Ionic diffusion sensor

Abstract

An ionic diffusion sensor includes a substrate of electrically insulating material, and an anode comprising an anode body formed on the substrate and having conductively linked nanoparticles on the surface of the anode body. The ionic diffusion sensor also includes a cathode formed on the substrate and spaced from the anode body. An anode lead is coupled to the anode, and a cathode lead coupled to the cathode, the anode lead and cathode lead are utilized for measuring current between the anode and the cathode.

Description

IONIC DIFFUSION SENSORFIELD OF TECHNOLOGY

[0001] The present disclosure relates to sensors for high sensitivity applications, such as biosensors. An example of such a biosensor is a glucose detection device.BACKGROUND

[0002] Sensors for high sensitivity applications, such as glucose detection, rely on many different technologies. For example, enzymatic methods may be utilized to apply glucose oxidase (GOD) for the detection of glucose in bodily fluids, such as blood, sweat, and / or urine. The stability of GOD limits the lifetime and long-term storage of such glucose sensors, particularly for continuous glucose monitoring (CGM).

[0003] Electrochemical sensors may include three electrodes, including a working electrode, counter electrode and reference electrode of Ag / AgCI, to provide a stable potential. GOD is coated on the working electrode and, in use, is in contact with the analyte. An enzymatic reaction occurs when the GOD reacts with glucose and generates gluconic acid and hydrogen peroxide (H2O2).

[0004] Non-enzymatic sensors are preferred for increased stability of the sensor and reduced cost. Thus, different catalytic materials have been introduced for glucose detection. For example, Au nanoparticles (Au-NP) have been studied for use as a glucose oxidation catalyst material. The oxidation potential of glucose is found at 0.55 V and the Au-NP deposited on the working electrode may catalyze the glucose oxidation reaction and generate electrical current when the 0.4 to 0.6 V is applied. The generated current is proportional to the glucose concentration, enabling detection utilizing the electrochemical sensors.

[0005] An applied bias close to the peak of oxidation potential is utilized in an attempt to maximize the current signal and initiate the oxidation of glucose. Other chemical components in the analyte solution may also be oxidized at the applied bias, thus limiting the sensitivity for low concentration of glucose, particularly for glucose detection in the sweat, for example. The glucose concentration in sweat and blood are in the range of 0.01 to 1 mM and 2 to 40 mM, respectively.

[0006] Other nanoparticle materials that mimic the functionality of GOD have been also been studied. The applied voltage, however, impacts other molecules in the analyte, also limiting sensitivity.

[0007] Colorimetric glucose sensors use GOD or nanoparticles to catalyze the reaction of glucose and generate H2O2. The H2O2 interacts with chromogenic substrates to change the color of the sensor for glucose detection. Although GOD provides specific selectivity for glucose detection, such sensors are expensive with a limited lifetime. The aggregation of nanoparticles impacts detection reliability and stability and further development is still required.

[0008] The cost of enzymatic material, such as GOD, and the stability of such material, limits the application, and the aggregation of nanoparticles limits the reliability and lifetime. In addition, detection sensitivity is limited.

[0009] Improvements in sensors for high sensitivity applications, such as biosensors for use in glucose detection, are desirable.SUMMARY

[0010] According to one aspect of an embodiment, an ionic diffusion sensor includes a substrate of electrically insulating material, and an anode comprising an anode body formed on the substrate and having conductively linked nanoparticles on the surface of the anode body. The ionic diffusion sensor also includes a cathode formed on the substrate and spaced from the anode body. Ananode lead is coupled to the anode, and a cathode lead coupled to the cathode, the anode lead and cathode lead are utilized for measuring current between the anode and the cathode.

[0011] In some embodiments, the anode body and the cathode comprise silver.

[0012] The conductively linked nanoparticles may comprise gold nanoparticles. The gold nanoparticles may be conductively linked to the surface of the anode body utilizing benzene-dithiol oligomeric self-assembled monolayer on the anode body.

[0013] In other embodiments, the anode body and the cathode comprise MXene.

[0014] The conductively linked nanoparticles may comprise platinum nanoparticles.

[0015] The spacing between the anode body with conductively linked nanoparticles and the cathode is sized to be covered by an analyte drop that at least partially covers both the anode and the cathode.

[0016] A membrane may be disposed on the anode and the cathode. The membrane may comprise a membrane that enhances selectivity of glucose by facilitating glucose penetration through the membrane.

[0017] According to another aspect, a method of fabricating an ionic diffusion sensor includes forming an anode body and a cathode on a substrate, the anode body spaced from the cathode on the substrate, conductively linking nanoparticles on the surface of the anode body, and providing an anode lead to the anode body and a cathode lead to the cathode for measuring current between the anode body and the cathode.

