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

Abstract

In some embodiments, a dispensable suspension composition may include a liquid vehicle, silver (Ag) particles, silver chloride (AgCl) particles, and cellulose nanofibers. The dispensable suspension composition can be used to effectively manufacture electrodes via micro-dispensing. Such Ag / AgCl electrodes can be used as reference or indicator electrodes in electrochemical sensing systems. Thus, Ag / AgCl electrodes formed from the dispensable suspension, and sensors utilizing them are provided, as well as methods of manufacturing Ag / AgCl electrodes using the dispensable suspension. Other aspects including the dispensable Ag / AgCl suspension composition are disclosed.

Description

DISPENSABLE SILVER / SILVER CHLORIDE COMPOSITIONS, SENSOR ELECTRODES, SENSORS, AND SENSOR STRIPS UTILIZING SAME, AND METHODS OF MANUFACTURE THEREOF

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

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

[0003] Electrochemical sensing systems are utilized in biomedical, food, and agriculture industries because of their relatively low-cost, variability in the measurable signals (voltage, current, conductivity), and relatively low theoretical detection limits. In particular, such electrochemical sensing systems are used in point-of-care diagnostics where diagnostic instruments are small, portable, and allow medical personnel to test blood at the patient’s bedside. Their use can increase the speed of testing, which can help to improve treatment.

[0004] An electrochemical sensing system can include a reference electrode. The reference electrode provides a stable and repeatable potential to the indicator electrodes as a reference point needed for operation. Among many available types of reference electrodes, silver (Ag) coated by its insoluble salt (i.e., silver chloride (AgCl)) has been commonly used in commercial applications due to itssuitability for miniaturization and low toxicity. Although typically Ag / AgCl electrodes are immersed in an electrolyte of known chloride concentration (which serves to stabilize the potential), bare Ag / AgCl (pseudo-reference electrodes) have also been used, specifically in micro- and / or disposable systems.

[0005] Such Ag / AgCl electrodes are not only used for reference electrodes, they have been successfully utilized as indicator electrodes, as well. For instance, Ag / AgCl is used in ion-selective electrode sensors typically covered by a polymeric membrane selective to desired ions.

[0006] Ag / AgCl electrodes are typically made by the chloridization of bulk silver through chemical or electrochemical treatment (via anodization in the presence of chloride ions). However, such chloridization methods require post-washing, can have complex set-ups, and are generally not suitable for continuous fabrication.

[0007] With that in mind, a screen-printing technique has been developed exploiting commercial Ag / AgCl pastes. Some manufacturers offer ink-jettable formulations of different Ag:AgCl ratios. Nevertheless, in most cases, Ag / AgCl electrodes are obtained by printing with Ag ink followed by chemical chloridization via bleach or FeCl3. Inks used for those methods are typically prepared by dispersing silver and silver chloride particles in solvent-based polymer (binder) solutions.

[0008] Despite some available Ag / AgCl electrode preparation methods, micro-dispense continuous fabrication is still very challenging. Typically, in micro-dispense continuous fabrication, it is desirable that the ink be mechanically stable for many hours. This means there should be no significant change in the quality of the ink dispensed and thus the properties of the electrodes formed therefrom.SUMMARY

[0009] In some embodiments, a dispensable silver / silver chloride (Ag / AgCl) composition is provided. The dispensable suspension composition comprises a liquid vehicle (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 micro-dispense methods. The composition has excellent shelf-life stability, i.e., excellent anti-settling properties, and can be micro-printed in very small droplet sizes.

[0010] In other embodiments, an electrically-conductive electrode is provided. The electrically-conductive electrode comprises a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized.

[0011] In a further embodiment, a method of manufacturing an electrically-conductive electrode is provided. The method comprises micro-dispensing a dispensable suspension onto a substrate of a body, the dispensable suspension comprising: a liquid vehicle, silver particles, silver chloride particles, and cellulose nanofibers. The method further includes allowing a droplet of the suspension to dry.

[0012] In another embodiment, a sensor is provided. The sensor comprises an insulator body, a substrate formed on the insulator body, and an electrically-conductive electrode formed on the substrate having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

[0013] In a further embodiment, a strip assembly is provided. The strip assembly comprises an insulator body, multiple spaced substrates formed on the insulator body, and an electrically-conductive electrode formed on each of the multiple spaced substrates, each electrically-conductiveelectrode having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

[0014] Numerous other aspects are provided in accordance with the disclosure. Other features and aspects of the present disclosure will become fully apparent from the following detailed description, the claims, and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a schematic diagram of a sensor comprising an Ag / AgCl-based electrode dispensed over a conductive substrate according to embodiments of the disclosure.

