A micro-volume pH sensor, its manufacturing method, and pH detection device

Abstract

This invention provides a micro-volume pH sensor, its manufacturing method, and a pH detection device. The pH sensor includes a substrate layer and a cover layer covering the surface of the substrate layer. A groove is formed on the surface of the cover layer facing the substrate layer. The surface of the groove, after being covered by the substrate layer, forms a microfluidic channel. A working electrode, a counter electrode, and a reference electrode are disposed on the surface of the substrate layer extending into the microfluidic channel. The working electrode includes a substrate electrode and a first electrode layer covering the surface of the substrate electrode. The counter electrode includes a substrate electrode and a second electrode layer covering the surface of the substrate electrode. The reference electrode includes a substrate electrode. The micro-volume pH sensor provided by this invention has a Nernst constant close to the theoretically calculated value, enabling accurate pH detection of small volumes of solution, and exhibits strong stability.

Description

Technical Field

[0001] This invention belongs to the field of pH detection technology, and relates to a micro-volume pH sensor, and more particularly to a micro-volume pH sensor, its manufacturing method and pH detection device. Background Technology

[0002] Currently, widely available pH detection methods primarily employ pH test strips, glass acid-base probes, and pH indicators. pH test strips and indicators mainly rely on color changes, allowing for subjective judgment; however, this change is determined by human perception, and their sensitivity is only 0.1 pH. On the other hand, while glass acid-base probes possess good sensitivity (reaching 0.01 pH), they are extremely fragile and cannot be used continuously in complex and harsh environments.

[0003] In many scenarios, researchers and certain specific situations require the ability to accurately measure the pH range of solutions or bodily fluids in very small volumes (20–100 μL). However, among almost all existing pH detection methods and machines on the market and in academia, there is no stable pH sensor with good performance for small volumes.

[0004] CN109507253A discloses an iridium oxide composite electrode, comprising an iridium wire and an iridium oxide layer formed on the surface of the iridium wire, wherein the iridium oxide layer is composed of 60%–65% iridium dioxide and 35%–40% iridium trioxide. The invention also provides a method for preparing the above-mentioned iridium oxide composite electrode, including pretreatment, activation treatment, sintering treatment, and water cooling treatment. The activation treatment step includes first activating the clean iridium wire with dilute hydrochloric acid, followed by washing and drying to obtain the activated iridium wire. The sintering treatment step includes first soaking the activated iridium wire in sodium hydroxide solution, followed by high-temperature sintering to obtain the sintered iridium wire. The invention also provides a pH sensor using the above-mentioned iridium oxide composite electrode. The above-mentioned iridium oxide composite electrode has good consistency and stability, resulting in a pH sensor with good stability and sensitivity. Furthermore, the preparation method is simple and low-cost. However, this iridium oxide composite electrode is difficult to stably detect solutions of very small volumes.

[0005] CN112903774A discloses an all-solid-state pH sensor and its preparation method, belonging to the field of pH sensor technology. The all-solid-state pH sensor of this invention includes an electrode protective housing. Inside the electrode protective housing are a pH sensor fixed by an encapsulation material, as well as sealing and encapsulation materials for sealing, and a protective cover at the lower end. The pH sensor includes an all-solid-state iridium oxide pH-responsive electrode and an all-solid-state Ag / AgX reference electrode. The all-solid-state iridium oxide pH-responsive electrode includes an iridium metal core and an iridium oxide film wrapped around the outer surface of the iridium metal core. The iridium oxide film is prepared by a high-temperature thermal oxidation method. The all-solid-state iridium oxide pH-responsive electrode and the all-solid-state Ag / AgX reference electrode are respectively connected to wires. This sensor device has the characteristics of high pressure resistance, high stability, and small size, and can be applied to deep-sea high-pressure environments. However, this all-solid-state pH sensor still has difficulty in stably detecting solutions of very small volumes.

[0006] Existing pH sensors all have certain drawbacks, including difficulty in stably and accurately detecting the pH of solutions with small volumes. Therefore, it is crucial to develop and design a novel micro-volume pH sensor, its manufacturing method, and a pH detection device. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a micro-volume pH sensor, its manufacturing method, and a pH detection device. The micro-volume pH sensor provided by the present invention has a Nernst constant close to the theoretically calculated value, enabling accurate pH detection of small volumes of solution, and exhibits strong stability. The pH sensor also has the advantages of low manufacturing cost, high portability, and ease of large-scale deployment.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a micro-volume pH sensor, the pH sensor comprising a base layer and a cover layer covering the surface of the base layer, the cover layer having a groove on the surface facing the base layer, the surface of the groove forming a microfluidic channel after being covered by the base layer, and the surface of the base layer having a working electrode, a counter electrode and a reference electrode extending into the microfluidic channel.

