductive electrodes 106 formed on each of the plurality of spacer substrates 105, 105N, each conductive electrode 106 having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers. A sensor assembly including a plurality of sensors can be formed from the strip assembly 245 to include, for example, Figure 1 The sensor structure shown or other suitable sensor structures.

[0068] As described above, the method 300 for micro-distributing the suspension 225 forms one or more droplets 240 with a maximum size of less than 150 µm. Specifically, the method 300 for micro-distributing the distributable suspension 225 forms a conductive electrode 106, which, upon drying, can have a very small diameter, as described herein as the maximum diameter size (e.g., electrode diameter De). Advantageously, the method 300 for micro-distributing the distributable suspension 225 does not undergo post-printing chlorination as in prior art methods. Therefore, this method 300 is simpler and more efficient. Due to its excellent printability and anti-settling properties, the micro-distribution of the suspension 225 on the substrate 105 can continue for at least 12 hours or longer.

[0069] Although embodiments have been described herein with reference to specific examples, the scope of this disclosure is not intended to be limited to the details and specific examples described herein. Rather, various modifications to the embodiments and details may be made within the scope and limits of the equivalents of the claims.

[0070] The following is a list of non-limiting exemplary implementations disclosed herein: 1. A dispensable suspension comprising: Liquid carrier; Silver particles; Silver chloride particles; and Cellulose nanofibers.

[0071] 2. The dispensable suspension of exemplary embodiment 1, wherein the liquid carrier is water.

[0072] 3. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers are oxidized.

[0073] 4. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers are oxidized by chemical, enzymatic or chemo-enzymatic methods.

[0074] 5. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers comprise carboxyl and / or carbonyl functional groups.

[0075] 6. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose fibers have a width W of 50 nm or less.

[0076] 7. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers have a length L of 0.5 µm or greater.

[0077] 8. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers have an aspect ratio (L / W) of length L to width W greater than or equal to 25.

[0078] 9. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers have an aspect ratio (L / W) of 25 to 1,600 in length L and width W.

[0079] 10. A dispensable suspension according to any of the foregoing exemplary embodiments, comprising at 20°C and 1,992 s -1 The dynamic viscosity is less than 20 mPa∙s at the shear rate.

[0080] 11. The dispensable suspension of any of the foregoing exemplary embodiments, further comprising a chloride-based salt.

[0081] 12. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the chloride-based salt comprises one or more of KCl, NaCl, and CaCl2.

[0082] 13. The dispensable suspension of any of the foregoing exemplary embodiments, further comprising an organosulfur compound.

[0083] 14. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the organosulfur compound comprises L-cysteine.

[0084] 15. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the dispensable suspension is substantially free of polymeric binders other than the cellulose nanofibers that stabilize the particles.

[0085] 16. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the dispensable suspension may contain less than 10% by weight of an organic solvent of the total weight of the liquid carrier.

[0086] 17. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the dispensable suspension is mechanically stable for 24 hours or longer.

[0087] 18. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the silver particles are provided at 60% to 95% by weight of the total dry components.

[0088] 19. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the silver particles have an average particle size D of less than or equal to 300 nm.

[0089] 20. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the silver chloride particles are provided at 5% to 30% by weight of the total dry components.

[0090] 21. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the silver chloride particles have an average particle size D of less than or equal to 500 nm.

[0091] 22. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers are provided at 1% to 5% by weight of the total dry components.

[0092] 23. A dispensable suspension of any of the foregoing exemplary embodiments, wherein the cellulose nanofibers have a width (W) of 5 nm to 50 nm and a length (L) of 0.2 µm to 80 µm.

[0093] 24. A conductive electrode comprising: Micro-partitions of silver particles, silver chloride particles and cellulose nanofibers.

[0094] 25. The conductive electrode of any of the foregoing exemplary embodiments, wherein the conductive electrode is a reference electrode.

[0095] 26. A method for manufacturing a conductive electrode, comprising: A dispensable suspension is micro-dispensed onto the substrate of a bulk matrix, the dispensable suspension comprising: Liquid carrier, Silver particles, Silver chloride particles, and Cellulose nanofibers; and Allow the droplets of the suspension to dry.

[0096] 27. The method of any of the foregoing exemplary embodiments, wherein the micro-dispersion of the dispensable suspension forms one or more droplets having a maximum droplet size of less than 150 µm.

[0097] 28. The method of any of the foregoing exemplary embodiments, wherein the micro-dispensing forms a conductive electrode having a diameter dimension De greater than or equal to 200 µm after drying.

[0098] 29. The method of any of the foregoing exemplary embodiments, wherein the conductive electrode does not undergo post-printing chlorination.

[0099] 30. The method of any of the foregoing exemplary embodiments, wherein the microdispensing of the dispensable suspension on the substrate 105 lasts for 12 hours or longer.