[0016] FIG. 2A is a partially cross-sectioned side view of a manufacturing assembly for microfabrication manufacturing of an Ag / AgCl electrode such as for an indicator electrode or reference electrode according to embodiments of the disclosure.

[0017] FIG. 2B is a side schematic view illustrating an example particle (e.g., a silver particle and a silver chloride particle) that are part of a chemical composition of matter useful for forming Ag / AgCl electrodes according to embodiments of the disclosure.

[0018] FIG. 2C is a side schematic view of a cellulose nanofiber that is part of a chemical composition of matter that provides improved stability of the silver and silver chloride particles in the composition (e.g., suspension) according to embodiments of the disclosure.

[0019] FIG. 2D is a graphical depiction of a three- dimensional network formed by cellulose nanofibers, silver particles, and silver chloride particles according to embodiments of the disclosure.

[0020] FIG. 3 is a flowchart depicting a method of manufacturing an electrode according to embodiments of the disclosure. DETAILED DESCRIPTION

[0021] Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

[0022] In diagnostic analyzers, such as blood gas analyzers, sensors including sensor electrodes are used to provide measurements of certain components in a bio-sample, such as the quantification or presence of a component (e.g., an analyte such as glucose, BUN (blood urea nitrogen), etc.) and / or a condition (e.g., pH) of the bio-sample. Such sensor assemblies may include an electrically-conductive electrode. Reference electrodes, for example, provide a stable and repeatable voltage potential for an indicator electrode as a reference point for the detection system, as is well known in the art.

[0023] In one embodiment, this disclosure is directed to a conductive composition comprising conductive silver (Ag) particles, silver chloride (AgCl) particles, cellulose nanofibers, and a liquid vehicle (e.g., a solvent). These Ag / AgCl compositions can be used to form (e.g., via a micro- dispensing manufacturing method) Ag / AgCl electrodes (e.g., Ag / AgCl micro-electrodes) on conductive substrates. These formed micro-electrodes can be used as reference or indicator electrodes in electrochemical sensing systems. The conductive Ag / AgCl compositions are particularly suitable for continuous micro-dispensing processes, as very small droplet sizes are achievable. For example, microfabrication of electrodes can commence and continue for at least 24 hours from a single, untouched, ink-container due to the relatively high stability of the composition of matter (e.g., Ag / AgCl suspensioncomposition). Further, advantageously, the printed electrode does not require curing at higher than room temperature. As used herein micro-dispensing is defined as forming via dispensing of compositions that have micro-particles therein having a size of less than 1,000 µm.

[0024] Commercially available Ag / AgCl-based inks are fluids that typically have relatively high viscosity. These prior art inks are suitable for dispensing larger droplet sizes (e.g., about 2.54 mm or more in diameter). Smaller droplet diameters may be attempted by thinning the inks with organic solvents, but this leads to substantial mechanical instability of the suspension. In particular, a density gradient of the particles is formed over a short time period in the volume of the ink. This makes these thinned inks unsuitable for continuous micro-dispense manufacturing applications. Such inks, once deposited, may still require post process chloridization.

[0025] Given the above issues and concerns, in a first embodiment, a dispensable suspension is provided. In particular, the dispensable suspension comprises a liquid vehicle, silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. The dispensable suspension composition may be substantially devoid of a polymeric binder (except the cellulose nanofibers). Substantially devoid of a polymeric binder means that the dispensable suspension composition contains polymer binder (other than the cellulose nanofibers) in an amount less than 0.5 wt% of the total weight of the dry ingredients. However, the dispensable suspension composition may contain a polymer binder (other than the cellulose nanofibers) up to 5 wt% of the total dry ingredients, but it is advantageous if the composition is substantially devoid of the polymer binder (other than the cellulose nanofibers). The silver particles and silver chloride particles are stabilizedin a suspension (e.g., an aqueous suspension) by a novel binder comprising cellulose fibers, specifically cellulose nanofibers 223. These cellulose nanofibers form a three- dimensional network (as schematically shown in FIG. 2D) holding the silver and silver chloride particles in place for an extended period in the dispensable suspension 225, thereby improving shelf-life and stability of the dispensable suspension 225 which contributes to the improved anti-settling and printability properties of the dispensable suspension 225. Addition of the cellulose nanofibers 223 provides a stable, low-viscosity suspension of the silver and silver chloride particles, which is desirable for micro-dispensing manufacturing.

