A highly sensitive and fast-response pH sensor and its working method

Abstract

This invention discloses a highly sensitive and fast-response pH sensor and its working method, belonging to the field of sensor technology. The preparation method of the pH sensor includes: (1) preparing an initial device; (2) using 3,4-ethylenedioxythiophene and an ionic liquid as electrolytes, applying alternating current to the initial device, and electropolymerizing an organic semiconductor layer on the channel via of a microelectrode chip using alternating current deposition; (3) using platinum as the counter electrode and a standard calomel electrode as the reference electrode, using the gate of the device obtained in step (2) as the working electrode, and modifying the gate of the device obtained in step (2) with a PEDOT:BTB film, and obtaining the highly sensitive and fast-response pH sensor after modification. The method of this invention is simple and easy to implement. The pH sensor prepared has high sensitivity and short response time under a specific working method, and has broad application prospects in the field of wearable electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a highly sensitive and fast-response pH sensor and its working method. Background Technology

[0002] Organic electrochemical transistors (OECTs) are three-terminal devices based on organic semiconductors, widely used in label-free biosensing, such as the detection of dopamine, adrenaline, ascorbic acid, adenosine triphosphate (ATP), and cell activity. The working principle of OECTs is similar to that of neural synapses, and they can replace traditional electronic devices. Synapses are the links between neurons in complex networks, giving the brain advantages of high efficiency, low power consumption, and fault tolerance. With the help of sensory receptors, synapses and neurons convert environmental information (such as chemical and physical stimuli) into electrochemical signals for the peripheral nervous system and even the central nervous system, endowing humans with sensory and perceptual abilities. Because the organic semiconductors used in OECTs possess excellent ionic and electronic conductivity, they can form a large capacitance when using an electrolyte as the dielectric layer, thus effectively amplifying the sensing signal. Their ultra-low driving voltage, good mechanical flexibility, and biocompatibility make them of significant research value in the sensing of biological signals (including bioelectrical and biochemical signals).

[0003] An OECT typically consists of a source, drain, gate, gate dielectric, and an organic semiconductor channel layer. Driven by the gate voltage, ions in the electrolyte enter / exit the channel, thereby electrochemically oxidizing / reducing the doped organic semiconductor layer and drastically changing the current between the source and drain electrodes. This achieves modulation of the source and drain current signals by the gate voltage signal, which is the inherent signal amplification capability of the transistor. Small potential changes at the interface can lead to significant changes in the drain current.

[0004] Chinese patent document CN114674897A discloses a probe-type organic electrochemical transistor sensor for detecting pH values ​​in single cells. The sensor includes an electrolytic cell containing an electrolyte, a probe-type transistor and a probe-type gate inserted into the electrolyte at one end, the probe-type transistor being a micron-sized dual-pore capillary structure, each pore of the micron-sized dual-pore capillary structure having a conductive layer disposed therein, and an organic semiconductor thin film layer in contact with the conductive layer being disposed at the bottom end of the micron-sized dual-pore capillary structure; the probe-type gate is a nano-sized single-pore capillary structure, the pore of the nano-sized single-pore capillary structure being modified with a pH-sensitive functional layer.

[0005] Chinese patent document CN115656299A discloses a method for preparing a pH-sensitive OECT based on PEDOT:PSS, including the following steps: (1) preparation of sensing electrode: fabrication of gate electrode, and electrodeposition of PEDOT:BTB thin film on gate electrode surface by cyclic voltammetry; (2) preparation of test solution: using phosphate buffer containing KNO3 and KH2PO4 as pH reference solution, adding HCl and NaOH to prepare test solutions with different pH values, and finally adding KCl solution to adjust the conductivity of all pH solutions to 38±0.5mS / cm; (3) preparation of signal amplification chip: using MEMS process to prepare spare chip 1, which includes a microelectrode layer including source electrode, drain electrode, source electrode PAD, and drain electrode PAD; preparing an organic semiconductor layer on the surface of source electrode and drain electrode and in the gap between source electrode and drain electrode; assembling gate electrode and gate dielectric with source electrode, drain electrode and organic semiconductor layer.

