Flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheet and preparation method of flexible organic field effect transistor respiratory ammonia sensor

Abstract

The invention discloses a flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets and a preparation method of the flexible organic field effect transistor respiratory ammonia sensor, and belongs to the technical field of gas sensors. The organic light emitting diode sequentially comprises a flexible substrate, a grid electrode, a flexible dielectric layer, an organic semiconductor layer and a source electrode / drain electrode from bottom to top, and raw materials of the organic semiconductor layer comprise poly [(dithiophene)-alternating-(2, 5-bis (2-octyldodecyl)-3, 6-bis (thienyl)-diketopyrrolopyrrole)], an elastomer and modified graphene oxide. The nano material OA-GO containing multiple functional groups has an adsorption effect on target gas, the porous film containing the OA-GO is prepared, the surface area in contact with the gas is increased, more binding sites can be exposed, and finally high-sensitivity and high-selectivity detection of the target gas NH3 is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of gas sensors, and in particular relates to a flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets and a preparation method thereof. Background Art

[0002] Biomarker detection is expected to play a key role in the upcoming cloud medical treatment (CMT) era due to its potential for early disease diagnosis and personalized health monitoring. Human exhaled breath contains thousands of different gases, some of which are closely related to the metabolism of different organs and have different levels between patients and healthy people, making them ideal in vitro biomarkers. Kidney disease is quietly becoming a hidden epidemic worldwide, and the mortality rate of kidney patients is high. The concentration of NH3 in exhaled breath is correlated with the concentration of urea in the blood and can be used to monitor the adequacy of dialysis in kidney patients. Traditional respiratory monitoring methods may require patients to wear uncomfortable equipment or undergo complex examinations, so flexible gas sensors have broad application prospects in the health field. Flexible gas sensors based on organic field effect transistors (OFETs) have the advantages of low operating temperature, signal amplification, low cost, and low power consumption. They can be directly attached to the skin or integrated into smart wristbands and clothes, can adapt well to human movement and posture changes, provide a more natural wearing experience, facilitate long-term monitoring, capture real-time changes in respiratory gases, achieve continuous health tracking, and provide valuable information for understanding patients' respiratory health status. In summary, since existing kidney disease detection often requires cumbersome and complicated operating procedures, specialized instruments and equipment, and skilled operators, there is an urgent need to develop low-cost detection devices with higher sensitivity, easier operation, and wider applicability to achieve detection and evaluation of early kidney disease. Summary of the invention

[0003] The purpose of the present invention is to provide a flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art.

[0004] One of the technical solutions provided by the present invention:

[0005] A flexible organic field-effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets comprises, from bottom to top, a flexible substrate, a gate, a flexible dielectric layer, an organic semiconductor layer and a source / drain electrode, wherein the raw materials of the organic semiconductor layer comprise poly[(dithiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)] (DPP-DTT), an elastomer (SEBS(H1221)) and modified graphene oxide; the modified graphene oxide is long-chain oleylamine-modified graphene oxide (OA-GO).

[0006] Preferably, the organic semiconductor layer is prepared by an organic semiconductor film; the method for preparing the organic semiconductor film comprises the following steps: shearing a mixed solution containing OA-GO, DPP-DTT and SEBS (H1221), then coating it on an octadecyltrichlorosilane-modified silicon wafer, and annealing to obtain the organic semiconductor film.

[0007] Since graphene oxide is modified by long-chain oleylamine, the adjacent OA-GO are entangled and aggregated with each other through the long-chain oleylamine groups during the shearing process of the mixed solution, resulting in the appearance of holes in the organic semiconductor film after the addition of OA-GO, forming a porous film, thereby increasing the surface area in contact with the gas and improving the gas response.

[0008] More preferably, the preparation method of the mixed solution is: mixing the organic solution of OA-GO and the polymer solution containing DPP-DTT and SEBS (H1221) to obtain the mixed solution.

