Gold nanorod enhanced photothermal elastic gas detection system and detection method

Abstract

The application discloses a gold nanorod enhanced photothermal elastic gas detection system and a detection method, which are used for improving the universality of the gas detection system. The system comprises an adjustable laser, a gas cell and a quartz tuning fork. The light receiving area of the quartz tuning fork is arranged at the corresponding position of the modulated laser output by the adjustable laser. The light receiving area is provided with a photoelectric conversion film coating. The photoelectric conversion film coating comprises gold nanorod material deposited on the surface of the quartz tuning fork. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material is matched with the absorption wavelength band of the to-be-detected gas. When the modulated laser emitted by the gas cell irradiates the photoelectric conversion film coating, the gold nanorod material enhances the absorption of the modulated laser through the localized surface plasmon resonance effect and converts the modulated laser into heat energy. The heat energy generated by the photoelectric conversion film coating is transmitted to the quartz tuning fork, so that the quartz tuning fork generates thermal elastic deformation and excites the quartz tuning fork to vibrate and output a gas concentration electric signal.

Description

Technical Field

[0001] This application relates to the field of gas detection, and more particularly to a gold nanorod-enhanced photothermal elastic gas detection system and method. Background Technology

[0002] With industrial development, the demand for monitoring greenhouse gas emissions, flammable and explosive gases, and toxic gas leaks is increasing. Traditional semiconductor and electrochemical gas detection methods are susceptible to environmental interference and mechanical wear, making it difficult to meet the requirements for high-sensitivity detection.

[0003] Light-induced thermoelastic spectroscopy (LITES) technology uses quartz tuning forks as photoelectric conversion elements, combining the advantages of miniaturization, low power consumption, low cost, and high quality factor, making it a novel gas detection technology. However, commercially available bare quartz tuning forks suffer from low light absorption efficiency and weak photothermal conversion capability, with only a small amount of laser energy being converted into heat energy, resulting in small thermoelastic vibration amplitude and limited detection sensitivity.

[0004] Existing technologies mostly employ structural optimization or conventional thin film deposition methods, which cannot achieve wavelength-selective light absorption and are difficult to match the absorption peaks of different gases, thus limiting the application of photoinduced thermoelastic spectroscopy in various scenarios. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a gold nanorod-enhanced photothermal elastic gas detection system and method, which improves the versatility of the gas detection system.

[0006] The technical solution provided in this application is described below:

[0007] The first aspect of this application provides a gold nanorod-enhanced photothermal elastic gas detection system, comprising: Adjustable laser, gas cell, quartz tuning fork; The gas cell is disposed between the adjustable laser and the quartz tuning fork, and the light-receiving area of ​​the quartz tuning fork is disposed at the corresponding position of the modulated laser output by the adjustable laser. The light-receiving area is provided with a photoelectric conversion thin film coating, which includes gold nanorod material deposited on the surface of the quartz tuning fork. The gold nanorod material has localized surface plasmon resonance effect and high thermal conductivity. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material matches the absorption band of the gas to be measured. This allows the gold nanorod material to enhance the absorption of the modulated laser through the localized surface plasmon resonance effect when the modulated laser emitted from the gas cell irradiates the photoelectric conversion thin film coating, and convert the absorbed light energy into heat energy. The heat energy generated by the photoelectric conversion thin film coating is transferred to the quartz tuning fork, causing the quartz tuning fork to undergo thermoelastic deformation and exciting the quartz tuning fork to vibrate. The quartz tuning fork outputs a gas concentration electrical signal based on the piezoelectric effect.

[0008] Optionally, the system further includes a signal reading and processing unit electrically connected to the quartz tuning fork. The signal reading and processing unit is used to read the gas concentration electrical signal output by the quartz tuning fork and extract the harmonic signals in the gas concentration electrical signal to obtain the detection result of the gas to be tested based on the harmonic signals.

[0009] Optionally, the light-receiving area is located in the electrode-free region of the quartz tuning fork, and the photoelectric conversion thin film coating is selectively applied to the electrode-free region by a drop-coating method.

[0010] Optionally, the aspect ratio of the gold nanorod material is matched with the absorption band of the gas to be tested, so that the longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material corresponds to the absorption band of the gas to be tested.

[0011] Optionally, the adjustable laser is connected to a laser driver, which receives a drive signal formed by the superposition of a scanning signal and a modulation signal to drive the adjustable laser to scan the absorption band of the gas to be tested and output the modulated laser.

[0012] Optionally, a laser collimator is provided between the adjustable laser and the gas pool, the laser collimator being used to collimate the output laser of the adjustable laser.

[0013] Optionally, a beam focusing component is provided between the gas cell and the quartz tuning fork, the beam focusing component being used to focus the modulated laser emitted from the gas cell onto the light-receiving area.

