A low-concentration free radical detection method and device based on a diamond quantum sensor

Abstract

The application provides a low-concentration free radical detection method and device based on a diamond quantum sensor, and the device comprises a laser, a microwave system, a fluorescence signal detection and collection device, a signal processing device and a computer control system. The laser is used for emitting 532nm laser, and the 532nm laser is divided into a reference path and a signal path through a beam splitter; the microwave system is used for generating a preset off-resonant hole burning microwave sequence; the fluorescence signal detection and collection device is used for generating a fluorescence signal, and converting the fluorescence signal and the laser of the reference path into a current signal; the signal processing device is used for processing the current signal to obtain a low-noise signal; and the computer control system is used for processing the low-noise signal and controlling the microwave system to generate a preset microwave. The application realizes the superposition and spectral line narrowing of the NV color center sensing signal by using the off-resonant hole burning microwave sequence under the condition of zero magnetic field, and effectively improves the free radical detection sensitivity by combining the quasi-three-dimensional structure of the nanodiamond and the wideband antenna design.

Description

Technical Field

[0001] This invention belongs to the field of quantum precision measurement technology, and in particular relates to a method and device for detecting low-concentration free radicals based on a diamond quantum sensor. Background Technology

[0002] In the biomedical field, free radicals have long been considered toxic byproducts of aerobic metabolism. However, with the deepening development of redox biology, modern perspectives emphasize the "dual effect" of free radicals: they can both induce oxidative damage and act as key signaling molecules for maintaining cellular homeostasis, and this effect exhibits a significant concentration dependence. Given the extremely low concentration of free radicals under physiological conditions (typically in the nM to fM range), developing highly reliable and ultrasensitive detection techniques has become a core requirement for studying their biological functions. Currently, common free radical detection methods include fluorescent probe methods, chemiluminescence methods, electrochemical detection methods, mass spectrometry, and electron paramagnetic resonance (EPR). Compared with other methods, EPR is currently the only method that can directly detect free radicals, and the spectroscopic signals it acquires not only contain quantitative concentration information but also reflect the chemical type and molecular structure of free radicals through spectral characteristics, earning it the reputation of the "gold standard" in the field of free radical detection. However, traditional EPR spectrometers, based on electromagnetic induction sensing mechanisms, have a free radical concentration detection limit of 10–100 nM, severely limiting their applicability in low-concentration free radical studies.

[0003] Existing patent CN118032733A discloses a rapid molecular information detection method and system based on a diamond NV center quantum sensor. It utilizes laser irradiation of the sample to polarize and read out the electronic state of the nitrogen-vacancy center sensor, obtaining a fluorescence signal. Off-resonance microwaves are applied to the sample to induce resonance between the nitrogen-vacancy center sensor and the analyte molecule. The fluorescence signal is then processed by a fluorescence signal processing module to obtain the molecular information of the analyte molecule. However, this patent still has the following technical limitations:

[0004] The traditional bulk diamond used has low adsorption efficiency for free radicals; the narrow bandwidth and small aperture size of the microwave radiation structure limit the effective number of NV color center sensors that can participate; the wide-field fluorescence collection method has low fluorescence collection efficiency; the signal processing system relies on a simple cyclic repetitive measurement strategy to improve the signal-to-noise ratio, which requires long-term accumulation to achieve a high signal-to-noise ratio signal, making it difficult to effectively suppress low-frequency noise; in addition, the traditional off-resonance microwave sequence used results in a large detection signal linewidth and poor resolution. Summary of the Invention

