Analyte sensors and methods for fabricating analyte sensors

Analyte sensors and methods for making analyte sensors

[0001] Cross-references to related applications

This application claims the following rights and interests: U.S. Provisional Patent Application Serial Number 62/504,670 submitted on May 11, 2017, the entire content of which is incorporated herein by reference; U.S. Patent Application submitted on February 20, 2018 Serial No. 15/900,630, the entire contents of which are incorporated herein by reference; U.S. Patent Application Serial No. 15/900,639, filed on February 20, 2018, the entire contents of which are incorporated herein by reference.

Technical field

[0003] Embodiments of the subject matter described herein generally relate to sensors for monitoring analyte levels in patients and methods for making such sensors. More specifically, embodiments of the subject matter relate to glucose sensors, such as for continuously or substantially continuously monitoring blood glucose levels.

Background technique

[0004] The pancreas in normal healthy humans produces and releases insulin into the bloodstream in response to elevated plasma glucose levels. 8 cells (B-cells) that reside in the pancreas produce and secrete insulin into the bloodstream when needed. If the e-cells become incapacitated or die, the condition is called type 1 diabetes (or in some cases, if the e-cells do not produce an adequate amount of insulin, the condition is called type 2 diabetes), the body can be supplied from another source Insulin to maintain life or health.

[0005] Traditionally, since insulin cannot be taken orally, insulin has been injected with a syringe. Recently, the use of infusion pump therapy has been increasing in a variety of medical situations, including for the delivery of insulin to patients with diabetes. For example, external infusion pumps can be worn on a belt, pocket, etc., and they can deliver insulin into the body via an infusion tube with a transcutaneous needle or a cannula placed in the subcutaneous tissue.

[0006] As of 1995, less than 5% of patients with type 1 diabetes in the United States used infusion pump therapy. Currently, more than 7% of the more than 900,000 people with type 1 diabetes in the United States are using infusion pump therapy. The percentage of people with type 1 diabetes who use infusion pumps is increasing at a rate of more than 2% per year. In addition, the number of patients with type 2 diabetes is growing at a rate of 3% or more per year, and an increasing number of patients with type 2 diabetes who use insulin are using infusion pumps. Additionally, physicians have recognized that continuous infusions provide better control of the condition in diabetic patients and are increasingly prescribing them to their patients as a result.

[0007] An infusion pump system may include an infusion pump that is automatically and/or semi-automatically controlled to inject insulin into a patient. Infusion of insulin may be controlled to occur at times and in amounts based on, for example, blood glucose measurements obtained in real time from an embedded analyte sensor injecting a glucose sensor.

[0008] There are two main types of blood glucose monitoring systems used by patients: single-point or discontinuous and continuous. Discontinuous systems consist of a meter and test strips and require a blood sample to be drawn from a fingertip or alternative site, such as the forearm and leg. These systems rely on the pricking and manipulation of a finger or alternative blood draw site, which can be extremely painful and inconvenient, especially for children.

[0009] Continuous monitoring sensors are typically implanted subcutaneously and measure glucose levels in the interstitial fluid at different times throughout the day, thereby providing data showing trends in glucose measurements over time. These sensors are painful to insert and often require the assistance of a healthcare professional. Furthermore, these sensors are designed to be used only for short durations

used (e.g., monitoring for several days to determine blood glucose patterns). Sensors implanted under the skin may lead to infection and immune response complications. [0010] Another major disadvantage of currently available continuous monitoring devices is that they require frequent, often daily, calibration using blood glucose results that must be obtained through painful finger pricks using traditional meters and test strips. . This calibration and recalibration is necessary to maintain the accuracy and sensitivity of the sensor, but it can be cumbersome and painful.

[0011] A typical glucose sensor works according to the following chemical reaction: Equation 1

[0012] Glucose + 0₂ Grape tang oxyalcohol gluconic acid-H2O?

[0013] H₃0₂^0₂+2H⁺+2e^-Formula 2

In Formula 1, glucose oxidase is used to catalyze the reaction between glucose and oxygen to produce gluconic acid and hydrogen peroxide (H₂0₂). Hydrogen peroxide reacts electrochemically, as shown in Equation 2, and the resulting current can be measured with a potentiostat. These reactions, which occur in a variety of oxidoreductases known in the art, are used in many sensor designs.

