Air microorganism quantitative detection method and system based on impedance sensing

Abstract

The invention provides an air microorganism quantitative detection method and system based on impedance sensing, and relates to the technical field of air microorganism detection.The method comprises the steps that air microorganisms are adsorbed through interdigital electrodes, and the interdigital electrodes with microorganisms of different concentrations are obtained; connecting the interdigital electrodes with the microorganisms with different concentrations with an impedance detection module, and carrying out impedance measurement to obtain impedance data; the humidity monitoring module is used for monitoring the air humidity around the interdigital electrode in real time to obtain a corresponding air humidity value; fitting the impedance data to obtain a linear relation between an electrode interface resistance change value and the total number of microorganisms on the electrode; based on the linear relation of the air humidity value, the electrode interface resistance change value and the total number of microorganisms on the electrode, a standard relation curve is constructed, an air microorganism detection result is obtained, and quantitative detection of the air microorganisms is completed. The invention solves the problems of difficulty in direct detection of air microorganisms, long detection time, dependence on large expensive instruments and influence of composition of a detection medium solution.

Description

Technical Field

[0001] This specification relates to the technical field of air microorganism detection, and particularly to a method and system for quantitatively detecting air microorganisms based on impedance sensing. Background Art

[0002] Pathogenic microorganisms in the air have the characteristics of infecting more people, spreading faster, and being more difficult to block. Therefore, the research on portable and rapid detection methods for pathogenic microorganisms has attracted much attention. At present, the detection methods for pathogenic microorganisms in the air still have limitations, including: (1) Traditional culture methods and immunological detection methods are time-consuming and have complex operation processes, making it difficult to achieve rapid detection; (2) Polymerase chain reaction methods require expensive analysis equipment and additional purification steps; (3) Fluorescence methods require stable fluorescence probes and large microscope instruments to complete the detection. Existing technologies require sampling and transferring air microorganisms to solid media or solutions, with complex operations, many steps, and long time consumption. Summary of the Invention

[0003] Aiming at the above deficiencies in the prior art, the method and system for quantitatively detecting air microorganisms based on impedance sensing provided by the present invention solve the problems of difficult direct detection of air microorganisms, long detection time, dependence on large and expensive instruments, and influence by the composition of the detection medium solution.

[0004] To achieve the above invention objective, the technical solution adopted by the present invention is: A system for quantitatively detecting air microorganisms based on impedance sensing, comprising:

[0005] An acquisition module, configured to adsorb air microorganisms by using interdigital electrodes to obtain interdigital electrodes with different concentrations of microorganisms;

[0006] An impedance detection module, configured to measure the impedance of the interdigital electrodes to obtain impedance data;

[0007] A humidity monitoring module, configured to monitor the air humidity around the interdigital electrodes in real time to obtain corresponding air humidity values;

[0008] A parameter fitting module, configured to fit the impedance data to obtain a linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode;

[0009] A detection module, configured to construct a standard relationship curve based on the air humidity value, the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode, obtain the air microorganism detection result, and complete the quantitative detection of air microorganisms.

[0010] Further, the impedance detection module includes: an STM32C8T6 single-chip microcomputer, an AD5933 chip, and an off-chip circuit; wherein, the PB10 pin of the STM32C8T6 single-chip microcomputer is connected to the SCL pin of the AD5933 chip, the PB11 pin of the STM32C8T6 single-chip microcomputer is connected to the SDA pin of the AD5933 chip, the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin, PA6 pin, and VDD pin of the STM32C8T6 single-chip microcomputer are connected to the off-chip circuit, and the VDD pin, VOUT pin, RFB pin, and VIN pin of the AD5933 chip are connected to the off-chip circuit.

[0011] Further, the off-chip circuit includes a signal processing circuit, a multi-channel resistor network circuit, and a power supply module circuit; wherein, one end of the signal processing circuit is connected to the VOUT pin of the AD5933 chip, the other end of the signal processing circuit is respectively connected to one end of the multi-channel resistor network circuit and the power supply module circuit, one end of the multi-channel resistor network circuit is connected to the power supply module circuit, the other end of the multi-channel resistor network circuit is respectively connected to the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin, and PA6 pin of the STM32C8T6 single-chip microcomputer, and the power supply module circuit is respectively connected to the VDD pin of the STM32C8T6 single-chip microcomputer and the VDD pin of the AD5933 chip.

[0012] Further, the power supply module circuit includes: a +5V output terminal, a -5V output terminal, and a +3.3V output terminal; wherein, the +5V output terminal and the -5V output terminal are respectively connected to the signal processing circuit and the multi-channel resistor network circuit, and the +3.3V output terminal is respectively connected to the multi-channel resistor network circuit, the VDD pin of the STM32C8T6 single-chip microcomputer, and the VDD pin of the AD5933 chip.

[0013] Further, the signal processing circuit includes a Butterworth second-order low-pass filter circuit, a Butterworth second-order high-pass filter circuit, and a voltage follower circuit; wherein, the first pin of the Butterworth second-order low-pass filter circuit is connected to the VOUT pin of the AD5933 chip, the second pin of the Butterworth second-order low-pass filter circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the Butterworth second-order low-pass filter circuit is connected to the -5V output terminal of the power supply module circuit, the fourth pin of the Butterworth second-order low-pass filter circuit is connected to the first pin of the Butterworth second-order high-pass filter circuit, the second pin of the Butterworth second-order high-pass filter circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the Butterworth second-order high-pass filter circuit is connected to the -5V output terminal of the power supply module circuit, the fourth pin of the Butterworth second-order high-pass filter circuit is connected to the first pin of the voltage follower circuit, the second pin of the voltage follower circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the voltage follower circuit is connected to the -5V output terminal of the power supply module circuit, and the fourth pin of the voltage follower circuit is connected to the multi-channel resistor network circuit.