[0005] The purpose of this invention is to use diamond NV centers as quantum sensors to detect the electron paramagnetic resonance spectrum of target free radical molecules, and to overcome the sensitivity limitations of traditional EPR in the detection of low-concentration free radicals by utilizing the unique advantages of diamond NV centers, so as to achieve the goal of efficient detection of low-concentration free radical samples.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A low-concentration free radical detection device based on a diamond quantum sensor includes: a laser, a microwave system, a fluorescence signal detection and collection device, a signal processing device, and a computer control system; The laser is used to emit 532nm laser light. The 532nm laser light is split into two paths by a beam splitter, one path is used as a reference path and the other path is used as a signal path. The microwave system is used to generate a preset off-resonance hole-burning microwave sequence; The fluorescence signal detection and collection device is used to generate fluorescence signals and convert the fluorescence signals and the laser from the reference path into current signals. The device includes: a sample to be tested, an optical module, a signal acquisition device, and a snap-fit ​​magnetic ring. The sample to be tested includes nanodiamonds containing NV centers and free radical samples. Fluorescence signals are generated by the interaction of microwaves and the laser from the signal path with the nanodiamonds containing NV centers. The optical module includes a light guide and a filter. The light guide is used to confine and transmit the fluorescence signal, and the filter is used to filter out the 532nm laser. The signal acquisition device is a photodetector used to receive the fluorescence signals and the laser from the reference path and convert them into current signals respectively. The snap-fit ​​magnetic ring is used to suppress electromagnetic interference on the cable. The signal processing device is used to process current signals to obtain low-noise signals; The computer control system is used to process low-noise signals and control the microwave system to generate preset microwaves.

[0007] Furthermore, the microwave system includes: Wave source, used to generate sweeping microwaves; Arbitrary wave generator, used to generate resonant microwaves; A microwave combiner is used to combine a swept microwave signal and a resonant microwave signal into a single off-resonance hole-burning microwave sequence. Microwave power amplifier, used to amplify off-resonance hole-burning microwave sequences; A broadband antenna is used to radiate an amplified off-resonance burned-hole microwave sequence onto the nanodiamond sample containing NV color centers.

[0008] Furthermore, the patch material of the broadband antenna is metallic copper, the substrate material is FR4, the feeding method is SMA side-feed, the bandwidth of the broadband antenna is greater than 200MHz, and the size of the central through hole is on the order of millimeters.

[0009] Furthermore, the light guide has an irregular frustum-shaped structure.

[0010] Furthermore, the filter is a 637nm long-pass filter, used to filter 532nm laser light and allow red fluorescence from diamond containing NV color centers to pass through.

[0011] Furthermore, the photosensitive area of ​​the photodetector is 1 cm². 2 .

[0012] Furthermore, a high-refractive-index liquid is added between the interfaces of the light guide, filter, and photodetector.

[0013] Furthermore, the signal processing device includes: Differential circuits are used to suppress common-mode noise in current signals; A transimpedance amplifier is used to convert current signals into voltage signals and amplify their gain. A high-pass filter is used to filter out low-frequency noise from an amplified voltage signal. A data acquisition card is used to acquire signals that have been filtered by a high-pass filter. A lock-in amplifier is used to perform phase-sensitive demodulation of signals in a data acquisition card.

[0014] A method for detecting low-concentration free radicals based on a diamond quantum sensor includes the following steps: (1) The free radical sample to be tested is mixed with nanodiamond containing NV color centers to prepare the test sample and placed on the light guide of the optical module; (2) The 532nm laser generated by the laser is split into two paths by a beam splitter. One path is used as a signal path to polarize the electronic state of the NV color center, and the other path is used as a reference path to be directly incident on the photodetector. (3) Under zero magnetic field conditions, the microwave system emits a preset partial resonance burning microwave sequence and radiates it onto the nanodiamond containing NV color centers using a broadband antenna. When the partial resonance burning microwave sequence resonates with the laser passing through the signal path and interacts with the nanodiamond containing NV color centers and the molecule to be tested, the fluorescence changes. (4) The fluorescence signal is transmitted to the photodetector through the optical module. The photodetector receives the fluorescence signal and the laser from the reference path respectively, and converts them into current signals. (5) The current signal is processed by a signal processing device to obtain a low-noise signal. The low-noise signal is converted into a digital signal and transmitted to the computer control system. The electron paramagnetic resonance spectrum of the free radical molecule to be tested is obtained through phase correction, integration and subtraction operations, and the information of the target free radical molecule is extracted from it.