[0015] In the case of a three-electrode design (working electrode, counter electrode and reference electrode), the reference electrode is not consumed, and the O2 produced is reduced at the counter electrode according to reaction (Formula 2) 0

[0016] 0₂+2H₂0+4e^-^40H⁺ （3）

[0017] In the case of a two-electrode design (working electrode and reference electrode only), the following reaction occurs at the reference electrode

AgCl+e"-Ag+Cr (4)

[0019] It is necessary here to discuss the relative merits of 2-electrode and 3-electrode designs. In the case of the 3-electrode design, oxygen is consumed at the counter electrode, which is also required by glucose oxidase (Equation 1). However, the Ag/AgCl reference remains stable; despite the increased dependence of the sensor on oxygen. In the case of the 2-electrode design, the dependence of the sensor on oxygen is reduced; although AgCl is consumed over time (according to Equation 4), a sufficient amount of AgCl must be provided to sustain the sensor life. [0020] As analyte sensor technology matures and new applications of sensor technology are developed, there is a need for improved analyte sensors, such as continuous monitoring sensors for use over longer durations. Additionally, there is a need to develop advanced methods for sensor fabrication that can produce factory-calibrated analyte sensors without the need for further external calibration.

[0021] In addition, there is a need for low-cost mass production of analyte sensors, such as glucose sensors. Conventional batch processing is not suitable for mass production or significant cost reduction.

[0022] Accordingly, it would be desirable to have an improved analyte sensor and related manufacturing methods that address the shortcomings of traditional sensor systems. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

Contents of the invention

[0023] The present invention provides analyte sensors and methods for making analyte sensors. In an exemplary embodiment, a planar flexible analyte sensor includes a flexible substrate layer and a first electrode formed from a sputter clamp layer on the substrate layer. Additionally, the analyte sensor includes an insulating dielectric layer over the base layer, wherein the insulating dielectric layer exposes a portion of the first electrode. Additionally, the analyte sensor includes an electrochemical sensing stack over the exposed portion of the first electrode, including a glucose oxidase layer over the sputtered aluminum layer and a glucose limiting membrane over the glucose oxidase layer.

[0024] In another embodiment, an analyte sensor includes a polyester substrate, an aluminum layer on the polyester substrate, an aluminum layer on

a protective layer above, and an electrochemical sensing stack above the platinum layer.

[0025] Another embodiment provides a planar flexible analyte sensor that includes a polyester base layer and a working electrode and a reference electrode formed from a sputtered platinum layer on the base layer. Additionally, the planar flexible analyte sensor includes an insulating dielectric layer over a polyester base layer and a sputtered platinum layer. The insulating dielectric layer exposes portions of the first electrode and portions of the second electrode. Additionally, planar flexible analyte sensors include silver/silver chloride ink on the exposed portion of the reference electrode. The planar flexible analyte sensor also includes a glucose oxidase layer over the exposed portion of the working electrode and a glucose limiting membrane over the glucose oxidase layer.

[0026] In another exemplary embodiment, a method for fabricating a planar flexible analyte sensor includes sputtering platinum onto a polyester base layer to form a platinum layer. The method includes patterning a platinum layer to form a working electrode and additional electrodes. Additionally, the method includes forming an insulating dielectric layer over the base layer, wherein the insulating dielectric layer is formed with openings exposing portions of the working electrode and portions of the additional electrodes. Additionally, the method includes partially detaching the individual sensors from the base layer, wherein each individual sensor is connected to the base layer via an interposer. The method also includes depositing an enzyme layer over the exposed portion of the working electrode and coating the working electrode with a glucose limiting film.

[0027] Another exemplary embodiment provides a method for fabricating a planar flexible analyte sensor. The method includes providing a polyester base layer having a first side sputtered with a platinum layer and a second side opposite the first side. The method includes patterning a platinum layer to form a working electrode. Additionally, the method includes forming an insulating dielectric layer over a first side of the base layer, wherein the insulating dielectric layer is formed with an opening exposing a portion of the working electrode. The method also includes printing silver/silver chloride ink on the second side of the base layer. The method also includes partially detaching the individual sensors from the base layer, wherein each individual sensor is connected to the base layer by an interposer. The method involves depositing an enzyme layer over an exposed portion of a working electrode and coating the working electrode with a glucose limiting film.

[0028] In another embodiment, a method for fabricating an analyte sensor in a roll-to-roll process includes providing a polyester substrate roll having a first side coated with a platinum layer. The method feeds the polyester substrate from roll to the electrode patterning stage. Additionally, the method includes patterning the platinum layer to form a working electrode and a reference electrode. This method feeds the polyester substrate to the insulation stage. The method includes forming an insulating dielectric layer over a polyester substrate. This method feeds the polyester substrate to the insulation curing stage. The method includes curing the insulating dielectric layer. This method feeds the polyester substrate to the ink printing stage. The method involves depositing a silver/silver chloride ink over a reference electrode. This method feeds the polyester substrate to the drying stage. The method involves drying silver/silver chloride ink. This method feeds the polyester substrate to the stamping stage. The method includes stamping a polyester substrate to form strips, wherein each strip is connected to a remaining polyester substrate web by an insert, and wherein each sensor includes a working electrode and a reference electrode. The method feeds the remaining polyester substrate to the enzyme deposition stage. The method involves depositing an enzyme layer over a working electrode. This method feeds the remaining polyester substrate to the enzymatic curing stage. The method involves immobilizing the enzyme layer. This method feeds the remaining polyester substrate to the film formation stage. The method involves coating a working electrode with a glucose limiting membrane.