[0014] Further, the multi-channel resistance network circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, a resistor R13, a resistor R14, a first analog switch, a second analog switch, an amplifier, and interdigital electrodes; wherein, a first pin of the first analog switch is connected to the +5V output terminal of the power supply module circuit, a second pin of the first analog switch is connected to the fourth pin of the voltage follower circuit, a third pin of the first analog switch is connected to the PA1 pin of the STM32C8T6 single-chip microcomputer, a fourth pin of the first analog switch is connected to the PA2 pin of the STM32C8T6 single-chip microcomputer, a fifth pin of the first analog switch is connected to the PA3 pin of the STM32C8T6 single-chip microcomputer, a sixth pin of the first analog switch is respectively connected to one end of the resistor R3, one end of the resistor R4, one end of the resistor R5, one end of the resistor R6, one end of the resistor R7, and one end of the interdigital electrodes, the other ends of the resistor R3, the resistor R4, the resistor R5, the resistor R6, the resistor R7, and the interdigital electrodes are respectively connected to the second pin of the amplifier and the second pin of the second analog switch, a first pin of the amplifier is connected to one end of the resistor R13, the other end of the resistor R13 and one end of the resistor R14 are both grounded, the other end of the resistor R14 is connected to the +3.3V output terminal of the power supply module circuit, a third pin of the amplifier is connected to the -5V output terminal of the power supply module circuit, a fourth pin of the amplifier is respectively connected to one end of the resistor R2, one end of the resistor R8, one end of the resistor R9, one end of the resistor R10, one end of the resistor R11, and one end of the resistor R12, a fifth pin of the amplifier is connected to the +5V output terminal of the power supply module circuit, the other end of the resistor R2 is respectively connected to one end of the resistor R1 and the VIN pin of the D5933 chip, the other end of the resistor R1 is connected to the RFB pin of the D5933 chip, the other ends of the resistor R8, the resistor R9, the resistor R10, the resistor R11, and the resistor R12 are all connected to the sixth pin of the second analog switch, a first pin of the second analog switch is connected to the +5V output terminal of the power supply module circuit, a third pin of the second analog switch is connected to the PA6 pin of the STM32C8T6 single-chip microcomputer, a fourth pin of the second analog switch is connected to the PA5 pin of the STM32C8T6 single-chip microcomputer, and a fifth pin of the second analog switch is connected to the PA4 pin of the STM32C8T6 single-chip microcomputer.

[0015] An air microorganism quantitative detection method based on impedance sensing includes:

[0016] S1: Adsorb air microorganisms by using interdigital electrodes to obtain interdigital electrodes with different concentrations of microorganisms;

[0017] S2: Connect the interdigital electrodes with different concentrations of microorganisms to the impedance detection module for impedance measurement to obtain impedance data;

[0018] S3: Use the humidity monitoring module to monitor the air humidity around the interdigital electrodes in real time to obtain the corresponding air humidity value;

[0019] S4: Fit the impedance data to obtain the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode;

[0020] S5: Based on the air humidity value, the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode, construct a standard relationship curve to obtain the air microorganism detection result and complete the quantitative detection of air microorganisms.

[0021] Further, the expression for the change value of the electrode interface resistance is:

[0022] ΔR i (Ω) = R effect ·N bac +B;

[0023] R effect = R 1 ·A;

[0024]

[0025] Among them, R i represents the electrode interface resistance, R effect represents the equivalent resistance value of a single microorganism after correction, N bac represents the total number of microorganisms on the electrode, A and B represent correction coefficients, R 1 represents the equivalent resistance value of a single microorganism, Φ represents the volume fraction of a single microorganism, σ i represents the cytoplasmic conductivity of microorganisms in the air, σ m represents the conductivity of the environmental medium at the interdigital electrode interface, σ out represents the equivalent shell membrane conductivity of microorganisms in the air, R represents the radius of a single microorganism, d represents the shell membrane thickness of a single microorganism, E represents the electrode constant, N represents the total electrode index, L represents the electrode finger length, K represents the complete elliptic integral of the first kind, k represents the modulus of the complete elliptic integral of the first kind, w e represents the spacing of the interdigital electrodes, s e represents the width of the interdigital electrodes.

[0026] Further, the expression for the volume fraction of a single microorganism is:

[0027]

[0028] The beneficial effects of the present invention are as follows: (1) Based on existing sampling techniques such as natural sedimentation method, after adsorbing airborne microorganisms onto the interdigitated electrodes, the impedance change generated by the interaction between the interdigitated microelectrodes and the surface of airborne microorganisms is directly monitored, that is, impedance detection is directly carried out in the air, overcoming the influence of the composition of the detection medium solution on the electrochemical impedance detection method; (2) An equivalent circuit of AIDEB (Air Interdigitated Electrodes and Bacteria) is proposed to simulate the impedance spectrum and electrical response of the interdigitated electrodes attached with microorganisms, and a standard curve between the logarithm of the total number of microorganisms N bac on the electrode and the change value ΔR i of the electrode interface resistance of the AIDEB equivalent circuit is established, providing a new data analysis method for detecting airborne microorganisms by electrochemical impedance method and obtaining more accurate analysis data; (3) The impedance detection module and the humidity monitoring module can be further integrated. The overall module size is within the range of 10 cm × 10 cm, and the detection duration is less than 5 minutes, enabling rapid and portable detection; (4) Direct detection of airborne microorganisms is achieved without sampling and transferring to solid medium or solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] This specification will further illustrate in the form of exemplary embodiments, and these exemplary embodiments will be described in detail through the drawings. These embodiments are not restrictive. In these embodiments, the same numbers represent the same structures, where:

[0030] Figure 1 is a schematic diagram of the modules of a quantitative detection system for airborne microorganisms based on impedance sensing according to some embodiments of this specification;

[0031] Figure 2 is an exemplary flowchart of a method for quantitatively detecting airborne microorganisms based on impedance sensing according to some embodiments of this specification;

[0032] Figure 3 is an exemplary schematic diagram of an impedance detection module according to some embodiments of this specification;

[0033] Figure 4 is an exemplary schematic diagram of a humidity monitoring module according to some embodiments of this specification;

[0034] Figure 5 is an exemplary schematic diagram of an AIDEB equivalent circuit according to some embodiments of this specification. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The specific embodiments of the present invention will be described below to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0036] Embodiment 1

[0037] Figure 1 It is a schematic diagram of the modules of a quantitative air microorganism detection system based on impedance sensing shown in some embodiments of this specification.