[0026] The aqueous suspension of Ag and AgCl particles, and cellulose nanofibers, which may be oxidized, are stable from the standpoint of settling for a long manufacturing period, such as greater than 12 hours or greater than a day, for example. Further, the dispensable suspension is chemically stable, i.e., no substantial reaction between the solution components for an extended period of time, such as for a month or more at room temperature. Thus, the dispensable suspension provides a useful shelf life. Further, the dispensable suspension exhibits relatively low viscosity, such that it may be effectively micro-dispensed and micro-printed. For example, the dispensable suspension can comprise a dynamic viscosity of less than about 20 mPa ^s when measured (at 20°C and at shear rate 19921 / s using a microVisc-mTMviscometer available from RheoSense, Inc. of San Ramon, CA). Generally, if the viscosity is too low, the shelf life will be insufficient, but if the viscosity is too high then it will not be able to be effectively micro-printed.

[0027] In another embodiment of the present disclosure, an electrically conductive electrode is provided. The electrode, which may be embodied as a reference or indicator electrode,comprises a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. Micro-dispensed, as used herein, means a method of dispensing onto a conductive substrate one or more droplets 240 of the suspension, wherein each droplet 240 has a droplet volume of 20 nanoliters or less. In this embodiment, the micro-dispensed mass is the collective mass of silver particles, silver chloride particles, and cellulose nanofibers making up the composition of the electrically conductive electrode.

[0028] The Ag / AgCl electrode can be micro-dispensed from an amber barrel (e.g., to protect the suspension from UV light) that may be equipped with a precision dispense tip, for example. The dispense tip may have a small internal diameter of from 100 µm to 150 µm. Air pressure may be used to produce a primary driving pressure that pushes the droplet 240 of Ag / AgCl / cellulose nanofiber suspension through the dispense tip allowing for precise fluid micro-dispense and deposition on the substrate 105. The size of the droplet 240 is controlled by the dispense time and air pressure.

[0029] The droplet 240 may be dispensed in a predefined region, such as in a well 242 of a body 103 containing the substrate 105, such as at a center of the substrate 105. The substrate 105 may be disposed in and fully or partially cover the bottom surface of the well 242. The droplet 240 may have a maximum dimension (e.g., diameter) of less than 150 µm. The dispensed droplet 240 may cover the substrate 105 completely or partially. The dispensed droplet 240 may have an electrode diameter dimension De, after drying, of greater than or equal to 200 µm. For example, the electrode 106, in the dried condition, may have an electrode diameter dimension De from about 300 µm to about 600 µm in some embodiments. Other suitable electrode diameters De may be used. Thus, it should be recognized that a sensor 100 as shown in FIG. 1, forexample, can include the electrode 106. The sensor 100 can comprise an insulator body 103, a substrate 105 formed on the insulator body 103, and an electrically-conductive electrode 106 formed on the substrate 105. The electrically-conductive electrode 106 can 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 does not require any post-printing or post-dispensing chemical processing such as chloridization thereby simplifying electrode production.

[0030] In another embodiment of the present disclosure, a method of manufacturing an electrically-conductive electrode 106 is provided. The method comprises micro-dispensing a dispensable suspension (e.g., dispensable suspension 225) onto a substrate (e.g., substrate 105) of a body (e.g., body 103), the dispensable suspension (e.g., dispensable suspension 225) further comprising: a liquid vehicle, silver particles, silver chloride particles, and cellulose nanofibers. The cellulose nanofibers may be oxidized. The substrate (e.g., substrate 105) can comprise a thin gold film formed on an insulator body (e.g., body 103) by any suitable method, such as chemical vapor deposition or the like.

[0031] The Ag / AgCl electrode 106 can be micro-dispensed and printed from the present dispensable suspension composition by an ink-jet method. The dispensed Ag / AgCl electrode does not require post-forming chloridization or any other post-forming chemical or electrochemical treatment. The dispensed drop of Ag / AgCl / cellulose nanofiber composition can dry by evaporation at room temperature or optionally can be slightly heated.

[0032] These and other embodiments of the present disclosure will be described with reference to FIGS. 1-3 herein.

[0033] Referring again to FIG. 1, an embodiment of a sensor 100 is shown. Sensor 100 may be a reference sensor that is made up of a body 103 comprising an insulator. The body 103 may include a base 103B, a top layer 103T, and possibly an intermediate layer 103I. At least the base 103B comprises an insulating layer. The base 103B may be made from any suitable insulator material, such as a plastic, for example. Further, all three of the base 103B, intermediate layer 103I, and top layer 103T may be manufactured from insulating materials that are sandwiched and adhered together, as is conventional. Base 103B, intermediate layer 103I, and top layer 103T may cooperate to form a passageway 120 in the body 103. In operation, passageway 120 receives a flow of a sample 122 (e.g., a bio-fluid) in the direction of the arrow shown, for example. Other suitable constructions of the sensor 100 may be used.