[0029] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

Description of the drawings

[0030] A more complete understanding of the present subject matter may be obtained by referring to the detailed description and claims in conjunction with the following drawings, wherein like reference numerals refer to similar elements throughout.

[0031] Figure 1 is a side cross-sectional view of a partially fabricated analyte sensor according to one embodiment.

[0032] Figure 2 is a side cross-sectional view of an analyte sensor according to one embodiment.

[0033] Figure 3 is a side cross-sectional view of an analyte sensor according to another embodiment.

[0034] Figure 4 is a schematic diagram of a system and method for fabricating an analyte sensor, according to one embodiment.

[0035] FIG. 5 is a top view of a partially separated substrate manufactured according to the method of FIG. 4.

[0036] FIG. 6 is a schematic diagram of a system and method for fabricating a platinum sputtered substrate for use in the method of FIG. 4, according to one embodiment.

Detailed ways

[0037] The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of these embodiments. As used herein, the word "exemplary" means "serving as an example, instance, or illustration." Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. Additionally, although the foregoing background discusses glucose sensing and exemplary analyte sensors are described herein as glucose sensors, this description is for convenience and is not limiting. Claimed subject matter may include any type of analyte sensor utilizing embodiments of sensor electrodes described herein.

[0038] Blood glucose measurement may be used in infusion systems for regulating the rate of fluids injected into the body. In certain instances, the control system may be adapted to regulate the infusion of insulin, glucagon, and/or glucose into the patient based at least in part on glucose concentration measurements obtained from the body (e.g., from an analyte sensor such as a glucose sensor). rate.

[0039] According to certain embodiments, embodiments of the analyte sensors described herein may be implemented in a hospital setting to monitor glucose levels in a patient. Alternatively, according to certain embodiments, embodiments of analyte sensors as described herein may be implemented in non-hospital settings to monitor glucose levels in patients. Here, the patient or other non-medical professional may be responsible for interacting with the analyte sensor.

[0040] To maintain healthy glucose levels, people with Type 1 diabetes can manage their blood sugar by monitoring blood sugar levels, controlling diet, exercising, and self-administering the appropriate amounts of insulin at the appropriate times. Such deviations in blood glucose management, such as skipping insulin bolus at mealtimes or underestimating the carbohydrate content of meals, may lead to prolonged hyperglycemia. Likewise, receiving too much insulin (e.g., by overbolus) for a given blood glucose level and/or meal can lead to severe hypoglycemia. Other external factors such as exercise or stress can also cause blood sugar deviations.

[0041] Errors in reading glucose levels may result in delivering too much or too little insulin. Therefore, sensor accuracy is of greatest concern. Additionally, accurate sensor determination must be maintained throughout the life of the continuous glucose monitoring device. There is a desire for longer life continuous glucose monitoring devices, ie, continuous glucose monitoring devices that are implanted for longer durations, such as seven to fourteen days or more. Therefore, in the future, the sensor's accuracy must remain in the body for seven to fourteen days or longer. Continuous glucose monitoring sensors provide the ability to continuously track glucose levels in a patient's body and correlate them with their physical activity and diet, thereby informing treatment decisions and adjustments when necessary.

[0042] By monitoring a patient's glucose levels more accurately and maintaining an appropriate infusion rate, extreme blood glucose changes can be reduced or completely avoided. This may provide patients with improved glycemic control in situations where the patient would otherwise be exposed to undesirable glycemic extremes.

[0043] Embodiments herein provide improved accuracy compared to currently commercialized sensors and will reduce sensor cost through new manufacturing processes. For example, the sensor herein may utilize a sputtered layer of platinum on a polyester film substrate.

Excimer patterned electrodes.

[0044] FIG. 1 is a cross-sectional view of an example analyte sensor 10 for use with a glucose control system, according to one embodiment. Specific embodiments of analyte sensor 10 include a planar flexible polymer substrate layer 12, such as a polyester film or substrate. As shown, base layer 12 includes a first side 14 and an opposing second side 16 and an end 18 . Exemplary base layer 12 has a thickness of about 25 microns (um) (about 1 mil) to about 381 um (about 15 mils), such as about 178 um (about 7 mils) or about 254 um (about 10 mils).

In certain embodiments, base layer 12 has a surface roughness of about 1 nm to about 240 nm, such as 5 nm to about 80 nm, such as about 5 nm to 10 nm, or about 10 nm to 20 nm, or about 20 nm to 30 nm, or about Surface roughness of 30nm to 50nm, or about 50nm to 70nm.

[0046] In addition, the platinum layer 20 is formed on the first side 14 of the base layer 12. In the exemplary embodiment, platinum layer 20 is formed by sputtering platinum onto first side 14 of base layer 12 . Exemplary platinum layer 20 may have a thickness of about 5 to about 120 nm, such as a thickness of about 10 nm to about 50 nm.