[0010] The working electrode includes a base electrode and a first electrode layer covering the surface of the base electrode; the counter electrode includes a base electrode and a second electrode layer covering the surface of the base electrode; and the reference electrode includes a base electrode.

[0011] The micro-volume pH sensor provided by this invention has a Nernst constant close to the theoretically calculated value, enabling accurate pH detection of small volumes of solution and exhibiting strong stability. The pH sensor also has the advantages of low manufacturing cost, high portability, and ease of large-scale deployment.

[0012] Preferably, the substrate layer comprises a silicon wafer substrate.

[0013] Preferably, the covering layer comprises a polydimethylsiloxane layer.

[0014] Preferably, the surface of the substrate layer is further covered with a silicon dioxide layer.

[0015] Preferably, the thickness of the silicon dioxide layer is 100-200 nm, for example, it can be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] Preferably, a titanium layer is disposed between the silicon dioxide layer and the working electrode, counter electrode and reference electrode.

[0017] Preferably, the thickness of the titanium layer is 12 to 40 nm, for example, it can be 12 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 27 nm, 29 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm or 40 nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] Preferably, the first electrode layer comprises an iridium dioxide layer.

[0019] Preferably, the thickness of the iridium dioxide layer is 150-250 nm, for example, it can be 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm or 250 nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] Preferably, the second electrode layer comprises a cobalt hydroxide layer.

[0021] Preferably, the thickness of the cobalt hydroxide layer is 150-250 nm, for example, it can be 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm or 250 nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] Preferably, the base electrode comprises a gold electrode or a platinum electrode.

[0023] Preferably, the thickness of the substrate electrode is 120–400 nm, for example, it can be 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm, 390 nm or 400 nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] In a second aspect, the present invention provides a method for manufacturing the pH sensor described in the first aspect, the method comprising:

[0025] Three substrate electrodes are prepared on the surface of the substrate layer to obtain a cover layer with grooves on the surface. The side surface of the cover layer with grooves is attached to the side surface of the substrate layer where the substrate electrodes are disposed, and the substrate electrodes extend into the grooves. A first electrode layer and a second electrode layer are sequentially electrochemically deposited on the surfaces of the two substrate electrodes to obtain a pH sensor.

[0026] The manufacturing method of the pH sensor provided by this invention is relatively simple, easy to operate, and has low requirements for production equipment.

[0027] Preferably, the method for fabricating three substrate electrodes on the surface of the substrate layer includes forward photolithography.

[0028] Preferably, the forward photolithography includes: forming a silicon dioxide layer on the surface of the substrate layer by dry etching, depositing a hexamethyldisilazane layer on the silicon dioxide layer and baking it, then spin-coating a forward photosensitive material onto the surface of the baked hexamethyldisilazane layer; covering the surface of the forward photosensitive material with a mask having three through holes, irradiating with ultraviolet light to wash away the forward photosensitive material not covered by the mask, removing the mask, and then removing the hexamethyldisilazane layer and residual forward photosensitive material in the areas not covered by the mask by oxygen plasma treatment; then filling the pits formed after ultraviolet light irradiation and oxygen plasma treatment by electron beam deposition of gold or platinum, and then washing away the hexamethyldisilazane layer and forward photosensitive material on the surface of the silicon dioxide layer, forming three base electrodes on the surface of the substrate layer.

[0029] In this invention, the purpose of baking after depositing a hexamethyldisilazane layer on a silicon dioxide layer is to increase the adhesion of subsequent photosensitive materials.

[0030] Preferably, the dry etching method includes treating the substrate layer with oxygen at a flow rate of 15-25 sccm at 1000-1200°C for 4-6 hours.

[0031] The dry etching method described in this invention is performed at 1000–1200°C, for example, 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, 1120°C, 1140°C, 1160°C, 1180°C, or 1200°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The oxygen flow rate used in the dry etching method described in this invention is 15 to 25 sccm, for example, it can be 15 sccm, 16 sccm, 17 sccm, 18 sccm, 19 sccm, 20 sccm, 21 sccm, 22 sccm, 23 sccm, 24 sccm or 25 sccm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the baking temperature is 120-130°C and the baking time is 2-8 minutes.

[0034] The baking temperature described in this invention is 120-130°C, for example, 120°C, 125°C or 130°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] The baking time described in this invention is 2 to 8 minutes, for example, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes or 8 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the spin coating includes a first spin coating of a first positive photosensitive material and a second spin coating of a second positive photosensitive material.

[0037] Preferably, the first spin coating includes: spin coating at a speed of 80-120 rpm / s for 2-8 seconds, and then spin coating at a speed of 2500-3500 rpm / s for 30-45 seconds.

