CN110208334B - Preparation method of humidity sensor for exhaled air and detection system thereof - Google Patents

Preparation method of humidity sensor for exhaled air and detection system thereof Download PDF

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CN110208334B
CN110208334B CN201910395561.9A CN201910395561A CN110208334B CN 110208334 B CN110208334 B CN 110208334B CN 201910395561 A CN201910395561 A CN 201910395561A CN 110208334 B CN110208334 B CN 110208334B
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detection system
data
humidity
sensor
humidity sensor
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CN110208334A (en
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张冬至
王兴伟
宫礼坤
李博论
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China University of Petroleum East China
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/74—Details of notification to user or communication with user or patient ; user input means
    • A61B5/7405—Details of notification to user or communication with user or patient ; user input means using sound
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/74—Details of notification to user or communication with user or patient ; user input means
    • A61B5/746—Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • G01N27/225—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity by using hygroscopic materials
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2503/00—Evaluating a particular growth phase or type of persons or animals
    • A61B2503/08—Elderly

Abstract

The invention discloses a preparation method of a humidity sensor for exhaled breath and a detection system thereof, belonging to the field of sensor materials and gas detection systems.

Description

Preparation method of humidity sensor for exhaled air and detection system thereof
Technical Field
The invention belongs to the field of sensor materials and gas detection systems, and particularly relates to a preparation method of an expired air humidity sensor and a portable detection system thereof.
Background
Human health, particularly the health of the elderly, is drawing increasing attention throughout society. Most of the elderly live alone, and their children do not care for them. Thus, when certain fatal diseases occur, these diseases can be extremely dangerous. Traditional physical examination such as nuclear magnetic resonance, CT, blood drawing chemical examination, endoscope, B ultrasonic, X-ray inspection, these tests not only spend a large amount of money and time of us, also can bring certain wound for the health simultaneously, more can't give the detection warning in the very first time when the solitary patient morbidity.
A recent research effort published by the federal institute of technology, zurich, switzerland, has shown that the exhaled components of everyone in their breath are as unique as the human fingerprint, and that physicians are even able to diagnose diseases (such as cancer) from these compounds. Human exhaled breath contains abundant physiological and disease-indicative information, such as respiratory rate, humidity, ammonia gas and acetone content. Wherein, ammonia gas and acetone are always the biological gas markers for clinical diagnosis of diseases such as liver function, kidney function, diabetes and the like, and moisture and frequency are the important indexes for clinical diagnosis of diseases such as acute pneumonia, allergic asthma and the like, and are all used for noninvasive early diagnosis of diseases. However, the traditional detection system for measuring the content of ammonia and acetone also has the defects of high concentration detection limit, high working temperature, poor selectivity, easy interference and the like. The humidity and the respiratory frequency of the respiratory air mainly depend on inquiry and auscultation of clinicians at the present stage, and the limitation is large.
Currently, most of the common materials used in humidity sensors, such as metal oxides, electrolytes, polymers, etc., still need to be improved in terms of sensitivity, linearity, stability, response and recovery. Therefore, it is necessary and important to search for a new sensing material to manufacture an enhanced humidity sensor. Recently, graphene oxide (abbreviated as GO) has attracted attention as a two-dimensional nanosheet having a large specific surface area. It is rich in oxygenated functional groups such as hydroxyl, carboxyl and epoxy groups, which increase its hydrophilicity, making it easier to form films during manufacture. However, there is reported room for further improvement in the original GO. The research and application of the breathing sensor which is more convenient are widely concerned by people.
Disclosure of Invention
In order to solve the problems that the prior art cannot accurately detect the exhaled breath information of a human body in real time and has poor monitoring timeliness, the invention combines a micro-nano sensor and an MEMS (micro-electromechanical systems) process to construct an exhaled breath humidity sensor, so that the sensing response efficiency and the tolerance performance are improved.
The technical scheme provided by the invention is as follows:
a method for preparing humidity sensor of exhaled breath uses indium oxide-graphene oxide (In for short) on the surface of humidity sensor2O3GO) composite material, In2O3-GO humidity sensor preparation step comprising:
1) firstly, In is prepared by a hydrothermal method2O3；
2) Then, using an epoxy resin material as a substrate of the interdigital electrode; winding electrode materials on the center in the same direction at two different starting points on the substrate by using a photoetching technology to form an interdigital electrode back pattern;
3) further, In was prepared2 O 3① mixing In2O3The powder (0.01g) was mixed with a 0.3 wt% aqueous GO solution (1.71g) to keep In2O3Stirring the mixture for 20 minutes at the mass percent ratio of GO being 7:3 at ②, then carrying out ultrasonic treatment for 30 minutes to obtain a uniform solution, absorbing the solution ③ by a rubber head dropper, and dropping the solution on an epoxy resin substrate with interdigital electrodes to form a humidity-sensitive sensing film, and drying the sensor for 4 hours at ④ in a vacuum oven at the temperature of 60 ℃;
wherein In is produced on the surface of the epoxy resin substrate2O3After the GO is mixed with the film, the capacitance of the interdigital electrode changes along with the change of humidity.