[0047] During in vivo use, the platinum is challenged by the immune response generated by the body upon implantation of the sensor. For example, constant mechanical forces exerted by body tissue around the implant can compromise the adhesion of platinum to the polyester substrate. Accordingly, the first side 14 of the base layer 12 may undergo surface modification to adjust the adhesion between the platinum layer 20 and the base layer 12 . Such surface modifications may allow controlled and reproducible tuning of electrode surface area to improve in vivo sensor performance. Additionally, surface modification may provide for grafting functional moieties to the first side 14 of the base layer 12 to increase adhesion. Surface modification may be performed by plasma pretreatment of base layer 12 . Other processes may be performed to roughen the surface of base layer 12 .

[0048] Additionally, the platinum layer 20 may be formed with an outer surface 26 having a selected surface roughness. Sputtering of platinum onto polyester substrates is a well-known method that produces high uniformity and reproducibility in the surface roughness of the outer surface 26. The surface roughness of the outer surface 26 of the platinum layer 20 is the controlling factor for the electrode surface area. By adjusting the process parameters of the platinum sputtering process, the surface roughness of the platinum layer 20 and the outer surface 26 of the electrode can be controlled.

[0049] As shown, analyte sensor 10 is formed with electrodes required for sensor operation. For example, analyte sensor 10 may be formed with a working electrode, a reference electrode, and a counter electrode. In Figure 1, two electrodes 22 and 24 are shown for simplicity; however, analyte sensor 10 may include one or more working, reference, and counter electrodes. In certain embodiments, analyte sensor 10 may include pairs of working and counter electrodes.

[0050] Electrodes 22 and 24 may be formed by patterning platinum layer 20. For example, a laser ablation process may be performed to pattern platinum layer 20. In an exemplary embodiment, platinum layer 20 is patterned with ultraviolet light using an excimer laser, such as a 248 nanometer excimer laser, to form electrodes 22 and 24 . Laser ablation provides high throughput and is highly reproducible during sensor manufacturing processing. For example, in certain embodiments, eighteen electrodes of analyte sensor 10 may be patterned per second through a laser ablation process.

[0051] As shown, analyte sensor 10 also includes an insulating dielectric layer 30 over first side 14 of base layer 12. Exemplary insulating dielectric layer 30 may be a polymer that is cross-linked by ultraviolet radiation or by thermal treatment such that, after cross-linking, the insulating dielectric is impermeable to solvents and water in the analytes containing the fluid, as well as other electrochemically active components. . The insulating dielectric layer 30 is provided to prevent diffusion of electrochemically active components to the electrochemically active surface of the electrode in order to accurately control the electrode signal level.

[0052] The electrode signal is proportional to the surface area exposed to the fluid-containing analyte. An insulating dielectric layer 30 impermeable to electrochemically active components in the fluid-containing analyte may be applied and patterned to define the electrochemically active surface area of the electrode. Methods for applying and patterning dielectric layers include screen printing, drop-on-demand inkjet, transfer pad printing, gravure coating, or technology

Other photolithographic patterning coating methods are known to those skilled in the art.

[0053] Exemplary insulating dielectric layer 30 may be a thermally cross-linked acrylic polymer. Exemplary insulating dielectric layer 30 has a thickness of about 1 wn to about 20 μlh, such as about 7 um.

[0054] In an exemplary embodiment, insulating dielectric layer 30 is formed by screen printing or spin printing of an insulating dielectric material. In certain embodiments, insulating dielectric layer 30 is patterned or otherwise formed with openings 31 that expose portions 32 of electrodes 22 and portions 34 of electrodes 24 . In other words, after the insulating dielectric layer 30 is formed, the portion 32 of the electrode 22 and the portion 34 of the electrode 24 are not covered by the insulating dielectric layer 30 . Opening 31 defines the geometric surface area of electrodes 22 and 24. In other words, the exposed portions 32 and 34 of electrodes 22 and 24 are the geometric surface areas of electrodes 22 and 24.

[0055] In the exemplary embodiment, electrode 22 is the working electrode, electrode 24 is the counter electrode, and the width of the insulating dielectric layer 30 is adjusted such that the end-to-end opening 31 of the platinum working electrode 22 and the platinum counter electrode 24 Distance 28 was varied to improve overall sensor sensitivity and reduce the sensor's dependence on oxygen concentration. The end-to-end distance between openings may be from about 5 microns to about 200 microns, such as from about 15 microns to about 100 microns, such as about 50 microns.