[0015] Further, in step (5), the laser and fluorescence signals of the reference path are converted into current signals by photodetectors, and the two current signals are converted into voltage signals by transimpedance amplifiers. Then, non-target frequency noise is suppressed by a high-pass filter. The two filtered signals are then entered into a lock-in amplifier for phase-sensitive demodulation to obtain a low-noise signal. The low-noise signal is transmitted to the computer control system, which determines the optimal differential cancellation coefficient according to the least squares method and performs weighted differential processing on the low-noise signal. The electron paramagnetic resonance spectrum of the free radical molecule to be tested is obtained through phase correction, integration and subtraction operations, and the information of the target free radical molecule is extracted from it.

[0016] The beneficial effects of this invention are as follows: (1) This invention uses nanodiamonds instead of traditional bulk diamonds as the quantum sensor carrier. Nanodiamonds have a larger specific surface area, which can provide more interfaces for contact with the free radicals to be measured, increasing the probability of free radicals approaching the sensing interface and the probability of effective magnetic interaction with NV color centers; at the same time, the porous bulk structure formed by stacking or bonding can build a three-dimensional interconnected pore network inside the material, realizing three-dimensional detection of internal pores, thereby effectively solving the problem of limited sensing interface and low sample utilization caused by the detection area being concentrated on a two-dimensional surface in traditional bulk diamonds, and significantly improving the effective measurement volume and detection sensitivity.

[0017] (2) The present invention adopts a broadband antenna design with a bandwidth greater than 200MHz, which can realize the effective manipulation of all NV color centers within the non-uniform broadening; at the same time, the size of the central through hole is on the order of millimeters, allowing millimeter-sized laser spots to pass through, so that more NV color centers can participate in quantum manipulation at the same time. This solves the problem in the prior art that the number of effective NV color centers that can participate in detection is limited due to the narrow bandwidth of the microwave radiation structure and the small size of the through hole, further increasing the number of available sensors and improving detection efficiency.

[0018] (3) The present invention uses light guide to constrain the transmission path of fluorescence signal, reduces the fluorescence divergence angle by using irregular frustum-shaped light guide, combines a large area photodetector (photosensitive area 1cm²) and adds a high refractive index liquid between the light guide, filter and photodetector interface to form a high-efficiency fluorescence collection light path, effectively solves the problem of low efficiency of wide field fluorescence collection method in the prior art, and improves fluorescence collection efficiency.

[0019] (4) The present invention adopts a signal processing system integrating differential circuit, transimpedance amplifier, high-pass filter, data acquisition card and lock-in amplifier. The differential circuit suppresses common-mode noise, the transimpedance amplifier realizes current-to-voltage conversion and gain amplification, the high-pass filter suppresses low-frequency noise, and the lock-in amplifier extracts the target signal from the background noise through phase-sensitive detection technology. At the same time, combined with the optimal differential cancellation coefficient weighted differential processing, low-frequency noise can be effectively suppressed, and the system noise is suppressed to about 2 times the shot noise level. This solves the technical defects of the prior art that rely solely on long-term repeated measurement accumulation and is difficult to effectively suppress low-frequency noise, and greatly shortens the measurement time required to achieve the same signal-to-noise ratio.

[0020] (5) This invention utilizes an arbitrary wave generator to produce narrow-linewidth resonant microwaves as hole-burning microwaves, which are combined with sweeping microwaves generated by a wave source to form a partial resonant hole-burning microwave sequence. In this sequence, the resonant microwaves selectively saturate some NV color centers. When the frequency of the sweeping microwaves resonates with the NV-radical system, a narrow-linewidth hole-burning signal is formed at the original signal position, thereby compressing the wide signal measured by the traditional partial resonant sequence into a narrow hole-burning signal. This effectively solves the problems of large signal linewidth and poor resolution in the prior art of partial resonant sequence signals and improves spectral resolution.