[0018] The anode body and the cathode may be selectively printed on the substrate. Alternatively, the anode body and the cathode may be deposited on the substrate.

[0019] Forming the anode body and the cathode may include selectively printing or depositing silver on the substrate.

[0020] Conductively linking nanoparticles may include conductively linking gold nanoparticles.

[0021] Conductively linking nanoparticles may comprise utilizing benzenedithiol oligomeric self-assembled monolayer on the anode body to link the gold nanoparticles.

[0022] Alternatively, forming the anode body and the cathode may comprise selectively printing or depositing MXene on the substrate.

[0023] Conductively linking nanoparticles may comprise conductively linking platinum nanoparticles.

[0024] The spacing between the anode body with conductively linked nanoparticles and the cathode is sized to be covered by an analyte drop that at least partially covers both the anode and the cathode.

[0025] A membrane may be applied to the anode body including the nanoparticles on the surface of the anode body, and to the cathode. Applying the membrane may comprise coating with a membrane that enhances selectivity of glucose by facilitating glucose penetration through the membrane.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached figures.

[0027] FIG. 1 shows an ionic diffusion sensor in accordance with an aspect of an embodiment.

[0028] FIG. 2 is a flowchart illustrating a method of fabricating an ionic diffusion sensor in accordance with an aspect of an embodiment.

[0029] FIG. 3 is a graph illustrating current measured between the anode and cathode of the ionic diffusion sensor of FIG. 1 with different concentrations of glucose.

[0030] FIG. 4 is a graph illustrating the current measured with glucose concentrations of from 10 pM to 1 mM utilizing the ionic diffusion sensor of FIG. 1.

[0031] FIG. 5 is a graph illustrating selectivity for glucose utilizing the glucose ionic diffusion sensor with selective membrane coating.DETAILED DESCRIPTION

[0032] For simplicity and clarity of illustration, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Numerous details are set forth to provide an understanding of the examples described herein. The examples may be practiced without these details. In other instances, well-known methods, procedures, and components are not described in detail to avoid obscuring the examples described. The description is not to be considered as limited to the scope of the examples described herein.

[0033] While reference is made herein to glucose detection, the configuration of the sensor is not limited to glucose detection. Sensors may be utilized for other sensing applications, for example, for use as agriculture sensors, gas sensors, and others. Glucose detection is referred to herein as one particular example.

[0034] Reference is first made to FIG. 1, which shows an ionic diffusion sensor indicated generally by the numeral 100. The ionic diffusion sensor 100 includes a substrate 102 of electrically insulating material, and an anode 104 comprising an anode body 106 formed on the substrate 102 and having conductively linked nanoparticles 108 on the surface 110 of the anode body 106. The ionic diffusionsensor 100 also includes a cathode 112 comprising a cathode body 114 formed on the substrate 102 and spaced from the anode body 106. An anode lead 118 is coupled to the anode 104, and a cathode lead 116 is coupled to the cathode 112. The anode lead 118 and cathode lead 116 are utilized for measuring current between the anode 104 and the cathode 112.

[0035] Reference is made to FIG. 2 with continued reference to FIG. 1, to describe the fabrication of the ionic diffusion sensor 100 in accordance with an aspect of an embodiment. For the purpose of the present example, the substrate 102 is a polyethylene terephthalate (PET) substrate. Other substrates, however, may be successfully implemented. For example, the substrate may be polyimide or a paper, or other electrically insulating material.

[0036] At 202, the anode body 106 and the cathode body 114 are formed on the substrate 102. In one example, the anode body 106 and the cathode body 114 are silver that is printed by aerosol jet printing onto the substrate 102. Alternatively, the anode body 106 and cathode body 114 may be screen printed, ink jet printed, or deposited onto the substrate 102. The anode body 106 and the cathode body 114 may each be, for example, about 500 nm to about 1 pm in thickness. Other conductive materials may also be successfully implemented. For example, the anode body 106 and the cathode body 114 may be MXene.

[0037] The spacing between the anode body 106 and the cathode body 114 is sized such that a drop of analyte at least partially covers the anode body 106 and the cathode body 114, as well as the space between the anode body 106 and the cathode body 114.

[0038] At 204, a self-assembled monolayer of oligomer is applied to the surface of the anode body 106. In the present example, the substrate with anode body 106 and cathode body 114, is dip coated in 1,4-benzene-dithiol oligomer to provide a self-assembled monolayer on the surface of anode body 106 and on the cathode body 114.