[0056] Thus, FIG. 1 may be viewed as illustrating a pair of working electrode 22 and counter electrode 24 having a selected inter-pair distance 28. It is contemplated that the sensor 10 includes a plurality of working electrodes (WE) and counter electrodes (CE), with each WE/CE pair having a specific, independently selected end-to-end distance 28 between the openings 31 of the working and counter electrodes. . In other words, sensor 10 may be provided with multiple WE/CE pairs, each pair having an independently selected intra-pair distance. Although WE/CE pairs can set different intra-pair distances from each other, some WE/CE pairs can have the same intra-pair distance.

[0057] The differential responses from these multiple WE/CE pairs can provide insight into the sensor's dependence on oxygen, which can be used to calibrate sensor performance for sensitivity drift. For example, sensitivity may drift due to sensor degradation caused by exposure to various electrical analytes, such as oxygen radicals. Furthermore, post-implantation effects such as biofouling and xenobiotic reactions can also lead to passivated electrodes electrocatalytic activity.

[0058] In FIG. 2, further processing may be performed on the analyte sensor 10. In Figure 2, electrode 22 is processed to form a working electrode, and electrode 24 is processed to form a reference electrode (as mentioned above, multiple electrodes are not shown for clarity). For reference electrode 24, a silver/silver chloride (Ag/AgCl) ink layer 40 is formed over electrode 24. Silver/silver chloride layer 40 may be selectively deposited by screen printing or spin printing. Unlike conventional electrodeposition or electro-oxidation treatments, when screen printing or spin printing silver/silver chloride inks, the loading of silver chloride is not limited by the surface area of the electrode. In the exemplary embodiment, the silver/silver chloride layer 40 is overloaded such that the amount of AgCl is always in excess compared to the amount required for 14 days of sensor operation. In some cases, the ratio of AgCl to Ag is greater than 1, and can be from about 1 to about 10, such as about 5. It should be noted that the silver/silver chloride (Ag/AgCl) ink layer 40 may be formed before or after the insulating dielectric layer 30 is formed, but preferred embodiments include depositing the silver/silver chloride ink prior to the dielectric material.

[0059] In an exemplary embodiment, a silver/silver chloride ink is formulated with micron and nanoparticles of silver and silver chloride in a polymer binder to enhance the silver/chloride during screen printing or rotary printing. Overload of silver ink. In an exemplary embodiment, the silver/silver chloride layer has a thickness (or height) of about 5 μln to about 50 μln, such as about 10 μln. In an exemplary embodiment, the reference electrode is composed of metal oxide particles and nanoparticles supported within a polymer binder. An exemplary metal oxide is iridium oxide.

[0060] As noted above, during in vivo use, the platinum is challenged by the immune response generated by the body upon implantation of the sensor. For example, the degradation of platinum can be induced by biological contamination and the body's immune response. Unless otherwise specified, platinum may not be resistant to degradation caused by biological contamination and the body's immune response. Accordingly, the analyte sensor 10 may be provided with a protective layer 45 over the first side 14 of the base layer 12 for protecting the platinum from biological contamination and other immune response degradation. Exemplary warranty

The protective layer 45 may be a hydrophilic hydrogel layer and may be made of a variety of materials known to be suitable for such purposes, such as polyvinyl alcohol, poly(N-isopropylacrylamide), poly(N- vinylpyrrolidone), polyethylene glycol, polyurethane, polyacrylic acid, cellulose acetate, Nafion, polyester sulfonic acid hydrogel, or any other suitable hydrophilic membrane known to those skilled in the art.

[0061] Exemplary protective layer 45 has a thickness of about 5 nm to about 200 nm, such as about 50 nm. As shown in FIG. 2 , protective layer 45 covers the entire top side 14 of base layer 12 and completely encapsulates the platinum layers of electrodes 22 and 24 .

[0062] In an exemplary embodiment, the protective layer 45 is formed by screen printing, spin printing, spray coating, dip coating, spin coating, or brush coating. In certain embodiments, the diffusion properties of protective layer 45 are carefully controlled so that the magnitude of the sensor signal is not compromised due to a smaller diffusion coefficient that would not allow hydrogen peroxide to pass through, thereby causing the sensor signal to pass according to the above Formula 2 has minimal or no signal. In such embodiments, hydrophobic moieties such as acrylate polymers or surfactants or oxygen-carrying substances such as fluorocarbons or oxygen-containing enzymes such as myoglobin or hemoglobin or oxygen-generating enzymes such as catalase are incorporated into the hydrogel layer to improve adhesion and tuned permeability to hydrogen peroxide and oxygen.

[0063] FIG. 2 shows that the silver/silver chloride layer 40 is formed before the protective layer 45, so that the silver/silver chloride layer 40 is disposed below the protective layer 45. However, it should be noted that the formation sequence can be reversed so that the protective layer 45 is underneath the silver/silver chloride layer 40.