[0014] Optionally, the modulation frequency of the modulated laser output by the adjustable laser is located within the resonant response frequency band of the quartz tuning fork.

[0015] Optionally, the system further includes a gas supply regulating unit connected to the gas pool, which is used to supply the gas to be tested to the gas pool and regulate the gas pressure or gas flow rate in the gas pool.

[0016] A second aspect of this application provides a method for detecting photothermal elastic gases enhanced by gold nanorods, the method comprising: A scanning signal and a modulation signal are generated by a signal reading and processing unit, and the scanning signal and the modulation signal are superimposed to form a driving signal. The laser driver receives the driving signal and drives the adjustable laser to output a modulated laser corresponding to the absorption band of the gas under test. Obtain the gas concentration electrical signal output by the quartz tuning fork based on the piezoelectric effect; The gas concentration electrical signal is subjected to harmonic demodulation to obtain a harmonic signal; Extract the peak amplitude of the harmonic signal; The detection result of the gas to be tested is calculated based on the linear fitting relationship between the peak amplitude of the harmonic signal and the concentration of the gas to be tested.

[0017] As can be seen from the above technical solutions, this application has the following advantages: By setting a gold nanorod photoelectric conversion film in the light-receiving area of ​​a quartz tuning fork that matches the absorption band of the gas to be measured, the local surface plasmon resonance effect and high thermal conductivity are utilized to enhance the absorption of modulated laser and heat transfer, thereby increasing the intensity of thermoelastic vibration and piezoelectric output signal of the quartz tuning fork and thus improving the gas detection sensitivity of photoinduced thermoelastic spectroscopy. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of an embodiment of the gold nanorod-enhanced photothermal elastic gas detection system in this application; Figure 2 This is a schematic flowchart illustrating the preparation process of gold nanorod material in the gold nanorod-enhanced photothermal elastic gas detection system of this application. Figure 3 This is a simulated extinction cross section of gold nanorod materials with different aspect ratios in the gold nanorod-enhanced photothermal elastic gas detection system of this application. Figure 4 This is an electric field enhancement distribution diagram of the gold nanorod material in the gold nanorod-enhanced photothermal elastic gas detection system of this application; Figure 5 The image shows the resonance curves and fitting results of the modified and unmodified quartz tuning forks in the photoelectric conversion thin film coating of the gold nanorod-enhanced photothermal elastic gas detection system in this application. Figure 6 The graph shows the response results of the photoelectric conversion thin film coating-modified quartz tuning fork and the unmodified quartz tuning fork in the gold nanorod-enhanced photothermal elastic gas detection system of this application under different incident laser powers. Figure 7 The graph shows the linear fitting results of the peak amplitude of the second harmonic signal as a function of carbon dioxide concentration in the gold nanorod-enhanced photothermal elastic gas detection system of this application. Figure 8 The graph shows the detection results of carbon dioxide concentration changing over time in the gold nanorod-reinforced photothermal elastic gas detection system of this application. Figure 9 The figure shows the Allen bias analysis results of the gold nanorod-reinforced photothermal elastic gas detection system in this application. Figure 10 This is a schematic flowchart of an embodiment of the gold nanorod-enhanced photothermal elastic gas detection method in this application. Detailed Implementation

[0020] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] Please see Figures 1 to 9 This application first provides an embodiment of a gold nanorod-enhanced photothermal elastic gas detection system, which includes: Adjustable laser 1, gas cell 2, quartz tuning fork 3; The gas cell 2 is disposed between the adjustable laser 1 and the quartz tuning fork 3, and the light-receiving area of ​​the quartz tuning fork 3 is disposed at the corresponding position of the modulated laser output by the adjustable laser 1. The light-receiving area is provided with a photoelectric conversion thin film coating, which includes gold nanorod material deposited on the surface of the quartz tuning fork 3. The gold nanorod material has localized surface plasmon resonance effect and high thermal conductivity. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material matches the absorption band of the gas to be tested. This allows the gold nanorod material to enhance the absorption of the modulated laser through the localized surface plasmon resonance effect when the modulated laser emitted from the gas cell irradiates the photoelectric conversion thin film coating, and convert the absorbed light energy into heat energy. The heat energy generated by the photoelectric conversion thin film coating is transferred to the quartz tuning fork 3, causing the quartz tuning fork 3 to undergo thermoelastic deformation and exciting the quartz tuning fork 3 to vibrate. The quartz tuning fork 3 outputs a gas concentration electrical signal based on the piezoelectric effect.