[0034] Referring again to FIG. 1, the sensor 100 comprises a substrate 105 onto which the electrode 106 is formed. The substrate 105 can be a thin metal electrically-conductive layer such as a gold layer. Optionally, substrate 105 may be any suitable conductive layer such as platinum, tungsten, or possibly iridium. Substrate 105 can have a thickness Ts of from about 0.25 µm to about 5 µm, for example. Other suitable thicknesses and / or suitable electrically conductive materials may be used for the substrate 105. Substrate 105 may be a deposited layer such as by a vapor deposition or other suitable layer forming process. An electrical conductor, such as a conductive trace may be formed including an electrical contact 110. The electrical contact 110 is connected electrically to the substrate 105 in any suitable manner. Further, the electrical contact 110 is configured to interface with a like engaging electrical contact 112, which may be a part of a diagnostic analyzer, for example. Engaging electrical contact 112 may be interconnected to a detectionsystem 114, as is shown. Any suitable configuration or process for forming the conductive trace or electrical contact 110 may be used.

[0035] Detection system 114 can include connections to one or more other sensors 115, which can be various ISE (ion- selective electrode) sensors, for example. The other sensors and the sensor 100 may be embodied as part of a sensor cartridge, card, diagnostic analyzer, or the like. The detection system 114 may include suitable electronics configured to enable the reading and determining of a difference between an electrical potential (or current) from the one or more other sensors 115 and the reference sensor 100, such electronics being known to those of skill in the art. In the case of a potential difference, the detection system 114 can include a potentiometer. In the case of a current difference, the detection system 114 can include an ammeter.

[0036] In more detail, the sensor 100 including the electrode 106 manufactured using the disclosed Ag / AgCl dispensable composition (Ag / AgCl ink) can comprise a membrane 116. In some embodiments, membrane 116 may be a heterogenous membrane, such as a heterogenous membrane as disclosed in US20040231984A1, for example. The membrane 116 may act as a salt bridge providing ionic conductivity but preventing mixing of the internal electrolyte with the sample 122. The membrane 116 can improve the robustness to interferences present in blood or plasma samples, like halides.

[0037] In some embodiments, the membrane 116 can be an ion selective membrane (ISM) or protective membrane, for example. The membrane 116 may be formed from a semi-permeable material, such as a polymer material. For example, the polymer material may be an inert polytetrafluoroethylene (PTFE) material, a PVC material, a polyurethane material, or the like.

[0038] In some embodiments, the walls of the body 103 and the membrane 116 can form a reservoir 117. The membrane 116 can be formed as a thin polymer sheet that is selective to certain cations. In short, the membrane 116 functions to allow the selective cations to pass through the membrane 116, while not allowing other non-selected cations to pass through the membrane 116.

[0039] It should be understood that the sensor 100 including the membrane 116 can be used with or without an internal electrolyte 118. For example, the reference sensor 100 can contain a dry internal electrolyte. It can comprise a chloride-based salt entrapped in a polymeric matrix, such as polyvinyl alcohol (PVA) or a cellulose ester such as Methocel ^ available from Sigma Aldrich of Saint Louis, MO. However, in some embodiments, a sensor comprising the reference electrode 106 based on the disclosed Ag / AgCl dispensable composition can be membrane-free.

[0040] In yet other embodiments, the electrode 106 can be formed and operated as an indicator electrode based on the Ag / AgCl dispensable composition and can be directly coated or contacted with an ion selective membrane, i.e., polyvinyl chloride (PVC) based with ionophores providing selectivity towards the desired ions, wherein such conventional ion selective membranes are known to those of skill in the art.

[0041] In other embodiments, an indicator electrode based on the disclosed Ag / AgCl dispensable composition can be separated from the membrane by a reservoir 117 containing an electrolyte, thus potentially improving the stability of the measurable signal. The internal electrolyte 118 can be in any suitable form (e.g., a dry or wet form of chloride-based salts (e.g., KCl or NaCl) incorporated in a polymeric matrix).

[0042] Attachment of the membrane 116 to the body 103 may be by any suitable means, such as different types of adhesion, bonding, compression and sealing using a sealing ring, orother suitable mechanical or chemical attachment means for sealing the membrane-body interface. The electrode 106 based on the disclosed Ag / AgCl composition can be placed in a well 242 formed in an insulator body 103. Such wells may improve the dispense quality and may help the sealing of the membrane 116.

[0043] The electrically-conductive electrode 106 of the present disclosure comprises a mass of silver particles 219 (FIG. 2B), silver chloride particles 221 (FIG. 2B), and cellulose nanofibers 223 (FIG. 2C), which can be substantially homogeneous. In some embodiments, the cellulose nanofibers 223 may be oxidized cellulose nanofibers. The schematic particles shown in FIG. 2B are for reference purposes only, as the actual particles may not be exactly spherical, but may be oblong or other shapes. The mass of silver particles 219, silver chloride particles 221, and cellulose nanofibers 223 (which may be oxidized) are suitable for micro-dispensing, as is described herein.