[0009] More preferably, the weight ratio of DPP-DTT to SEBS (H1221) is 2:1, and the total concentration of DPP-DTT and SEBS (H1221) in the polymer solution is 7.5 mg / mL.

[0010] More preferably, the mass concentration of OA-GO in the organic solution is 5 mg / mL.

[0011] More preferably, the OA-GO accounts for 1-6% by weight of the DPP-DTT; more preferably, the modified graphite oxide accounts for 4% by weight of the DPP-DTT.

[0012] Preferably, the preparation method of the OA-GO comprises the following steps: mixing an aqueous suspension of GO (graphene oxide) and an ethanol solution of OA (oleylamine) in equal volumes, vigorously stirring at room temperature, and vacuum drying to prepare the OA-GO.

[0013] More preferably, the concentration of GO in the aqueous suspension is 8 mg / mL, and the concentration of OA in the ethanol solution is 10 μL / mL.

[0014] Nanomaterial GO has many advantages such as significant specific surface area, easy synthesis, low preparation cost, good biocompatibility, green environmental protection, and multi-functional groups. However, since graphene oxide does not disperse in the organic solvent chlorobenzene, oleylamine-modified graphene oxide (OA-GO) was designed and synthesized. Due to the introduction of hydrophobic long-chain alkyl groups, OA-GO disperses well in chlorobenzene solvent and can be evenly mixed with the polymer solution.

[0015] The second technical solution provided by the present invention is:

[0016] A method for preparing the above-mentioned flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets, wherein the gate, flexible dielectric layer, organic semiconductor layer and source / drain are transferred layer by layer on the flexible substrate to prepare the flexible organic field effect transistor respiratory ammonia sensor.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] The nanomaterial OA-GO containing multiple functional groups has an adsorption effect on the target gas. The present invention prepares a porous film containing OA-GO to increase the surface area in contact with the gas, thereby exposing more binding sites and ultimately achieving highly sensitive and highly selective detection of the target gas NH3.

[0019] OA-GO has a large specific surface area and many oxygen-containing polar functional groups (including carboxyl, hydroxyl, ether, etc.) on the surface, which indicates that it has the potential to be used as a gas receptor material. The large specific surface area can expose abundant binding sites to facilitate the adsorption of more gases, and the polar functional groups can form weak interactions such as hydrogen bonds and molecular dipoles with ammonia. In short, the addition of OA-GO improves the response of gas sensing without affecting the electrical properties and stability of the device itself. Compared with other detection methods, this gas sensor based on flexible organic field-effect transistors is expected to become a high-performance sensing platform for detecting various gas molecules due to its small size, simple operation, high sensitivity and strong reliability.

[0020] The present invention detects the concentration of NH3 by monitoring the change of the source-drain current (Ids) electrical signal in the It curve of the flexible organic field-effect transistor gas sensor before and after NH3 is introduced. By comparing whether there are holes formed by OA-GO aggregation in the organic semiconductor film, it is confirmed that the introduction of the porous film containing OA-GO can efficiently adsorb gas and improve the sensitivity of the device, and the theoretical detection limit can reach ppb level. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 is the synthesis route of OA-GO in Example 1;

[0023] Figure 2 Infrared spectra of GO (a) and OA-GO (b);

[0024] Figure 3 (a) is a schematic diagram of the solution shearing process in S5 in Example 2; (b) is an AFM height image of the OA-GO / DPP-DTT / SEBS mixed film (4%), and (c) is an AFM phase image of the OA-GO / DPP-DTT / SEBS mixed film (4%);

[0025] Figure 4 (a) is an atomic force microscope (AFM) characterization image of the roughness of the DPP-DTT / SEBS blend film in Example 2, (b) is an atomic force microscope (AFM) characterization image of the roughness of the OA-GO / DPP-DTT / SEBS (4%) blend film; (c) is the pore size distribution of different films and the relative height of the pores to the horizontal plane of the film, wherein the red line is the OA-GO / DPP-DTT / SEBS (4%) blend film, and the black line is the DPP-DTT / SEBS blend film;