Further, In step 1), In2O3The preparation method comprises ① mixing 12g of CO (NH)2)2And 1.52g of In (NO)3)3·4.5H2O is mixed and dissolved in 80mL of deionized water, and then stirred for 20 minutes and sonicated for 30 minutes, ② the resulting mixture is hydrothermally treated at 120 ℃ for 12 hours, then dried in a vacuum oven at 60 ℃ for 6 hours, ③ the indium oxide is obtained after annealing at 500 ℃ for 2 hours in argon.
Further, In step 2), the sensor is prepared by MEMS technology, ① sputtering and depositing a 50 μm thick copper/nickel layer on the cleaned epoxy resin substrate, ② drawing an interdigital pattern by etching technology using Photoresist (PR) to make two coil-shaped nickel-copper interdigital electrodes, ③ etching and removing excessive copper/nickel by exposure and development, ④ forming In film on the surface of the interdigital electrode2O3-GO self-assembly.
The interdigital electrodes are preferably made of a nickel/copper material.
The invention also provides a detection system of the sensor obtained by the preparation method, which is characterized in that when the structure size of the interdigital electrode is reduced to be below micron level, the humidity change with the capacitance value of below 250nf can be detected, and the capacitance sensitivity of the interdigital electrode sensor reaches pf level;
in particular, In2O3The water adsorption process on the surface of the-GO mixed membrane is ① In2O3Exposure of the GO mixed film to water molecules, adsorption of water molecules starting with In2 O 3② with increasing RH, the second phase begins with the subsequent multi-layer adsorption, ③ then In2O3Water molecules on the GO surface forming a continuous layer, ④ adsorbed water molecules being ionized into H3O+The Grottthus chain reaction, H2O+H3O+→H3O++H2O ⑤ when water molecule permeates to GO membrane and In2O3With an intermediate layer between the films, the dielectric constant increases and the capacitance value increases accordingly.
Further, the integrated circuit of the detection system comprises an STM32 minimum system module, a peripheral interface circuit, a power supply and a capacitive sensing chip.
Further, the STM32 minimum system module comprises an STM32 single chip microcomputer, a WiFi module and a clock module;
the STM32 single chip microcomputer is an STM32F405, realizes digital-to-analog conversion, receives and sends data, is responsible for transmitting real-time data acquired from the humidity sensor to the mobile communication port, and is provided with an alarm device for alarming when the system is abnormal so as to remind people of abnormal movement;
preferably, the WiFi module is an ESP8266 chip, and its connection with the STM32 singlechip includes 3 lines: a CE pin, an SCLK serial clock pin and an I/O serial data pin, wherein Vcc2 is a standby power supply and is externally connected with a 32.768kHz crystal oscillator to provide timing pulse for a chip;
preferably, the clock module is a DS1302 chip, and is in an SPI bus driving mode, and not only the control word needs to be written into the register, but also the data of the corresponding register needs to be read; the control word is always output from the lowest order bit, data is written into the clock module at the rising edge of the next SCLK clock after the control word instruction is input, and the data input is started from the 0 bit of the lowest order bit; similarly, the data of the clock module is read at the falling edge of the next SCLK pulse following the 8-bit control word instruction, the read data also being from the least significant bit to the most significant bit.
Further, an I2C internal integrated circuit is used as the external interface circuit, and the external interface circuit is connected with an OLED and a serial port Wifi in parallel; four-way ADCs are reserved, including: and sampling, namely, the FFT converts the waveform time domain signal into a frequency domain signal, one path of oscilloscope connection is reserved, and the other path of oscilloscope connection is connected to the WiFi module to keep real-time communication.
Furthermore, Microusb is used as a power supply for supplying 5V power, and an LDO linear voltage regulator is used for stabilizing the 5V power at 3.3V for the singlechip and the capacitance sensing chip; in addition, a code is set to judge that two LED lamps are connected in parallel, and the code is used for detecting a processing scheme when the code has a problem and indicating that the program runs normally when a green lamp is displayed; and/or
The capacitive sensing chip is preferably an FDC2214 chip; the highest resolution is 28 bits, the maximum sampling rate is 13.3ksps, the capacitance with the maximum value of 250nF can be detected, the operation in a temperature range from minus 40 ℃ to 125 ℃ is met, and an application circuit is arranged in the capacitor; and the waveform as a whole is shifted up in the presence of negative voltage using a dc bias.
Furthermore, the WiFi module supports three working modes of STA, AP and STA + AP, preferably uses the STA + AP mode, can be connected to the Internet through a router, and can also be used as a WiFi hotspot to enable other equipment to be connected to the module, so that the switching between a wide area network and a local area network is realized;
the communication is carried out by utilizing high and low levels through a TTL signal channel and a WiFi module, and the TTL is preferably converted into 232 or 485 signals generally;
preferably, the curve is stable and smooth when breathing normally; when the curve becomes jumble disorderly along with the rush of breathing, the occurrence of an accident situation is judged, and alarm information is sent to a plurality of connected mobile terminals immediately when the accident situation occurs, so that the user can be timely treated and cured under the accident situation.