[0044] The manufacturing method and materials used for the construction of the electrode 106 will now be described in detail. As shown in FIG. 2A, the dispensable suspension 225 comprising at least a mixture of the liquid vehicle (e.g., solvent), the silver particles 219 (e.g., silver nanoparticles), the silver chloride particles 221 (e.g., silver chloride nanoparticles), and the cellulose nanofibers 223 (which may be oxidized) can be provided in a supply vessel 230 of a micro-dispensing apparatus 200. For example, the supply vessel 230 can include a reservoir of sufficient volume to enable a production run over at least a few hours or longer (e.g., 12 hours or more), for example. The supply vessel 230 may be replenished without stopping the micro-printing method in some embodiments. A dispense portion 235 may be provided at a lower end or otherwise attached thereto that is configured to print droplets 240 of the dispensable suspension 225 onto asubstrate (e.g., substrate 105). The micro-dispensing apparatus 200 can be operated continuously as a manufacturing line for producing electrodes 106 for a period of at least 12 hours or more.

[0045] The dispense portion 235 can be configured as a print head in some embodiments and may dispense a single droplet 240 of the dispensable suspension 225 onto the substrate 105. The droplet 240 may be dispensed in a predefined region of a well 242 formed in the body 103 containing the previously deposited or formed substrate 105, such as at a center of the substrate 105. The dispensed droplet 240 may have a droplet diameter of less than 150 µm. Upon being dispensed onto each of the substrates 105, the droplet 240 will spread out on the surface of substrate 105. For example, the droplet 240 may spread out as shown in FIG. 2A and upon drying, form the electrode 106. The electrode 106, in the dried condition, may have an electrode maximum diameter dimension De from about 300 µm to about 600 µm, for example, and an electrode thickness Te from about 2 µm to about 50 µm, for example. Other suitable electrode diameters De and electrode thicknesses Te may be used. Thus, it should be recognized that the sensor 100 can comprise an insulator body 103, a substrate 105 formed on the insulator body 103, and an electrically-conductive electrode 106 formed on the substrate 105 having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers (which may be oxidized).

[0046] Regarding the cellulose nanofibers 223, when they are mixed into the dispensable suspension 225, the cellulose nanofibers (which may be oxidized cellulose nanofibers) form a three-dimensional network 226 of nanofillibrated cellulose as shown schematically in FIG. 2D. This three-dimensional network 226 aids in preventing settling of the silver particles 219and silver chloride particles 221, while not appreciably increasing the viscosity of the dispensable suspension 225. Silver Particles

[0047] The silver particles 219 can be provided in the dispensable suspension 225 from about 60 wt% to about 95 wt% of a total weight of the ingredients when in a dried condition as is shown in Table 1 below. The silver particles 219 of the dispensable suspension 225 may have an average transverse dimension (referred to herein as the “average particle size D”) of less than or equal to 300 nm. For example, the average particle size D may range from about 5 nm to about 300 nm, or even from about 5 nm to about 150 nm, as shown in FIG. 2B, for example.

[0048] Silver particles 219 may be provided in powder or fluid form. In some embodiments, they may include a dispersant such as a water-soluble polymer like polyvinylpyrrolidone (PVP). Moreover, in some embodiments, the silver particles 219 may contain a hydrophobic coating such as dodecanethiol functional groups. Silver Chloride (AgCl) Particles

[0049] The silver chloride (AgCl) particles 221 of the dispensable suspension 225 can be provided from about 5 wt% to about 30 wt% of a total weight of the dry ingredients. Further, the silver chloride particles 221 may have an average transverse dimension (average particle size D) of the silver chloride particles of less than or equal to 500 nm. For example, the average particle size D may range from about 50 nm to about 500 nm. The silver chloride particles 221 may be provided in powder form or water suspension form. An example water suspension form of silver chloride particles 221 is available from Cerion Nanomaterials of Rochester, NY and may also contain a gelatin or other type of stabilizer. The AgClparticles 221 can be formed from silver (Ag) particles by treatment with chlorine bleach or KCl followed by washing and drying. Cellulose Nanofibers

[0050] The composition comprises cellulose nanofibers 223 such as oxidized cellulose nanofibers. Cellulose nanofibers 223 of the dispensable suspension 225 can be provided from 1 wt% to 5 wt% of a total weight of the dry ingredients.