[0038] In this invention, the first spin coating includes spin coating for 2 to 8 seconds at a speed of 80 to 120 rpm / s. The spin coating speed can be, for example, 80 rpm / s, 90 rpm / s, 100 rpm / s, 110 rpm / s or 120 rpm / s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] In this invention, the first spin coating includes spin coating at a speed of 80 to 120 rpm / s for 2 to 8 seconds. The spin coating time can be, for example, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, or 8 seconds, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In this invention, the first spin coating involves spin coating at a speed of 2500 to 3500 rpm / s for 30 to 45 seconds. The spin coating speed can be, for example, 2500 rpm / s, 2600 rpm / s, 2700 rpm / s, 2800 rpm / s, 2900 rpm / s, 3000 rpm / s, 3100 rpm / s, 3200 rpm / s, 3300 rpm / s, 3400 rpm / s, or 3500 rpm / s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In this invention, the first spin coating includes spin coating at a speed of 2500 to 3500 rpm / s for 30 to 45 seconds. The spin coating time can be, for example, 30 seconds, 32 seconds, 34 seconds, 36 seconds, 38 seconds, 40 seconds, 42 seconds, 44 seconds or 45 seconds, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the first positive photosensitive material includes LOR10A.

[0043] Preferably, the second spin coating includes: spin coating at a speed of 80-120 rpm / s for 2-8 seconds, and then spin coating at a speed of 2500-3500 rpm / s for 30-45 seconds.

[0044] In this invention, the second spin coating includes spin coating at a speed of 80 to 120 rpm / s for 2 to 8 seconds. The spin coating time can be, for example, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, or 8 seconds, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this invention, the second spin coating involves spin coating for 30 to 45 seconds at a speed of 2500 to 3500 rpm / s. The spin coating speed can be, for example, 2500 rpm / s, 2600 rpm / s, 2700 rpm / s, 2800 rpm / s, 2900 rpm / s, 3000 rpm / s, 3100 rpm / s, 3200 rpm / s, 3300 rpm / s, 3400 rpm / s, or 3500 rpm / s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In this invention, the second spin coating involves spin coating for 30 to 45 seconds at a speed of 2500 to 3500 rpm / s. The spin coating speed can be, for example, 2500 rpm / s, 2600 rpm / s, 2700 rpm / s, 2800 rpm / s, 2900 rpm / s, 3000 rpm / s, 3100 rpm / s, 3200 rpm / s, 3300 rpm / s, 3400 rpm / s, or 3500 rpm / s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] In this invention, the second spin coating includes spin coating at a speed of 2500 to 3500 rpm / s for 30 to 45 seconds. The spin coating time can be, for example, 30 seconds, 32 seconds, 34 seconds, 36 seconds, 38 seconds, 40 seconds, 42 seconds, 44 seconds or 45 seconds, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the second positive photosensitizing material includes Shipley 1805.

[0049] Preferably, the method for preparing the grooved cover layer includes: obtaining a silicon wafer mold for preparing a grooved cover layer by negative photolithography, and then using the silicon wafer mold to prepare the grooved cover layer.

[0050] Preferably, the electrochemical deposition includes: obtaining a first electrode layer through a first electrode deposition, and then obtaining a second electrode layer through a second electrode deposition.

[0051] Preferably, the first electrodeposition includes: injecting iridium electrolyte into a microfluidic channel formed after the surface of the groove is covered by the substrate layer, and then performing the first electrodeposition.

[0052] The main component of the iridium electrolyte in this invention is iridium tetrachloride. The specific preparation method includes: dissolving 75 mg of IrCl4·xH2O in 50 mL of distilled water and stirring for 10 min; then adding 0.5 mL of 30% hydrogen peroxide and stirring for another 10 min; then adding 365 mg of potassium oxalate and stirring for another 10 min; then adjusting the pH of the solution to 10.5 by adding a small amount of anhydrous potassium carbonate; finally, heating the pH-adjusted solution at 90 °C for 10 min to obtain the iridium electrolyte.

[0053] Preferably, the current density of the first electrodeposition is 15–25 A / m. 2 For example, it could be 15A / m 2 16A / m 2 17A / m 2 18A / m 2 19A / m 2 20A / m 2 21A / m 2 22A / m 2 23A / m 2 24A / m 2 Or 25A / m 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0054] Preferably, the first electrodeposition time is 120 to 180 s, for example, it can be 120 s, 130 s, 140 s, 150 s, 160 s, 170 s or 180 s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the second electrodeposition includes: injecting cobalt electrolyte into a microfluidic channel formed after the surface of the groove is covered by the substrate layer, and then performing the second electrodeposition.