Further, the mobile terminal connected with the WiFi module is a mobile phone, and the APP of the mobile terminal receives data in two modes: one is to read data directly from the device, and the other is to read data from a server database; meanwhile, the obtained data is used for drawing a breathing curve, and the curve is displayed on a screen; the user can check the data at any time or permanently store the data in a memory card of the mobile phone; in addition, a scanning frequency can be performed; setting upper and lower thresholds in the APP program, if the value is too low or too high, the information will be sent to the lower computer for adjustment, when the middle of the two thresholds is reached, no adjustment is needed so that the system can operate at the optimum frequency and plot the curve in the appropriate range; meanwhile, an alarm function can be realized, when an emergency occurs, a buzzer in the portable device starts to operate, and then the device transmits alarm information to all users connected thereto, so that an accident can be dealt with at the first time.
The comprehensive technical scheme and the comprehensive effect of the invention comprise:
1. the common humidity sensor in the market has the defects of poor sensitivity and low integration, and the product has a portable humidity sensor with ultra-fast response. The fastest response recovery time for sensors made by the present invention to respond to and recover from humidity has been 2 seconds to date.
2. Prolonged exposure to high humidity environments often causes device degradation or failure surfaces caused by excessive water adsorption on the sensor. And the most fatal problem of the humidity sensor is a temperature compensation problem with respect thereto. The humidity sensor made of the graphene film has the advantages that the hydrophobic surface and the uniformly distributed annular wrinkles are designed, and the humidity sensor shows excellent performance in the aspect of respiration sensing. The wrinkle morphology of the graphene sensor can effectively prevent the water droplets from being gathered, so that the evaporation is carried out at the maximum rate, and the interference caused by the adsorption of excessive water is effectively prevented.
3. Humidity is a key factor in maintaining human comfort. Among the various transduction techniques used, capacitive techniques are the most popular. However, the capacitive sensor suffers from hysteresis, has poor long-term stability, and is not suitable for a wide humidity range. Today, resistive sensors are becoming increasingly important due to their simple design and easy integration with Complementary Metal Oxide Semiconductor (CMOS) platforms. The product is used for carrying out accurate relative humidity sensing on high-sensitivity materials such as metal oxide graphene and graphene oxide on a polymer film and the like.
Drawings
FIG. 1 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to an embodiment of the present invention2O3Water adsorption mechanism diagram for GO humidity sensor.
Fig. 2 is a flow chart of a method for manufacturing a humidity sensor for exhaled breath and a material manufacturing method thereof according to an embodiment of the present invention.
FIG. 3 shows In obtained by the method for manufacturing humidity sensor for exhaled breath In accordance with the embodiment of the present invention2O3GO, In humidity sensor2O3And In2O3-XRD characteristic contrast pattern of GO.
FIG. 4 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to the embodiment of the present invention2O3SEM image of GO humidity sensor, (a) is In2O3Nanocubes, (b) GO nanosheets, (c) and (d) In2O3SEM images of GO hybrids.
FIG. 5 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to the embodiment of the present invention2O3TEM images of GO humidity sensor, (a), (b) In2O3-GO hybrid, (c) is In2O3And (d) is a TEM image of GO nano-sheets.
FIG. 6 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to the embodiment of the present invention2O3(a), (b), (c) and (d) of the GO humidity sensor are XPS survey, C, O and XPS spectrogram of In, respectively.
FIG. 7 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to an embodiment of the present invention2O3-capacitance-frequency characteristic diagram of GO humidity sensor.
FIG. 8 shows In obtained by the method for manufacturing a humidity sensor for exhaled breath according to an embodiment of the present invention2O3GO, In of GO humidity sensor2O3And In2O3-capacitance versus relative humidity characteristic graph of GO.
FIG. 9 an embodiment of the inventionEXAMPLES In preparation of humidity sensor for exhaled breath2O3GO humidity sensor versus comparative examples pure GO and pure In2O3The capacitance values of (a) and (b) are compared to each other.
FIG. 10 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3GO humidity sensor pure GO and pure In of comparative examples2O3Response and recovery characteristics at 43% RH are compared.
FIG. 11 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3Different mass percentages of In for GO humidity sensor2O3And capacitance plot of GO at 43% RH.
FIG. 12 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3Up-going and down-going test patterns of the sensor at 100Hz for the GO humidity sensor.
FIG. 13 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3Hysteresis characteristics of GO humidity sensor under relative humidity variation from 0% RH to 97% RH.
FIG. 14 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-repeated performance plots of GO humidity sensor at 23%, 52% and 75% RH.
FIG. 15 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-complex impedance plot of GO humidity sensor.
FIG. 16 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-a general block diagram of the detection system hardware of the GO humidity sensor.
FIG. 17 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-the detection system of GO humidity sensor overall 3D circuit diagram (left) back, (right) front.
FIG. 18 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3of-GO humidity sensorsAnd detecting the operation flow of the hardware part of the system.
FIG. 19 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-circuit diagram of minimum system components of detection system STM32F405 of GO humidity sensor.
FIG. 20 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-a detection system peripheral interface circuit diagram of a GO humidity sensor.
