Apparatus for quantifying an analyte in a liquid sample - Patent Application 20070122997

Abstract

The present disclosure relates to an electrochemical detection device for quantifying an analyte in a liquid sample, the electrochemical detection device comprising: a substrate; a plurality of electrodes disposed on the substrate, one of the plurality of electrodes being functionalized with a catalyst, the catalyst comprising an inorganic compound; and a hydrophilic channel disposed on the substrate, the hydrophilic channel configured to receive the liquid sample and direct the liquid sample to the electrode.

Description

[Technical Field]

[0001] The present technology relates to devices for quantifying an analyte in a liquid sample. [Background technology]

[0002] Enzyme electrochemical sensors are one of the most commercially successful biosensing technologies for quantifying analytes in liquid samples. In particular, this technology has been widely adopted in home glucose testing strips for monitoring chronic disease in diabetic patients. This example demonstrates the potential usefulness of electrochemical assays for rapid and accurate quantification of analytes suitable for enzymatic reactions. However, the enzymes used as catalysts in conventional enzymatic electrochemical sensors have poor stability to environmental conditions and, more importantly, limited sensitivity in quantifying low-concentration molecules. One example is the quantification of glucose in human saliva, where the glucose concentration is significantly lower than that in blood. Existing enzymatic electrochemical biosensor technologies cannot accurately quantify the glucose level in saliva. Accurately quantifying glucose levels in subjects using saliva would enable a noninvasive means of managing the condition of diabetic patients.

[0003] Therefore, it is desirable to improve the reliability and sensitivity of devices for quantifying analytes in liquid samples. Summary of the Invention [Means for solving the problem]

[0004] In view of the above, one aspect of the present technology provides an electrochemical detection device for quantifying an analyte in a liquid sample, the electrochemical detection device comprising: a substrate; a plurality of electrodes disposed on the substrate, one of the plurality of electrodes being functionalized with a catalyst, the catalyst comprising an inorganic compound; and a hydrophilic channel disposed on the substrate, the hydrophilic channel configured to receive the liquid sample and direct the liquid sample to the electrode.

[0005] According to an embodiment of the present technology, an electrochemical detection device is provided for quantifying an analyte, such as glucose, in a liquid sample, such as blood or saliva. In use, the liquid sample is deposited on a hydrophilic channel, e.g., at a dedicated sample inlet or window that exposes the hydrophilic channel. The liquid sample is then transported along the hydrophilic channel toward a plurality of electrodes, where a measurement is performed. One of the electrodes comprises an inorganic catalyst, functionalized with the inorganic catalyst, which reacts with the analyte in the liquid sample, allowing the concentration or amount of the analyte to be measured. Compared to conventional enzyme catalysts, inorganic catalysts exhibit high stability to environmental conditions and, more importantly, have high sensitivity to low concentrations of analytes. The use of an inorganic catalyst enables the quantification of low concentrations of analytes, such as glucose, in saliva, and improves the stability of the resulting detection device.

[0006] Copper oxide as an inorganic alternative has been shown to quantify glucose with increased sensitivity at low concentrations and specificity compared to the glucose oxidase enzyme. Thus, in some embodiments, the inorganic compound may include copper oxide. In other embodiments, the inorganic compound may include other metal oxides, such as cobalt oxide, nickel oxide, iron oxide, or zinc oxide.

[0007] The potential for high performance of some inorganic catalysts depends on the acidity and basicity (pH) of the solution with which they react. For example, copper oxide exhibits excellent performance in glucose quantification, but technically requires that the local pH of the solution be within a specific range near the functionalized electrode on which the catalyst is deposited. While serum pH in blood is generally stable around the physiological range (approximately 7.4), salivary pH can vary significantly between individuals, and even within the same individual at different times of the day depending on food and beverage intake and oral hygiene. Therefore, simply replacing an enzyme catalyst with an inorganic catalyst on a simple screen-printed electrode strip, such as those used in existing enzymatic electrochemical saccharometers, may not be sufficient. Therefore, in some embodiments, the device may further include a pH control system positioned adjacent to the multiple electrodes configured to control the acidity / basicity of at least the area surrounding the functionalized electrode. This allows for local control of the acidity and / or basicity around the functionalized electrode, enabling the use of catalysts that may be sensitive to pH fluctuations.