[0056] Preferably, the current density of the second electrodeposition is 25–35 A / m. 2 For example, it could be 25A / m 2 26A / m 2 27A / m 2 28A / m 2 29A / m 2 30A / m 2 31A / m 2 32A / m2 33A / m 2 34A / m 2 Or 35A / m 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0057] Preferably, the second electrodeposition time is 40 to 80 s, for example, it can be 40 s, 45 s, 50 s, 55 s, 60 s, 65 s, 70 s, 75 s or 80 s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Thirdly, the present invention provides a pH detection device, the pH detection device comprising the pH sensor described in the first aspect and a syringe pump connected to the pH sensor.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The pH sensor for small volumes provided by the present invention has a Nernst constant close to the theoretically calculated value, which can accurately detect the pH of a solution with a small volume and has strong stability; the pH sensor also has the advantages of low manufacturing cost, strong portability and easy large-scale promotion and use.

[0061] (2) The manufacturing method of the pH sensor provided by the present invention is relatively simple, easy to operate and has low requirements for production equipment. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of a micro-volume pH sensor according to a specific embodiment of the present invention.

[0063] Figure 2 This is a schematic diagram of the pH sensor in the microfluidic channel in a specific embodiment of the present invention.

[0064] Figure 3 This is a schematic diagram of the pH detection device in a specific embodiment of the present invention.

[0065] Figure 4 This is a curve showing the stability test results of the pH sensor in Example 1 of the present invention over a period of 7 weeks.

[0066] Among them, 1-base layer; 2-capping layer; 3-microfluidic channel; 4-base electrode; 5-first electrode layer; 6-second electrode layer; 7-syringe pump. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0068] In one specific implementation, such as Figure 1 As shown, this invention provides a micro-volume pH sensor, which includes a substrate layer 1 and a cover layer 2 covering the surface of the substrate layer 1. The cover layer 2 has a groove on its surface facing the substrate layer 1. The surface of the groove, after being covered by the substrate layer 1, forms a microfluidic channel 3. Figure 2 As shown, the surface of the substrate layer 1 is provided with a working electrode, a counter electrode, and a reference electrode extending into the microfluidic channel 3;

[0069] The working electrode includes a base electrode 4 and a first electrode layer 5 covering the surface of the base electrode 4; the counter electrode includes a base electrode 4 and a second electrode layer 6 covering the surface of the base electrode 4; and the reference electrode includes a base electrode 4.

[0070] The micro-volume pH sensor provided by this invention has a Nernst constant close to the theoretically calculated value, enabling accurate pH detection of small volumes of solution and exhibiting strong stability. The pH sensor also has the advantages of low manufacturing cost, high portability, and ease of large-scale deployment.

[0071] Furthermore, the substrate layer 1 includes a silicon wafer substrate.

[0072] Furthermore, the cover layer 2 includes a polydimethylsiloxane layer.

[0073] Furthermore, the surface of the substrate layer 1 is also covered with a silicon dioxide layer.

[0074] Furthermore, the thickness of the silicon dioxide layer is 100–200 nm.

[0075] Furthermore, a titanium layer is disposed between the silicon dioxide layer and the working electrode, counter electrode, and reference electrode.

[0076] Furthermore, the thickness of the titanium layer is 12–40 nm.

[0077] Furthermore, the first electrode layer 5 includes an iridium dioxide layer.

[0078] Furthermore, the thickness of the iridium dioxide layer is 150–250 nm.

[0079] Furthermore, the second electrode layer 6 includes a cobalt hydroxide layer.

[0080] Furthermore, the thickness of the cobalt hydroxide layer is 150–250 nm.

[0081] Furthermore, the base electrode 4 includes a gold electrode or a platinum electrode.

[0082] Furthermore, the thickness of the base electrode 4 is 120–400 nm.

[0083] In another specific implementation, such as Figure 3 As shown, the present invention provides a pH detection device, which includes the pH sensor described in the first aspect and a syringe pump 7 connected to the pH sensor.

[0084] Example 1

[0085] This embodiment provides a micro-volume pH sensor, which includes a silicon wafer substrate and a polydimethylsiloxane layer covering the surface of the silicon wafer substrate. The polydimethylsiloxane layer has a groove on the surface facing the silicon wafer substrate, and the surface of the groove is covered by the silicon wafer substrate to form a microfluidic channel.

[0086] The surface of the silicon wafer substrate is also covered with a silicon dioxide layer with a thickness of 120 nm. A working electrode, a counter electrode, and a reference electrode extending into the microfluidic channel are disposed on the surface of the silicon dioxide layer on the silicon wafer substrate. A 35 nm titanium layer is disposed between the silicon dioxide layer and the working electrode, the counter electrode, and the reference electrode.

[0087] The working electrode includes a gold electrode with a thickness of 350 nm and an iridium dioxide layer with a thickness of 200 nm covering the surface of the gold electrode; the counter electrode includes a gold electrode with a thickness of 350 nm and a cobalt hydroxide layer with a thickness of 200 nm covering the surface of the gold electrode; and the reference electrode includes a gold electrode with a thickness of 350 nm.