FIG. 21 In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-a detection system power module circuit diagram of a GO humidity sensor.
FIG. 22 shows In obtained by the method for manufacturing humidity sensor for exhaled breath according to the embodiment of the present invention2O3-a detection system capacitive sensing chip circuit diagram of a GO humidity sensor.
Detailed Description
The nano material has the properties of strong surface property, high surface adsorption capacity, good conductivity and the like. According to the special properties of the nano material, particularly the surface effect, the prepared micro-nano gas sensor has strong interaction with the surrounding medium and is quite sensitive to the external environment. According to the invention, the micro-nano sensor is combined with the MEMS process, so that more excellent performance can be obtained.
The respiration sensor array can generate large resistance change by utilizing the adsorption effect of gas through a special surface area of the surface and a porous nano structure. In particular, highly selective novel sensing biomarkers, capable of forming multisensor arrays for the analysis of human exhaled breath by means of different functionalized noble metal catalysts, such as Au, Pt, Pd and Rh. These sensor arrays can be integrated into portable devices to provide real-time monitoring of physical conditions.
The invention adopts the combination of the MEMS technology and the micro-nano sensing device, researches the sensitivity mechanism and the humidity sensitivity performance of the micro-structure and the sensitive film of the sensing device on the humidity detection, performs experimental test on the response characteristic of the sensor, performs performance evaluation on the sensor from the parameters of sensitivity, detection limit, response recovery characteristic, linearity and the like, and provides theoretical and experimental basis for the manufacture and medical application of the high-sensitivity gas-sensitive sensor.
The invention is described in detail below with reference to the figures and the specific embodiments.
Examples
Sensor material preparation
The GO used in the experiment was a commercially available high-purity graphene oxide nanoplate (> 99%) provided by the chengdu organic chemistry limited (chengdu, china), a tan suspension, at a concentration of 0.3 wt% at ph 4.5.
As shown In FIG. 2, In used In the examples2O3Is prepared by a hydrothermal method. First, CO (NH)2)2(12g) And In (NO)3)3·4.5H2O (1.52g) was mixed and dissolved in 80mL deionized water, then stirred for 20 minutes and sonicated for 30 minutes. Thereafter, the resulting mixture was subjected to hydrothermal treatment at 120 ℃ for 12 hours, and then dried in a vacuum oven at 60 ℃ for 6 hours. Finally, indium oxide was obtained after annealing at 500 ℃ for 2 hours under argon.
An epoxy resin material with low cost and high stability is used as a substrate of the interdigital electrode. The interdigital electrodes are made of a copper material and are wound on the center in the same direction at two different starting points on the substrate using a conventional photolithography technique to form a back surface shape. In the manufacture of In2O3After the GO is mixed with the film, the capacitance of the interdigital electrode changes along with the change of humidity. When the structure size of the interdigital electrode is reduced below the micrometer level, a very small humidity change can be sensitively detected, which indicates that the sensitivity of the interdigital electrode sensor is significantly improved.
Humidity sensor In2O3-GO hybrid film preparation method: first, In is mixed2O3The powder (0.01g) was mixed with a 0.3 wt% GO solution (1.71g) such that the mass fraction ratio was 7: 3. then, the mixture was stirred for 20 minutes and then sonicated for 30 minutes to give a homogeneous solution. Then, the solution is absorbed by a rubber head dropper and dropped on an epoxy resin substrate with interdigital electrodes to form humidity-sensitive In2O3-a GO sensing membrane. Finally, the sensor was placed in a vacuum oven at 60 ℃ and dried for 4 hours.
At the same time, pure In was prepared2O3(comparative example 1), In2O3GO 17:3 (comparative example 2), In2O3GO 5:5 (comparative example 3), In2O3GO 3:7 (comparative example 4), In2O3GO 3:17 (comparative example 5) and pure GO (comparative example 6) to match the In used In this example2O3GO 7:3 for comparison.
In2O3-GO humidity sensor material characterization
Characterization by X-ray diffraction:
to study In2O3GO and In2O3Structural differences of GO samples, using wavelengths of
Figure BDA0002058050490000121
The X-ray diffraction (XRD) of the Cu K α radiation was performed at room temperature 25 deg.c, the diffraction angles were limited to the range of 10-80 deg. the XRD patterns of the three samples are shown in fig. 3, in which there is no impurity crystalline phase
Figure BDA0002058050490000122
In2O3In the-GO composite, the peak is clearly weaker, indicating In2O3Hindering the formation of ordered structures. In2O3The diffraction peaks of (a) are located at 21.55 °, 30.64 °, 35.50 °, 51.11 ° and 67.76 °, corresponding to In of the (211), (222), (400), (116) and (622) planes2O3. Meanwhile, In was found In addition to the peak at 11.5 ° 2 θ2O3the-GO complexes are all pristine In2O3Superposition with GO peak, evidence of In2O3And GO successfully synthesize In2O3-a GO complex.
Scanning electron microscopy characterization:
characterization of GO by Scanning Electron Microscopy (SEM)And In2O3The form of (1): FIG. 4(a) shows In a cubic form2O3Nanostructure, fig. 4(b) shows GO is composed of wrinkled nanoplatelets. FIGS. 4(c) and (d) show In2O3The nanocubes coherently attach on the GO surface, forming In2O3-GO hybrid membranes.
