RESUMO
A novel TT-type resonator was proposed for the first time, to our knowledge, to realize differential photoacoustic (PA) detection for trace gas measurement. The special design of the TT-type resonator allows us to install the microphone at the resonant center of the acoustic field to maximize the use of the absorption-induced PA signal. To meet the requirement of low gas consumption and easy integration, the TT-type resonator-based PA cell was fabricated as a fiber-coupled module with an inner volume of only 1.1â ml. For validation, the TT-type PA cell was integrated to a photoacoustic spectroscopy (PAS) system for acetylene detection. As a result, a linearity of 0.99999 was achieved in a concentration range from 0 to 5000â ppm with a noise equivalent sensitivity of 101â ppb. The proposed TT-type resonator contributes a new style of PA cell structure to the field of PAS gas detection, combining the advantages of easy integration, low gas consumption, differential detection, and photoacoustic enhancement together.
RESUMO
In addition to the atmospheric measurement, detection of dissolved carbon oxides and hydrocarbons in a water region is also an important aspect of greenhouse gas monitoring, such as CH4 and CO2. The first step of measuring dissolved gases is the separation process of water and gases. However, slow degassing efficiency is a big challenge which requires the gas detection technology itself with low gas consumption. Photoacoustic spectroscopy (PAS) is a good choice with advantages of high sensitivity, low gas consumption, and zero background, which has been rapidly developed in recent years and is expected to be applied in the field of dissolved gas detection. In this study, a miniaturized differential photoacoustic cell with a volume of 7.9 mL is designed for CH4 and CO2 detection, and a dual differential method with four microphones is proposed to enhance the photoacoustic signal. What we believe to be a new method increases photoacoustic signal by 4 times and improves the signal to noise ratio (SNR) over 10 times compared with the conventional single-microphone mode. Two distributed feedback (DFB) lasers at 1651â nm and 2004nm are employed to construct the PAS system for CH4 and CO2 detection respectively. Wavelength modulation spectroscopy (WMS) and 2nd harmonic demodulation techniques are applied to further improve the SNR. As a result, sensitivity of 0.44â ppm and 7.39â ppm for CH4 and CO2 are achieved respectively with an integration time of 10 s. Allan deviation analysis indicates that the sensitivity can be further improved to 42 ppb (NNEA=4.7×10-10cm-1WHz-1/2) for CH4 and 0.86â ppm (NNEA=5.3×10-10cm-1WHz-1/2) for CO2 when the integration time is extended to 1000 s.
RESUMO
Accurate and sensitive analysis of p53 DNA is important for early diagnosis of cancer. In this work, a fluorescence sensing system based on DNA supersandwich nanowires and cation exchange (CX)-triggered multiplex signal amplification was constructed for the detection of p53 DNA. In the presence of p53 DNA, the DNA self-assembles to form a DNA supersandwich nanowire that generates long double-stranded DNA. Subsequently, the cation exchange (CX) reaction between ZnS and Ag+ was utilized to release free Zn2+. With the participation of Zn2+, DNAzyme catalyzes the hydrolysis of numerous catalytic molecular beacons, resulting in a greatly enhanced fluorescence signal due to the cycling of DNAzyme. The fluorescence values increased in proportion to the concentrations of p53 DNA in the range of 10 pM to 200 nM, and a detection limit (LOD) of 2.34 pM (S/N = 3) was obtained. This method provides an effective strategy for the quantitative detection of p53 DNA.
RESUMO
In the wavelength modulation spectroscopy (WMS) gas detection system, the laser diode is usually stabilized at a constant temperature and driven by current injection. So, a high-precision temperature controller is indispensable in every WMS system. To eliminate wavelength drift influence and improve detection sensitivity and response speed, laser wavelength sometimes needs to be locked at the gas absorption center. In this study, we develop a temperature controller to an ultra-high stability level of 0.0005 °C, based on which a new laser wavelength locking strategy is proposed to successfully lock the laser wavelength at a CH4 absorption center of 1653.72 nm with a fluctuation of fewer than 19.7 MHz. For 500 ppm CH4 sample detection, the 1σ SNR is increased from 71.2 dB to 80.5 dB and the peak-to-peak uncertainty is improved from 1.95 ppm down to 0.17 ppm with the help of a locked laser wavelength. In addition, the wavelength-locked WMS also has the absolute advantage of fast response over a conventional wavelength-scanned WMS system.