[0021] (6) The present invention performs detection under zero magnetic field conditions. It utilizes the characteristic that the free radicals to be tested have the same energy level under zero field to realize the superposition of the sensing signals of NV color centers with different orientations. At the same time, the NV color centers with different orientations are modulated to the same energy level through the partial resonance hole burning microwave sequence to realize the superposition of the sensor's sensing capability. Thus, without the need for an external static magnetic field, the signal contributions of all NV color centers are superimposed in the same direction, further improving the detection sensitivity and signal strength. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the low-concentration free radical detection device provided by the present invention; Figure 2 This is a schematic diagram of the structure of the fluorescence signal detection and collection component provided by the present invention; Figure 3 This is a schematic diagram of the fluorescent broadband antenna structure provided by the present invention; Figure 4 This is a signal processing flowchart provided by the present invention; Figure 5 This is the noise spectrum of the experimental measurement system after processing by the signal processing system provided by the present invention; Figure 6 This is a schematic diagram of the parabolic concentrator structure provided by the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] The application principle of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1: Please refer to Figure 1 A low-concentration free radical detection device based on a diamond quantum sensor includes: a laser, a microwave system, a fluorescence signal detection and collection device, a signal processing device, and a computer control system.

[0026] The laser is used to emit a 532nm laser to excite the NV color center. The 532nm laser is split into two paths by a beam splitter: one is the reference path and the other is the signal path.

[0027] A microwave system is used to generate a preset off-resonance hole-burning microwave sequence to manipulate nanodiamonds containing NV color centers. The system includes a wave source, an arbitrary wave generator, a microwave combiner, a microwave power amplifier, and a self-designed broadband antenna. The wave source generates scanning microwaves (spectral scanning microwaves); the arbitrary wave generator (AWG) generates specifically modulated resonant microwaves, equivalent to applying hole-burning microwaves to saturate some NVs. This application uses the arbitrary wave generator to generate narrow-linewidth resonant microwaves, replacing the wide-linewidth signals used in existing off-resonance sequences, thereby effectively compressing the signal linewidth and improving spectral resolution. The microwave combiner combines the scanning microwaves generated by the wave source and the resonant microwaves generated by the arbitrary wave generator into a single path to obtain the off-resonance hole-burning microwave sequence; the microwave power amplifier amplifies the off-resonance hole-burning microwave sequence, as the microwaves directly emitted from the wave source and AWG are very weak and require amplification to obtain the amplified off-resonance hole-burning microwave sequence; the broadband antenna radiates the amplified off-resonance hole-burning microwave sequence onto the nanodiamonds containing NV color centers. Please refer to [reference needed]. Figure 3 The broadband antenna uses copper as the patch material and FR4 as the substrate material, and is fed by SMA side-feed. This structure has a bandwidth greater than 200MHz, and the resonant frequency can be changed by altering the size of the central aperture. The broadband antenna used in this invention has a resonant frequency of 2.9GHz and a bandwidth of 250MHz. Furthermore, the size of the central aperture is on the order of millimeters, allowing laser beams as small as millimeters to pass through.

[0028] Please refer to Figure 2The fluorescence signal detection and collection device is used to generate fluorescence signals and convert the fluorescence signals and the laser of the reference path into current signals. It includes: the sample to be tested (including nanodiamond and free radical samples), optical module, signal acquisition device, snap-fit ​​magnetic ring, and frame structure that fixes the components together.

[0029] The test samples include nanodiamonds containing NV color centers and free radical samples. The nanodiamonds containing NV color centers generate fluorescence signals using the combined action of a laser and a microwave sequence with off-resonance hole burning in the signal path. The intensity of these signals changes with the microwave frequency, thus reflecting the free radical concentration.

[0030] The optical module includes a light guide and a filter. The light guide is used to confine the transmitted fluorescence signal, reducing fluorescence loss during its journey to the photodetector end face and improving fluorescence collection efficiency. Please refer to [reference needed]. Figure 6 The light guide is designed in an irregular frustum shape to reduce the fluorescence divergence angle and improve fluorescence collection efficiency. The filter is used to filter the 532nm laser. A 637 long-pass filter is used to filter the 532nm laser while allowing red NV fluorescence to pass through.

[0031] The signal acquisition and signal processing devices are the core components of the entire detection device. In this application, a low-noise, large-area photodetector is used to collect fluorescence signals and the laser light from the reference path, converting these signals into current signals. The photodetector itself is the fluorescence collection device, using a photosensitive area of ​​1 cm². 2 The photodetector can receive fluorescence over a wide range, improving fluorescence collection efficiency. Adding a high-refractive-index liquid between the light guide, filter, and photodetector interface enhances fluorescence transmission efficiency.