Transmission electron microscopy characterization:
pure In was investigated by Transmission Electron Microscopy (TEM)2O3GO and In2O3Morphology of GO samples, images are shown in figure 5. FIG. 5(a) shows In2O3-structure of GO complex. Fig. 5(d) shows the corrugated structure of GO.
Characterization of X-ray photoelectron spectroscopy:
x-ray photoelectron spectroscopy (XPS) was used to study the elemental composition and ionic state of all experimental samples. In2O3XPS measurement spectra of/GO are plotted In FIG. 6(a), indicating that the experimental complex is composed primarily of C, O and In. Fig. 6(b) shows that the three major peaks at 284.50eV, 286.48eV and 288.08eV are assigned to aromatic carbon (C-C), epoxy (C-O) and carbonyl (C ═ O). FIG. 6(C) clearly shows that the O1 s spectrum can be divided into three major peaks, located at 530.41eV, 531.22eV and 532.42eV respectively, which point to In-O, C-O and surface adsorbed oxygen respectively. In the XPS spectrum of the In element of FIG. 16(d), two strong peaks were observed at 444.68eV and 452.08eV, corresponding to In 3d, respectively3/2And In 3d5/2。
In2O3-GO humidity sensor and detection system characterization thereof
All experiments were performed at an ambient temperature of 20 ℃. The sensor is placed in different bottles filled with saturated salt solution to form environments with different humidity, the TH2828 precise LCR instrument and the sensor are connected by two leads, and the complex impedance spectrum and the capacitance value of the sensor under different humidity levels are measured. The sensitivity (S) and response (R) are given by the equation S ═ C, respectivelyi-C0) Δ RH and R ═ Ci/C0Is determined in which CiAnd C0Is the capacitance value of the sensor at x% RH and 0% RH.
The response speed of the sensor is reflected by the response time and the recovery time, and therefore the performance and the measurement accuracy of the sensor can be obtained.
The capacitance-frequency characteristics of the detection system are shown in fig. 7. In at different humidity (RH) levels2O3The capacitance of GO thin film sensors varies significantly with frequency. The RH level ranges from 11% to 97% and the sweep frequency ranges from 100Hz to 1 MHz.
For the proposed In2O3GO thin film sensors, it can be seen from the figure that the capacitance increases monotonically with increasing RH level when the frequency is fixed, indicating that absorbed water molecules can enhance the polarization effect. At the same time, the dielectric constant also increases.
When the RH level is fixed, the capacitance value decreases with increasing frequency, and the capacitance-frequency curve becomes more gradual as the frequency increases. In addition, the capacitance of the sensor at 100Hz is much higher than other frequencies. When the frequency was 100Hz and the RH level was changed from 11% to 97%, the capacitance of the sensor was changed from 13pF to 4395pF, which showed high sensitivity. Therefore, 100Hz is preferred as the operating frequency.
Fig. 8 is a graph of the capacitance measured at RH level of the sensor of the present embodiment from 0% to 97% as a function of relative humidity. At 0% RH, the capacitance of the sensor is about 12.2 pF. As the RH level was gradually increased, a significant increase in real-time capacitance could be observed. At 97% RH, the capacitance can reach 102,989pF, an increase of 4 orders of magnitude over the capacitance at 0% RH.
At the same time, the measured data is fitted nonlinearly, In2O3-GO thin film sensor fitted equation of y-0.24 x8.87Coefficient of regression R2It was 0.999, and the degree of fitting was high. Accordingly, the equation for fitting pure indium oxide is y 0.000054x4.38(R20.876), pure GO corresponds to y 0.51x8.96(R2＝0.999)。
FIG. 9 compares In2O3-GO hybrid thin film sensor with pure In2O3And capacitance values of pure GO at different relative humidity levels. In a 0% RH drying bottle and 11-97% RH waterCapacitance measurements were made between the levels to achieve response measurements at different RH levels and recovery measurements at 0% RH with a response and recovery interval of 150 seconds. FIG. 9 illustrates that pure In rises from 0% to 97% RH level2O3The sensor capacitance increases from 12pF to 25335pF, In2O3The capacitance change of the GO hybrid film sensor is from 12 to 102989 pF. In contrast, the mixed film sensor can be considered to exhibit the highest sensitivity among the three sensors. When the humidity is low, In2O3The capacitance values of the GO hybrid membrane sensors also show a significant change in capacitance values, indicating that the sensors have good sensitivity even at low humidity. Thus, In is mixed2O3Forming a thin film sensor with GO can improve overall performance.
In is shown In FIG. 102O3-GO mixed film sensor and pure In2O3And response recovery characteristics of the GO sensor. The system response time is defined as the time required for the capacitance to reach 90% of its maximum value. The recovery time is the time required for the capacitance to reach 10% of its minimum value. The response time of the hybrid film sensor is much shorter than that of a single material, the response only needs 15 seconds, and the recovery time is 2 seconds.