[0051] The cellulose nanofibers 223 may be oxidized by chemical, enzymatic, or chemo-enzymatic manner. The chemical oxidation of the cellulose nanofibers 223 can be done in the presence of a catalyst such as by TEMPO (2,2,6,6- tetramethylpiperidine-1-oxyl radical)- mediated oxidation while undergoing a successive gentle mechanical disintegration in water. This process can introduce carboxyl groups on the surfaces of cellulose micro-fibrils. The cellulose nanofibers 223 can include carbonyl functional groups.

[0052] Thus, the oxidized cellulose nanofibers 223 may contain carboxyl and / or carbonyl functional groups, which can provide relatively strong repulsive forces between the nanofibers 223 and thus can improve the stability of the nanofibers 223 in an aqueous suspension.

[0053] The cellulose nanofibers 223 may have an end-to-end length (hereinafter “length L”) as shown in FIG. 2C that is much greater than their maximum width (W), such as L ≥ 50 * W for example. In some embodiments, an aspect ratio (L / W) of length L to width W may be greater than or equal to 25, or even greater than or equal to 100, or more. In some embodiments, the aspect ratio (L / W) of length L to width W may be from 25 to 1,600.

[0054] The length (L) of the cellulose nanofibers 223 can be 0.2 µm or more, from 0.2 µm to 5 µm, or even from 0.2 µm to 80 µm in some embodiments. The width W of the cellulosenanofibers 223 can be 50 nm or less. For example, the width W may range from 2 nm to 50 nm in some embodiments, and from 5 nm to 50 nm in other embodiments.

[0055] In some embodiments, the cellulose nanofibers have a width (W) of from 5 nm to 50 nm, and a length (L) of from 0.2 µm to 80 µm. The width W and length L of the cellulose nanofibers 223 are measured as shown in FIG. 2C. Liquid Vehicle

[0056] The liquid vehicle may be water. In particular, the liquid vehicle may be devoid of organic solvents (e.g., may be substantially alcohol free). Being devoid of organic solvents is desirable not only because of lower toxicity but also slower evaporation, which has been found to extend the shelf- life of the composition and thus may improve its overall stability. The weight percentage (wt%) of liquid vehicle (e.g., water) can range from 80 wt% to 97 wt% of the total weight of the dry ingredients (WDI) plus the weight of the liquid vehicle (WLV) as shown below: Wt% LV = [WLV / (WDI +WLV)] * 100 Being devoid of organic solvents, as described herein, means the liquid vehicle may contain an organic solvent below 10 wt% of a total weight of the liquid vehicle. Other Ingredients

[0057] In some embodiments, the dispensable suspension 225 can optionally comprise a chloride-based salt, such as one or more of potassium chloride (KCl), sodium chloride (NaCl), and calcium chloride (CaCl2). The chloride-based salt can function within the dispensable suspension 225 to increase robustness to interferences present in blood and plasma, and / or to further stabilize the electrode potential. The chloride-based salt can be provided in the dispensable suspension 225 below 1.0% of the total dry ingredients.

[0058] In some embodiments, the dispensable suspension 225 can optionally comprise a nonionic surfactant, such as Tween ^- 20 or TritonTMX-100 available from Sigma-Aldrich, Inc. of Saint Louis, MO. The surfactant functions within the dispensable suspension 225 to increase dispersibility of the particles. The surfactant can be provided in the dispensable suspension 225 in an amount less than 3.0 wt% of the total dry ingredients.

[0059] The dispensable suspension 225 can, in some embodiments, optionally comprise an organosulfur compound. The organosulfur compound can function within the dispensable suspension 225 to increase robustness to interferences present in blood and plasma. Examples of organosulfur compound comprise L-cysteine. The organosulfur compound can be provided in the dispensable suspension 225 in an amount below 1.0% of the total dry ingredients.

[0060] When referring to the weight percentage wt% of a component of the dispensable suspension 225, what is referred to is the weight of a particular ingredient in a dried form divided by the weight of all of the ingredients in dried form. It should be understood that some ingredients are sold with water included. In this case, the weight of the water would be included only in determining the wt% of the liquid vehicle of the dispensable suspension 225, and only the calculated dry weight of the particular ingredient and total ingredients would be used for the wt% calculations for that ingredient. For example, the weight percentage wt% of an ingredient is calculated as follows: Wt% of ingredient = (weight of the particular dried ingredient / weight of all the dried ingredients) * 100.

[0061] Table 1 – Example dispensable suspension compositionComponents Wt% Average Nanofiber Nanofiber Particle Length WidthManufacturing Method

[0062] The manufacturing method for forming the electrode 106 can utilize a dispense and evaporation method. Referring now to FIG. 2A and FIG. 3, a method 300 of manufacturing the electrically conductive electrode (e.g., electrode 106) is described. The method 300 includes, in block 302, micro- dispensing a suspension (e.g., dispensable suspension 225) onto a substrate (e.g., substrate 105) formed on a body (e.g., body 103). The suspension (e.g., dispensable suspension 225) further comprises: a liquid vehicle, 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), as described herein.