[0064] In FIG. 2, analyte sensor 10 also includes an electrochemical sensing stack 50 over the exposed portion 32 of the working electrode 22. Electrochemical sensing stack 50 may include multiple layers not shown individually in FIG. 2 . In an exemplary embodiment, electrochemical sensing stack 50 includes an analyte sensing layer, such as an enzyme layer, such as a glucose oxidase layer. Exemplary glucose oxidase layers have an activity of about 1 KU/mL to about 45 KU/mL, such as about 5 KU/mL to about 20 KU/mL, such as about 15 KU/mL. Additionally, an exemplary glucose oxidase layer has a thickness of about 3 microns to about 10 microns (um), such as about 4 um to about 5 um, such as about 4.2 um to about 4.4 um, such as a thickness of about 4.3 um. In an exemplary embodiment, the enzyme layer is deposited over working electrode 32 by rotary screen printing. In another embodiment, the enzyme layer is deposited over the working electrode 32 via aerosol-based drop-on-demand inkjet technology. In another embodiment, the enzyme layer is deposited over the working electrode 32 by spin coating or spray coating. In another embodiment, an enzyme layer is deposited over the working electrode 32 by one of the techniques described above and further cross-linked by UV radiation or exposure to vapor of a cross-linking agent such as glutaraldehyde.

[0065] In certain embodiments, electrochemical sensing stack 50 may include additional layers, such as protein layers. Typically, the protein layer includes proteins such as human serum albumin, bovine serum albumin, etc.

[0066] In certain embodiments, the electrochemical sensing stack 50 may include an adhesion promoter layer disposed over the analyte sensing or enzyme layer to facilitate the analyte sensing layer and another overlying layer. contact and/or adhesion. The adhesion promoter layer may be made from any of a variety of materials known in the art to facilitate bonding between such layers. Typically, the adhesion promoter layer contains a silane compound. In alternative embodiments, the proteins or similar molecules in the analyte sensing layer may be sufficiently cross-linked or otherwise prepared to allow the analyte modulating membrane layer to interact with the adhesion promoter layer in the absence of the adhesion promoter layer. The analyte sensing layer is in direct contact. In certain embodiments, additional layers such as interference suppression layers may be included in electrochemical sensing stack 50 . Such layers may be formed by spin or screen printing or spin coating or spray coating or by chemical vapor deposition. In another embodiment, an adhesion promoter layer is deposited over the working electrode 32 by one of the techniques described above and further cross-linked by ultraviolet radiation or exposure to vapor of a cross-linking agent such as glutaraldehyde.

[0067] Thus, in certain embodiments, stack 50 includes a protein layer, such as a human serum albumin (HSA) layer, on a glucose oxidase layer, and an adhesion promoting layer on the protein layer. In other embodiments, no protein layer or adhesion promoting layer is included in the electrochemical sensing stack 50 .

[0068] In FIG. 2, electrochemical sensing stack 50 is shown further including an analyte modulation layer 60 above the enzyme layer, such that

Such as glucose limiting membrane (GLM)60. Analyte modulation layer 60 is provided to regulate analyte contact with the analyte sensing layer or enzyme layer. For example, the analyte modulating membrane layer may be a glucose limiting membrane that regulates the amount of glucose exposed to an enzyme present in the analyte sensing layer, such as glucose oxidase. Such glucose limiting membranes can be made from a variety of materials known to be suitable for such purposes, such as silicone compounds such as polydimethylsiloxane, polyurethane, polyurea cellulose acetate, Nafion, polyester sulfonate (e.g., Kodak AQ), hydrogel, or any other suitable membrane known to those skilled in the art. In an exemplary embodiment, glucose limiting membrane 60 has a thickness of about 10 microns to about 30 microns (um), such as about 18 um to about 25 um, such as about 20 um to about 22 μm, such as about 21 μm.

As shown, the glucose limiting membrane 60 may be formed around the entire end 18 of the analyte sensor 10, i.e., over both the first side 14 and the second side 16 of the base layer 12, including over the reference electrode. and above the counter electrode. In an exemplary embodiment, glucose limiting membrane 60 may be formed by dip coating end 18 of analyte sensor 10 such that glucose limiting membrane 60 encapsulates analyte sensor 10 for insertion into the interstitial fluid of a patient.

[0070] In addition to the glucose limiting membrane 60, other membranes may be formed on the end 18 of the analyte sensor 10 to inhibit foreign body reactions after implantation. For example, a foreign body responsive (FBR) membrane may be formed on the glucose limiting membrane 60 , such as by dip coating the end 18 of the analyte sensor 10 .

[0071] FIG. 3 illustrates an alternative or additional embodiment of analyte sensor 10. In FIG. 3 , the reference electrode 24 is not formed by the platinum layer 20 on the first side 14 of the base layer 12 . In contrast, the reference electrode 24 is formed on the second side 16 of the base layer 12 . Specifically, reference electrode 24 is formed from a silver/silver chloride ink layer 40 deposited over second side 16 of base layer 12 . Silver/silver chloride ink may be selectively deposited onto the second side 16 of the base layer 12 by screen printing or spin printing. In such embodiments, the entire second side 16 may be overprinted or overloaded with silver/silver chloride ink to allow for greater silver chloride loading. Additionally, such implementations eliminate position alignment process capabilities to reduce overall manufacturing process errors. As shown in FIG. 3 , the glucose limiting film 60 completely covers the reference electrode 24 formed by the silver/silver chloride ink layer 40 on the second side 16 of the base layer 12 .