[0088] The method for manufacturing the pH sensor includes:

[0089] A silicon dioxide layer is formed on the surface of a silicon substrate using dry etching. A hexamethyldisilazane layer is then deposited on the silicon dioxide layer and baked. Subsequently, LOR10A and Shipley1805 are spin-coated sequentially onto the baked hexamethyldisilazane layer. A mask with three through-holes is used to cover the surface of the Shipley1805. Ultraviolet light irradiation is used to wash away the LOR10A and Shipley1805 not covered by the mask. The mask is removed, and oxygen plasma treatment is used to remove the hexamethyldisilazane layer and residual LOR10A and Shipley1805 from the areas not covered by the mask. Gold is then deposited by electron beam deposition to fill the pits formed after ultraviolet light irradiation and oxygen plasma treatment. After washing away the hexamethyldisilazane layer, LOR10A, and Shipley1805 from the surface of the silicon dioxide layer, three gold electrodes are formed on the surface of the silicon substrate.

[0090] A silicon wafer mold for preparing a polydimethylsiloxane layer with grooves on its surface is obtained by negative photolithography, and then the polydimethylsiloxane layer with grooves is prepared by using the silicon wafer mold.

[0091] The grooved side of the polydimethylsiloxane layer is attached to the side of the silicon substrate on which the gold electrode is located, with the gold electrode extending into the groove; iridium electrolyte is injected into the microfluidic channel formed after the surface of the groove is covered by the silicon substrate, and then the flow rate is increased to 20 A / cm. 2 A first electrodeposition was performed at a current density of 150 s to obtain an iridium dioxide layer; then, cobalt electrolyte was injected into the microfluidic channel formed after the surface of the groove was covered by the silicon wafer substrate, and the electrodeposition was carried out at 31 A / cm². 2 A second electrodeposition of cobalt hydroxide was performed at a current density for 60 seconds to obtain a pH sensor.

[0092] The pH sensor was subjected to stability testing, and the stability test results over a 7-week period are shown in the curve below. Figure 4 As shown (the absolute value of the Nernst constant has been taken), it can be found that the pH sensor has results close to the theoretically calculated Nernst constant over a period of 7 weeks, indicating that the pH sensor has strong stability.

[0093] Example 2

[0094] This embodiment provides a micro-volume pH sensor, which includes a silicon wafer substrate and a polydimethylsiloxane layer covering the surface of the silicon wafer substrate. The polydimethylsiloxane layer has a groove on the surface facing the silicon wafer substrate, and the surface of the groove is covered by the silicon wafer substrate to form a microfluidic channel.

[0095] The surface of the silicon wafer substrate is also covered with a silicon dioxide layer with a thickness of 200 nm. A working electrode, a counter electrode, and a reference electrode extending into the microfluidic channel are disposed on the surface of the silicon dioxide layer on the silicon wafer substrate. A 12 nm titanium layer is disposed between the silicon dioxide layer and the working electrode, the counter electrode, and the reference electrode.

[0096] The working electrode includes a platinum electrode with a thickness of 120 nm and an iridium dioxide layer with a thickness of 120 nm covering the surface of the platinum electrode; the counter electrode includes a platinum electrode with a thickness of 120 nm and a cobalt hydroxide layer with a thickness of 150 nm covering the surface of the platinum electrode; and the reference electrode includes a platinum electrode with a thickness of 120 nm.

[0097] The method for manufacturing the pH sensor includes:

[0098] A silicon dioxide layer is formed on the surface of a silicon substrate using dry etching. A hexamethyldisilazane layer is then deposited on the silicon dioxide layer and baked. Subsequently, LOR10A and Shipley1805 are spin-coated sequentially onto the baked hexamethyldisilazane layer. A mask with narrow channels is used to cover the surface of the Shipley1805. Ultraviolet light irradiation is used to wash away the LOR10A and Shipley1805 not covered by the mask. The mask is removed, and oxygen plasma treatment is used to remove the hexamethyldisilazane layer and residual LOR10A and Shipley1805 from the areas not covered by the mask. Platinum is then deposited by electron beam deposition to fill the pits formed after ultraviolet light irradiation and oxygen plasma treatment. After washing away the hexamethyldisilazane layer, LOR10A, and Shipley1805 from the surface of the silicon dioxide layer, three platinum electrodes are formed on the surface of the silicon substrate.

[0099] A silicon wafer mold for preparing a polydimethylsiloxane layer with grooves on its surface is obtained by negative photolithography, and then the polydimethylsiloxane layer with grooves is prepared by using the silicon wafer mold.