[0022] Specifically, gas cell 2 is arranged along the output optical path of adjustable laser 1. Gas cell 2 has an incident end and an exit end for the modulated laser to pass through. After the gas to be tested is filled into gas cell 2, the modulated laser absorbs the gas to be tested within gas cell 2. The beam emitted from gas cell 2 continues to reach the light-receiving area of ​​quartz tuning fork 3. After a photoelectric conversion thin film coating is formed on the light-receiving area of ​​quartz tuning fork 3, the light-receiving area changes from an exposed quartz surface to a photothermal response area with selective light absorption capability. Gold nanorods have a strong longitudinal localized surface plasmon resonance response in the target absorption band. After the modulated laser irradiates the photoelectric conversion thin film coating, the gold nanorods enhance the absorption of the incident light energy and accumulate heat in the thin film area. Due to the high thermal conductivity of gold nanorods, the heat generated in the thin film area is transferred to quartz tuning fork 3, causing the local temperature of quartz tuning fork 3 to change periodically with the intensity of the modulated laser, thereby producing periodic thermoelastic deformation. The thermoelastic deformation excites the quartz tuning fork 3 to vibrate mechanically, and the quartz tuning fork 3 uses the piezoelectric effect to convert the mechanical vibration into an electrical signal of gas concentration.

[0023] In this embodiment, the system further includes a signal reading and processing unit 4, which is electrically connected to the quartz tuning fork 3. The signal reading and processing unit 4 is used to read the gas concentration electrical signal output by the quartz tuning fork 3 and extract the harmonic signals in the gas concentration electrical signal to obtain the detection result of the gas to be tested based on the harmonic signals.

[0024] Specifically, the signal reading and processing unit 4 includes a low-noise preamplifier 41, a data acquisition card 42, and a computer 43. The gas concentration electrical signal output by the quartz tuning fork 3 first enters the low-noise preamplifier 41. The low-noise preamplifier 41 adopts a transimpedance amplification structure and uses a 10MΩ feedback resistor to convert the piezoelectric current generated by the quartz tuning fork 3 into a voltage signal. The data acquisition card 42 receives the amplified voltage signal and transmits it to the computer 43. The computer 43 has built-in LabVIEW software to store and process the received gas concentration electrical signal. The signal reading and processing unit 4 also forms a signal connection with the control terminal of the adjustable laser 1, enabling signal acquisition, laser scanning control, and modulation control to operate collaboratively under the same signal processing link.

[0025] In this embodiment, the light-receiving area is located in the electrode-free region of the quartz tuning fork 3, and the photoelectric conversion thin film coating is selectively applied to the electrode-free region by a drop-coating method.

[0026] Specifically, the light-receiving area of ​​the quartz tuning fork 3 is located in the electrode-free region, and the gold nanorod material is deposited away from the electrode region. This allows the photoelectric conversion thin film coating to enhance the photothermal response while reducing the impact on the electrode structure and resonance quality of the quartz tuning fork 3. During preparation, a gold nanorod suspension is drop-coated onto the electrode-free central region at the root of the quartz tuning fork 3. The drop-coated quartz tuning fork 3 is then dried in a vacuum environment at 40°C for 30 minutes, allowing the gold nanorod material to form a stable photoelectric conversion thin film coating on the surface of the quartz tuning fork 3. In this specific embodiment, the maximum thickness of this photoelectric conversion thin film coating is 35.2 μm. The film area corresponds to the focusing position of the modulated laser, concentrating the modulated laser energy onto the gold nanorod material deposition area.

[0027] In this embodiment, the aspect ratio of the gold nanorod material is matched with the absorption band of the gas to be tested, so that the longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material corresponds to the absorption band of the gas to be tested.

[0028] Specifically, the aspect ratio of the gold nanorod material is determined based on the absorption band of the gas to be measured. Figure 2 The preparation process of gold nanorod materials is shown. The gold nanorod materials are prepared by seed-mediated growth method, in which gold nanoparticle seeds are first formed, and then the morphology and aspect ratio of the gold nanorod materials are controlled by the growth system. Figure 3 The simulation results of normalized extinction cross sections for gold nanorods with different aspect ratios are shown. As the aspect ratio changes, the wavelength shift of the longitudinal localized surface plasmon resonance absorption peak of the gold nanorods is observed. In a specific embodiment using CO2 as the analyte gas, the aspect ratio of the gold nanorods is 14.5, and its longitudinal localized surface plasmon resonance absorption peak matches the characteristic absorption peak of CO2 in the 1600 nm band. Figure 4 The electric field enhancement distribution of the gold nanorod material at this aspect ratio is shown. The gold nanorod material generates a local electric field enhancement in the target wavelength band, thereby improving the absorption capacity of modulated laser and improving the photothermal conversion efficiency of the photoelectric conversion thin film coating.