Assuntos
Febre , Lasers Semicondutores , Humanos , Temperatura , Análise Espectral , MetanoRESUMO
We propose to replace the traditional time-frequency domain filtering with feature domain filtering to realize an innovation of filtering algorithm. A feature domain transform filter (FDTF) is composed of the feature domain transform layer based on principal component analysis (PCA) algorithm, the feature domain information extractor based on deep learning and the time domain transform layer. It is established to filter out the noise with the same frequency and phase as the signal and is verified on methane gas. Although FDTF is established based on the simulated data set, the filtering effects of the simulation test set and the experimental data set show that the proposed FDTF outperforms other widely used time-frequency filtering algorithms. The FDTF-assisted methane sensor has good linearity at different concentrations of methane gas. With the FDTF enhancement, the optimized methane sensor performs excellent precision and stability in real-time measurements and achieves the minimum detectable column density of 2.50 ppm·m. This is undoubtedly a successful attempt to move the signal to a new domain for parsing and separation.
Assuntos
Algoritmos , Metano , Simulação por Computador , Análise de Componente Principal , Processamento de Sinais Assistido por Computador , Razão Sinal-RuídoRESUMO
In view of the problems of low pre-screening efficiency, a weak Raman signal, and strong fluorescence interference in the detection of microplastics by traditional Raman spectroscopy, a set of rapid detection system and research methods for microplastics, including fluorescence imaging technology, differential Raman spectroscopy technology, and confocal microscopic Raman technology, are constructed in this paper. A 784/785 nm dual-wavelength laser was used as the excitation light source in the rapid detection system for microplastics. The sediment in the coastal waters of Qingdao Shilaoren was taken as the research object. Polycarbonate and high-density polyethylene with a particle size of 40 µm in the samples were accurately detected and analyzed. The research method for microplastics proposed in this study breaks through relevant key technologies, which we believe will help promote the development of microplastic monitoring technology in the global marine environment and provide strong technical support for the healthy development of the global marine ecological environment.
Assuntos
Microplásticos , Poluentes Químicos da Água , Plásticos/análise , Plásticos/química , Poluentes Químicos da Água/análise , Análise Espectral Raman , Monitoramento Ambiental/métodos , Sedimentos GeológicosRESUMO
A highly compact hyperspectral imager with an automatic geometric rectification function is developed in this study, which can be mounted on a UAV for ultra-wide range hyperspectral imaging. For better application, the system can provide visible light image transmission and hyperspectral imaging in the real-time mode. A specific design is proposed to allow the visible light camera and hyperspectral camera to share the same telescope optical path, making the system have a high integration level with a total mass of 1.9 kilograms. Thanks to the sharing-optical-path design, the field of view (FOV), frame rate, and spatial resolution are modified the same between the visible light camera and hyperspectral camera. As a result, the geometric rectification is easily performed, and repeated rectifications are eliminated to improve the imaging efficiency. A FOV of 40 degrees in the frame direction and 26 degrees in the flight direction are realized with a focal length of 13mm, providing a large spectral range from 400 nm to 1000 nm and an excellent spectral resolution of 2.5 nm. An automatic geometric rectification workflow is presented and verified in experiments, which can improve the geometric rectification of hyperspectral images in the presence of low-quality UAV navigation data through the incorporation of frame images. Experimental results show that the relative accuracy of geometric rectification is less than 2 pixels when applying the algorithm to our system dataset.
RESUMO
In this paper, a compact fluorescence hyperspectral imaging system based on a prism-grating-prism (PGP) structure is designed. Its spectrometer spectral range is 400-1000 nm with a spectral resolution of 2.5 nm, and its weight is less than 1.7 kg. The PGP imaging spectrometer combines the technical advantages of prism and grating, by not only using six lenses for imaging and collimation to realize the dual telecentres of object and image but also having a "straight cylinder" structure, which makes the installation and adjustment simple, compact, and stable. By the push-broom method, we obtained the three-dimensional cubic data of different oil products. By normalization processing, minimum noise separation transformation processing, visualization processing, and support vector machine classification processing of different oil fluorescence hyperspectral data, we demonstrate that the fluorescence hyperspectral imaging system can identify different kinds of oil and recognize the oil film thickness. The fluorescence hyperspectral imaging system can be used in oil spill detection, resource exploration, natural disaster monitoring, environmental pollution assessment, and many other fields.
RESUMO
An underwater hyperspectral imager (UHI) detection system is designed and developed, and a push-broom scan imaging mode was used. The telescope system adopts an image-side telecentric design with 22 mm focal length and 11∘×11∘ field of view. A prism-grating-prism structure was used as the spectral unit of spectrometer system to reduce spectral line bending. The UHI system reaches 5 nm spectral resolution in spectral range from 400 nm to 800 nm, and its modulation transfer function is greater than 0.62 at characteristic frequency in spectral range. An underwater hyperspectral detection experiment was carried out with an electric turntable, and the UHI system is of good imaging quality and spectral resolution, being able to distinguish various underwater targets.