[0006] However, the aforementioned existing technologies suffer from complex processes and the need for further improvement in sensor sensitivity. Summary of the Invention

[0007] This invention provides a method for preparing a highly sensitive and fast-response pH sensor. The method is simple and easy to implement. The pH sensor prepared by this method has high sensitivity and short response time under a specific working method, and has broad application prospects in the field of wearable electronic devices.

[0008] The specific technical solution adopted is as follows:

[0009] A method for preparing a highly sensitive and fast-response pH sensor includes the following steps:

[0010] (1) A substrate is provided, an insulating layer is deposited on the substrate, and an adhesion layer is deposited on the insulating layer to further adhere the source, drain and gate on the surface of the insulating layer. After the source, drain and gate are deposited, a microelectrode chip is prepared. A passivation layer is further coated on the surface of the microelectrode chip as an initial device. The microelectrode chip includes a rigid microelectrode chip or a flexible microelectrode chip, and a channel via is formed in the microelectrode chip.

[0011] (2) Using 3,4-ethylenedioxythiophene and ionic liquid as electrolytes, an alternating current is applied to the initial device, and an organic semiconductor layer is formed by electropolymerization on the channel via of the microelectrode chip using an alternating current deposition method.

[0012] (3) Using platinum as the counter electrode and a standard calomel electrode as the reference electrode, the gate of the device obtained in step (2) is used as the working electrode. The gate of the device obtained in step (2) is modified with a PEDOT:BTB film. After the modification is completed, the highly sensitive and fast-response pH sensor is obtained.

[0013] This invention utilizes alternating current deposition to prepare an organic semiconductor layer, and then further modifies the gate with a PEDOT:BTB film, which helps to improve the stability of the gate, simplify the preparation process, and produce a pH sensor with excellent performance.

[0014] Preferably, the substrate material is silicon wafer, silicon carbide, silicon nitride, or sapphire.

[0015] Preferably, the insulating layer material is silicon dioxide or polyimide.

[0016] Preferably, the adhesive layer material is titanium, chromium, nickel, or tungsten.

[0017] The source, drain, and gate materials are metals or conductive carbon materials; gold, silver, carbon nanotubes, graphene, graphyne, etc. are optionally selected.

[0018] Preferably, the passivation layer material is poly(p-dichlorotoluene), polyimide, benzocyclobutene, silicon dioxide, or silicon nitride.

[0019] More preferably, when the insulating layer material is silicon dioxide, the thickness of the insulating layer is 400-600 nm; when the insulating layer material is polyimide, the thickness of the insulating layer is 5-7 μm.

[0020] More preferably, the thickness of the passivation layer is 1-2 μm.

[0021] Preferably, in step (2), the ionic liquid includes 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tricyanomethane, or 1-butyl-3-methyltetrafluoroborate.

[0022] Preferably, in step (2), the ratio of 3,4-ethylenedioxythiophene to the ionic liquid is 10 mM: 0.4 ml to 0.5 ml.

[0023] Preferably, in step (3), a PBS buffer containing 3,4-ethylenedioxythiophene, bromothymol blue, and KNO3 is prepared. Platinum is used as the counter electrode, and a standard calomel electrode is used as the reference electrode. The gate of the device obtained in step (2) is used as the working electrode and connected to an electrochemical workstation. The gate is modified with a PEDOT:BTB film by a 0-1V frequency sweep.

[0024] The present invention also provides a highly sensitive and fast-response pH sensor prepared by the aforementioned method.

[0025] The present invention also provides a method for operating the aforementioned highly sensitive and fast-response pH sensor. Specifically, standard solutions with different pH values ​​are prepared and used as dielectric layers to measure the source-drain current of the highly sensitive and fast-response pH sensor as a function of the gate voltage. The gate voltage is further differentiated to obtain the corresponding transconductance curve. The optimal gate operating voltage is determined based on the intersection of the transconductance curves, so that the highly sensitive and fast-response pH sensor operates at the optimal gate operating voltage.

[0026] Preferably, the optimal gate operating voltage is set to V. G，i ±0.002V, where V G，i This represents the voltage at the intersection of the transconductance curves.