[0063] After micro-dispensing the suspension (e.g., dispensable suspension 225) onto the substrate 105, the droplet may be dried, such as through passive evaporation. Thus, once dried, an electrically-conductive electrode 106, comprising a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers is formed.

[0064] To manufacture additional electrically conductive electrodes (e.g., electrode 106), the method 300 can further optionally comprise, in block 304, advancing (e.g., in the direction of arrow 244) the 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 micro-dispensing apparatus (e.g., micro-dispensing apparatus 200). The advancement may be by any suitable advancement mechanism. For example, a body 103 including many substrates 105, 105N may be provided on a reel and individual next substrates 105N may be advanced by a pulling or pushing mechanism into the direct vicinity of the dispensing portion 235.

[0065] Next, in block 306, the dispensing portion (e.g., dispensing portion 235) dispenses a droplet (e.g., droplet 240) onto the next substrate (e.g., next substrate 105N).

[0066] Next, in block 308, blocks 304 and 306 are repeated for a predetermined time period (e.g., continuously for at least 12 hours or longer in some embodiments). In block 310, method 300 includes allowing any droplets of the suspension to dry.

[0067] After a desired number of multiple ones of the electrodes 106 have been formed on the substrates 105, 105N, a length of the body 103 may be cut to form a strip assembly 245. The cutting may be accomplished by any suitable cutting mechanism 246, such as a blade, saw, or the like to cut the body 103 at the desired location (e.g., along line 247) to form the strip assembly 245. Full drying, without air flow or heat assist may be accomplished before or after the cutting.

[0068] Thus, it should be recognized that a strip assembly 245 having multiple electrodes 106 based on the disclosed dispensable composition formed thereon may be manufactured. For example, the strip assembly 245 may include 10 or more electrodes formed thereon. The strip assembly 245 thus comprises an insulator body 103, multiple spaced substrates 105, 105N formed on the insulator body 103, and an electrically-conductive electrode 106 formed on each of the multiple spaced substrates 105, 105N, each electrically- conductive electrode 106 having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers. From the strip assembly 245, a sensor assembly including multiple sensors may be formed to include a sensor structure as shown in FIG. 1 or other suitable sensor structure(s).

[0069] As discussed above, the method 300 of micro- dispensing of the suspension 225 forms one or more droplets 240 having a maximum dimension of less than 150 µm. In particular, the method 300 of micro-dispensing the dispensable suspension 225 forms the electrically-conductive electrode 106, which after drying, may have a very small diameter, such as a maximum diameter dimension (e.g., electrode diameter De) described herein. Advantageously, the method 300 of micro- dispensing the dispensable suspension 225 undergoes no post- printing chloridization, as do prior art processes. Thus, the present method 300 is simpler and more efficient. Because of the excellent printability and anti-settling properties, the micro-dispensing of the suspension 225 onto substrates 105 can be continuous for at least 12 hours or more.

[0070] Although embodiments are described herein with reference to specific examples, the scope of the disclosure is not intended to be limited to the details and specific examples described herein. Rather, various modifications maybe made to the embodiments and details within the scope and range of equivalents of the claims.