[0029] In this embodiment, the adjustable laser 1 is connected to a laser driver, which is used to receive a driving signal formed by the superposition of a scanning signal and a modulation signal, so as to drive the adjustable laser 1 to scan the absorption band of the gas to be tested and output the modulated laser.

[0030] Specifically, the adjustable laser 1 employs a distributed feedback diode laser. The laser driver receives a drive signal formed by the superposition of a scanning signal and a modulation signal, and then drives the adjustable laser 1. The scanning signal ensures that the output wavelength of the adjustable laser 1 covers the absorption band of the gas under test, while the modulation signal modulates the output laser intensity according to a set frequency. In a specific embodiment, the data acquisition card 42 generates a triangular wave and a sine wave. The triangular wave serves as the scanning signal, and the sine wave as the modulation signal; the two are superimposed and input to the laser driver. The laser driver controls the adjustable laser 1 to output modulated laser light according to the superimposed drive signal, enabling the modulated laser to complete scanning within the absorption band of the gas under test and forming an intensity modulation suitable for exciting the thermoelastic vibration of the quartz tuning fork 3.

[0031] In this embodiment, a laser collimator 5 is provided between the adjustable laser and the gas pool 2. The laser collimator 5 is used to collimate the output laser of the adjustable laser 1.

[0032] Specifically, the laser collimator 5 is positioned between the adjustable laser 1 and the gas cell 2. The laser beam output from the adjustable laser 1 enters the laser collimator 5 and is shaped into a collimated beam. This collimated beam enters the gas cell 2 along its incident end and propagates along the optical path to the exit end. The laser collimator 5 reduces the impact of laser beam divergence on the propagation path and subsequent focusing position within the gas cell 2, ensuring that the modulated laser exiting the gas cell 2 maintains a stable incident direction. This provides the optical path basis for the accurate irradiation of the light-receiving area of ​​the quartz tuning fork 3 by the modulated laser.

[0033] During optical path calibration, a visible light source was used to assist in aligning the optical path positions of the adjustable laser 1, laser collimator 5, gas cell 2, beam focusing assembly 6, and quartz tuning fork 3. Visible light output from the visible light source passed through the gas cell 2 and beam focusing assembly 6 along the propagation direction of the modulated laser, illuminating the light-receiving area of ​​the quartz tuning fork 3. By observing the landing point of the visible light spot on the surface of the quartz tuning fork 3, the positions of the laser collimator 5 and beam focusing assembly 6 were adjusted to ensure that the modulated laser, after exiting the gas cell 2, could be stably focused onto the area where the photoelectric conversion thin film coating was located. After optical path alignment, the gold nanorod material deposition area corresponded to the focused spot of the modulated laser, thereby reducing the impact of beam deviation on the stability of the gas concentration electrical signal.

[0034] In this embodiment, a beam focusing component 6 is provided between the gas cell and the quartz tuning fork 3. The beam focusing component 6 is used to focus the modulated laser emitted from the gas cell 2 onto the light-receiving area.

[0035] Specifically, the beam focusing component 6 is positioned between the light-emitting end of the gas cell 2 and the quartz tuning fork 3, and is used to receive the modulated laser emitted from the gas cell 2 and focus the modulated laser onto the light-receiving area of ​​the quartz tuning fork 3. In a specific embodiment, the beam focusing component 6 uses a CaF2 lens with a diameter of 25 mm and a focal length of 50 mm. The CaF2 lens is adapted for near-infrared laser transmission and can focus the modulated laser after passing through the gas cell 2 onto the area where the photoelectric conversion thin film coating is located, enabling the gold nanorod material to obtain a high incident light power density. After the modulated laser is focused by the beam focusing component 6, the spot position corresponds to the photoelectric conversion thin film coating in the electrodeless area of ​​the quartz tuning fork 3, thereby improving the effective absorption ratio of the modulated laser by the gold nanorod material.

[0036] In this embodiment, the modulation frequency of the modulated laser output by the adjustable laser is located within the resonant response frequency band of the quartz tuning fork 3.

[0037] Specifically, the modulation frequency of the modulated laser output by the adjustable laser 1 is set within the resonant response band of the quartz tuning fork 3. The quartz tuning fork 3 possesses a high quality factor; when the modulation frequency is close to the resonant frequency, periodic thermoelastic deformation can effectively excite the mechanical vibration of the quartz tuning fork 3, thereby enhancing the piezoelectric output. In experimental verification, the photoelectric conversion thin film coating formed by gold nanorods improved the response of the quartz tuning fork 3 to light intensity modulation. The signal at the resonant frequency increased from 0.0563V for the bare quartz tuning fork to 0.3336V, and the quality factor changed from 8756.16 to 6018.04. This result indicates that although the photoelectric conversion thin film coating alters the surface load of the quartz tuning fork 3, it still maintains an effective resonant response and significantly improves the photothermal elastic response intensity to the modulated laser.