[0032] A snap-fit ​​ferrite ring is a ferrite ring with an openable snap-fit ​​structure. It is an anti-interference electronic component used to suppress electromagnetic interference (EMI) on cables.

[0033] The signal processing unit processes the current signal to obtain a low-noise signal. It integrates a differential circuit, a transimpedance amplifier, a high-pass filter, a data acquisition card, and a lock-in amplifier, with the transimpedance amplifier, filter, data acquisition card, and lock-in amplifier all integrated on a single board. The current signal output from the photodetector first passes through a differential circuit to suppress common-mode noise. Then, the transimpedance amplifier converts the current signal from the differential circuit output into a voltage signal and amplifies it. The high-pass filter removes low-frequency noise from the amplified signal. The data acquisition card acquires the filtered signal, and the lock-in amplifier uses phase-sensitive detection technology to extract the target signal from the background noise, reducing the impact of noise on the detection results. After processing by the signal processing unit, the signal noise can be optimized to only twice the shot noise level.

[0034] The computer control system is used to process low-noise signals and control the microwave system to generate preset microwaves.

[0035] A novel parallel EPR detection sequence: using a partial resonant hole-burning microwave sequence under zero-field conditions, which allows the sensing signals of the free radical molecules to be measured to be superimposed and the sensing capabilities of the sensors to be superimposed, while narrowing the linewidth of the signal spectrum to the intrinsic linewidth level.

[0036] Among them, the partial resonance hole-burning microwave sequence is obtained through a wave source and an AWG. That is, the resonance microwave will saturate a part of the NV. When the frequency of the scanning microwave happens to resonate with the NV-radical system, a very narrow "hole" will be burned out where the signal should have appeared. In other words, this sequence can turn the originally measured wide signal into a very narrow "hole" signal, thus improving the spectral resolution.

[0037] Electron paramagnetic resonance (EPR) detection of free radicals is based on the magnetic moment characteristics of unpaired electrons in free radicals. Under the influence of an applied static magnetic field, the spin energy levels of unpaired electrons undergo Zeeman splitting; when the applied microwave frequency satisfies the resonance condition, the electron spins transition between different energy levels and absorb microwave energy. By recording the changes in the absorption signal with the magnetic field or microwave frequency, characteristic spectral information of free radicals can be obtained, thereby enabling the analysis and detection of the type, concentration, and local chemical environment of free radicals. However, traditional EPR spectrometers based on electromagnetic induction sensing mechanisms are usually limited by factors such as resonant cavity volume, sample fill factor, microwave field-sample coupling efficiency, and receiving coil / detector noise, limiting the detection limit of free radical concentration to 10–100 nM.

[0038] This invention utilizes a diamond NV center quantum sensor to detect free radicals, leveraging the single-molecule detection capability and atomic-scale size of NV centers to achieve a breakthrough in the sensitivity of traditional EPR detection. The diamond NV center quantum sensor is a highly sensitive quantum detector constructed based on nitrogen-vacancy defect centers in diamond. NV centers possess electron spin states that can exist stably at room temperature; their spin energy levels can be initialized and fluorescence readout using a green laser, and can be coherently manipulated by a microwave field. By overcoming the inhomogeneity of the target signal under zero-field conditions to achieve superposition of sensing signals, and then using a newly designed off-resonance hole-burning sequence to modulate NV centers with different orientations to the same energy level, superposition of sensing capabilities is achieved, while simultaneously narrowing the linewidth to the intrinsic linewidth level. The atomic-scale size of diamond NV centers allows for the integration of a large number of NV centers within a limited space, significantly increasing the effective detection volume and enabling the detection of low-concentration free radicals.