[0039] Other methods of application of 1,4-benzene-dithiol oligomer may be successfully implemented. For example, the 1,4-benzene-dithiol may be drop cast onto the anode body 106.

[0040] Thus, in the present example, both the anode body 106 and the cathode body 114 are coated with the self-assembled monolayer. Alternatively, the anode body 106 may be coated without coating the cathode body 114 with the self-assembled monolayer. In this alternative, the anode body may be coated by drop casting the oligomer on the anode body 106. In yet another alternative, the cathode body 114 may be printed after coating the anode body 106 with the self-assembled monolayer.

[0041] At 206, nanoparticles 108 are deposited on the surface of the anode body 106. In the present example, the nanoparticles are drop casted on the surface of the anode body 106 after coating with the self-assembled monolayer of 1,4-benzene-dithiol oligomer. The nanoparticles are fixed to the surface of the anode body 106 via 1,4-benzene-dithiol oligomer. Alternatively, the nanoparticles 108 may be deposited on the surface of the anode body 106 utilizing any suitable method.

[0042] Thus, the anode 104 includes the anode body 106 and the nanoparticles 108 conductively linked to the anode body 106. The work function of the anode 104 differs from the cathode 112 as a result of the nanoparticles attached on the anode body 106. Thus, a built-in potential between the anode 104 and cathode 112 is provided which drives ion diffusion between the anode 104 and the cathode 112.

[0043] Electrical leads are then provided at 208. The electrical leads include an anode lead 118 electrically connected to the anode body 106, and a cathode lead 116 electrically connected to the cathode body 114. The anode lead 118 may be connected to an exposed surface of the anode 104 or may be connected utilizing a probe or portion of the lead that extends through the substrate to the anode body 106. Similarly, the cathode lead 116 may be connected to anexposed surface of the cathode 112 or may be connected utilizing a probe or portion of the cathode lead that extends through the substrate to the cathode body 114.

[0044] The electrical leads are utilized for connection to an ammeter to measure current between the anode 104 and the cathode 112.

[0045] A membrane may be applied to the anode body 106 including the nanoparticles 108 on the surface of the anode body 106, to the cathode body 114, and to the exposed surface of the substrate 102. In the present example, the membrane is a coating that enhances selectivity of glucose by selectively facilitating glucose penetration through the membrane while inhibiting other molecules from the analyte from penetrating through the membrane. For example, the membrane may be a Nation™ coating.

[0046] Other selective membranes may be utilized based on the application and may be successfully implemented.

[0047] In use, a drop of analyte liquid is placed on the ionic diffusion sensor such that the drop covers at least a portion of the anode 104, at least a portion of the cathode 112, and the substrate 102 between the anode 104 and the cathode 112, as illustrated in FIG. 1. An ammeter is coupled to the anode lead 118 and to the cathode lead 116 to measure current between the anode 104 and the cathode 112 without any external bias applied or under a very small bias, e.g., 1 mV.

[0048] In the particular example of the glucose ionic diffusion sensor, the anode 104 includes an anode body 106 comprised of silver with gold nanoparticles conductively linked to the surface of the anode body 106 utilizing 1,4-benzene-dithiol oligomer, and the cathode body 114 is silver. The membrane, such as Nation™, is utilized. In this example, the analyte is any suitable bodily fluid such as blood, urine, saliva, sweat, tears, or breath.

[0049] The gold nanoparticles oxidize glucose and produce gluconate, a proton, and an electron. A portion of the silver anode body 106 that is in contact with the analyte solution, adsorbs hydroxide (OH-), enhancing the catalyst reaction between gold nanoparticles and the glucose, and increases detection sensitivity.

[0050] With the gold nanoparticles conductively linked only the surface of the anode body 106, and not to the cathode body 114, a work function difference results, serving as the driving force for ion diffusion between the anode 104 and the cathode 112.

[0051] Measurement of the current response between the anode 104 and the cathode 112 is carried out without any external bias. The measured current correlates with glucose concentration.

[0052] FIG. 3 illustrates the current between the anode and the cathode obtained at OV, without external bias, at different concentrations of glucose.

[0053] To obtain the results illustrated in FIG. 3, analytes with known concentrations of glucose were utilized. The current was measured utilizing the ammeter connected to the glucose ionic diffusion sensor shown in FIG. 1. The results show that the higher the concentration of glucose, the higher the measured current.

[0054] FIG. 4 is a graph showing the measured current v. glucose concentration. To obtain the graph of FIG. 4, the current was measured utilizing the ammeter connected to the glucose ionic diffusion sensor as described, for different concentrations of glucose. As shown in FIG. 4, the current shows a generally linear response with glucose concentration from about 10 pM to about 1 mM.