[0038] like Figure 5 As shown, during the resonance response verification process, Lorentz curve fitting was performed on the resonance curves of the quartz tuning fork 3 after photoelectric conversion thin film coating modification and the unmodified quartz tuning fork to obtain their resonance peak signals and quality factors. The fitting results were used to determine the modulation frequency setting range of the modulated laser and to evaluate the influence of the photoelectric conversion thin film coating on the resonance performance and photothermal elastic response intensity of the quartz tuning fork 3.

[0039] like Figure 6As shown, during the intensity modulation response verification process, the light-receiving area of ​​the quartz tuning fork 3 was irradiated with modulated lasers at different incident laser powers, and the output signals of the quartz tuning fork 3 with and without the photoelectric conversion thin film coating were acquired respectively. Experimental results show that the quartz tuning fork 3 with the photoelectric conversion thin film coating has a stronger response output at different laser powers, and the output signal increases linearly with increasing incident laser power. This result indicates that increasing the incident laser power can further improve the thermoelastic vibration amplitude of the quartz tuning fork 3 and enhance the system's response sensitivity to changes in the concentration of the target gas.

[0040] In this embodiment, the system further includes a gas supply regulating unit 7, which is connected to the gas pool 2 and is used to supply the gas to be tested to the gas pool 2 and regulate the gas pressure or gas flow rate in the gas pool 2.

[0041] Specifically, the gas supply regulating unit 7 is connected to the inlet and outlet of the gas cell 2. The gas supply regulating unit 7 includes an N2 cylinder 71, a CO2 cylinder 72, a gas mixer 73, a pressure controller 74, and a vacuum pump 75. The N2 cylinder 71 and CO2 cylinder 72 are connected to the gas mixer 73 via gas pipes. The gas mixer 73 mixes CO2 and N2 in different ratios to form the gas to be tested and delivers it to the gas cell 2. The outlet of the gas cell 2 is connected to the pressure controller 74, which is connected to the vacuum pump 75 to regulate the pressure and flow state of the gas to be tested within the gas cell 2. The gas cell 2 can be configured as a single-pass cell, a long-range cell, or a resonant cavity. Taking CO2 detection as an example, the gas cell 2 uses a 50cm long single-pass cell. The gas supply regulating unit 7 provides CO2 and N2 mixtures of different concentrations to the gas cell 2, enabling the system to obtain corresponding gas concentration electrical signals under different gas concentration conditions.

[0042] It should be noted that, Figure 2 The gold nanorod material shown was prepared using a seed-mediated growth method. In the preparation process, chloroauric acid and sodium borohydride were first reacted to generate gold nanoparticle seeds. These seeds were then introduced into a growth system containing hexadecyltrimethylammonium bromide, an oil phase component, chloroauric acid, ascorbic acid, and sodium hydroxide, allowing the seeds to grow longitudinally within the system to form gold nanorod materials. By adjusting the proportions of the components and the reaction conditions in the growth system, gold nanorod materials with an aspect ratio of 14.5 were obtained. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material was matched with the characteristic absorption peak of CO2 in the 1600 nm band. This enabled the gold nanorod material, when used to form a photoelectric conversion thin film coating, to enhance and modulate laser absorption within the absorption band of the target gas.

[0043] The photoelectric conversion thin film coating is formed by selective deposition of a gold nanorod suspension on the surface of a quartz tuning fork 3. During preparation, the gold nanorod suspension is drop-coated onto the electrodeless region at the base of the quartz tuning fork 3, ensuring the gold nanorod deposition position corresponds to the light-receiving area and avoiding covering the electrode region of the quartz tuning fork 3. After drop-coating, the quartz tuning fork 3 is dried in a vacuum environment at 40℃ for 30 minutes, allowing the gold nanorod material to solidify on the surface of the quartz tuning fork 3, forming a stable photoelectric conversion thin film coating. The formed photoelectric conversion thin film coating is used to receive the modulated laser emitted from the gas cell 2 and focused by the beam focusing assembly 6, thereby converting the absorbed light energy into heat energy and transferring it to the quartz tuning fork 3.