[0026] Figure 5 This is a flow chart of constructing a flexible organic field effect transistor respiratory ammonia sensor (OFET) using modified graphene oxide nanosheets in Example 2;

[0027] Figure 6 Characterization diagram of the transfer and output curves of the OA-GO / DPP-DTT / SEBS (4%) flexible OFET gas sensor prepared in Example 2, wherein (a) is the transfer curve; (b) is the output curve;

[0028] Figure 7 It is a comparison chart of the mobility of OA-GO / DPP-DTT-SEBS mixed membranes with different OA-GO dosages (0%, 1%, 2%, 4%, 6% and 10%) in Example 2;

[0029] Figure 8 (a) is a UV spectrum characterization diagram of OA-GO and the blended film before and after adding OA-GO in Example 2; (b) is an infrared spectrum characterization diagram of the blended film before and after adding OA-GO in Example 2;

[0030] Fig. 9 The X-ray photoelectron spectroscopy (XPS) of the blended film before and after adding OA-GO in Example 2, wherein the blended film after adding OA-GO is OA-GO / DPP-DTT / SEBS (4%); wherein (a), (b) and (c) are respectively O 1s 、N 1s and C 1s X-ray photoelectron spectroscopy;

[0031] Fig.10The mobility changes of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) along the direction parallel to the charge transfer (a, c) and perpendicular to the charge transfer (b, d) under 0-100% strain conditions;

[0032] Fig.11 Comparison of the responsiveness of the flexible OFET gas sensor to different concentrations of NH3 (1ppm and 2ppm) before and after the addition of OA-GO;

[0033] Fig.12 (a) is the response and recovery of the real-time ISD electrical signal of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) to 1 to 5 ppm NH3; (b) is the real-time response diagram of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) to 1 to 5 ppm NH3;

[0034] Fig.13 (a) shows the selectivity of OA-GO / DPP-DTT / SEBS (4%) flexible OFET gas sensor to different gases; Fig.13 (b) shows a well-fitting linear curve of the responsiveness of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) exposed to different concentrations of NH3. DETAILED DESCRIPTION

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0037] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0038] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0039] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0040] The room temperature in the present invention refers to 25±2°C.

[0041] The embodiment of the present invention constructs a flexible gas sensor based on a blended polymer DPP-DTT, an elastomer SEBS and a gas receptor material OA-GO as an active layer for use in an OFET-based flexible gas sensor. SEBS is selected as an elastomer because it has a high fracture strain (550% strain). The addition of SEBS improves the stretchability of the semiconductor layer, and a stretchable flexible gas sensor is prepared. The device can be comfortably adhered to human skin, and is well adapted to various deformations such as bending, twisting, and stretching, and has a high strain stability. The gas receptor material OA-GO has a large specific surface area and many polar functional groups (including carboxyl, hydroxyl, ether, etc.). The large specific surface area can expose abundant binding sites to facilitate more gas adsorption, and weak interactions such as hydrogen bonds and molecular dipoles can be formed between polar functional groups and ammonia. By preparing a porous film containing OA-GO, the surface area in contact with the gas is increased, more binding sites can be exposed, and finally a highly sensitive and highly selective detection of the target gas NH3 is achieved. The addition of OA-GO improves the response of gas sensing without affecting the electrical properties and stability of the device itself, achieving rapid, ultra-sensitive and real-time monitoring of NH3.