[0008] In some embodiments, the plurality of electrodes may include at least a working electrode, a counter electrode, and a reference electrode, and the pH control system may be disposed adjacent to the working electrode.

[0009] In some embodiments, the pH control system may include a set of pH control electrodes.

[0010] In some embodiments, the set of pH-controlling electrodes may comprise a pH-sensing electrode and an active pH-controlling electrode.

[0011] There are many different suitable forms that a pH sensing electrode can take. In some embodiments, the pH sensing electrode may comprise an ion-selective detector or an ion-sensitive extended gate electrode arranged to allow an electronic readout of the measured pH value.

[0012] Similarly, there are many different suitable forms that the active pH-controlling electrode can take. In some embodiments, the active pH-controlling electrode can comprise a quinone-functionalized electrode configured to electrochemically direct electrons or protons around at least the functionalized electrode. In other embodiments, the active pH-controlling electrode can be configured to act as a controlled release valve for an alkalinity source stored on the device.

[0013] In some embodiments, the pH control system may be configured to communicate with and be controlled by an electronic reader that implements a predetermined pH calibration algorithm.

[0014] In some embodiments, each of the plurality of electrodes may extend into an electrical connection pad configured to interface with an electronic reader.

[0015] In some embodiments, the plurality of electrodes may include at least a working electrode, a counter electrode, and a reference electrode, and the plurality of electrodes may be arranged such that upon application of a potential between the working electrode and the reference electrode, a current is measured via the counter electrode.

[0016] In some embodiments, the functionalized electrode may be a working electrode and a catalyst may be deposited thereon.

[0017] The hydrophilic channels can take many different suitable forms as desired. In some embodiments, the hydrophilic channels may be formed in paper. In other embodiments, the hydrophilic channels may be formed by photolithography in dry film photoresist.

[0018] In some embodiments, the hydrophilic channels may be formed with surface micropatterns configured to promote the diffusion of liquid samples, for example, following either a chemical or plasma-induced hydrophilization treatment.

[0019] In some embodiments, the substrate may comprise a printed circuit board. The printed circuit board on which the plurality of electrodes and hydrophilic channels, and optionally the pH control system, are disposed may, in some embodiments, be enclosed in a housing (e.g., a plastic housing) to protect the various elements of the electrochemical detection device. An opening or window may be formed in the housing to allow access to a portion of the hydrophilic channels so that the hydrophilic channels can receive a liquid sample. A second opening or window may be formed in the housing to allow access to the plurality of electrodes (and optionally the pH control system), for example, to allow interfacing with an electronic reader.

[0020] Each embodiment of the present technology will have at least one, but not necessarily all, of the above-described objects and / or aspects, and it will be understood that some aspects of the present technology, while attempting to achieve the above-described object, may not satisfy that object and / or may satisfy other objects not specifically set forth herein.

[0021] Additional and / or alternative features, aspects, and advantages of embodiments of the present technology will become apparent from the following description, the accompanying drawings, and the appended claims.

[0022] Embodiments will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows an exemplary electrochemical sensing device according to one embodiment of the present technology. [Figure 2] 1 illustrates another exemplary electrochemical detection device. [Figure 3] 1 illustrates a schematic diagram of one embodiment of a pH control system. [Figure 4] 4A-4B. The effect of liquid sample pH on the measurement results between two analytes. DETAILED DESCRIPTION OF THE INVENTION

[0024] The inventors of the present technology have recognized that enzymes used as catalysts in conventional enzymatic electrochemical sensors have low stability to environmental conditions and, more importantly, limited sensitivity in quantifying low concentration molecules.

[0025] In this approach, the organic enzyme catalyst (e.g., glucose oxidase in the case of glucose) in a conventional enzymatic electrochemical sensor is replaced with an inorganic catalyst (e.g., copper oxide) that, when properly designed and operated, is sensitive to lower concentrations of the analyte and has equivalent selectivity for the target analyte. Thus, this approach can provide a device / system capable of quantifying analytes suitable for enzymatic assays at a much lower sensitivity range than conventional methods.