[0038] In some embodiments, the quantitative air microorganism detection system based on impedance sensing may include an acquisition module, an impedance detection module, a humidity monitoring module, a parameter fitting module, and a detection module.

[0039] The acquisition module is used to adsorb air microorganisms using interdigital electrodes to obtain interdigital electrodes with different concentrations of microorganisms.

[0040] The air microorganisms may include BL21 Escherichia coli.

[0041] In some embodiments, the ratio of the width to the spacing of the interdigital electrodes is 1:1, the spacing and width range is 1 - 30 μm, the length range is 1.5 - 2.5 mm, the number of interdigital pairs ranges from 50 to 80 pairs, and the interdigital electrodes are formed by patterning a metal layer on a quartz glass or alumina ceramic substrate. Among them, the specific structure of the metal layer is a titanium layer of 20 - 30 nm and a gold layer of 100 - 200 nm; among them, the microorganisms on the interdigital electrodes are one or a combination of more than one of bacteria or fungi, and the total number of microorganisms on the interdigital electrodes ranges from 3000 to 50000 CFU.

[0042] The impedance detection module is used to measure the impedance of the interdigital electrodes to obtain impedance data.

[0043] The impedance data is data reflecting the resistance value and reactance value of the interdigital electrodes.

[0044] In some embodiments, the interdigital electrodes with different concentrations of attached microorganisms can be connected to the impedance detection module, and a swept - frequency direct impedance measurement in the air is performed in the frequency band of 100 - 100000 Hz to obtain impedance data.

[0045] In some embodiments, such as Figure 3As shown, the impedance detection module may include: an STM32C8T6 single-chip microcomputer, an AD5933 chip, and an external circuit; among them, the PB10 pin of the STM32C8T6 single-chip microcomputer is connected to the SCL pin of the AD5933 chip, the PB11 pin of the STM32C8T6 single-chip microcomputer is connected to the SDA pin of the AD5933 chip, the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin, PA6 pin, and VDD pin of the STM32C8T6 single-chip microcomputer are connected to the external circuit, and the VDD pin, VOUT pin, RFB pin, and VIN pin of the AD5933 chip are connected to the external circuit.

[0046] In some embodiments, the AD5933 chip is controlled by the STM32C8T6 single-chip microcomputer through the IIC-compatible serial interface protocol. The AD5933 chip internally includes a 27-bit phase accumulator, a waveform memory, a digital-to-analog converter, and a low-pass filter to form an excitation signal generation part, and a current-voltage amplifier, a programmable gain amplifier, an anti-aliasing filter, and an analog-to-digital converter to form an AD acquisition part; a signal processing part is formed based on the digital signal processor core of the AD5933 chip, that is, the digital data output by the analog-to-digital converter is transmitted to the digital signal processor core, and the discrete Fourier transform processing is performed on the sampled data to obtain the real part value and the imaginary part value of the discrete Fourier transform as impedance data.

[0047] In some embodiments, the external circuit may include a signal processing circuit, a multi-channel resistance network circuit, and a power supply module circuit; among them, one end of the signal processing circuit is connected to the VOUT pin of the AD5933 chip, the other end of the signal processing circuit is respectively connected to one end of the multi-channel resistance network circuit and the power supply module circuit, one end of the multi-channel resistance network circuit is connected to the power supply module circuit, the other end of the multi-channel resistance network circuit is respectively connected to the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin, and PA6 pin of the STM32C8T6 single-chip microcomputer, and the power supply module circuit is respectively connected to the VDD pin of the STM32C8T6 single-chip microcomputer and the VDD pin of the AD5933 chip.

[0048] In some embodiments, the signal processing circuit is used to filter out signal noise and improve the driving ability. The multi-channel resistance network is used to switch between two modes: an unknown resistance impedance to be measured and a series of calibration resistors with known resistances. When switched to the calibration impedance with known resistance, the impedance detection module detects the series of calibration resistors with known resistances, and then calculates the corresponding series of gain coefficients. When switched to the unknown resistance impedance to be measured, the impedance detection module combines the real part value and the imaginary part value of the discrete Fourier transform obtained from the impedance measurement to be made with the aforementioned series of gain coefficients to calculate the resistance value (real part of the impedance) and the reactance value (imaginary part of the impedance). The selection of the gain coefficient needs to match the appropriate impedance range to be measured to avoid saturation of the analog-to-digital converter beyond its linear operating range. The power supply module circuit is used to provide the operating voltages required by the microcontroller and the chips and devices used.

[0049] In some embodiments, the power supply module circuit may include: a +5V output terminal, a -5V output terminal, and a +3.3V output terminal; wherein, the +5V output terminal and the -5V output terminal are respectively connected to the signal processing circuit and the multi-channel resistance network circuit, and the +3.3V output terminal is respectively connected to the multi-channel resistance network circuit, the VDD pin of the STM32C8T6 single-chip microcomputer, and the VDD pin of the AD5933 chip.

[0050] In some embodiments, the power supply module circuit consists of a 5V DC power adapter, a voltage inversion conversion circuit for outputting -5V voltage based on the MC34063ADR chip, and a chip of AMS1117 low-dropout linear regulator for stably outputting 3.3V voltage to meet the ±5V power supply requirements of the OPA820IDBVR operational amplifier chip; the 3.3V power supply requirements of the STM32 series single-chip microcomputer, the AD5933 impedance conversion chip, the MC34063ADR chip, and the AMS1117-3.3 chip; and the 5V power supply requirement of the 74HC4051N eight-channel multiplexer.