[0100] The grooved side of the polydimethylsiloxane layer is attached to the side of the silicon substrate on which a platinum electrode is located, with the platinum electrode extending into the groove. Iridium electrolyte is then injected into the microfluidic channel formed after the surface of the groove is covered by the silicon substrate, at a speed of 15 A / cm. 2 A first electrodeposition was performed at a current density of 120 s to obtain an iridium dioxide layer; then, cobalt electrolyte was injected into the microfluidic channel formed after the surface of the groove was covered by the silicon wafer substrate, and the electrodeposition was carried out at 25 A / cm². 2 A second electrodeposition of cobalt hydroxide was performed at a current density for 40 seconds to obtain a pH sensor.

[0101] Example 3

[0102] This embodiment provides a micro-volume pH sensor, which includes a silicon wafer substrate and a polydimethylsiloxane layer covering the surface of the silicon wafer substrate. The polydimethylsiloxane layer has a groove on the surface facing the silicon wafer substrate, and the surface of the groove is covered by the silicon wafer substrate to form a microfluidic channel.

[0103] The surface of the silicon wafer substrate is also covered with a silicon dioxide layer with a thickness of 100 nm. A working electrode, a counter electrode, and a reference electrode extending into the microfluidic channel are disposed on the surface of the silicon dioxide layer on the silicon wafer substrate. A 40 nm titanium layer is disposed between the silicon dioxide layer and the working electrode, the counter electrode, and the reference electrode.

[0104] The working electrode includes a gold electrode with a thickness of 400 nm and an iridium dioxide layer with a thickness of 250 nm covering the surface of the gold electrode; the counter electrode includes a gold electrode with a thickness of 400 nm and a cobalt hydroxide layer with a thickness of 250 nm covering the surface of the gold electrode; and the reference electrode includes a gold electrode with a thickness of 400 nm.

[0105] The method for manufacturing the pH sensor includes:

[0106] A silicon dioxide layer is formed on the surface of a silicon substrate using dry etching. A hexamethyldisilazane layer is then deposited on the silicon dioxide layer and baked. Subsequently, LOR10A and Shipley1805 are spin-coated sequentially onto the baked hexamethyldisilazane layer. A mask with three through-holes is used to cover the surface of the Shipley1805. Ultraviolet light irradiation is used to wash away the LOR10A and Shipley1805 not covered by the mask. The mask is removed, and oxygen plasma treatment is used to remove the hexamethyldisilazane layer and residual LOR10A and Shipley1805 from the areas not covered by the mask. Gold is then deposited by electron beam deposition to fill the pits formed after ultraviolet light irradiation and oxygen plasma treatment. After washing away the hexamethyldisilazane layer, LOR10A, and Shipley1805 from the surface of the silicon dioxide layer, three gold electrodes are formed on the surface of the silicon substrate.

[0107] A silicon wafer mold for preparing a polydimethylsiloxane layer with grooves on its surface is obtained by negative photolithography, and then the polydimethylsiloxane layer with grooves is prepared by using the silicon wafer mold.

[0108] The grooved side of the polydimethylsiloxane layer is attached to the side of the silicon substrate where a gold electrode is located, with the gold electrode extending into the groove. Iridium electrolyte is then injected into the microfluidic channel formed after the surface of the groove is covered by the silicon substrate, and the solution is applied at 25 A / cm. 2A first electrodeposition was performed at a current density of 180 s to obtain an iridium dioxide layer; then, cobalt electrolyte was injected into the microfluidic channel formed after the surface of the groove was covered by the silicon wafer substrate, and the electrodeposition was carried out at 35 A / cm. 2 A second electrodeposition of cobalt hydroxide was performed at a current density for 80 seconds to obtain a pH sensor.

[0109] Example 4

[0110] This embodiment provides a micro-volume pH sensor. Except for omitting the silicon dioxide layer covering the surface of the silicon wafer substrate, the working electrode, counter electrode, and reference electrode are directly disposed on the surface of the silicon wafer substrate extending into the microfluidic channel. Otherwise, it is the same as in Embodiment 1.

[0111] Example 5

[0112] This embodiment provides a micro-volume pH sensor, which is the same as in Embodiment 1 except that the titanium layer between the silicon dioxide layer and the working electrode, counter electrode and reference electrode is omitted.

[0113] Example 6

[0114] This embodiment provides a micro-volume pH sensor, which is identical to Embodiment 1 except that the working electrode includes a gold electrode with a thickness of 350 nm and an iridium dioxide layer with a thickness of 60 nm covering the surface of the gold electrode.

[0115] Example 7

[0116] This embodiment provides a micro-volume pH sensor, which is identical to Embodiment 1 except that the working electrode includes a gold electrode with a thickness of 350 nm and an iridium dioxide layer with a thickness of 350 nm covering the surface of the gold electrode.

[0117] Example 8

[0118] This embodiment provides a micro-volume pH sensor, which is identical to Embodiment 1 except that the counter electrode includes a gold electrode with a thickness of 350 nm and a cobalt hydroxide layer with a thickness of 60 nm covering the surface of the gold electrode.