[0039] Meanwhile, the nanodiamonds used in this invention can serve as a distributed quasi-three-dimensional quantum sensor. Traditional bulk diamonds primarily concentrate their detection area near a two-dimensional surface. The target free radical must diffuse to the vicinity of the diamond surface to be effectively detected. In short, as a two-dimensional sensor, traditional bulk diamonds suffer from limited sensing interfaces and low sample utilization during detection. The nanodiamonds used in this invention, however, can function as quasi-3D sensors, possessing a larger specific surface area, thus improving the effective measurement volume and sample utilization. Under the same mass conditions, nanodiamonds can provide more interfaces for contact with the target free radicals, thereby increasing the probability of free radicals approaching the sensing interface and the probability of effective magnetic interaction with NV color centers. Furthermore, through stacking or bonding, nanodiamonds can form porous bulk materials. These porous bulk structures can maintain macroscopic bulk morphological stability while constructing a three-dimensional interconnected pore network within the material, enabling three-dimensional detection of internal pores.

[0040] Please refer to Figure 4 A method for detecting low-concentration free radicals based on a diamond sensor, comprising the following steps: (1) The free radical sample to be tested is mixed with nanodiamond containing NV color centers to form the test sample, and then placed on the light guide of the optical module; (2) The 532nm laser generated by the laser is split into two paths by a beam splitter. One laser is used as the signal path to polarize the electronic state of the NV color center sensor, and the other laser is used as the reference path to directly hit the photosensitive surface of the photodetector. (3) Under zero magnetic field conditions, the microwave system emits a preset partial resonance burning microwave sequence and radiates it onto the nanodiamond containing NV color centers using a broadband antenna. When the partial resonance burning microwave sequence resonates with the laser passing through the signal path and interacts with the nanodiamond containing NV color centers and the molecule to be tested, the fluorescence changes. (4) The NV fluorescence is transmitted to the photodetector through the optical module. The photodetector receives the NV fluorescence signal and the laser of the reference path and converts the fluorescence signal and the laser of the reference path into a current signal. (5) The current signal is processed by the signal processing system to obtain a low-noise signal. At the same time, the analog signal is converted into a digital signal and then the digital signal is transmitted to the computer. The electron paramagnetic resonance spectrum of the free radical molecule to be tested is obtained through phase correction, integration and subtraction algorithms, and the information of the target free radical molecule is extracted from it.

[0041] Phase correction is performed because the signal demodulated by the lock-in amplifier is divided into two parts, Asinθ and Acosθ, and the optimal θ is obtained through the SVD algorithm (singular value decomposition). Integration is performed because the original signal is a differential signal, which needs to be integrated. Subtraction is performed to make the hole-burning signal more obvious, which requires subtracting the signal obtained without resonant microwave from the signal obtained with resonant microwave.

[0042] The specific signal processing flow is as follows: Figure 4 As shown, the laser and fluorescence signals from the reference path are input to the photodetector, converting them into current signals. These current signals are first converted into voltage signals by a transimpedance amplifier, and then filtered by a high-pass filter to suppress high-frequency non-target noise components. The filtered signals then enter a lock-in amplifier for phase-sensitive demodulation, obtaining the demodulated signal at the corresponding modulation frequency, i.e., the low-noise signal. The low-noise signal is transmitted to a computer, where the computer control system determines the optimal differential cancellation coefficient using the least squares method and performs weighted differential processing on the low noise, effectively eliminating common-mode noise in the two signals and obtaining a low-noise signal. Finally, the system uses phase correction, integration, and subtraction operations to obtain the electron paramagnetic resonance spectrum of the target free radical molecule from the processed signals corresponding to different modulation frequencies, and extracts the information of the target free radical molecule from it. Through the above data processing flow, the system noise level can be significantly reduced, bringing the final signal noise close to the shot noise limit, with the noise level reduced to about twice that of shot noise. The transimpedance amplifier, high-pass filter, lock-in amplifier, and other components are all integrated on a single board. In addition, this invention can also employ a digital lock-in processing method. This method involves directly inputting the filtered analog signal into a data acquisition card for digital acquisition without using a separate lock-in amplifier. The computer then performs digital phase-locked demodulation, optimal differential coefficient selection, and differential cancellation. This approach is essentially the same as the analog phase-locked loop processing flow in terms of signal extraction principles and noise reduction effects; the main differences lie in the data processing method and speed. Please refer to [reference needed]. Figure 5 The diagram describes the noise characteristics of the system at different modulation frequencies. The dashed line represents the shot noise (SN) level in the current state. It can be seen that when the modulation frequency is 3kHz, the noise level after differential modulation is approximately twice the shot noise level. This measurement device can suppress the noise to an extremely low level, so that the final detection sensitivity is mainly affected by the shot noise.