[0051] In some embodiments, the specific structure of the voltage inversion conversion circuit based on the MC34063ADR chip is the voltage inversion conversion circuit structure of the typical application example in the MC34063ADR chip manual of Texas Instruments. The parameters of the peripheral passive components are designed around the following conditions: maximum output current of 200 - 400 mA, output voltage ripple of 20 - 50 mV, chip operating frequency of 45 - 75 kHz, and output -5V voltage.

[0052] In some embodiments, the excitation signal is output from the output port of the AD5933 chip, processed by an active band-pass filter circuit and a voltage follower circuit, and then applied to the interdigital electrodes. The interdigital electrodes respond, and the current signal thereon flows into a multi-channel resistance network, that is, into the OPA820IDBVR operational amplifier chip, and is converted into a voltage output to the input port of the AD5933 chip by acting with different feedback channel resistances. Then, the AD5933 chip completes the subsequent AD acquisition work.

[0053] In some embodiments, the signal processing circuit may include a Butterworth second-order low-pass filter circuit, a Butterworth second-order high-pass filter circuit, and a voltage follower circuit; wherein, the first pin of the Butterworth second-order low-pass filter circuit is connected to the VOUT pin of the AD5933 chip, the second pin of the Butterworth second-order low-pass filter circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the Butterworth second-order low-pass filter circuit is connected to the -5V output terminal of the power supply module circuit, the fourth pin of the Butterworth second-order low-pass filter circuit is connected to the first pin of the Butterworth second-order high-pass filter circuit, the second pin of the Butterworth second-order high-pass filter circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the Butterworth second-order high-pass filter circuit is connected to the -5V output terminal of the power supply module circuit, the fourth pin of the Butterworth second-order high-pass filter circuit is connected to the first pin of the voltage follower circuit, the second pin of the voltage follower circuit is connected to the +5V output terminal of the power supply module circuit, the third pin of the voltage follower circuit is connected to the -5V output terminal of the power supply module circuit, and the fourth pin of the voltage follower circuit is connected to the multi-channel resistance network circuit.

[0054] In some embodiments, the signal processing circuit may be composed of an active band-pass filter circuit and a voltage follower circuit based on the OPA820IDBVR operational amplifier chip. The active band-pass filter circuit is composed of a Butterworth second-order low-pass filter circuit and a Butterworth second-order high-pass filter circuit based on the Sallen Key topology structure, and the passband frequency range is from 100Hz to 300KHz.

[0055] In some embodiments, the multi-channel resistance network circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, a resistor R13, a resistor R14, a first analog switch, a second analog switch, an amplifier, and interdigital electrodes; wherein, a first pin of the first analog switch is connected to the +5V output terminal of the power supply module circuit, a second pin of the first analog switch is connected to a fourth pin of the voltage follower circuit, a third pin of the first analog switch is connected to the PA1 pin of the STM32C8T6 single-chip microcomputer, a fourth pin of the first analog switch is connected to the PA2 pin of the STM32C8T6 single-chip microcomputer, a fifth pin of the first analog switch is connected to the PA3 pin of the STM32C8T6 single-chip microcomputer, a sixth pin of the first analog switch is respectively connected to one end of the resistor R3, one end of the resistor R4, one end of the resistor R5, one end of the resistor R6, one end of the resistor R7, and one end of the interdigital electrodes, the other ends of the resistor R3, the resistor R4, the resistor R5, the resistor R6, the resistor R7, and the interdigital electrodes are respectively connected to a second pin of the amplifier and a second pin of the second analog switch, a first pin of the amplifier is connected to one end of the resistor R13, the other end of the resistor R13 and one end of the resistor R14 are both grounded, the other end of the resistor R14 is connected to the +3.3V output terminal of the power supply module circuit, a third pin of the amplifier is connected to the -5V output terminal of the power supply module circuit, a fourth pin of the amplifier is respectively connected to one end of the resistor R2, one end of the resistor R8, one end of the resistor R9, one end of the resistor R10, one end of the resistor R11, and one end of the resistor R12, a fifth pin of the amplifier is connected to the +5V output terminal of the power supply module circuit, the other end of the resistor R2 is respectively connected to one end of the resistor R1 and the VIN pin of the D5933 chip, the other end of the resistor R1 is connected to the RFB pin of the D5933 chip, the other ends of the resistor R8, the resistor R9, the resistor R10, the resistor R11, and the resistor R12 are all connected to a sixth pin of the second analog switch, a first pin of the second analog switch is connected to the +5V output terminal of the power supply module circuit, a third pin of the second analog switch is connected to the PA6 pin of the STM32C8T6 single-chip microcomputer, a fourth pin of the second analog switch is connected to the PA5 pin of the STM32C8T6 single-chip microcomputer, and a fifth pin of the second analog switch is connected to the PA4 pin of the STM32C8T6 single-chip microcomputer.

[0056] In some embodiments, the resistance value of resistor R1 can be 10 kΩ, the resistance value of resistor R2 can be 10 kΩ, the resistance value of resistor R3 can be 5 kΩ, the resistance value of resistor R4 can be 10 kΩ, the resistance value of resistor R5 can be 50 kΩ, the resistance value of resistor R6 can be 100 kΩ, the resistance value of resistor R7 can be 300 kΩ, the resistance value of resistor R8 can be 5 kΩ, the resistance value of resistor R9 can be 10 kΩ, the resistance value of resistor R10 can be 50 kΩ, the resistance value of resistor R11 can be 100 kΩ, the resistance value of resistor R12 can be 300 kΩ, the resistance value of resistor R13 can be 10 kΩ, and the resistance value of resistor R14 can be 10 kΩ.

[0057] In some embodiments, the multi-channel resistor network circuit can be a current-voltage conversion circuit, and the specific structure is that the OPA820IDBVR operational amplifier chip introduces voltage shunt negative feedback. The current input terminal and the feedback terminal of the OPA820IDBVR operational amplifier chip are respectively composed of a 74HC4051N eight-channel multiplexer and a series of resistor values. One of the channels of the 74HC4051N eight-channel multiplexer in the current input terminal is connected to the sensing electrode. Selecting different series of resistor values for the 74HC4051N eight-channel multiplexer in the current input terminal and the feedback terminal introduces different gain coefficients.