[0119] Example 9

[0120] This embodiment provides a micro-volume pH sensor, which is the same as in Embodiment 1 except that the counter electrode includes a gold electrode with a thickness of 350 nm and a cobalt hydroxide layer with a thickness of 350 nm covering the surface of the gold electrode.

[0121] Comparative Example 1

[0122] This comparative example provides a micro-volume pH sensor, which is identical to Example 1 except that the working electrode includes a gold electrode with a thickness of 350 nm and an iridium dioxide layer with a thickness of 200 nm covering the surface of the gold electrode, the counter electrode includes a gold electrode with a thickness of 350 nm, and the reference electrode includes a gold electrode with a thickness of 350 nm.

[0123] Comparative Example 2

[0124] This comparative example provides a micro-volume pH sensor, which is identical to Example 1 except that the working electrode includes a gold electrode with a thickness of 350 nm, the counter electrode includes a gold electrode with a thickness of 350 nm, and the reference electrode includes a gold electrode with a thickness of 350 nm.

[0125] The Nernst constants of the pH sensors in Examples 1-9 and Comparative Examples 1 and 2 were tested at 25°C using a three-electrode method. The obtained Nernst constants are shown in Table 1.

[0126] Table 1

[0127] Nernst constant (mV / pH) Example 1 -51.49 Example 2 -47.25 Example 3 -49.83 Example 4 -20.05 Example 5 -50.50 Example 6 -9.70 Example 7 -45.64 Example 8 -35.76 Example 9 -18.36 Comparative Example 1 -11.13 Comparative Example 2 -1.6

[0128] From Table 1, we can obtain:

[0129] (1) The micro-volume pH sensor provided by the present invention has a Nernst constant that is close to the standard calculated value, which can accurately detect the pH of a small volume of solution and has strong stability.

[0130] (2) By comparing Example 1 and Example 4, it can be seen that the silicon dioxide layer covering the surface of the silicon wafer substrate in this invention will affect the performance of the pH sensor. When the silicon dioxide layer covering the surface of the silicon wafer substrate is removed, the performance of the pH sensor will be reduced. This is because the semiconductor performance of the silicon wafer substrate is not as good as that of silicon dioxide.

[0131] (3) By comparing Example 1 and Example 5, it can be seen that the titanium layer disposed between the silicon dioxide layer and the working electrode, counter electrode and reference electrode in this invention will affect the performance of the pH sensor. When the titanium layer is removed, the performance of the pH sensor decreases. This is because the titanium layer can enhance the adhesion of gold, thereby enhancing the stability of the pH sensor.

[0132] (4) By comparing Example 1 with Examples 6 and 7, it can be seen that the thickness of the iridium dioxide layer in this invention affects the performance of the pH sensor. When the thickness of the iridium dioxide layer is too small, the Nernst constant of the pH sensor will deviate significantly from the standard calculated value. This is because the iridium dioxide layer is too thin and cannot provide enough reaction sites to bind with hydrogen ions. When the thickness of the iridium dioxide layer is too large, the Nernst constant of the pH sensor will deviate significantly from the standard calculated value. This is because the internal pressure of the channel increases and the iridium dioxide signal is greatly affected.

[0133] (5) By comparing Example 1 with Examples 8 and 9, it can be seen that the thickness of the cobalt hydroxide layer in this invention affects the performance of the pH sensor. When the thickness of the cobalt hydroxide layer is too small, the Nernst constant of the pH sensor will deviate significantly from the standard calculated value. This is because the cobalt hydroxide layer cannot provide a good electron transfer pathway when the thickness is too small. When the thickness of the cobalt hydroxide layer is too large, the Nernst constant of the pH sensor will deviate significantly from the standard calculated value. This is because the internal pressure of the microfluidic increases, causing it to deviate from the standard value.

[0134] (6) By comparing Example 1 and Comparative Example 1, it can be seen that when the counter electrode only includes a gold electrode with a thickness of 350 nm, the Nernst constant of the pH sensor deviates significantly from the standard calculated value. This is because the counter electrode cannot provide a good electron transfer pathway.

[0135] (7) By comparing Example 1 and Comparative Example 2, it can be seen that when the working electrode, counter electrode and reference electrode all consist of only gold electrodes, the Nernst constant of the pH sensor deviates significantly from the standard calculated value. This is because there is no material on the electrode surface that provides reaction sites for hydrogen ions.

[0136] In summary, the micro-volume pH sensor provided by this invention has a Nernst constant close to the theoretically calculated value, enabling accurate pH detection of small volumes of solution and exhibiting strong stability. Furthermore, the pH sensor has advantages such as low manufacturing cost, high portability, and ease of large-scale deployment. The manufacturing method of the pH sensor provided by this invention is relatively simple, easy to operate, and requires less sophisticated production equipment.