[0026] Embodiments of the present technology provide an improved electrochemical detection device for quantifying an analyte, such as glucose, in a liquid sample, such as blood or saliva. Embodiments of the device include a substrate, a plurality of electrodes disposed on the substrate, including inorganic catalyst-functionalized electrodes, and hydrophilic channels disposed on the substrate for receiving the liquid sample and directing the liquid sample to the electrodes.

[0027] In use, a liquid sample is deposited onto a hydrophilic channel, e.g., at a sample inlet that exposes the hydrophilic channel. The liquid sample is then transported along the hydrophilic channel toward a plurality of electrodes where measurements can be taken. One of the electrodes is functionalized with an inorganic catalyst, which reacts with an analyte in the liquid sample to allow for quantification of the analyte. Compared to traditional enzyme catalysts, inorganic catalysts exhibit greater stability to environmental conditions and are more sensitive to low concentrations of analyte. The use of inorganic catalysts can enable quantification of analytes at low concentrations, and the resulting detection device has improved stability.

[0028] 1 shows an exemplary electrochemical detection device 100 in accordance with one embodiment of the present technology. Device 100 includes a substrate 109 upon which the elements of device 100 are disposed. Substrate 109 can be formed of any suitable material as desired, and in one embodiment, substrate 109 can include a printed circuit board (PCB), while in another embodiment, substrate 109 can be the base (e.g., made of plastic) of a screen-printed strip (e.g., for glucose quantification). In this embodiment, device 100 is implemented using flexible lab-on-PCB technology.

[0029] The device 100 comprises a hydrophilic channel 101 disposed on a substrate 109, the hydrophilic channel 101 having an inlet 102 toward one end for receiving a liquid sample and a detection area toward the end opposite the inlet 102. In this embodiment, the inlet 102 is wider than the rest of the hydrophilic channel 101 to facilitate deposition of the liquid sample, but this need not be the case; in other embodiments, the inlet 102 may be the same width as the rest of the hydrophilic channel 101. Once the liquid sample is deposited on the inlet 102, the hydrophilic channel 101 passively transports the liquid sample along its length by diffusion toward the detection area, where multiple electrochemical detection electrodes 103a, 104a, 105a are disposed.

[0030] In this embodiment, the multiple electrochemical detection electrodes 103a, 104a, and 105a include a working electrode (WE) 103a, a reference electrode (RE) 104a, and a counter electrode (CE) 105a. An inorganic catalyst material (e.g., copper oxide nanoparticles) is deposited on the WE surface by, for example, drop coating or printing from a solution, and then dried to functionalize the WE electrode. The detection electrodes 103a, 104a, and 105a are formed with conductive tracks plated with an inert metal (e.g., gold). The conductive tracks enable good current transfer, for example, toward instrumentation electrically connected to the electrodes, and the inert metal plating reduces undesired chemical reactions between the electrodes and the liquid sample. In some embodiments, if improved stability and / or signal amplification are desired, the inorganic catalyst may be further encapsulated with a suitable material in addition to the inert metal plating. Each of the conductive tracks forming each of the WE 103a, RE 104a and CE 105a extends towards the edge of the device 100 to a respective connection pad 103b, 104b, 105b arranged to electrically interface with, for example, an electronic reader 120 via a suitable connection (e.g., an electrical cable) 110. During use of the device 100, a potential is applied between the WE 103a and the RE 104a (e.g., by the electronic reader 120 via connection pads 103b and 104b) and the resulting current is read via the CE 105a, e.g., by the electronic reader 120 via connection pad 105b.

[0031] In this embodiment, device 100 further comprises a pH control system, in this example comprising a set of pH control electrodes 106a, 107a disposed on substrate 109 adjacent WE 103a at the same end as the plurality of electrodes 103a, 104a, 105a. The set of pH control electrodes comprises a pH sensing electrode (PHSE) 106a and an active pH control electrode (PHCE) 107a, extending to connection pads 106b and 107b, respectively, positioned to electrically interface with electronic reader 120.

[0032] PHSE 106a can be any suitable commercially available ion-selective detection device, as desired. For example, PHSE 106a can be an ion-sensitive field-effect transistor (ISFET) or an ion-sensitive extended-gate field-effect transistor such as ITO, ZnO, parylene, etc. PHCE 107a can be, for example, a quinone-functionalized electrode for electrochemically inducing the release of electrons or protons at the electrode locale. PHCE 107a can alternatively be configured to function as a controlled release valve for a source of alkali (e.g., NaOH) stored on-chip.