[0042] The raw materials used in the embodiments of the present invention are all commercially available chemically pure reagents, among which graphene oxide was purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.; oleylamine was purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd.; polymer DPP-DTT was purchased from Shenzhen Ruixun Optoelectronic Materials Technology Co., Ltd., and elastomer SEBS was purchased from Asahi Kasei Technology Co., Ltd. of Japan; anhydrous ethanol was purchased from Tianjin Xiensiopude Technology Co., Ltd.; isopropanol was purchased from Tianjin Jiangtian Chemical Technology Co., Ltd.; octadecyltrichlorosilane (OTS) was purchased from Beijing Bailingwei Technology Co., Ltd.; carbon nanotube aqueous dispersion was purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences; N-doped silicon wafers containing 300nm SiO2 layer used for device preparation were purchased from China Electronics Technology Group Corporation, and carbon nanotubes were purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences.

[0043] In the embodiments of the present invention, the electrochemical performance is measured by a Keithley 4200SCS semiconductor parameter analyzer. A homemade gas analysis system is used to detect NH3, including a flow monitoring system, a homemade test chamber and a Keithley 2636B semiconductor parameter analyzer. Ultraviolet visible spectrometer (UV-3600 Plus), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) are used to characterize the blending of the semiconductor layer.

[0044] Example 1 Preparation method of OA-GO

[0045] S1. 40 mg of GO was dispersed in 5 mL of deionized water and ultrasonicated for 0.5 h to obtain a brown graphene oxide / water suspension; 50 μL of oleylamine was dissolved in 5 mL of ethanol to obtain a transparent solution, and the graphene oxide / water suspension was mixed with the oleylamine / ethanol solution and vigorously stirred at room temperature for 24 h;

[0046] S2. The above liquid was placed in a vacuum oven at 80°C and vacuum dried for 12 h to obtain a black powder, namely OA-GO.

[0047] Figure 1 is the synthesis route of OA-GO in Example 1;

[0048] Figure 2 Infrared spectra of GO (a) and OA-GO (b) are shown in Figure 1. Figure 2 In (b), we can see that after the condensation reaction between GO and OA, various oxygen-containing functional groups still exist, 1356 cm -1 The peak at 1100 cm -1 The peak at 1743 cm-1 is due to the stretching vibration of CO in the ether group. When the nitrogen atom is connected to the carbonyl carbon, the lone pair of nitrogen electrons stabilizes the resonance form. Therefore, relative to GO, the peak of C=O in OA-GO increases from 1743 cm-1 to 1750 cm-1. -1 Red shift to 1700 cm -1 In addition, at 3400cm -1 and 1461cm -1 A new band appeared at 2921 cm, indicating that an amide group was formed during the condensation with OA. -1 and 2825cm -1 The alkyl CH stretching vibration peak at is caused by the long alkyl chain of OA.

[0049] Example 2 A method for preparing a flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets

[0050] S1. Substrate cleaning: First, use ultrapure water to ultrasonically clean the SiO2 layer formed by thermal growth. + Dope the silicon wafer for 10 minutes to remove dust on the substrate surface that is easy to clean, then use acetone ultrasound for 10 minutes to remove dust on the substrate surface that is difficult to clean, and finally use isopropanol ultrasound for 10 minutes to complete the final cleaning;

[0051] S2. Interface modification: First, the cleaned substrate was treated with plasma in an oxygen environment for 10 min at a power of 80 W. Then, the silicon wafer was placed in an OTS modification solution (mixed with n-heptane and OTS in a volume ratio of 1000:1) and allowed to stand at room temperature for modification for 3 h. Then, the silicon wafer was taken out and placed in a beaker containing n-hexane solution, chloroform solution, and isopropanol solution in turn for ultrasonic treatment for 10 min.