[0137] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A micro-volume pH sensor characterized in that, The pH sensor comprises a substrate layer and a cover layer covering the surface of the substrate layer, the cover layer is provided with a groove towards the surface of the substrate layer, the surface of the groove is covered by the substrate layer to form a microfluidic channel, the surface of the substrate layer is provided with a working electrode, a counter electrode and a reference electrode extending into the microfluidic channel; The working electrode comprises a substrate electrode and a first electrode layer covering the surface of the substrate electrode, the counter electrode comprises a substrate electrode and a second electrode layer covering the surface of the substrate electrode, and the reference electrode comprises a substrate electrode; The substrate electrode comprises a gold electrode or a platinum electrode, the first electrode layer comprises an iridium dioxide layer, and the second electrode layer comprises a cobalt hydroxide layer; The substrate layer comprises a silicon wafer substrate; The cover layer comprises a polydimethylsiloxane layer; The surface of the substrate layer is further covered with a silicon dioxide layer.

2. The pH sensor of claim 1, wherein, The thickness of the silicon dioxide layer is 100-200 nm.

3. The pH sensor of claim 1, wherein, Titanium layers are arranged between the silicon dioxide layer and the working electrode, the counter electrode and the reference electrode.

4. The pH sensor of claim 3, wherein, The thickness of the titanium layer is 12-40 nm.

5. The pH sensor of claim 1, wherein, The thickness of the iridium dioxide layer is 150-250 nm.

6. The pH sensor of claim 1, wherein, The thickness of the cobalt hydroxide layer is 150-250 nm.

7. The pH sensor of claim 1, wherein, The thickness of the substrate electrode is 120-400 nm.

8. A method of manufacturing the pH sensor according to any one of claims 1 to 7, characterized in that, The manufacturing method comprises: Three substrate electrodes are prepared on the surface of the substrate layer, a cover layer with a groove is prepared, the surface of the cover layer with the groove is attached to the surface of the substrate layer provided with the substrate electrodes, the substrate electrodes extend into the groove, a first electrode layer and a second electrode layer are sequentially deposited on the surfaces of the two substrate electrodes by electrochemical deposition to obtain a pH sensor.

9. The production method according to claim 8, wherein The method for preparing three substrate electrodes on the surface of the substrate layer comprises positive photoetching.

10. The manufacturing method according to claim 9, wherein The positive photoetching comprises: forming a silicon dioxide layer on the surface of the substrate layer by dry etching, baking after depositing a hexamethyldisilazane layer on the silicon dioxide layer, then spin-coating a positive photosensitive material on the surface of the baked hexamethyldisilazane layer; using a mask with three through holes to cover the surface of the positive photosensitive material, washing off the positive photosensitive material not covered by the mask by ultraviolet irradiation, removing the mask, and then removing the hexamethyldisilazane layer and residual positive photosensitive material in the area not covered by the mask by oxygen plasma treatment; filling the pits formed after the ultraviolet irradiation and oxygen plasma treatment by depositing gold or platinum by electron beam, then washing off the hexamethyldisilazane layer and the positive photosensitive material on the surface of the silicon dioxide layer, and forming three substrate electrodes on the surface of the substrate layer.

11. The manufacturing method according to claim 10, wherein The spin-coating comprises first spin-coating of a first positive photosensitive material and second spin-coating of a second positive photosensitive material.

12. The manufacturing method according to claim 8, wherein The method for preparing the cover layer with a groove comprises: obtaining a silicon wafer mold for preparing the cover layer with a groove by negative photoetching, and then using the silicon wafer mold to prepare the cover layer with a groove.

13. The manufacturing method according to claim 8, wherein The electrochemical deposition comprises: obtaining a first electrode layer by first electrodeposition, and obtaining a second electrode layer by second electrodeposition.

14. The manufacturing method according to claim 13, wherein The first electrodeposition comprises: injecting iridium electrolyte into the microfluidic channel formed after the surface of the groove is covered by the base layer, and then performing first electrodeposition.

15. The manufacturing method according to claim 13, wherein The first electrodeposition has a current density of 15-25 A / m 2 .

16. The manufacturing method according to claim 13, wherein The time of the first electrodeposition is 120-180s.

17. The manufacturing method according to claim 13, wherein The second electrodeposition comprises: injecting cobalt electrolyte into the microfluidic channel formed after the surface of the groove is covered by the base layer, and then performing second electrodeposition.

18. The manufacturing method according to claim 13, wherein The second electrodeposition has a current density of 25-35 A / m 2 .

19. The manufacturing method according to claim 13, wherein The time of the second electrodeposition is 40-80s.

20. A pH detecting device, characterized by The pH detection device comprises the pH sensor according to any one of claims 1-7 and a needle pump connected with the pH sensor.

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