[0058] In some embodiments, the selection range of the series resistor values of the multi-channel resistor network circuit can be 5 - 300 kHz.

[0059] In some embodiments, the impedance detection module provides a sine signal with a frequency in the range of 10 - 100,000 Hz and an amplitude in the range of 400 - 1000 mV as the excitation signal.

[0060] The humidity monitoring module is used to monitor the air humidity around the interdigital electrodes in real time to obtain the corresponding air humidity value.

[0061] The air humidity value is data reflecting the humidity index around the interdigital electrodes.

[0062] In some embodiments, as Figure 4 shown, the humidity monitoring module can include a DC power adapter, a resistive humidity sensor, a microcontroller, and a display screen; among them, the resistive humidity sensor, the microcontroller, and the display screen are connected in series in sequence, and the DC power adapter is connected to the microcontroller.

[0063] In some embodiments, the 12V DC power adapter can be connected to the microcontroller through an external power interface.

[0064] In some embodiments, the resistive humidity sensor can be a DHT22 digital temperature and humidity sensor; among them, the VCC pin, the GND pin, and the Signal pin of the DHT22 digital temperature and humidity sensor are all connected to the microcontroller.

[0065] In some embodiments, the microcontroller can be an Arduino Uno R3 development board; wherein, the 5V pin of the microcontroller is connected to the VCC pin of the DHT22 digital temperature and humidity sensor, the GND pin of the microcontroller is connected to the GND pin of the DHT22 digital temperature and humidity sensor, the Digital9 pin of the microcontroller is connected to the Signal pin of the DHT22 digital temperature and humidity sensor, and the 3.3V pin, SCL pin and SDA pin of the microcontroller are all connected to the display screen.

[0066] In some embodiments, the display screen can be an OLED liquid crystal display screen; wherein, the VCC pin of the OLED liquid crystal display screen is connected to the 3.3V pin of the microcontroller, the SCL pin of the OLED liquid crystal display screen is connected to the SCL pin of the microcontroller, and the SDA pin of the OLED liquid crystal display screen is connected to the SDA pin of the microcontroller.

[0067] In some embodiments, the humidity signal port of the DHT22 digital temperature and humidity sensor is connected to the digital input port No. 9 of the Arduino Uno R3 development board to transmit the humidity signal, and the Arduino Uno R3 development board communicates with the OLED liquid crystal screen with the control chip SSD1306 through IIC to display the humidity value in real time.

[0068] In some embodiments, the circuit board sizes of the impedance detection module and the humidity monitoring module are within the range of 10 cm × 10 cm.

[0069] In some embodiments, the DHT22 digital temperature and humidity sensor of the humidity monitoring module is closely attached around the interdigital electrode attached with air microorganisms to accurately monitor the air humidity value near the interdigital electrode interface.

[0070] A parameter fitting module, configured to fit the impedance data to obtain a linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode.

[0071] In some embodiments, the parameter fitting module can use an FPGA device to fit the measured impedance data with an AIDEB equivalent circuit, analyze the variation laws of the electrical parameters of different concentrations of microorganisms and the AIDEB equivalent circuit, and perform linear fitting on the change values of the electrode interface resistance of the AIDEB equivalent circuits of a series of different concentrations of microorganisms obtained by using the least squares method to obtain a linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode.

[0072] In some embodiments, the parameter fitting module may control the STM32C8T6 chip to transmit the measured impedance data to the FPGA device, and use the FPGA device to implement the fitting of the AIDEB equivalent circuit parameters. First, set the initial parameters of each part of the AIDEB equivalent circuit according to empirical values, and then use the Levenberg-Marquardt Algorithm (LMA) in the FPGA device for non-linear least squares fitting to calculate the parameters of each part of the AIDEB equivalent circuit, and analyze the difference ΔR i in the electrode interface resistance R i obtained by fitting the AIDEB equivalent circuit with different total numbers of microorganisms and with and without microorganisms on the interdigital electrodes, so as to obtain the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode; wherein, the hardware for implementing the algorithm may include High Level Synthesis Tools (HLST) high-level synthesis tools.

[0073] In some embodiments, as Figure 5 shown, the AIDEB equivalent circuit includes a constant phase element Z CPE representing the double-layer capacitance at the interdigital electrode-microorganism-air medium interface; the equivalent capacitance C bac of the microorganisms and their metabolites at the electrode interface; the electrode interface resistance R i and the electrode interface capacitance C g ; wherein, one end of the constant phase element Z CPE is connected to one end of the equivalent capacitance C bac , the other end of the constant phase element Z CPE is connected to one end of the electrode interface resistance R i , and the other end of the electrode interface resistance R i is respectively connected to the other end of the equivalent capacitance C bac and the electrode interface capacitance C g . For example, the initial parameters may be that the Y CPE of Z 0 is 1.46×10 -6 F·sec n-1 , the n of Z CPE is 0.2899; C g is 1.72×10 -8 F; R i is 4.39×10 4 Ω; C bac is 7.68×10 -12 F.

[0074] The change value of the electrode interface resistance is the data of the change of the electrode interface resistance with the total number of microorganisms on the electrode.

[0075] In some embodiments, the expression of the change value of the electrode interface resistance can be:

[0076] ΔR i (Ω) = R effect ·N bac +B;

[0077] R effect = R 1 ·A;

[0078]

[0079] Wherein, R i represents the electrode interface resistance, R effect represents the corrected equivalent resistance value of a single microorganism, N bac represents the total number of microorganisms on the electrode, A and B represent correction coefficients, R 1 represents the equivalent resistance value of a single microorganism, Φ represents the volume fraction of a single microorganism, σ i represents the cytoplasmic conductivity of microorganisms in the air, σ m represents the conductivity of the environmental medium at the interdigitated electrode interface, σ out represents the equivalent shell membrane conductivity of microorganisms in the air, R represents the radius of a single microorganism, d represents the shell membrane thickness of a single microorganism, E represents the electrode constant, N represents the total electrode index, L represents the electrode finger length, K represents the value of the first complete elliptic integral, k represents the modulus of the value of the first complete elliptic integral, w e represents the spacing of the interdigitated electrodes, s e represents the width of the interdigitated electrodes.