[0044] During the material and coating morphology verification process, the prepared gold nanorod material and the quartz tuning fork 3 modified with a photoelectric conversion thin film coating were observed and tested. Transmission electron microscopy revealed that the gold nanorod material exhibits a rod-like structure. Extinction spectroscopy showed that the gold nanorod material possesses a longitudinal localized surface plasmon resonance absorption peak in the near-infrared band, which matches the absorption band of the gas being tested. Scanning electron microscopy confirmed that the gold nanorod material can be deposited on the surface of the quartz tuning fork 3 to form a photoelectric conversion thin film coating. Visual comparison between the unmodified quartz tuning fork and the quartz tuning fork 3 modified with the photoelectric conversion thin film coating confirmed that the photoelectric conversion thin film coating is located in the light-receiving area of ​​the quartz tuning fork 3. Cross-sectional scanning electron microscopy confirmed the coverage and thickness distribution of the photoelectric conversion thin film coating on the surface of the quartz tuning fork 3. These verification results demonstrate that the gold nanorod material can be stably deposited on the surface of the quartz tuning fork 3, forming a photoelectric conversion thin film coating for enhancing modulated laser absorption and photothermal conversion. In the specific experiment, the maximum thickness of the photoelectric conversion thin film coating was 35.2 μm.

[0045] This embodiment achieves selective enhanced absorption of modulated laser light emitted from the gas cell 2 by depositing a photoelectric conversion thin film coating containing gold nanorods on the light-receiving region of the quartz tuning fork 3. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorods matches the absorption band of the gas being measured, improving the absorption efficiency of the modulated laser in the target band. Simultaneously, the high thermal conductivity of the gold nanorods enhances the heat transfer efficiency to the quartz tuning fork 3, resulting in stronger thermoelastic deformation and piezoelectric output signals. Therefore, this system addresses the problems of low light absorption efficiency, weak photothermal conversion capability, and limited detection sensitivity in bare quartz tuning forks, thereby overcoming the shortcomings of ordinary thin films that lack wavelength selectivity and are difficult to adapt to different gas absorption peaks.

[0046] The above provides a detailed description of the gold nanorod-enhanced photothermal elastic gas detection system in the embodiments of this application. The following will provide a detailed description of the gold nanorod-enhanced photothermal elastic gas detection method.

[0047] Please see Figure 10 This application provides an embodiment of a gold nanorod-enhanced photothermal elastic gas detection method, which includes: S1001. A scanning signal and a modulation signal are generated by the signal reading and processing unit, and the scanning signal and the modulation signal are superimposed to form a driving signal; The signal readout and processing unit 4 generates a scanning signal and a modulation signal to control the operation of the adjustable laser 1. The scanning signal uses a low-frequency triangular wave signal to make the output wavelength of the adjustable laser 1 scan back and forth near the absorption band of the gas under test; the modulation signal uses a sine wave signal to periodically modulate the output light intensity of the adjustable laser 1. The signal readout and processing unit 4 superimposes the triangular wave signal and the sine wave signal to form a drive signal that simultaneously contains wavelength scanning components and intensity modulation components, so that the subsequently output modulated laser can both cover the absorption peak of the gas under test and form periodic excitation within the resonant response frequency band of the quartz tuning fork 3.

[0048] S1002. Receive the driving signal through the laser driver and drive the adjustable laser to output modulated laser corresponding to the absorption band of the gas to be measured. The laser driver receives the drive signal output from the signal reading and processing unit 4, and controls the adjustable laser 1 to output modulated laser according to the drive signal. Under the action of the scanning signal, the adjustable laser 1 scans the absorption band of the gas to be tested, and under the action of the modulation signal, it forms light intensity modulation. After being collimated by the laser collimator 5, the modulated laser enters the gas cell 2. The gas to be tested in the gas cell 2 absorbs the modulated laser in the corresponding absorption band. After exiting the gas cell 2, the modulated laser is focused by the beam focusing component 6 onto the light-receiving area of ​​the quartz tuning fork 3, so that the modulated laser acts on the photoelectric conversion thin film coating.

[0049] S1003. Obtain the gas concentration electrical signal output by the quartz tuning fork based on the piezoelectric effect; After the modulated laser irradiates the photoelectric conversion thin film coating, the gold nanorod material enhances its absorption of the modulated laser under the longitudinal localized surface plasmon resonance, converting the absorbed light energy into heat energy. This heat energy is transferred to the quartz tuning fork 3, causing it to undergo thermoelastic deformation that varies with the intensity of the modulated laser, further exciting the quartz tuning fork 3 to vibrate mechanically. Based on the piezoelectric effect, the quartz tuning fork 3 converts the mechanical vibration into a gas concentration electrical signal. The signal reading and processing unit 4 receives this gas concentration electrical signal, converts the piezoelectric current into a voltage signal through a low-noise preamplifier 41, and then completes the acquisition through a data acquisition card 42.

[0050] S1004. The gas concentration electrical signal is subjected to harmonic demodulation to obtain a harmonic signal; The signal reading and processing unit 4 performs harmonic demodulation on the acquired gas concentration electrical signal. During demodulation, the modulation signal is used as a reference signal to extract the harmonic components related to the modulation frequency in the gas concentration electrical signal. Since the output wavelength of the adjustable laser 1 scans near the absorption band of the gas under test, the light intensity change caused by the absorption of the gas under test is converted into harmonic components in the output signal of the quartz tuning fork 3. The signal reading and processing unit 4 demodulates the harmonic signal from the gas concentration electrical signal. In a specific embodiment, the harmonic signal is the second harmonic signal.