[0071] The following is a list of non-limiting illustrative embodiments disclosed herein: 1. A dispensable suspension, comprising: a liquid vehicle; silver particles; silver chloride particles; and cellulose nanofibers. 2. The dispensable suspension of illustrative embodiment 1, wherein the liquid vehicle is water. 3. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers are oxidized. 4. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers are oxidized chemically, enzymatically, or chemo- enzymatically. 5. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers comprise carboxyl and / or carbonyl functional groups. 6. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose fibers have a width W of 50 nm or less. 7. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers have a length L of 0.5 µm or more.8. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers have an aspect ratio (L / W) of length L to width W of greater than or equal to 25. 9. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers have an aspect ratio (L / W) of length L to width W of from 25 to 1,600. 10. The dispensable suspension of any one of the preceding illustrative embodiments, comprising a dynamic viscosity of less than 20 mPa ^s at 20°C and a shear rate of 1,992 s-1. 11. The dispensable suspension of any one of the preceding illustrative embodiments, further comprising a chloride-based salt. 12. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the chloride-based salt comprises one or more of KCl, NaCl, and CaCl2. 13. The dispensable suspension of any one of the preceding illustrative embodiments, further comprising an organosulfur compound. 14. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the organosulfur compound comprises L-cysteine. 15. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the dispensablesuspension is substantially devoid of a polymeric binder stabilizing the particles other than the cellulose nanofibers. 16. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the dispensable suspension may contain an organic solvent below 10 wt% of a total weight of the liquid vehicle. 17. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the dispensable suspension is mechanically stable for 24 hours or more. 18. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the silver particles are provided from 60 wt% to 95 wt% of a total weight of dry ingredients. 19. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the silver particles have an average particle size D of less than or equal to 300 nm. 20. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the silver chloride particles are provided from 5 wt% to 30 wt% of a total weight of the dry ingredients. 21. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the silver chloride particles have an average particle size D of less than or equal to 500 nm. 22. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulosenanofibers are provided from 1 wt% to 5 wt% of a total weight of dry ingredients. 23. The dispensable suspension of any one of the preceding illustrative embodiments, wherein the cellulose nanofibers have a width (W) of from 5 nm to 50 nm, and a length (L) of from 0.2 µm to 80 µm. 24. An electrically-conductive electrode, comprising: a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers. 25. The electrically-conductive electrode of any one of the preceding illustrative embodiments, wherein the electrically-conductive electrode is a reference electrode. 26. A method of manufacturing an electrically-conductive electrode, comprising: micro-dispensing a dispensable suspension onto a substrate of a body, the dispensable suspension comprising: a liquid vehicle, silver particles, silver chloride particles, and cellulose nanofibers; and allowing a droplet of the suspension to dry. 27. The method of any one of the preceding illustrative embodiments, wherein the micro-dispensing of the dispensable suspension forms one or more droplets having a maximum droplet dimension of less than 150 µm. 28. The method of any one of the preceding illustrative embodiments, wherein the micro-dispensing forms theelectrically-conductive electrode, after drying, to have a diameter dimension De of greater than or equal to 200 µm. 29. The method of any one of the preceding illustrative embodiments, wherein the electrically-conductive electrode undergoes no post-printing chloridization. 30. The method of any one of the preceding illustrative embodiments, wherein the micro-dispensing of the dispensable suspension onto substrates is continuous for 12 hours or more. 31. A sensor, comprising: an insulator body; a substrate formed on the insulator body, and an electrically-conductive electrode formed on the substrate having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers. 32. A sensor strip assembly, comprising: an insulator body; multiple spaced substrates formed on the insulator body, and an electrically-conductive electrode formed on each of the multiple spaced substrates, each electrically- conductive electrode having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A dispensable suspension, comprising: a liquid vehicle; silver particles; silver chloride particles; and cellulose nanofibers.

2. The dispensable suspension of claim 1, wherein the liquid vehicle is water.

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

4. The dispensable suspension of claim 3, wherein the cellulose nanofibers are oxidized chemically, enzymatically, or chemo-enzymatically.

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

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

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

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

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

10. The dispensable suspension of claim 1, comprising a dynamic viscosity of less than 20 mPa ^s at 20°C and a shear rate of 1,992 s-1.

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

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

13. The dispensable suspension of 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 devoid of a polymeric binder stabilizing the particles other than the cellulose nanofibers.

16. The dispensable suspension of claim 1, wherein the dispensable suspension may contain an organic solvent below 10 wt% of a total weight of the liquid vehicle.

17. The dispensable suspension of claim 1, wherein the dispensable suspension is mechanically stable for 24 hours or more.

18. The dispensable suspension of claim 1, wherein the silver particles are provided from 60 wt% to 95 wt% of a total weight of dry ingredients.

19. The dispensable suspension of 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 from 5 wt% to 30 wt% of a total weight of dry ingredients.

21. The dispensable suspension of 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 from 1 wt% to 5 wt% of a total weight of dry ingredients.

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

24. An electrically-conductive electrode, comprising: a micro-dispensed mass of silver particles, silver chloride particles, and cellulose nanofibers.

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

26. A method of manufacturing an electrically-conductive electrode, comprising:micro-dispensing a dispensable suspension onto a substrate of a body, the dispensable suspension comprising: a liquid vehicle, silver particles, silver chloride particles, and cellulose nanofibers; and allowing a droplet of the suspension to dry.

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

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

29. The method of claim 26, wherein the electrically- conductive electrode undergoes no post-printing chloridization.

30. The method of claim 26, wherein the micro-dispensing of the dispensable suspension onto substrates is continuous for 12 hours or more.

31. A sensor, comprising: an insulator body; a substrate formed on the insulator body, and an electrically-conductive electrode formed on the substrate having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

32. A sensor strip assembly, comprising:an insulator body; multiple spaced substrates formed on the insulator body, and an electrically-conductive electrode formed on each of the multiple spaced substrates, each electrically-conductive electrode having a chemical composition comprising silver particles, silver chloride particles, and cellulose nanofibers.

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