[0072] Referring now to FIG. 4, a system 100 and method for fabricating an analyte sensor 10 is described. As shown, system 100 fabricates an analyte sensor in a roll-to-roll process by processing a roll 101 of a flexible substrate (such as a polyester film) including a sputtered platinum layer as described above. In system 100, polyester substrate 105 is fed from roll 101 to electrode patterning stage 110. At the electrode patterning stage 110, the platinum layer is patterned according to the desired analyte sensor, such as by laser ablation, to form working and counter electrodes, and optionally a reference electrode. The polyester substrate 115 is then fed from the electrode patterning stage 110 to the insulation stage 120 . At insulation stage 120 , an insulating dielectric material is selectively deposited over polyester substrate 115 . For example, the insulating dielectric material can be screen printed or spin printed over a polyester substrate.

[0073] The polyester substrate 125 is then fed from the insulation stage 120 to the insulation curing stage 130 where the insulating dielectric material is cured to form the insulating dielectric layer. For example, a UV curing process can be performed. The polyester substrate 135 is then fed from the insulation curing stage 130 to the ink printing stage 140 . At the ink printing stage 140, if such a reference electrode has been formed from sputtered platinum, silver/silver chloride ink is deposited over the reference electrode. Alternatively, a silver/silver chloride ink is deposited on the second side or back of the polyester substrate to form a reference electrode. Silver/silver chloride inks can be selectively deposited by screen printing or by rotary printing.

[0074] As shown, the polyester substrate 145 is then fed from the ink printing stage 140 to the drying stage 150. In drying stage 150, the silver/silver chloride ink is dried to form a silver/silver chloride ink layer on the polyester substrate. After drying, the polyester substrate 155 is then fed to a protective layer stage 160 where protective material is deposited over the polyester substrate 155 . Specifically, protective material is deposited on the entire side of the polyester substrate 155 where the sputtered platinum electrodes are located. Protective materials can be screen printed

Deposited by brush or by rotary printing. The polyester substrate 165 is then fed to a curing stage 170 where the protective material is cured to form a protective layer.

[0075] The polyester substrate 175 is then fed to the stamping stage 180. At stamping stage 180, the polyester substrate is punched, or otherwise cut, to form partially separated strips for use in forming separate analyte sensors. For example, a polyester substrate can be laser cut to form partially separated strips. As shown, the polyester substrate 175 may be passed under a visual alignment device 178 to ensure that the polyester substrate 175 is properly aligned for stamping. After stamping, each strip remains connected to the remaining polyester base stock via an insert. In an exemplary embodiment, each strip or analyte sensor includes a working electrode and a reference electrode. Specifically, each strip or analyte sensor includes the desired number of working, reference, and counter electrodes without further formation of electrodes.

[0076] The punched out or scrap portion 181 of the polyester substrate 175 may be wound into a roll 184 from the stamping stage 180 . The remaining polyester substrate 185 (including the separated analyte sensor in strip form) is fed to the enzyme deposition stage 190 . At enzyme deposition stage 190, an enzyme such as glucose oxidase is deposited over the working electrode. For example, enzymes can be screen-printed or spin-printed onto polyester substrates. Alternatively, enzymes can be deposited via aerosol-based drop-on-demand inkjet technology. In addition to enzymes, other materials used to form the electrochemical sensing stack may be deposited over the polyester substrate at enzyme deposition stage 190 .

[0077] The polyester substrate 195 is then fed to the enzyme curing stage 200. In the enzyme curing stage 200, the enzyme (and other deposited material) is cured, for example by a UV light-initiated curing method. During the curing process, enzymes cross-link and immobilize. Polyester substrate 205 may then be fed to film formation stage 210. At the membrane formation stage 210, the ends of each strip can be coated with glucose limiting membranes and other desired membranes. For example, the ends of each strip can be dip-coated or slot-coated to form the desired film. In certain embodiments, the system 100 may terminate roll-to-roll processing at this stage and produce a polyester substrate 215 that includes individual analyte sensors in the form of strips attached to a web of polyester substrate. In strip form, ready for further integration with the production of glucose monitoring systems. Alternatively, roll-to-roll processing may continue to process individual analyte sensors on polyester substrate 215 . Specifically, individual analyte sensors on polyester substrate 215 may be processed through a functional check stage 220 . At a functional check stage 220, each analyte sensor is exposed to a buffer solution containing glucose, and the sensor's signal time distribution is recorded and evaluated.