[0052] S3. Formation of an organic semiconductor film: DPP-DTT and SEBS (H1221) were dissolved in a chlorobenzene solvent at a weight ratio of 2:1 to prepare a 7.5 mg / mL polymer solution (referred to as a DPP-DTT / SEBS mixed solution), and the OA-GO prepared in Example 1 was dispersed in chlorobenzene to prepare an OA-GO organic solution with a concentration of 5 mg / mL;

[0053] S4. Take 5 portions of the above OA-GO organic solution with different volumes by pipette, add 5 portions of polymer solution respectively and mix, the obtained 5 portions of OA-GO / DPP-DTT / SEBS mixed solution, in which OA-GO accounts for 1%, 2%, 4%, 6% and 10% of DPP-DTT weight respectively, place the obtained 5 portions of OA-GO / DPP-DTT / SEBS mixed solution and DPP-DTT / SEBS mixed solution (0%) on a hot plate at 80°C and heat and stir for 2h;

[0054] S5. The OA-GO / DPP-DTT / SEBS mixed solution and the DPP-DTT / SEBS mixed solution (0%) were respectively scraped onto the OTS-modified silicon wafer using a solution shearing device at a shearing speed of 0.37 mm / s and a substrate temperature of 60° C., and then annealed on a hot stage at 150° C. for 30 min to reduce the morphology of the polymer film and the generation of molecular structure defects, thereby obtaining an organic semiconductor film;

[0055] S6. Preparation of flexible substrate: SEBS (H1062) was dissolved in toluene to prepare a toluene solution with a concentration of 200 mg / mL, and then heated and stirred on a hot plate at 70°C for 15 h. The toluene solution was poured into a culture dish and allowed to stand overnight to obtain a flexible and stretchable transparent thick film, which is a flexible substrate;

[0056] S7. Preparation of flexible dielectric layer: SEBS (H1052) was dissolved in toluene to prepare a toluene solution with a concentration of 60 mg / mL, and then heated and stirred on a hot plate at 70°C for 10 h. Finally, the dissolved SEBS toluene solution was spin-coated on the OTS-modified silicon wafer at 1000 rpm for 50 s, and then annealed on a hot plate at 90°C for 15 min to obtain a flexible and stretchable transparent dielectric layer, i.e., a flexible dielectric layer;

[0057] S8. Preparation of electrodes: For the gate and source / drain electrodes, a commercial spray gun was used to spray a carbon nanotube aqueous dispersion onto an unmodified silicon wafer. Specifically, the gate was prepared by fixing a silicon wafer (1×2 cm) on a table and using a commercial spray gun to evenly spray 5 mL of a carbon nanotube aqueous dispersion (concentration 0.2 wt%) onto the silicon wafer; source / drain preparation: an iron precision mask was fixed on a silicon wafer (1×1 cm) with a magnet and 5 mL of a carbon nanotube aqueous dispersion (concentration 0.2 wt%) was evenly sprayed onto the silicon wafer using a commercial spray gun. The mask used had a channel width of 400 μm and a channel length of 100 μm.

[0058] S9. The gate, flexible dielectric layer, organic semiconductor layer and source / drain are transferred layer by layer on the prepared flexible substrate to prepare a flexible organic field effect transistor respiratory ammonia sensor (flexible OFET gas sensor) using modified graphene oxide nanosheets.

[0059] Figure 3 (a) is a schematic diagram of the solution shearing process in S5; (b) is the AFM height image (10nm) of the OA-GO / DPP-DTT / SEBS mixed film (4%), and (c) is the AFM phase image of the OA-GO / DPP-DTT / SEBS mixed film (4%); it shows the nanofiber network structure, and nanofibers are an ideal morphology that is conducive to charge transfer and mechanical deformation.

[0060] Figure 4(a) is an atomic force microscope (AFM) characterization image of the roughness of the DPP-DTT / SEBS blend film in Example 2, (b) is an atomic force microscope (AFM) characterization image of the roughness of the OA-GO / DPP-DTT / SEBS (4%) blend film; (c) is the pore size distribution of different films and the relative height of the pores and the horizontal plane of the film, where the red line is the OA-GO / DPP-DTT / SEBS (4%) blend film, and the black line is the DPP-DTT / SEBS blend film; taking the film as the horizontal plane, because the film has holes, there will be positive and negative values. The positive value represents that the hole part is higher than the horizontal plane of the film, and the negative value represents that the hole part is lower than the horizontal plane of the film. It can be seen that after adding 4% OA-GO, the holes formed by shearing increase the surface roughness of the film from 0.69nm to 2.12nm. The formation of holes and the increase in roughness are conducive to the adsorption of gas.