[0033] In this embodiment, the PHSE 106a and the PHCE 107a are controlled by an electronic reader that implements a predetermined sensor pH calibration algorithm. The sensor pH calibration algorithm defines an appropriate operating pH value (or operating pH value range) for the chemical reaction between the analyte in the liquid sample and the inorganic catalyst on the WE 103a and defines instructions for controlling the PHCE 107a based on the pH value measured by the PHSE 106a to achieve the desired pH value or range of pH values. Thus, the present device 100 enables electronically tunable detection of different analytes by algorithmically adapting the sensitivity and selectivity of the WE 103a by adjusting the pH value of the sample liquid in the area surrounding the WE 103a based on the pH value read by the PHSE 106a and the specific properties of the non-enzymatic inorganic catalyst on the WE 103a.

[0034] The hydrophilic channels 101 may be formed by paper in a hybrid implementation, or by photolithography in a dry film photoresist in a seamless integrated implementation, in which case a hydrophilization process may be performed after formation, such as oxygen plasma treatment of the micropatterned interior.

[0035] An exemplary micropatterned hydrophilic channel 201 is shown in Figure 2. In this embodiment, diamond-shaped micropatterns 200-1, 200-2, 200-3 promote passive (i.e., without application of external pressure) flow of liquid sample from inlet 202 toward a detection region toward the opposite end of channel 201. Micropatterns of shapes other than the diamond shape herein, including the same shape or a combination of two or more shapes, are of course possible, if desired.

[0036] In different embodiments, the dimensions of the hydrophilic channels (e.g., hydrophilic channel 101) can range from 250 μm to 1 mm in width, as desired and as dictated by manufacturing limitations. The length and thickness of the hydrophilic channel may be determined by the sample volume of the intended liquid sample that the hydrophilic channel needs to accommodate for analysis and quantification, which may be determined by the clinical concentration range of the target analyte in the liquid sample and the molecular diffusion time of the analyte toward the working electrode region.

[0037] In one practical example, copper oxide, for example in the form of nanoparticles, is used as an inorganic alternative to the glucose oxidase enzyme in glucose analysis. This is due to its sensitivity at lower analyte (glucose) concentrations and improved specificity. However, the potential of copper oxide as an alternative catalyst has not been practically adopted due to the technical requirement of precisely controlling the acidity / basicity of the liquid sample locally at the WE where it is deposited. In the case of glucose analysis using blood samples, the serum pH of blood is generally stable in the physiological range (7.4), and therefore active pH control is not required. However, the pH of human saliva can vary significantly from person to person and can also vary over time within the same person due to food and beverage intake and oral hygiene. pH fluctuations introduce inaccuracies and uncertainties into glucose analysis performed on saliva samples when copper oxide is used. In such cases, a pH control system, such as a pH control system comprising PHSE 106a and PHCE 107a, may be implemented in embodiments of the present technology to measure and actively control the acidity / basicity of the liquid sample adjacent to WE 103a.

[0038] FIG. 3 shows the detection area of ​​device 100 from a side view, illustrating the pH control mechanism implemented by PHSE 106a and PHCE 107a, which are controlled by a pH control algorithm through electronic reader 120. As described above, WE 103a, located between PHSE 106a and PHCE 107a, is functionalized with an inorganic catalyst that enables a chemical reaction with a target analyte (e.g., glucose molecules). In this embodiment, the inorganic catalyst may be copper oxide (CuO) nanoparticles 300. In use, PHSE 106a enables an electronic reading of the pH value of a liquid sample to be obtained by external electronic reader 120. Electronic reader 120 executes a pH control algorithm that defines instructions for providing an electronic signal stimulus (e.g., voltage or current) to PHCE 107a. The magnitude of the electronic signal stimulus is determined by (e.g., proportional to) the pH value measured by PHSE 106a, and the electronic signal stimulus causes PHCE 107a to release protons into the region of WE 103a, thereby adjusting the local acidity / basicity to a predetermined level (e.g., a predetermined pH value).