FIG. 11 shows In2O3GO 7:3 and different percentages of In2O3And GO, i.e. In2O3GO-1: 0, 17:3, 5:5, 3:7, 3:17 and 0:1, and their maximum capacitance at 43% RH is plotted in fig. 11. Obviously, when In2O3And GO is 7:3, its maximum capacitance is the largest under the same conditions, proving it to be more sensitive than sensors made from other ratios.
The capacitance value test for switching RH levels between 0% RH and another 9 different RH (11-97% RH) at a scanning frequency of 100Hz is shown in fig. 12. We compared using an up-going test with a low to high RH level and a down-going test with a high to low RH level. The response and recovery time was still 150 seconds. As can be seen from the figure, the capacitance values obtained by the up test and the down test are substantially identical. Thus, a sensor with accurate measurement and good recovery can be obtained.
The circular and star curves in fig. 13 represent the capacitance change of the sensor under adsorption and desorption, respectively. It represents the hysteresis characteristics of the sensor, based on the entire process of RH levels from 0% to 97%. Formula H ═ CU-CD) (ii) S (% RH) represents the hysteresis characteristic, where S is the sensitivity of the sensor, CUAnd CDRespectively, the capacitance values during adsorption and desorption. A maximum was obtained at 85% RH, which was 0.054% RH.
In2O3Repeated measurements of the GO thin film sensor are shown in fig. 14, verified by the change in capacitance at 23%, 52% and 75% RH values. Substitution measurements of 0% RH and the corresponding RH were performed under each condition and cycled three times. From the measurement results, it can be seen that the trend and magnitude of the three measured capacitances are approximately the same under the same conditions. The response time and recovery time are also substantially the same, exhibiting the same sensitivity. Thus, the sensor has good consistency and repeatability.
The Complex Impedance Spectroscopy (CIS) measurements of the sensor at different humidity levels are shown in fig. 15. In order to make it more intuitive to display the complex impedance plot, some of the real and imaginary parts are enlarged at different scales.
In2O3Water adsorption mechanism for GO humidity sensors
The above studies indicate that In2O3The humidity sensitivity of the-GO mixed membrane sensor is excellent, so that the-GO mixed membrane sensor is an ideal material for humidity detection. GO and In2O3The integration of (a) greatly enhances the humidity sensing capability. As shown In FIG. 1, In2O3Has a cubic nano structure, and greatly helps to absorb and disperse water molecules. At the same time, it has a larger surface specific surface area, In, than the original GO2O3GO hybrid membranes can provide a higher proportion of active sites available for water diffusion and can accelerate adsorption and desorption reactions on the surface.
In is shown In FIG. 12O3-water adsorption process on GO mixed membrane surface. Initially, In2O3-GO hybrid membranesExposure to water molecules, adsorption of which starts with In2O3The active site of (1). This is the first stage of water adsorption, the water layer being discrete. With increasing RH, the second phase begins, followed by multilayer adsorption. Then, In2O3Water molecules on the GO surface form a continuous layer. The adsorbed water molecules are ionized to H3O+The Grottthus chain reaction is H2O+H3O+→H3O++H2And O. When water molecules penetrate to GO membrane and In2O3With an intermediate layer between the films, the dielectric constant is greatly increased and the capacitance value is correspondingly increased.
The following details the detection system of the sensor obtained by the above preparation method provided in this embodiment
When the structure size of the interdigital electrode is reduced to be below the micron level, the detection system can detect the humidity change below the capacitance peak value of 250nf, and the capacitance sensitivity of the interdigital electrode sensor reaches the pf level;
in particular, In2O3The water adsorption process on the surface of the-GO mixed membrane is ① In2O3Exposure of the GO mixed film to water molecules, adsorption of water molecules starting with In2 O 3② with increasing RH, the second phase begins with the subsequent multi-layer adsorption, ③ then In2O3Water molecules on the GO surface forming a continuous layer, ④ adsorbed water molecules being ionized into H3O+The Grottthus chain reaction, H2O+H3O+→H3O++H2O ⑤ when water molecule permeates to GO membrane and In2O3With an intermediate layer between the films, the dielectric constant increases and the capacitance value increases accordingly.
In obtained by the production method of this example is shown In sequence from FIG. 16 to FIG. 182O3-the hardware overall framework, the overall 3D circuitry and the hardware part of the exhaled breath humidity detection system of the GO humidity sensor operational flow.
The integrated circuit of the detection system comprises an STM32 minimum system module, a peripheral interface circuit, a power supply and a capacitive sensing chip.
As shown in fig. 19, the STM32 minimum system module includes an STM32 single chip microcomputer, a WiFi module, and a clock module; the STM32 single chip microcomputer is an STM32F405, realizes digital-to-analog conversion, receives and sends data, is responsible for transmitting real-time data acquired from the humidity sensor to the mobile communication port, and is provided with an alarm device for alarming when the system is abnormal so as to remind people of abnormal movement;
the WiFi module is the ESP8266 chip, and its connection with STM32 singlechip includes 3 lines: a CE pin, an SCLK serial clock pin and an I/O serial data pin, wherein Vcc2 is a standby power supply and is externally connected with a 32.768kHz crystal oscillator to provide timing pulse for a chip;
the clock module is a DS1302 chip, is in an SPI bus driving mode, and not only needs to write control words into the register, but also needs to read data of the corresponding register; the control word is always output from the lowest order bit, data is written into the clock module at the rising edge of the next SCLK clock after the control word instruction is input, and the data input is started from the 0 bit of the lowest order bit; similarly, the data of the clock module is read at the falling edge of the next SCLK pulse following the 8-bit control word instruction, the read data also being from the least significant bit to the most significant bit.