[0080] In some embodiments, the characteristic length L is the sum of the width s e of the interdigitated electrodes and the spacing w e of the interdigitated electrodes. When the ratio of the width to the spacing of the interdigitated electrodes is 1:1, nearly 98% of the current is carried within the height layer with a thickness of 0.8×L above the interdigitated electrodes, thereby obtaining the volume fraction of a single microorganism on the interdigitated electrodes.

[0081] In some embodiments, the expression of the volume fraction of a single microorganism can be:

[0082]

[0083] The detection module is configured to construct a standard relationship curve based on the linear relationship between the air humidity value, the change value of the electrode interface resistance, and the total number of microorganisms on the electrode, obtain the air microorganism detection result, and complete the quantitative detection of air microorganisms.

[0084] The air microorganism detection result is a detection result reflecting the air microorganism concentration in the corresponding air humidity value.

[0085] In some embodiments, in the same air humidity environment, for the interdigital electrodes attached with airborne microorganisms, the electrode interface resistance value of the AIDEB equivalent circuit of its impedance value increases with the increase in the concentration of airborne microorganisms. According to the dielectric properties of airborne microbial cells, biological cells are very poor conductors at low frequencies (at least below 50 kHz), so the current is forced to bypass them. The attachment of microbial cells will delay the interfacial electron transfer kinetics and increase the electron transfer resistance. The adhesion of microbial cells to the electrodes will effectively reduce the electrode area, resulting in an increase in the interface resistance value. The interface resistance value is inversely proportional to the total electrode area reached by the current. The electrode interface resistance value R related to the surface conductivity i shows higher reproducibility and greater scale variation, thus obtaining the detection results of airborne microorganisms.

[0086] In some embodiments, the detection module can establish a standard curve between the logarithm of the total number of microorganisms on the electrode and the change value of the electrode interface resistance of the AIDEB equivalent circuit in the same air humidity environment. Under the same detection conditions, the concentration of airborne microorganisms can be obtained by detecting the change value of the electrode interface resistance of the AIDEB equivalent circuit as the detection result of airborne microorganisms.

[0087] In some embodiments, an impedance-sensing-based quantitative detection system for airborne microorganisms can be used to perform an impedance-sensing-based quantitative detection method for airborne microorganisms, including: S1: Adsorbing airborne microorganisms by using interdigital electrodes to obtain interdigital electrodes with different concentrations of microorganisms; S2: Connecting the interdigital electrodes with different concentrations of microorganisms to an impedance detection module for impedance measurement to obtain impedance data; S3: Using a humidity monitoring module to monitor the air humidity around the interdigital electrodes in real time to obtain the corresponding air humidity value; S4: Fitting the impedance data to obtain the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode; S5: Based on the air humidity value, the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode, constructing a standard relationship curve to obtain the detection results of airborne microorganisms and completing the quantitative detection of airborne microorganisms.

[0088] In some embodiments of this specification, the processor uses an impedance-sensing-based quantitative detection system for airborne microorganisms to perform an impedance-sensing-based quantitative detection method for airborne microorganisms. In this way, (1) after adsorbing airborne microorganisms onto the interdigital electrodes based on existing sampling techniques such as the natural sedimentation method, the impedance change generated by the interaction between the interdigital microelectrodes and the surface of airborne microorganisms is directly monitored, that is, impedance detection is directly performed in the air, overcoming the influence of the composition of the detection medium solution on the electrochemical impedance detection method; (2) an AIDEB equivalent circuit is proposed to simulate the impedance spectrum and electrical response of the interdigital electrodes attached with microorganisms, and the total number N of microorganisms on the electrode is established bacThe logarithmic value and the change value ΔR of the electrode interface resistance of the AIDEB equivalent circuit i The standard curve between them provides a new data analysis method for detecting airborne microorganisms by electrochemical impedance method, obtaining more accurate analysis data; (3) The impedance detection module and the humidity monitoring module can be further integrated. The overall module size is within the range of 10 cm × 10 cm, and the detection duration is less than 5 minutes, enabling rapid and portable detection.

[0089] Example Two

[0090] Figure 2 is an exemplary flowchart of a method for quantitatively detecting airborne microorganisms based on impedance sensing according to some embodiments of this specification. As Figure 2 shown, the process includes the following steps. In some embodiments, the process can be executed by a processor.

[0091] S1: Use interdigitated electrodes to adsorb airborne microorganisms to obtain interdigitated electrodes with different concentrations of microorganisms.

[0092] S2: Connect the interdigitated electrodes with different concentrations of microorganisms to the impedance detection module for impedance measurement to obtain impedance data.

[0093] In some embodiments, the processor can implement S2 based on the following steps.

[0094] S210: Connect the interdigitated electrodes attached with microorganisms to both ends of the detection of the impedance detection module, control the impedance detection module to switch to the known resistance calibration impedance mode, apply an excitation signal with a frequency of 100 Hz to a series of resistors with known resistances in the multi-channel resistance network and perform conversion to obtain the corresponding series of gain coefficients.

[0095] S220: Control the impedance detection module to continue in the known resistance calibration impedance mode, repeat the detection by increasing the frequency in steps of 1 KHz, that is, apply an excitation signal with a frequency of 1100 Hz to a series of resistors with known resistances in the multi-channel resistance network, perform conversion to obtain the corresponding series of gain coefficients, and then continue to repeat the detection by increasing the frequency in steps of 1 KHz until the frequency value is 99010 Hz.

[0096] S230: Control the impedance detection module to switch to the unknown resistance to be measured impedance mode, that is, the analog switch connects the channel with the interdigitated electrodes attached with microorganisms and cuts off the on-off of the rest of the series of known resistances. Apply an excitation signal with a frequency of 100 Hz to the interdigitated electrodes attached with microorganisms, and combine the foregoing corresponding excitation frequency signals, that is, calculate the resistance value (the real part of the impedance) and the reactance value (the imaginary part of the impedance) respectively based on the gain coefficient obtained by converting the excitation signal with a frequency of 100 Hz and the real part value and the imaginary part value of the discrete Fourier transform obtained by detecting the interdigitated electrodes attached with microorganisms.