[0061] Figure 5 This is a flow chart of constructing a flexible organic field effect transistor respiratory ammonia sensor (OFET) using modified graphene oxide nanosheets in Example 2.

[0062] Performance test

[0063] The electrical properties were characterized by Keithley 4200SCS semiconductor parameter analyzer. Figure 6 The transfer and output curve characterization diagrams of the OA-GO / DPP-DTT / SEBS (4%) flexible OFET gas sensor prepared in Example 2, where (a) is the transfer curve, indicating that the number of carriers can be controlled by the externally applied gate voltage Vg, that is, it has gate-adjustable hole charge transfer characteristics; (b) is the output curve, showing a clear transition from the linear state to the saturation state, and the saturation current is almost flat.

[0064] Figure 7 This is a mobility comparison chart of OA-GO / DPP-DTT-SEBS mixed films with different OA-GO dosages (0%, 1%, 2%, 4%, 6% and 10%) in Example 2. When 2% OA-GO is added, the device has the highest carrier mobility. When 6% OA-GO is added, the carrier mobility decreases significantly. Considering the needs of gas sensing and device performance, 4% OA-GO and DPP-DTT / SEBS are selected as the active layer.

[0065] Figure 8(a) is the UV spectra of OA-GO and the blended film before and after adding OA-GO in Example 2, where the blended film after adding OA-GO is OA-GO / DPP-DTT / SEBS (4%) blended film; the highest energy peak near 420nm is attributed to the π-π* transition of DPP-DTT, and the two peaks observed near 750nm and 820nm are respectively attributed to the 0-1 and 0-0 oscillator transitions of DPP-DTT, where the low-energy 0-0 peak is attributed to polymer aggregation, and after adding a small amount of OA-GO, the 0-0 peak intensity is enhanced. This shows that the addition of OA-GO can promote the formation of ordered DPP-DTT aggregates.

[0066] Figure 8 (b) is the infrared spectrum characterization diagram of the blended film before and after adding OA-GO in Example 2, where the blended film after adding OA-GO is OA-GO / DPP-DTT / SEBS (4%). For the OA-GO / DPP-DTT / SEBS mixed material, 3072 cm -1 The peak at 3500-3200 cm is the result of the NH stretching vibration of the secondary amide group in OA-GO. -1 The broad peak is the stretching vibration peak of the hydroxyl OH, which is invisible in the pure polymer (DPP-DTT+SEBS).

[0067] Fig. 9 The X-ray photoelectron spectroscopy (XPS) of the blended film before and after adding OA-GO in Example 2, wherein the blended film after adding OA-GO is OA-GO / DPP-DTT / SEBS (4%); wherein (a), (b) and (c) are respectively O 1s 、N 1s and C 1s X-ray photoelectron spectroscopy of O 1s 、N 1s and C 1s There are many oxygen-containing functional groups on the surface of OA-GO. After mixing with OA-GO, the O peak value increased significantly, and the N / C peak value did not show significant changes before and after mixing with OA-GO.

[0068] Testing of tensile strain stability of flexible OFET gas sensors:

[0069] Step 1: Fix the OA-GO / DPP-DTT / SEBS (4%) flexible OFET gas sensor prepared in Example 2 on a homemade stretching table;

[0070] Step 2: Stretch from the original state to 100%;

[0071] Step 3: The changes in the electrical properties of the flexible organic field-effect transistor before and after stretching are tested using a Keithley 4200SCS semiconductor parameter analyzer.