[0055] Other experiments carried out utilizing a gold anode and a gold cathode did not result in the linear response at OV. Further, the use of knownelectrochemical measurement techniques with 0.4 V to 0.6 V utilizing gold nanoparticles, resulted in a detection limit of about 1 mM.

[0056] FIG. 5 illustrates selectivity for glucose utilizing the glucose ionic diffusion sensor with Nation™ membrane coating. To obtain the results illustrated in the graph of FIG. 5, current was measured for analytes with known concentrations of glucose, potassium chloride (KCI), uric acid, and ascorbic acid.

[0057] Based on the results illustrated in FIG. 5, the current response resulting from glucose is not affected by the presence of KCI, uric acid, or ascorbic acid in the analyte solution which enhance the selectivity for glucose detection.

[0058] Other electrode materials that adsorb OH- when in contact with analyte solution, may be successfully implemented. For example MXene may be utilized. Further, platinum nanoparticles may be utilized rather than gold nanoparticles. Other nanomaterials may also be utilized as a catalyst for detection of, for example, a virus, specific molecules, disease, or chemicals.

[0059] Advantageously, highly sensitive sensors are provided. Such sensors may be utilized for specific applications, such as biosensors. The use of such sensors provides improved sensitivity over known sensors and do not require external power. In addition the sensors disclosed herein do not utilize enzymatic detection, providing an increase in the lifetime and may result in reduced cost of sensors.

[0060] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

What is claimed is:Claims1. An ionic diffusion sensor comprising: a substrate of electrically insulating material; an anode formed on the substrate and comprising an anode body having conductively linked nanoparticles on the surface of the anode body; a cathode formed on the substrate and spaced from the anode body; an anode lead coupled to the anode, and a cathode lead coupled to the cathode, the anode lead and cathode lead for measuring current between the anode and the cathode.

2. The ionic diffusion sensor according to claim 1, wherein the anode body and the cathode comprise silver.

3. The ionic diffusion sensor according to claim 1, wherein the conductively linked nanoparticles comprise gold nanoparticles.

4. The ionic diffusion sensor according to claim 3, wherein the gold nanoparticles are conductively linked to the surface of the anode body utilizing benzene-dithiol oligomeric self-assembled monolayer on the anode body.

5. The ionic diffusion sensor according to claim 1, wherein the anode body and the cathode comprise MXene.

6. The ionic diffusion sensor according to claim 1, wherein the conductively linked nanoparticles comprise platinum nanoparticles.

7. The ionic diffusion sensor according to claim 1, wherein the spacing between the anode body with conductively linked nanoparticles and the cathode is sized to be covered by an analyte drop that at least partially covers both the anode and the cathode.

8. The ionic diffusion sensor according to claim 1, comprising a membrane disposed on the anode and the cathode.

9. The ionic diffusion sensor according to claim 8, wherein the membrane comprises a membrane that enhances selectivity of glucose by facilitating glucose penetration through the membrane.

10. A method of fabricating an ionic diffusion sensor, the method comprising: forming an anode body and a cathode on a substrate, the anode body spaced from the cathode on the substrate; conductively linking nanoparticles on the surface of the anode body; providing an anode lead to the anode body and a cathode lead to the cathode for measuring current between the anode body and the cathode.

11. The method according to claim 10, wherein the anode body and the cathode are selectively printed on the substrate.

12. The method according to claim 10, wherein the anode body and the cathode are deposited on the substrate.

13. The method according to claim 10, wherein forming the anode body and the cathode comprise selectively printing or depositing silver on the substrate.

14. The method according to claim 10, wherein conductively linking nanoparticles comprises conductively linking gold nanoparticles.

15. The method according to claim 14, wherein conductively linking nanoparticles comprises utilizing benzene-dithiol oligomeric self-assembled monolayer on the anode body to link the gold nanoparticles.

16. The method according to claim 10, wherein forming the anode body and the cathode comprise selectively printing or depositing MXene on the substrate.

17. The method according to claim 10, wherein conductively linking nanoparticles comprises conductively linking platinum nanoparticles.

18. The method according to claim 10, wherein the spacing between the anode body with conductively linked nanoparticles and the cathode is sized to be covered by an analyte drop that at least partially covers both the anode and the cathode.

19. The method according to claim 10, comprising applying a membrane to the anode body including the nanoparticles on the surface of the anode body, and to the cathode.

20. The method according to claim 19, wherein applying the membrane comprises coating with a membrane that enhances selectivity of glucose by facilitating glucose penetration through the membrane.

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