As shown in fig. 20, the peripheral interface circuit uses an I2C internal integrated circuit, and is connected in parallel with an OLED and a serial Wifi; four-way ADCs are reserved, including: and sampling, namely, the FFT converts the waveform time domain signal into a frequency domain signal, one path of oscilloscope connection is reserved, and the other path of oscilloscope connection is connected to the WiFi module to keep real-time communication.
As shown in fig. 21, the power supply uses microsb for 5V power supply, and the 5V power supply is stabilized at 3.3V by an LDO linear regulator for use by the single chip and the capacitive sensing chip; in addition, a code is set to judge that two LED lamps are connected in parallel, and the code is used for detecting a processing scheme when the code has a problem and indicating that the program runs normally when a green lamp is displayed; and/or
As shown in fig. 22, the capacitive sensing chip is preferably an FDC2214 chip; the highest resolution is 28 bits, the maximum sampling rate is 13.3ksps, the capacitance with the maximum value of 250nF can be detected, the operation in a temperature range from minus 40 ℃ to 125 ℃ is met, and an application circuit is arranged in the capacitor; and the waveform as a whole is shifted up in the presence of negative voltage using a dc bias.
The WiFi module supports three working modes of STA, AP and STA + AP, the STA + AP mode is preferably used, the WiFi module can be connected to the Internet through a router, and can also be used as a WiFi hotspot to enable other equipment to be connected to the WiFi module, so that the switching between a wide area network and a local area network is realized;
the communication is carried out by utilizing high and low levels through a TTL signal channel and a WiFi module, and the TTL is preferably converted into 232 or 485 signals generally;
the curve is stable and smooth when breathing normally; when the curve becomes jumble disorderly along with the rush of breathing, the occurrence of an accident situation is judged, and alarm information is sent to a plurality of connected mobile terminals immediately when the accident situation occurs, so that the user can be timely treated and cured under the accident situation.
The mobile terminal who is connected with the wiFi module is the cell-phone, and mobile terminal's APP receives data with two kinds of modes: one is to read data directly from the device, and the other is to read data from a server database; meanwhile, the obtained data is used for drawing a breathing curve, and the curve is displayed on a screen; the user can check the data at any time or permanently store the data in a memory card of the mobile phone; in addition, a scanning frequency can be performed; setting upper and lower thresholds in the APP program, if the value is too low or too high, the information will be sent to the lower computer for adjustment, when the middle of the two thresholds is reached, no adjustment is needed so that the system can operate at the optimum frequency and plot the curve in the appropriate range; meanwhile, an alarm function can be realized, when an emergency occurs, a buzzer in the portable device starts to operate, and then the device transmits alarm information to all users connected thereto, so that an accident can be dealt with at the first time.
It will be understood that modifications and variations can be effected by a person skilled in the art in light of the above teachings and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims (14)

1. Aiming at the preparation method of the exhaled breath humidity sensor, the method is characterized In that the surface of the humidity sensor adopts indium oxide-graphene oxide In2O3-GO humidity sensor preparation step comprising:
1) firstly, In is prepared by a hydrothermal method2O3；
2) Then, using an epoxy resin material as a substrate of the interdigital electrode; winding electrode materials on the center in the same direction at two different starting points on the substrate by using a photoetching technology to form an interdigital electrode back pattern;
3) further, In was prepared2O3① mixing 0.01g of In2O3The powder was mixed with 1.71g of 0.3 wt% GO In water to get In2O3Stirring the mixture for 20 minutes at the mass percent ratio of GO being 7:3 at ②, then carrying out ultrasonic treatment for 30 minutes to obtain a uniform solution, absorbing the solution ③ by a rubber head dropper, and dropping the solution on an epoxy resin substrate with interdigital electrodes to form a humidity-sensitive sensing film, and drying the sensor for 4 hours at ④ in a vacuum oven at the temperature of 60 ℃;
wherein In is produced on the surface of the epoxy resin substrate2O3After the GO is mixed with the film, the capacitance of the interdigital electrode changes along with the change of humidity.
2. The method of claim 1, wherein In step 1) is In2O3The preparation method comprises ① mixing 12g of CO (NH)2)2And 1.52g of In (NO)3)3
Figure DEST_PATH_IMAGE002
4.5H2O is mixed and dissolved in 80mL of deionized water, and then stirred for 20 minutes and sonicated for 30 minutes, ② the resulting mixture is hydrothermally treated at 120 ℃ for 12 hours, then dried in a vacuum oven at 60 ℃ for 6 hours, ③ the indium oxide is obtained after annealing at 500 ℃ for 2 hours in argon.