[0100] 31. A sensor comprising: Insulator; The substrate formed on the insulator, and The conductive electrode formed on the substrate has a chemical composition comprising silver particles, silver chloride particles and cellulose nanofibers.

[0101] 32. A sensor strip assembly comprising: Insulator; Multiple spacer substrates formed on the insulator, and Conductive electrodes are formed on each of the plurality of spacer substrates, each conductive electrode having a chemical composition comprising silver particles, silver chloride particles and cellulose nanofibers.

Claims

1. A dispensable suspension comprising: Liquid carrier; Silver particles; Silver chloride particles; and Cellulose nanofibers.

2. The dispensable suspension according to claim 1, wherein the liquid carrier is water.

3. The dispensable suspension according to claim 1, wherein the cellulose nanofibers are oxidized.

4. The dispensable suspension according to claim 3, wherein the cellulose nanofibers are oxidized by chemical, enzymatic or chemo-enzymatic methods.

5. The dispensable suspension according to claim 1, wherein the cellulose nanofibers comprise carboxyl or carbonyl functional groups or both.

6. The dispensable suspension according to claim 1, wherein the cellulose nanofibers have a width W of 50 nm or less.

7. The dispensable suspension according to claim 1, wherein the cellulose nanofibers have a length L of 0.5 µm or greater.

8. The dispensable suspension according to claim 1, wherein the cellulose nanofibers have an aspect ratio (L / W) of length L to width W greater than or equal to 25.

9. The dispensable suspension according to claim 1, wherein the cellulose nanofibers have an aspect ratio (L / W) of 25 to 1,600 for length L and width W.

10. The dispensable suspension according to claim 1, comprising at 20°C and 1,992 s -1 The dynamic viscosity is less than 20 mPa∙s at the shear rate.

11. The dispensable suspension of claim 1, further comprising a chloride-based salt.

12. The dispensable suspension according to claim 11, wherein the chloride-based salt comprises one or more of KCl, NaCl, and CaCl2.

13. The dispensable suspension according to claim 1, further comprising an organosulfur compound.

14. The dispensable suspension of claim 13, wherein the organosulfur compound comprises L-cysteine.

15. The dispensable suspension of claim 1, wherein the dispensable suspension is substantially free of polymeric binders that stabilize the particles other than the cellulose nanofibers.

16. The dispensable suspension of claim 1, wherein the dispensable suspension may contain less than 10% by weight of organic solvent of the total weight of the liquid carrier.

17. The dispensable suspension according to claim 1, wherein the dispensable suspension is mechanically stable for 24 hours or longer.

18. The dispensable suspension of claim 1, wherein the silver particles are provided at 60% to 95% by weight of the total dry components.

19. The dispensable suspension according to claim 1, wherein the silver particles have an average particle size D of less than or equal to 300 nm.

20. The dispensable suspension of claim 1, wherein the silver chloride particles are provided at 5% to 30% by weight of the total dry components.

21. The dispensable suspension according to claim 1, wherein the silver chloride particles have an average particle size D of less than or equal to 500 nm.

22. The dispensable suspension of claim 1, wherein the cellulose nanofibers are provided at 1% to 5% by weight of the total dry components.

23. The dispensable suspension according to claim 1, wherein the cellulose nanofibers have a width (W) of 5 nm to 50 nm and a length (L) of 0.2 µm to 80 µm.

24. A conductive electrode, comprising: Micro-partitions of silver particles, silver chloride particles and cellulose nanofibers.

25. The conductive electrode of claim 24, wherein the conductive electrode is a reference electrode.

26. A method for manufacturing a conductive electrode, comprising: A dispensable suspension is micro-dispensed onto the substrate of a bulk matrix, the dispensable suspension comprising: Liquid carrier, Silver particles, Silver chloride particles, and Cellulose nanofibers; and Allow the droplets of the suspension to dry.

27. The method of claim 26, wherein the micro-distribution of the dispensable suspension forms one or more droplets having a maximum droplet size of less than 150 µm.

28. The method of claim 26, wherein the micro-distribution forms a conductive electrode having a diameter dimension De greater than or equal to 200 µm after drying.

29. The method of claim 26, wherein the conductive electrode does not undergo post-printing chlorination.

30. The method of claim 26, wherein the microdispersion of the dispensable suspension on the substrate lasts for 12 hours or longer.

31. A sensor comprising: Insulator; The substrate formed on the insulator, and The conductive electrode formed on the substrate has a chemical composition comprising silver particles, silver chloride particles and cellulose nanofibers.

32. A sensor strip assembly comprising: Insulator; Multiple spacer substrates formed on the insulator, and Conductive electrodes are formed on each of the plurality of spacer substrates, each conductive electrode having a chemical composition comprising silver particles, silver chloride particles and cellulose nanofibers.

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