[0039] Figures 4A and 4B show the specificity of copper oxide for glucose and lactate at different acidity / basicity levels. As shown in Figure 4A, when the pH value of the solution is adjusted to 8, copper oxide can be used as an inorganic catalyst in the electrochemical detection device described above to accurately quantify glucose. On the other hand, as shown in Figure 4B, when the pH value of the solution is adjusted to 7.5, the device described above can accurately quantify lactate.

[0040] The examples and conditional language set forth herein are intended to aid the reader in understanding the principles of the technology and are not intended to limit its scope to such specifically set forth examples and conditions. Those skilled in the art will appreciate that they can devise various configurations that, although not expressly described or shown herein, embody the principles of the technology and are within the scope defined by the appended claims.

[0041] Furthermore, to aid in understanding, the above description may describe relatively simplified implementations of the technology. As those skilled in the art will appreciate, various implementations of the technology may be more complex.

[0042] In some cases, what are believed to be useful examples of modifications of the technology may also be described. This is done solely to facilitate understanding and is not intended to limit or delimit the scope of the technology. These modifications are not an exhaustive list, and one of ordinary skill in the art may make other modifications while remaining within the scope of the technology. Furthermore, if examples of modifications are not described, it should not be interpreted as meaning that the modifications are not possible and / or that the description is the only way to implement that element of the technology.

[0043] Moreover, all statements herein reciting principles, aspects, and implementations of the present technology, as well as specific examples thereof, are intended to encompass all structural and functional equivalents thereof, whether now known or developed in the future.

[0044] As will be apparent to those skilled in the art, many improvements and modifications can be made to the exemplary embodiments described above without departing from the scope of the technology.

Claims

1. 1. An electrochemical detection device for quantifying an analyte in a liquid sample, comprising: A substrate; a plurality of electrodes disposed on the substrate, one of the plurality of electrodes being functionalized with a catalyst, the catalyst comprising an inorganic compound; a hydrophilic channel disposed on the substrate configured to receive the liquid sample and direct the liquid sample to the electrode; An electrochemical detection device comprising:

2. The device of claim 1 , wherein the inorganic compound comprises a metal oxide including one or more of copper oxide, cobalt oxide, nickel oxide, iron oxide, or zinc oxide.

3. 3. The device of claim 1, further comprising a pH control system disposed adjacent to the plurality of electrodes configured to control the acidity / basicity of at least a region surrounding the functionalized electrode.

4. 4. The device of claim 3, wherein the plurality of electrodes comprises at least a working electrode, a counter electrode, and a reference electrode, and the pH control system is disposed adjacent to the working electrode.

5. 5. The device of claim 3 or 4, wherein the pH control system comprises a set of pH control electrodes.

6. 6. The device of claim 5, wherein the set of pH-control electrodes comprises a pH-sensing electrode and an active pH-control electrode.

7. 7. The device of claim 6, wherein the pH sensing electrode comprises an ion-selective detector or an ion-sensitive extended gate electrode arranged to allow electronic reading of the measured pH value.

8. 8. The device of claim 6 or 7, wherein the active pH-controlling electrode comprises a quinone-functionalized electrode configured to electrochemically conduct electrons or protons around at least the functionalized electrode.

9. 8. The device of claim 6 or 7, wherein the active pH control electrode is configured to act as a controlled release valve for an alkalinity source stored on the device.

10. An apparatus according to any one of claims 3 to 9, wherein the pH control system is configured to communicate with and be controlled by an electronic reader implementing a predetermined pH calibration algorithm.

11. The device of any preceding claim, wherein each of the plurality of electrodes extends into an electrical connection pad configured to interface with the electronic reader.

12. 12. The device of claim 1, wherein the plurality of electrodes comprises at least a working electrode, a counter electrode, and a reference electrode, the plurality of electrodes being arranged such that upon application of a potential between the working electrode and the reference electrode, a current is measured via the counter electrode.

13. The device of claim 12 , wherein the functionalized electrode is the working electrode on which the catalyst is deposited.

14. A device according to any preceding claim, wherein the hydrophilic channel is formed from paper.

15. The device of any one of claims 1 to 14, wherein the hydrophilic channels are formed photolithographically in a dry film photoresist.

16. 16. The device of any one of claims 1 to 15, wherein the hydrophilic channel is formed with a surface micropattern configured to promote spreading of the liquid sample.

17. The apparatus of any preceding claim, wherein the substrate comprises a printed circuit board.

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