[0043] Application Example 1: An application of a low-concentration free radical detection device based on a diamond sensor is described below: Step 1: Sample preparation. A dispersion of nanodiamond containing a high concentration of NV centers (1 mg / mL) is prepared and mixed with a sample of the target free radical (e.g., Tempo) at a certain concentration.

[0044] Step 2: Assemble a signal acquisition device based on a diamond quantum sensor, such as... Figure 2 As shown. A specially shaped light guide is used to connect the sample cell and the photodetector; the reference path only requires fixing the photodetector so that the laser is perpendicular to the photosensitive surface of the photodetector; finally, an outer frame is used to fix all components.

[0045] Step 3: Connect the microwave system, photodetector, processing system, and computer control system. Install a fixed broadband antenna close enough to the sample, and connect the various microwave components using a microwave combiner and coaxial cable. Connect the photodetector to the signal processing system components using a coaxial cable, and then connect the signal processing system to the computer control system using a USB cable.

[0046] Step 4: Adjust the laser power. The laser emitted by the laser has strong high-frequency noise, so it is necessary to select an appropriate optical power level that ensures the signal fluctuation does not exceed the range of the data acquisition card while still generating a sufficiently strong fluorescence signal. At the same time, for better differential cancellation results (generally 300mW is selected based on experience), it is necessary to adjust the distribution ratio of the two laser paths so that the photocurrent of the reference path is equal to that of the photocurrent of the signal path.

[0047] Step 5: Send the preset microwave sequence to the wave source and AWG on the computer. The microwave sequence is amplified by the microwave amplifier and finally radiated to the sample through the broadband antenna.

[0048] Step 6: A photodetector collects fluorescence signals at different frequencies during the experiment. When the applied microwave resonates with the target system (free radical sample and NV color center), it causes changes in NV fluorescence. The raw signal collected by the photodetector is then processed... Figure 3 Following the procedure shown, the final electron paramagnetic resonance spectrum of the free radical sample to be tested will be obtained.

[0049] Step 7: By analyzing the intensity of the electron paramagnetic resonance spectrum signal, the concentration of the free radical sample can be determined.

[0050] First, this is an EPR spectroscopic method that measures spectroscopic signals, allowing for the determination of both linear reaction radical types and radical concentrations based on signal intensity. Second, this application utilizes NV color center quantum sensors, leveraging their atomic-level size for finite-space stacking to enhance sensing capabilities. Nanodiamonds, acting as quasi-3D sensors, possess a larger specific surface area and a larger effective detection volume. Compared to traditional NV detection methods, this application can utilize a larger spot size and more NV color centers. The signal processing incorporates differential and lock-in amplification steps to significantly suppress noise. This application, using nanodiamonds as a quasi-3D sensor, achieves a breakthrough in the traditional EPR concentration detection limit.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-concentration free radical detection device based on a diamond quantum sensor, characterized in that, include: Lasers, microwave systems, fluorescence signal detection and collection devices, signal processing devices, and computer control systems; The laser is used to emit 532nm laser light. The 532nm laser light is split into two paths by a beam splitter, one path is used as a reference path and the other path is used as a signal path. The microwave system is used to generate a preset off-resonance hole-burning microwave sequence; The fluorescence signal detection and collection device is used to generate fluorescence signals and convert the fluorescence signals and the laser from the reference path into current signals. The device includes: a sample to be tested, an optical module, a signal acquisition device, and a snap-fit ​​magnetic ring. The sample to be tested includes nanodiamonds containing NV centers and free radical samples. Fluorescence signals are generated by the interaction of microwaves and the laser from the signal path with the nanodiamonds containing NV centers. The optical module includes a light guide and a filter. The light guide is used to confine and transmit the fluorescence signal, and the filter is used to filter out the 532nm laser. The signal acquisition device is a photodetector used to receive the fluorescence signals and the laser from the reference path and convert them into current signals respectively. The snap-fit ​​magnetic ring is used to suppress electromagnetic interference on the cable. The signal processing device is used to process current signals to obtain low-noise signals; The computer control system is used to process low-noise signals and control the microwave system to generate preset microwaves.

2. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, Microwave systems include: Wave source, used to generate sweeping microwaves; Arbitrary wave generator, used to generate resonant microwaves; A microwave combiner is used to combine a swept microwave signal and a resonant microwave signal into a single off-resonance hole-burning microwave sequence. Microwave power amplifier, used to amplify off-resonance hole-burning microwave sequences; A broadband antenna is used to radiate an amplified off-resonance burned-hole microwave sequence onto the nanodiamond sample containing NV color centers.

3. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 2, characterized in that, The patch material of the broadband antenna is metallic copper, the substrate material is FR4, the feeding method is SMA side-fed, the bandwidth of the broadband antenna is greater than 200MHz, and the size of the center through hole is on the order of millimeters.

4. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, The light guide has an irregular frustum-shaped structure.

5. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, The filter is a 637nm long-pass filter, used to filter 532nm laser light and allow red fluorescence from diamond containing NV color centers to pass through.

6. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, The photosensitive area of ​​the photodetector is 1 cm². 2 .

7. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, A high-refractive-index liquid is added between the interfaces of the light guide, filter, and photodetector.

8. The low-concentration free radical detection device based on a diamond quantum sensor according to claim 1, characterized in that, The signal processing device includes: Differential circuits are used to suppress common-mode noise in current signals; A transimpedance amplifier is used to convert current signals into voltage signals and amplify their gain. A high-pass filter is used to filter out low-frequency noise from an amplified voltage signal. A data acquisition card is used to acquire signals that have been filtered by a high-pass filter. A lock-in amplifier is used to perform phase-sensitive demodulation of signals in a data acquisition card.

9. A method for detecting low-concentration free radicals based on a diamond quantum sensor, employing the detection device described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) The free radical sample to be tested is mixed with nanodiamond containing NV color centers to prepare the test sample and placed on the light guide of the optical module; (2) The 532nm laser generated by the laser is split into two paths by a beam splitter. One path is used as a signal path to polarize the electronic state of the NV color center, and the other path is used as a reference path to be directly incident on the photodetector. (3) Under zero magnetic field conditions, the microwave system emits a preset partial resonance burning microwave sequence and radiates it onto the nanodiamond containing NV color centers using a broadband antenna. When the partial resonance burning microwave sequence resonates with the laser passing through the signal path and interacts with the nanodiamond containing NV color centers and the molecule to be tested, the fluorescence changes. (4) The fluorescence signal is transmitted to the photodetector through the optical module. The photodetector receives the fluorescence signal and the laser from the reference path respectively, and converts them into current signals. (5) The current signal is processed by a signal processing device to obtain a low-noise signal. The low-noise signal is converted into a digital signal and transmitted to the computer control system. The electron paramagnetic resonance spectrum of the free radical molecule to be tested is obtained through phase correction, integration and subtraction operations, and the information of the target free radical molecule is extracted from it.

10. The method for detecting low-concentration free radicals using a diamond quantum sensor according to claim 9, characterized in that, In step (5), the laser and fluorescence signals of the reference path are converted into current signals by photodetectors, and then the two current signals are converted into voltage signals by transimpedance amplifiers. Subsequently, non-target frequency noise is suppressed by a high-pass filter. The filtered two signals are then entered into a lock-in amplifier for phase-sensitive demodulation to obtain a low-noise signal. The low-noise signal is transmitted to the computer control system, which determines the optimal differential cancellation coefficient according to the least squares method and performs weighted differential processing on the low-noise signal. The electron paramagnetic resonance spectrum of the free radical molecule to be tested is obtained through phase correction, integration and subtraction operations, and the information of the target free radical molecule is extracted from it.

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