[0072] Fig.10 The mobility of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) changes along the direction parallel to the charge transfer (a, c) and perpendicular to the charge transfer (b, d) under 0-100% strain conditions; the transfer curves of the flexible OFET gas sensor along the direction parallel to the channel length and perpendicular to the channel length do not change much under 0%, 20%, 40%, 60%, 80% and 100% strain. When the device is stretched to 100% strain along the direction parallel to the channel length, the mobility of the flexible OFET gas sensor decreases from 1.01 to 0.81 cm 2 V -1 s -1 ( Fig.10 (c)); When the flexible OFET gas sensor is stretched to 100% strain perpendicular to the channel length direction, the mobility of the device decreases from 0.98 to 0.72 cm 2 V -1 s -1 ( Fig.10 (d)).

[0073] The flexible OFET gas sensor is applied to gas detection, including the following steps:

[0074] Step 1: Use a self-made analysis system, including a flow monitoring system, a self-made test chamber, and a Keithley 2636B semiconductor parameter analyzer. Use dynamic gas distribution and accurately control the gas to be introduced into the chamber at a flow rate of 1000mL / min through a multi-channel gas flowmeter. Place the flexible gas sensor in the chamber, connect the electrodes using gold wire and gallium-indium alloy, and then seal the chamber. First, introduce dry air, then test the It curve of the flexible OFET and obtain the value of the output signal current I0;

[0075] Step 2: Adjust the gas distributor and introduce NH3 for 1 min. The source-drain current (I ds ) is significantly reduced, and the output signal current value I g ;

[0076] Step 3: Calculate the sensor output signal and test the response to NH3 in the concentration range of 1-5ppm. The sensitivity S is calculated based on the slope of the relationship between the response and concentration. The calculation formula for the sensor output signal is:

[0077]

[0078] Where (I0-I g ) is the source-drain current I before and after NH3 is introduced ds I0 is the reference value measured in dry air.

[0079] The gas sensing characteristics were studied using the self-made analysis system. Toxic gases (NO, SO2, H2S, NH3, CO, acetone, ethylene, methanol) were mixed with dry air (background gas) using dynamic gas distribution through a multi-channel gas flowmeter, and the concentration of the gas to be tested was accurately controlled and introduced into the chamber at a flow rate of 1000mL / min. The concentration of NH3 was detected by monitoring the change in the source-drain current (Ids) in the It curve of the flexible organic field-effect transistor. The direct evaluation response is as follows: R = (I0-I g ) / I g ×100%, where (I0-I g ) is the source-drain current I before and after the target gas is introduced ds I0 is the reference value measured in dry air.

[0080] The OA-GO / DPP-DTT / SEBS (4%) flexible OFET gas sensor prepared in Example 2 is applied to the detection of NH3 concentration, comprising the following steps:

[0081] Step 1: Place the flexible gas sensor in the chamber, connect the electrodes using gold wire and gallium-indium alloy, then seal the chamber and let dry air in, then test the It curve of the flexible OFET and obtain the value of the output signal current I0;

[0082] Step 2: Adjust the gas distribution instrument and introduce NH3 for 1 minute. It can be observed in the It curve that the source-drain current (Ids) is significantly reduced, and the output signal current value I is obtained. g ;

[0083] Step 3: Calculate R = (I0-I g ) / I g ×100% as the sensor output signal. The response to NH3 in the concentration range of 1-5ppm was tested, and the sensitivity S was calculated based on the slope of the relationship between the response and concentration.

[0084] The flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) and the flexible OFET gas sensor of DPP-DTT / SEBS prepared in Example 2 were respectively placed in the above-mentioned self-made test chamber. Dynamic gas distribution was adopted, and the gas was introduced into the chamber at a flow rate of 1000 mL / min by a multi-channel gas flowmeter to accurately control the sensor NH3 response.