[0051] S1005. Extract the peak amplitude of the harmonic signal; The signal reading and processing unit 4 extracts the peak amplitude of the harmonic signal. As the adjustable laser 1 scans past the absorption peak of the gas to be measured, the harmonic signal forms a peak at the corresponding position of the absorption peak. After completing harmonic demodulation, the signal reading and processing unit 4 performs waveform analysis on the harmonic signal to determine the peak position and extract the corresponding peak amplitude. This peak amplitude is related to the absorption intensity of the modulated laser by the gas to be measured and varies with the concentration of the gas to be measured in the gas cell 2.

[0052] S1006. Calculate the detection result of the gas to be tested based on the linear fitting relationship between the peak amplitude of the harmonic signal and the concentration of the gas to be tested.

[0053] The signal reading and processing unit 4 calculates the detection result based on the linear fitting relationship between the peak amplitude of the harmonic signal and the concentration of the gas to be tested. Before detection, different known concentrations of the gas to be tested are introduced into the gas cell 2, and the corresponding peak amplitudes of the harmonic signals are obtained. A linear fitting is then performed between the known concentration and the peak amplitude to obtain the concentration calculation relationship. During actual detection, the signal reading and processing unit 4 substitutes the currently extracted peak amplitude into this concentration calculation relationship to calculate the concentration value of the gas to be tested, and uses this concentration value as the detection result of the gas to be tested. Taking CO2 detection as an example, the gas supply adjustment unit 7 provides CO2 and N2 mixed gases with different ratios to the gas cell 2. CO2 concentration detection is achieved through the linear fitting relationship between the peak amplitude of the second harmonic signal and the CO2 concentration.

[0054] Specifically, such as Figure 7As shown, in a specific embodiment of CO2 detection, the gas supply regulating unit 7 sequentially supplies a mixture of CO2 and N2 gas with concentrations ranging from 3% to 40% into the gas pool 2. The signal reading and processing unit 4 acquires the peak amplitude of the second harmonic signal corresponding to each concentration condition and performs linear fitting between the CO2 concentration and the peak amplitude of the second harmonic signal. The fitting slope for the quartz tuning fork 3 modified with the photoelectric conversion thin film coating is 0.326, while the fitting slope for the unmodified quartz tuning fork is 0.035. The ratio of the two fitting slopes can determine the enhancement effect of the photoelectric conversion thin film coating on the gas concentration detection response. This linear fitting result shows that the peak amplitude of the second harmonic signal can form a stable linear response with changes in CO2 concentration, and can be used as the basis for calculating the detection result of the gas to be tested.

[0055] Based on the ratio between the fitting slope of 0.326 for the photoelectric conversion thin film coating-modified quartz tuning fork 3 and the fitting slope of 0.035 for the unmodified quartz tuning fork, the photoelectric conversion thin film coating improves the system's detection sensitivity by approximately 9.3 times. This result indicates that the localized surface plasmon resonance effect and high thermal conductivity of the gold nanorod material can synergistically enhance the photothermal elastic response of the quartz tuning fork 3, resulting in a larger peak amplitude of the second harmonic signal corresponding to the same change in CO2 concentration.

[0056] like Figure 8 As shown, during continuous detection, the signal reading and processing unit 4 converts the peak amplitude of the continuously acquired second harmonic signal into a CO2 concentration detection result according to a pre-established linear fitting relationship, and outputs a detection curve showing the change of CO2 concentration over time. The detection result shows that the CO2 concentration changes synchronously with the concentration of the mixed gas supplied by the gas supply adjustment unit 7, indicating that the system can continuously detect mixed gases with different CO2 concentrations and maintain a stable time response.

[0057] like Figure 9 As shown, during the system stability verification process, the signal reading and processing unit 4 performed Allen bias analysis on the continuously acquired gas concentration electrical signals. The Allen bias showed a monotonically decreasing trend with increasing signal averaging time. When the integration time was 331 s, the system's lowest detection limit for CO2 reached 7.2 ppm. The system's normalized noise equivalent absorption coefficient was 1.33 × 10⁻¹⁰ cm⁻¹ W·Hz⁻¹ / ², indicating that the main noise source of the system was white noise. This result demonstrates that the photoelectric conversion thin film coating formed by the gold nanorod material can improve the detection limit of the quartz tuning fork 3 for CO2 and maintain long-term detection stability under different CO2 concentration mixed gas conditions.