[0027] The optimal gate operating voltage in this invention is not related to the transconductance peak value g. m *The gate bias voltage V G (g m *) Instead of coinciding, the setting is based on the intersection of the transconductance curves, which can achieve higher sensitivity and eliminate g. m * and V G (g m *) The effect of different analyte concentrations on the performance of the calibration sensor.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The method of the present invention is simple, efficient and easy to implement. It uses AC electrodeposition to prepare organic semiconductor layers and cyclic voltammetry to modify the gate. The pH sensor prepared has high sensitivity and short response time under specific working methods and has broad application prospects in the field of wearable electronic devices.

[0030] (2) In practical applications, pH sensors based on OECT typically operate in a constant potential mode, with the gate operating voltage V... G Set to V G (g m *) is generally considered an optimal solution, while the highly sensitive and fast-response pH sensor provided by this invention has a gate operating voltage that is not related to the transconductance peak value g. m *The gate bias voltage V G (g m *) Instead of coinciding, the optimal gate operating voltage (V) is determined based on the intersection of the transconductance curves. G，i ±0.002V), after setting the operating voltage to the optimal gate operating voltage of this invention, g can be eliminated. m * and V G (g m*) The effect of analyte concentration fluctuations on the performance of the calibration sensor is greatly improved, significantly enhancing the sensitivity and response time of the pH sensor, achieving a sensitivity of 124 mV / pH and a response time as low as 8.75 ms. Attached Figure Description

[0031] Figure 1 Microscopic image of the highly sensitive and fast-response pH sensor prepared in Example 1;

[0032] Figure 2 The source-drain current I of the high-sensitivity, fast-response pH sensor in Example 1 DS With gate voltage V G A changing curve.

[0033] Figure 3 The high-sensitivity, fast-response pH sensor transconductance g in Example 1 m With gate voltage V G A changing curve. Detailed Implementation

[0034] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0035] Example 1

[0036] (1) Fabrication of flexible microelectrode chip: A silicon substrate is provided, and a 7 μm thick polyimide (PI) film is deposited on the substrate as an insulating layer. The photoresist NR9-1500PY is developed using RD6 developer. Then, a 30 nm thick titanium is sputtered as an adhesion layer. Then, a 100 nm thick gold is sputtered at the source, drain and gate respectively to prepare a flexible microelectrode chip. A 1 μm thick polyimide (PI) film is further deposited on the surface of the flexible microelectrode chip as a passivation layer to obtain the initial device. The flexible microelectrode chip has a channel via formed inside.

[0037] (2) Use tape to symmetrically assemble and fix the two initial devices onto the printed circuit board. Gold wires with a diameter of 200μm connect the microelectrode pads to the PCB board for external electrical connection.

[0038] (3) Organic semiconductor layers were prepared by alternating current deposition: 10 mM 3,4-ethylenedioxythiophene (EDOT) was dissolved in 0.5 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate as the electrolyte, and the electrolyte was prepared by 4V. p-p Driven by pulse amplitude and 50Hz AC power, an organic semiconductor layer is formed by electropolymerization within the channel via of the microelectrode chip.

[0039] (4) Prepare a PBS buffer (pH = 6.47) containing 1 mM BTB (bromothymol blue), 10 mM EDOT (3,4-ethylenedioxythiophene), and 100 mM KNO3. Use a platinum electrode as the counter electrode and a standard calomel electrode as the reference electrode. Use the gate of the device obtained in step (3) as the working electrode and connect it to an electrochemical workstation. Perform PEDOT:BTB film modification on the gate by a 0-1 V frequency sweep at a scan rate of 100 mV·s. -1 The highly sensitive and fast-response pH sensor was thus prepared.

[0040] Example 2

[0041] The preparation method of the pH sensor in this embodiment is the same as that in Example 1, the only difference being:

[0042] In step (1), a silicon substrate is provided, and a 500 nm silicon dioxide film is thermally grown on the substrate as an insulating layer. The photoresist NR9-1500PY is developed using RD6 developer. Then, a 30 nm thick titanium is sputtered as an adhesion layer. Next, a 100 nm thick gold is sputtered at the source, drain, and gate to prepare a rigid microelectrode chip. A 3 μm thick poly(p-dichlorotoluene) film is further deposited on the surface of the rigid microelectrode chip as a passivation layer to obtain the initial device. The rigid microelectrode chip has a channel via formed inside.