[0097] S240: Control the impedance detection module to continue to be in the unknown resistance to-be-detected impedance mode, and repeat the detection by increasing the frequency in steps of 1 KHz, that is, apply an excitation signal with a frequency of 1100 Hz to the interdigital electrode attached with microorganisms, and continue to combine with the corresponding excitation signal at the aforementioned frequency. At this time, the resistance value (real part of the impedance) and reactance value (imaginary part of the impedance) are calculated again from the gain coefficient obtained by converting the excitation signal of 1100 Hz and the real part value and imaginary part value of the discrete Fourier transform detected for the interdigital electrode attached with airborne microorganisms.

[0098] S250: Control the impedance detection module to still be in the unknown resistance to-be-detected impedance mode, continuously repeat the detection by increasing the frequency in steps of 1 KHz, and calculate the resistance value (real part of the impedance) and reactance value (imaginary part of the impedance) of the interdigital electrode attached with airborne microorganisms at different frequencies until the frequency value of the excitation signal is 99010 Hz.

[0099] S260: Connect the interdigital electrodes attached with different concentrations of microorganisms to the two detection ends of the impedance detection module in sequence, return to S230 to repeat the detection, and obtain the impedance data of the interdigital electrodes with different concentrations of microorganisms.

[0100] S3: Use the humidity monitoring module to monitor the air humidity around the interdigital electrode in real time to obtain the corresponding air humidity value.

[0101] S4: Fit the impedance data to obtain the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode.

[0102] In some embodiments, the expression of the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode can be:

[0103] ΔR i (Ω) = k 1 logN bac +b 1 ;

[0104] Wherein, R i represents the electrode interface resistance, k 1 represents the slope of the straight line, and b 1 represents the intercept of the straight line.

[0105] S5: Based on the air humidity value, the linear relationship between the change value of the electrode interface resistance and the total number of microorganisms on the electrode, construct a standard relationship curve to obtain the air microorganism detection result, and complete the quantitative detection of air microorganisms.

[0106] In this way, (1) based on existing sampling techniques such as natural sedimentation method, after adsorbing airborne microorganisms onto the interdigitated electrodes, the impedance changes generated by the interaction between the interdigitated microelectrodes and the surface of airborne microorganisms are directly monitored, that is, impedance detection is directly carried out in the air, overcoming the influence of the composition of the detection medium solution on the electrochemical impedance detection method; (2) an AIDEB equivalent circuit is proposed to simulate the impedance spectrum and electrical response of the interdigitated electrodes attached with microorganisms, and a standard curve between the logarithm of the total number of microorganisms N bac on the electrode and the change value ΔR i of the electrode interface resistance of the AIDEB equivalent circuit is established, providing a new data analysis method for detecting airborne microorganisms by electrochemical impedance method and obtaining more accurate analysis data; (3) the impedance detection module and the humidity monitoring module can be further integrated, the overall module size is within the range of 10 cm × 10 cm, and the detection duration is less than 5 minutes, enabling rapid portable detection; (4) direct detection of airborne microorganisms can be achieved without sampling and transferring to solid medium or solution.

Claims

1. A quantitative detection system for air microorganisms based on impedance sensing, characterized in that: include: An acquisition module, used for adsorbing air microorganisms using interdigital electrodes to obtain interdigital electrodes with different concentrations of microorganisms; An impedance detection module, used to measure the impedance of the interdigital electrodes to obtain impedance data; Humidity monitoring module, used to monitor the air humidity around the interdigital electrodes in real time and obtain the corresponding air humidity value; A parameter fitting module is used to fit the impedance data to obtain a linear relationship between the electrode interface resistance change value and the total number of microorganisms on the electrode; The detection module is used to construct a standard relationship curve based on the linear relationship between the air humidity value, the electrode interface resistance change value and the total number of microorganisms on the electrode, obtain the air microorganism detection result, and complete the quantitative detection of air microorganisms.

2. The air microorganism quantitative detection system based on impedance sensing according to claim 1 is characterized in that: The impedance detection module includes: an STM32C8T6 single-chip microcomputer, an AD5933 chip and an off-chip circuit; wherein the PB10 pin of the STM32C8T6 single-chip microcomputer is connected to the SCL pin of the AD5933 chip, the PB11 pin of the STM32C8T6 single-chip microcomputer is connected to the SDA pin of the AD5933 chip, the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin, PA6 pin and VDD pin of the STM32C8T6 single-chip microcomputer are connected to the off-chip circuit, and the VDD pin, VOUT pin, RFB pin and VIN pin of the AD5933 chip are connected to the off-chip circuit.

3. The air microorganism quantitative detection system based on impedance sensing according to claim 2 is characterized in that: The off-chip circuit includes a signal processing circuit, a multi-channel resistor network circuit and a power module circuit; wherein one end of the signal processing circuit is connected to the VOUT pin of the AD5933 chip, the other end of the signal processing circuit is respectively connected to one end of the multi-channel resistor network circuit and the power module circuit, one end of the multi-channel resistor network circuit is connected to the power module circuit, the other end of the multi-channel resistor network circuit is respectively connected to the PA1 pin, PA2 pin, PA3 pin, PA4 pin, PA5 pin and PA6 pin of the STM32C8T6 single-chip microcomputer, and the power module circuit is respectively connected to the VDD pin of the STM32C8T6 single-chip microcomputer and the VDD pin of the AD5933 chip.

4. The air microorganism quantitative detection system based on impedance sensing according to claim 3 is characterized in that: The power module circuit includes: a +5V output terminal, a -5V output terminal and a +3.3V output terminal; wherein the +5V output terminal and the -5V output terminal are respectively connected to the signal processing circuit and the multi-channel resistor network circuit, and the +3.3V output terminal is respectively connected to the multi-channel resistor network circuit, the VDD pin of the STM32C8T6 microcontroller and the VDD pin of the AD5933 chip.