[0079] Alternatively, the polyester substrate 225 may be removed from the functional inspection stage 220 and may be fed to the separation stage 230. At separation stage 230, individual analyte sensors in the form of strips attached to the polyester base web can be separated by complete separation from the polyester base web. The separation stage 230 may be part of the final system assembly and packaging system separate from the roll-to-roll processing system 100 described herein.

[0080] It should be noted that the system 100 of Figure 4 may include additional elements for fabricating analyte sensors, such as idlers, driven wheels, vacuum boxes, and additional, alternative, or repeated processing stages.

[0081] FIG. 5 is a top view of a partially separated substrate 70 fabricated according to the method of FIG. 4. In particular, the partially separated substrate 70 is shown formed after being punched out, after forming the enzyme layer, and after film formation, such as after the film formation stage 210 or the functional inspection stage 220 of FIG. 4 . Additionally, at separation stage 230 of Figure 4, partially separated substrate 70 is shown prior to complete separation of the analyte sensor from the polyester substrate.

[0082] As shown in Figure 5, the partially separated substrate 70 includes individual analyte sensors 72 in the form of strips. Each individual analyte sensor 72 is connected to a polyester base web 74 via a tab at end 76 . Complete isolation and separation of individual analyte sensors 72 may be accomplished by severing each tab at end 76 . As shown, each analyte sensor 72 terminates at an end 78 . End portion 78 may be dip-coated or otherwise coated with a film-forming material at film-forming stage 210 of FIG. 4 . Gaps 80 between adjacent analyte sensors 72 are formed by removing portions of the polyester substrate during the stamping process.

(For example, the punched out portion or scrap portion 181 in Figure 4).

[0083] FIG. 6 illustrates a system 300 and method for fabricating the platinum sputtered polyester substrate introduced in FIG. 4 on a roll 110. In Figure 6, a polyester substrate 305 is provided. Polyester substrate 305 may be introduced into polyester surface modification stage 310. At the polyester surface modification stage 310, the surface of one or both sides of the polyester substrate 305 is modified. Specifically, the polyester surface can be roughened to improve adhesion between the polyester and the platinum layer formed thereon. Additionally, polyester surface modification can provide for grafting functional moieties onto the surface to increase adhesion. Surface modification may be performed by plasma pretreatment of the polyester substrate 305. Other methods of surface modification may include electrical discharge, surface grafting, flame treatment, UV radiation, or wet chemical etching.

[0084] Other treatments may be performed to roughen the surface of the polyester substrate 305 and include wet chemical etching, hydrolysis in alkaline solutions, pickling, or laser irradiation.

[0085] As shown, the polyester substrate 315 is then fed to a platinum deposition stage 320. In platinum deposition stage 320, platinum is deposited onto one side of polyester substrate 315. For example, platinum can be sputtered onto a polyester substrate. Sputtering is a physical vapor deposition method. Sputtering can be performed using a commercially available sputtering reactor using RF (radio frequency). Magnetron sputtering can also be used. Magnetron sputtering uses a magnetic field to concentrate electrons near the target surface to increase the deposition rate. An exemplary sputtered platinum layer has a thickness from about 5 nm to about 100 nm, such as from about 10 nm to about 50 nm. When multiple layers are deposited, the total thickness of the layers may have a thickness within the above range.

[0086] The properties of platinum thin films produced by sputtering vary according to process parameters, such as the properties of the platinum sputtering target material, including purity and microstructure, sputtering rate, energy of the sputtered platinum atoms reaching the polyester substrate, temperature and/or other parameters.

[0087] Control of the process parameters can produce a platinum sputtered polyester substrate 325 with desired characteristics. For example, by adjusting the process parameters of the platinum sputtering process, the surface roughness of the outer surface of the platinum layer can be controlled. Alternatively, the platinum sputtered polyester substrate 325 may be subjected to further processing. For example, a platinum sputtered polyester substrate 325 may be introduced into the platinum surface modification stage 330 . At the platinum surface modification stage 330, plasma surface modification treatment or other surface modification treatment may be performed as needed to adjust the surface properties of the platinum layer. The platinum sputtered polyester layer 335 may then be wound onto a roll 340 for use in the manufacturing method 100 of FIG. 4 .

[0088] It should be noted that although aspects of the above-described methods, systems and sensors have been described in a specific order and specific arrangements, such specific orders and arrangements are merely examples and are protected by the claims. The subject matter is not limited to the order or arrangement depicted.

[0089] While what are presently considered to be features of the embodiments have been illustrated and described, those skilled in the art will understand that various other modifications may be made without departing from the subject matter protected by the claims. And equivalent substitutions are possible. In addition, many modifications may be made to adapt a particular situation to the teachings of the claimed subject matter without departing from the central concepts described herein. Therefore, it is intended that claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter may also include all matters falling within the scope of the appended claims and their equivalents. aspect.