[0043] Sample Analysis

[0044] Microscopic image of the highly sensitive and fast-response pH sensor prepared in Example 1 is shown below. Figure 1 As shown; standard solutions with different pH values ​​were prepared and used as dielectric layers to measure the source-drain current versus gate voltage curve of the high-sensitivity, fast-response pH sensor in Example 1. The source was grounded, the drain voltage was fixed at -0.6V, and the gate potential was cyclically scanned from -0.8V to 0.8V. The results are shown below. Figure 2 As shown, the transconductance curve obtained by further differentiating the gate voltage is as follows: Figure 3 As shown, the optimal gate operating voltage is determined to be 0.01±0.002V based on the intersection of the transconductance curves, so that the highly sensitive and fast-response pH sensor can operate at the optimal gate operating voltage. The pH sensor is measured to have a sensitivity of 124mV / pH and a response time as low as 8.75ms.

[0045] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for operating a highly sensitive and fast-response pH sensor, characterized in that, Standard solutions with different pH values ​​were prepared and used as dielectric layers to measure the source-drain current of the high-sensitivity and fast-response pH sensor as a function of the gate voltage. The corresponding transconductance curve was obtained by further differentiating the gate voltage. The optimal gate operating voltage was determined based on the intersection of the transconductance curves, so that the high-sensitivity and fast-response pH sensor could operate at the optimal gate operating voltage. The method for preparing the highly sensitive and fast-response pH sensor includes the following steps: (1) Provide a substrate, deposit an insulating layer on the substrate, deposit an adhesion layer on the insulating layer to further adhere the source, drain and gate on the surface of the insulating layer, and after the source, drain and gate are deposited, a microelectrode chip is prepared, and a passivation layer is further coated on the surface of the microelectrode chip as an initial device; the microelectrode chip includes a rigid microelectrode chip or a flexible microelectrode chip, and a channel via is formed in the microelectrode chip; (2) Using 3,4-ethylenedioxythiophene and ionic liquid as electrolytes, an alternating current is applied to the initial device, and an organic semiconductor layer is formed by electropolymerization on the channel via of the microelectrode chip using an alternating current deposition method. (3) Using platinum as the counter electrode and a standard calomel electrode as the reference electrode, the gate of the device obtained in step (2) is used as the working electrode. The gate of the device obtained in step (2) is modified with a PEDOT:BTB film. After the modification is completed, the highly sensitive and fast-response pH sensor is obtained.

2. The operating method of the highly sensitive and fast-response pH sensor according to claim 1, characterized in that, The substrate material is silicon wafer, silicon carbide, silicon nitride, or sapphire; The insulating layer material is silicon dioxide or polyimide; The adhesive layer material is titanium, chromium, nickel, or tungsten; The source, drain, and gate materials are metals or conductive carbon materials; The passivation layer material is poly(p-dichlorotoluene), polyimide, benzocyclobutene, silicon dioxide, or silicon nitride.

3. The operating method of the highly sensitive and fast-response pH sensor according to claim 1, characterized in that, In step (2), the ionic liquid includes 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tricyanomethane or 1-butyl-3-methyltetrafluoroborate.

4. The operating method of the highly sensitive and fast-response pH sensor according to claim 1, characterized in that, In step (2), the ratio of 3,4-ethylenedioxythiophene to ionic liquid is 10 mM: 0.4 ml to 0.5 ml.

5. The operating method of the highly sensitive and fast-response pH sensor according to claim 1, characterized in that, In step (3), a PBS buffer containing 3,4-ethylenedioxythiophene, bromothymol blue and KNO3 is prepared. Platinum is used as the counter electrode and a standard calomel electrode is used as the reference electrode. The gate of the device obtained in step (2) is used as the working electrode and connected to an electrochemical workstation. The gate is modified with PEDOT:BTB film by 0-1 V frequency sweep.

6. The operating method of the highly sensitive and fast-response pH sensor according to claim 1, characterized in that, The optimal gate operating voltage is set to V. G，i ±0.002 V, where V G，i This represents the voltage at the intersection of the transconductance curves.

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