[0058] This embodiment uses a superposition of scanning and modulation signals to form a driving signal, enabling the adjustable laser 1 to output modulated laser light within the absorption band of the gas to be measured. Harmonic signals are extracted from the gas concentration electrical signal output from the quartz tuning fork 3 through harmonic demodulation. The detection result is then calculated based on the linear fitting relationship between the peak amplitude of the harmonic signals and the concentration of the gas to be measured. This method can convert the intensity modulation change caused by the absorption of the gas to be measured into a quantifiable harmonic peak amplitude, improving the stability and accuracy of gas concentration calculation. It also adapts to the photothermal elastic response process enhanced by gold nanorod materials, thereby achieving highly sensitive gas concentration detection.

[0059] This application also relates to a computer-readable storage medium on which a program is stored, characterized in that, when the program is run on a computer, it causes the computer to perform any of the methods described above.

[0060] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0061] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0062] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0063] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0064] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A gold nanorod-enhanced photothermal elastic gas detection system, characterized in that, The system includes: Adjustable laser, gas cell, quartz tuning fork; The gas cell is disposed between the adjustable laser and the quartz tuning fork, and the light-receiving area of ​​the quartz tuning fork is disposed at the corresponding position of the modulated laser output by the adjustable laser. The light-receiving area is provided with a photoelectric conversion thin film coating, which includes gold nanorod material deposited on the surface of the quartz tuning fork. The gold nanorod material has localized surface plasmon resonance effect and high thermal conductivity. The longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material matches the absorption band of the gas to be measured. This allows the gold nanorod material to enhance the absorption of the modulated laser through the localized surface plasmon resonance effect when the modulated laser emitted from the gas cell irradiates the photoelectric conversion thin film coating, and convert the absorbed light energy into heat energy. The heat energy generated by the photoelectric conversion thin film coating is transferred to the quartz tuning fork, causing the quartz tuning fork to undergo thermoelastic deformation and exciting the quartz tuning fork to vibrate. The quartz tuning fork outputs a gas concentration electrical signal based on the piezoelectric effect.

2. The system according to claim 1, characterized in that, The system further includes a signal reading and processing unit, which is electrically connected to the quartz tuning fork. The signal reading and processing unit is used to read the gas concentration electrical signal output by the quartz tuning fork and extract the harmonic signals in the gas concentration electrical signal to obtain the detection result of the gas to be tested based on the harmonic signals.

3. The system according to claim 1, characterized in that, The light-receiving area is located in the electrode-free region of the quartz tuning fork, and the photoelectric conversion thin film coating is selectively applied to the electrode-free region by a drop-coating method.

4. The system according to claim 1, characterized in that, The aspect ratio of the gold nanorod material is matched with the absorption band of the gas to be tested, so that the longitudinal localized surface plasmon resonance absorption peak of the gold nanorod material corresponds to the absorption band of the gas to be tested.

5. The system according to claim 1, characterized in that, The adjustable laser is connected to a laser driver, which receives a drive signal formed by the superposition of a scanning signal and a modulation signal to drive the adjustable laser to scan the absorption band of the gas to be tested and output the modulated laser.

6. The system according to any one of claims 1 to 5, characterized in that, A laser collimator is disposed between the adjustable laser and the gas pool, and the laser collimator is used to collimate the output laser of the adjustable laser.

7. The system according to any one of claims 1 to 5, characterized in that, A beam focusing component is disposed between the gas cell and the quartz tuning fork, the beam focusing component being used to focus the modulated laser emitted from the gas cell onto the light-receiving area.

8. The system according to any one of claims 1 to 5, characterized in that, The modulation frequency of the modulated laser output by the adjustable laser is located within the resonant response frequency band of the quartz tuning fork.

9. The system according to any one of claims 1 to 5, characterized in that, The system also includes a gas supply regulation unit connected to the gas pool, which is used to supply the gas to be tested to the gas pool and regulate the gas pressure or gas flow rate in the gas pool.

10. A method for detecting gold nanorod-enhanced photothermal elastic gases, wherein the method is applied to the gold nanorod-enhanced photothermal elastic gas detection system according to any one of claims 1 to 9, characterized in that, The method includes: A scanning signal and a modulation signal are generated by a signal reading and processing unit, and the scanning signal and the modulation signal are superimposed to form a driving signal. The laser driver receives the driving signal and drives the adjustable laser to output a modulated laser corresponding to the absorption band of the gas under test. Obtain the gas concentration electrical signal output by the quartz tuning fork based on the piezoelectric effect; The gas concentration electrical signal is subjected to harmonic demodulation to obtain a harmonic signal; Extract the peak amplitude of the harmonic signal; The detection result of the gas to be tested is calculated based on the linear fitting relationship between the peak amplitude of the harmonic signal and the concentration of the gas to be tested.

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