3. A detection system of a humidity sensor obtained by the preparation method of claim 1 or 2, wherein when the structure size of the interdigital electrode is reduced below micron level, humidity change with capacitance value below 250nf can be detected, and the capacitance sensitivity of the interdigital electrode sensor reaches pf level;
in particular, In2O3The water adsorption process on the surface of the-GO mixed membrane is ① In2O3Exposure of the GO mixed film to water molecules, adsorption of water molecules starting with In2O3② with increasing humidity, the second phase begins, then multi-layer adsorption occurs, ③ then In2O3Water molecules on the GO surface forming a continuous layer, ④ adsorbed water molecules being ionized into H3O+The Grottthus chain reaction, H2O+H3O+→H3O++H2O ⑤ when water molecule permeates to GO membrane and In2O3With an intermediate layer between the films, the dielectric constant increases and the capacitance value increases accordingly.
4. The detection system according to claim 3, wherein the integrated circuit of the detection system comprises STM32 minimal system module, peripheral interface circuit, power supply and capacitive sensing chip.
5. The detection system according to claim 4, wherein the STM32 minimum system module comprises an STM32 single chip microcomputer, a WiFi module and a clock module;
the STM32 singlechip is STM32F405, realizes digital-to-analog conversion, and the receipt and the sending of data are responsible for the real-time data with humidity transducer collection, transmit the mobile communication port, set up alarm device simultaneously, report to the police when discovering the system appearance unusually, remind people to appear unusual abnormal change.
6. The detection system according to claim 5, wherein the WiFi module is an ESP8266 chip, and the connection with the STM32 singlechip comprises 3 lines: CE pin, SCLK serial clock pin and I/O serial data pin, Vcc2 is standby power supply, external 32.768kHz crystal oscillator, provides timing pulse for the chip.
7. The detection system according to claim 5, wherein the clock module is a DS1302 chip, and is in an SPI bus driving mode, and is required to not only write the control word into the register, but also read the data of the corresponding register; the control word is always output from the lowest order bit, data is written into the clock module at the rising edge of the next SCLK clock after the control word instruction is input, and the data input is started from the 0 bit of the lowest order bit; similarly, the data of the clock module is read at the falling edge of the next SCLK pulse following the 8-bit control word instruction, the read data also being from the least significant bit to the most significant bit.
8. The detection system as claimed in claim 4 or 5, wherein the external interface circuit uses an I2C internal integrated circuit, parallel connected OLED and serial Wifi; four-way ADCs are reserved, including: and sampling, namely, the FFT converts the waveform time domain signal into a frequency domain signal, one path of oscilloscope connection is reserved, and the other path of oscilloscope connection is connected to the WiFi module to keep real-time communication.
9. The detection system according to claim 4 or 5, wherein the power supply uses Microusb for 5V power supply, and the 5V power supply is stabilized at 3.3V by using an LDO linear regulator for the single chip microcomputer and the capacitance sensing chip; in addition, a code is set to judge that two LED lamps are connected in parallel, and the code is used for detecting a processing scheme when the code has a problem and indicating that the program runs normally when a green lamp is displayed; and/or
The capacitive sensing chip is an FDC2214 chip; the highest resolution is 28 bits, the maximum sampling rate is 13.3ksps, the capacitance with the maximum value of 250nF can be detected, the operation in a temperature range from minus 40 ℃ to 125 ℃ is met, and an application circuit is arranged in the capacitor; and the waveform as a whole is shifted up in the presence of negative voltage using a dc bias.
10. The detection system according to claim 5, wherein the WiFi module supports three operation modes of STA, AP and STA + AP.
11. The detection system according to claim 10, wherein the WiFi module uses STA + AP mode to connect to internet through router and also to serve as WiFi hotspot to enable other devices to connect to the module, thereby realizing switching between wan and lan.
12. The detection system of claim 11, wherein the TTL is converted to a 232 or 485 signal by communicating with the WiFi module via a TTL signal path at a high or low level.
13. The detection system of claim 12, wherein the curve is stable and smooth when breathing normally; when the curve becomes jumble disorderly along with the rush of breathing, the occurrence of an accident situation is judged, and alarm information is sent to a plurality of connected mobile terminals immediately when the accident situation occurs, so that the user can be timely treated and cured under the accident situation.
14. The detection system according to claim 4, wherein the mobile terminal connected to the WiFi module is a mobile phone, and the APP of the mobile terminal receives data in two ways: one is to read data directly from the device, and the other is to read data from a server database; meanwhile, the obtained data is used for drawing a breathing curve, and the curve is displayed on a screen; the user can check the data at any time or permanently store the data in a memory card of the mobile phone; in addition, a scanning frequency can be performed; setting upper and lower thresholds in the APP program, if the value is too low or too high, the information will be sent to the lower computer for adjustment, when the middle of the two thresholds is reached, no adjustment is needed so that the system can operate at the optimum frequency and plot the curve in the appropriate range; meanwhile, an alarm function can be realized, when an emergency occurs, a buzzer in the portable device starts to operate, and then the device transmits alarm information to all users connected thereto, so that an accident can be dealt with at the first time.
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