5. The air microorganism quantitative detection system based on impedance sensing according to claim 4 is characterized in that: The signal processing circuit includes a Butterworth second-order low-pass filter circuit, a Butterworth second-order high-pass filter circuit and a voltage follower circuit; wherein, a first pin of the Butterworth second-order low-pass filter circuit is connected to the VOUT pin of the AD5933 chip, a second pin of the Butterworth second-order low-pass filter circuit is connected to the +5V output end of the power module circuit, a third pin of the Butterworth second-order low-pass filter circuit is connected to the -5V output end of the power module circuit, a fourth pin of the Butterworth second-order low-pass filter circuit is connected to the first pin of the Butterworth second-order high-pass filter circuit, a second pin of the Butterworth second-order high-pass filter circuit is connected to the +5V output end of the power module circuit, a third pin of the Butterworth second-order high-pass filter circuit is connected to the -5V output end of the power module circuit, a fourth pin of the Butterworth second-order high-pass filter circuit is connected to the first pin of the voltage follower circuit, a second pin of the voltage follower circuit is connected to the +5V output end of the power module circuit, a third pin of the voltage follower circuit is connected to the -5V output end of the power module circuit, and a fourth pin of the voltage follower circuit is connected to the multi-channel resistor network circuit.

6. The air microorganism quantitative detection system based on impedance sensing according to claim 5 is characterized in that: The multi-channel resistor network circuit includes resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, resistor R10, resistor R11, resistor R12, resistor R13, resistor R14, a first analog switch, a second analog switch, an amplifier and interdigital electrodes; wherein the first pin of the first analog switch is connected to the +5V output terminal of the power module circuit, the second pin of the first analog switch is connected to the fourth pin of the voltage follower circuit, the third pin of the first analog switch is connected to the PA1 pin of the STM32C8T6 single chip microcomputer, and the fourth pin of the first analog switch is connected to the +5V output terminal of the power module circuit. The first pin of the first analog switch is connected to the PA2 pin of the STM32C8T6 single-chip computer, the fifth pin of the first analog switch is connected to the PA3 pin of the STM32C8T6 single-chip computer, the sixth pin of the first analog switch is respectively connected to one end of the resistor R3, one end of the resistor R4, one end of the resistor R5, one end of the resistor R6, one end of the resistor R7 and one end of the interdigital electrode, the other end of the resistor R3, the other end of the resistor R4, the other end of the resistor R5, the other end of the resistor R6, the other end of the resistor R7 and the other end of the interdigital electrode are respectively connected to the second pin of the amplifier and the second pin of the second analog switch, the first pin of the amplifier is connected to the resistor R 13, the other end of resistor R13 and one end of resistor R14 are both grounded, the other end of resistor R14 is connected to the +3.3V output end of the power module circuit, the third pin of the amplifier is connected to the -5V output end of the power module circuit, the fourth pin of the amplifier is respectively connected to one end of resistor R2, one end of resistor R8, one end of resistor R9, one end of resistor R10, one end of resistor R11 and one end of resistor R12, the fifth pin of the amplifier is connected to the +5V output end of the power module circuit, the other end of resistor R2 is respectively connected to one end of resistor R1 and the VIN pin of D5933 chip, the The other end is connected to the RFB pin of the D5933 chip, the other end of the resistor R8, the other end of the resistor R9, the other end of the resistor R10, the other end of the resistor R11 and the other end of the resistor R12 are all connected to the sixth pin of the second analog switch, the first pin of the second analog switch is connected to the +5V output end of the power module circuit, the third pin of the second analog switch is connected to the PA6 pin of the STM32C8T6 microcontroller, the fourth pin of the second analog switch is connected to the PA5 pin of the STM32C8T6 microcontroller, and the fifth pin of the second analog switch is connected to the PA4 pin of the STM32C8T6 microcontroller.

7. A quantitative detection method of air microorganisms based on impedance sensing, characterized in that: include: S1: Using interdigital electrodes to adsorb air microorganisms to obtain interdigital electrodes with different concentrations of microorganisms; S2: connecting the interdigital electrodes with different concentrations of microorganisms to an impedance detection module to perform impedance measurement to obtain impedance data; S3: Using the humidity monitoring module to monitor the air humidity around the interdigital electrodes in real time to obtain the corresponding air humidity value; S4: fitting the impedance data to obtain a linear relationship between the electrode interface resistance change value and the total number of microorganisms on the electrode; S5: Based on the linear relationship between the air humidity value, the electrode interface resistance change value and the total number of microorganisms on the electrode, a standard relationship curve is constructed to obtain the air microorganism detection result, thereby completing the quantitative detection of air microorganisms.

8. The method for quantitative detection of air microorganisms based on impedance sensing according to claim 7, characterized in that: The expression of the electrode interface resistance change value is: ΔR i (Ω)=R effect ·N bac +B; R effect =R1·A; Among them, R i Represents the electrode interface resistance, R effect Represents the corrected equivalent resistance value of a single microorganism, N bac represents the total number of microorganisms on the electrode, A and B represent correction coefficients, R1 represents the equivalent resistance value of a single microorganism, Φ represents the volume fraction of a single microorganism, σ i represents the cytoplasmic conductivity of microorganisms in the air, σ m represents the conductivity of the interdigital electrode interface environment, σ out represents the equivalent shell conductivity of microorganisms in the air, R represents the radius of a single microorganism, d represents the shell thickness of a single microorganism, E represents the electrode constant, N represents the total electrode index, L represents the electrode finger length, K represents the first kind of complete elliptic integral value, k represents the modulus of the first kind of complete elliptic integral value, w e represents the spacing between the interdigitated electrodes, s e Represents the width of the interdigital electrodes.

9. The method for quantitative detection of air microorganisms based on impedance sensing according to claim 8, characterized in that: The expression of the volume fraction of a single microorganism is:

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