[0085] Fig.11Comparison of the responsivity of the flexible OFET gas sensor to different concentrations of NH3 (1ppm and 2ppm) before and after the addition of OA-GO. When the device is exposed to the target gas environment, the gas molecules enter the semiconductor from the surface and diffuse into the conductive channel; for p-type OFET devices, when a negative VG is given, more hole carriers are enriched in the semiconductor layer near the gate position, and a conduction current will be generated after the source and drain electrodes are connected. The reducing gas NH3 carries lone pairs of electrons and has a strong electron donating effect. It contacts the molecules in the semiconductor layer to produce weak interaction forces including various forms such as molecular dipoles, hydrogen bonds, and π-π conjugation, which reduces the hole carrier density in the semiconductor layer. Under the same test conditions, Ids is reduced, and the response signal to NH3 can be determined by analyzing the relative change in current.

[0086] Fig.12 (a) shows the response and recovery of the real-time ISD electrical signal of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) to 1 to 5 ppm NH3; (b) shows the real-time response of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) to 1 to 5 ppm NH3.

[0087] Fig.13 (a) shows the selectivity of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) to different gases; it can be seen that the response value of the sensor to 2ppm NH3 is 128%, which is significantly higher than the response values ​​of organic volatile gases such as H2S, SO2, NO, CO at 10ppm, and methanol, acetone and ethylene at 50ppm, which means that the sensor has excellent NH3 detection selectivity and anti-interference ability; Fig.13 (b) is a good linear fitting curve of the responsiveness of the flexible OFET gas sensor of OA-GO / DPP-DTT / SEBS (4%) exposed to different concentrations of NH3, proving that the sensor has a good linear fitting curve of the responsiveness to different concentrations (1-5ppm) of NH3, with a detection limit of 9.19ppb, and has high sensitivity.

[0088] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets, characterized in that: The invention comprises, from bottom to top, a flexible substrate, a gate, a flexible dielectric layer, an organic semiconductor layer and a source / drain electrode, wherein the raw materials of the organic semiconductor layer comprise poly[(dithiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)], an elastomer and modified graphene oxide; the modified graphene oxide is graphene oxide modified with long-chain oleylamine.

2. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 1, characterized in that: The method for preparing the organic semiconductor layer comprises the following steps: A mixed solution containing modified graphene oxide, poly[(dithiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)] and an elastomer is sheared, then scraped on a silicon wafer modified with octadecyltrichlorosilane, and annealed to obtain an organic semiconductor film, namely the organic semiconductor layer.

3. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 2, characterized in that: The preparation method of the mixed solution is: mixing the organic solution of the modified graphite oxide and a polymer solution containing poly[(dithiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)] and an elastomer to obtain the mixed solution.

4. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 3, characterized in that: The weight ratio of the poly[(bis-thiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)] and the elastomer is 2:1, and the total concentration of the poly[(bis-thiophene)-alternating-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)] and the elastomer in the polymer solution is 7.5 mg / mL.

5. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 3, characterized in that: The mass concentration of modified graphite oxide in the organic solution is 5 mg / mL.

6. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 3, characterized in that: The modified graphite oxide accounts for 1-6% of the weight of the poly[(dithiophene)-alt-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)]].

7. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 6, characterized in that: The modified graphite oxide accounts for 4% by weight of the poly[(dithiophene)-alt-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolopyrroledione)]].

8. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 1, characterized in that: The preparation method of the modified graphene oxide comprises the following steps: mixing an aqueous suspension of graphene oxide and an ethanol solution of oleylamine in equal volumes, vigorously stirring at room temperature, and vacuum drying to prepare the modified graphene oxide.

9. The flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to claim 8, characterized in that: The concentration of graphene oxide in the water suspension is 8 mg / mL, and the concentration of oleylamine in the ethanol solution is 10 μL / mL.

10. A method for preparing a flexible organic field effect transistor respiratory ammonia sensor using modified graphene oxide nanosheets according to any one of claims 1 to 9, characterized in that: The gate, the flexible dielectric layer, the organic semiconductor layer and the source / drain are transferred layer by layer on the flexible substrate to prepare the flexible organic field effect transistor respiratory ammonia sensor.

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