RESUMO
This paper presents an underwater high-precision line laser three-dimensional (3D) scanning (LLS) system with rotary scanning mode, which is composed of a low illumination underwater camera and a green line laser projector. The underwater 3D data acquisition can be realized in the range of field of view of 50° (vertical) × 360° (horizontal). We compensate the refraction of the 3D reconstruction system to reduce the angle error caused by the refraction of light on different media surfaces and reduce the impact of refraction on the image quality. In order to verify the reconstruction effect of the 3D reconstruction system and the effectiveness of the refraction compensation algorithm, we conducted error experiments on a standard sphere. The results show that the system's underwater reconstruction error is less than 0.6 mm within the working distance of 140 mm~2500 mm, which meets the design requirements. It can provide reference for the development of low-cost underwater 3D laser scanning system.
RESUMO
A spaceborne limb hyperspectral imager for ozone detection is designed and developed. The hyperspectral imager can provide the limb hyperspectral radiances images with wide-band and large dynamic range. It is composed of an off-axis parabolic telescope and prism dispersive off-axis aspheric spectrometer, and large dynamic range detection can be realized by using a band-attenuation filter. The spectral range is from 280nm to 1000nm, the field of view is 2.4° (limb vertical direction) × 0.02° (horizontal direction), and the focal length is 69mm. The design results meet the requirements of image quality and have the characteristics of small volume and light weight, thereby making it especially suitable for the application of space remote sensing unlike existing methods that utilize complicated scanning mirror and multiple color separators. The limb hyperspectral imager is measured and calibrated on ground. It detected limb hyperspectral radiances on Tiangong-2 spacecraft of China.
RESUMO
A technique for elimination of residual amplitude modulation (ERAM) in photoacoustic spectroscopy based on dual path lock-in was proposed and experimentally demonstrated. There are two lock-in amplifiers, one is for gas concentration demodulation and another for residual amplitude modulation (RAM) measurement by tuning the reference signal in different phases, and then a dual path lock-in technique based on subtraction is applied to RAM removal, improving the second harmonic profile significantly. In this system, the signal to noise ratio (SNR) increases about two times based on our dual path lock-in technique compared to one distributed feedback laser diode (DFB-LD). The system achieved a good linear response (R-square = 0.99887) in a concentration range from 100 ppmv to 2400 ppmv and a minimum detection limit (MDL) of 1.47 ppmv.
RESUMO
We proposed a new method for gas detection in photoacoustic spectroscopy based on acousto-optic Q-switched fiber laser by merging a transmission PAS cell (resonant frequency f0 = 5.3 kHz) inside the fiber laser cavity. The Q-switching was achieved by an acousto-optic modulator, achieving a peak pulse power of ~679 mW in the case of the acousto-optic modulation signal with an optimized duty ratio of 10%. We used a custom-made fiber Bragg grating with a central wavelength of 1530.37 nm (the absorption peak of C2H2) to select the laser wavelength. The system achieved a linear response (R² = 0.9941) in a concentration range from 400 to 7000 ppmv, and the minimum detection limit compared to that of a conventional intensity modulation system was enhanced by 94.2 times.
RESUMO
A demodulation algorithm based on the head-tail technique is proposed for single-beam water vapor detection under rough environmental conditions, which is immune to fluctuations of light power. In the head-tail technique, collected data are processed by adding the head and tail data together and gradually approaching the center. The majority of photocurrent attenuation caused by optical loss can be effectively compensated by combining an optical intensity normalization coefficient in the method. The experiment indicates that, when the light power attenuates 4%, the deviation in a single-beam system is 1.29%, which is obviously superior to a dual-beam subtraction system whose deviation is 8.45%. The connection and advantages compared to a previous single-beam detection system have been discussed. The whole arrangement is simply designed without a beam splitter, of which the reliability and validity are fully verified by the experimental results.
RESUMO
Ochratoxin A (OTA) detection is critical for public health safety. This study proposes a G-quadruplex-Hemin/iodide (G4-Hemin/I-)-mediated non-enzyme redox cycling amplification (RCA) system for dual-modal (colorimetric and photothermal thermometer) OTA analysis. The proposed aptasensor platform for point-of-care testing employs a common thermometer for quantitative signal readouts. The OTA aptamer folds into a G4 structure, which significantly enhances the catalytic activity in the presence of I- after RCA reaction. Moreover, a notable temperature enhancement causes color changes, providing an ultrasensitive and label-free platform for OTA detection. Further, the designed sensor was applied to OTA content determination in corn samples and achieved satisfactory results compared to a commercial enzyme-linked immunoassay kit. The proposed dual-mode aptasensor is simple, highly sensitive (1 pg/mL for colorimetric method, 0.8 pg/mL for photothermal method), selective, and suitable for low-cost instrument-free bioanalysis in low-resource settings.
Assuntos
Aptâmeros de Nucleotídeos , Técnicas Biossensoriais , Ocratoxinas , Zea mays , Colorimetria/métodos , Hemina , Aptâmeros de Nucleotídeos/química , Técnicas Biossensoriais/métodos , Ocratoxinas/análise , Limite de DetecçãoRESUMO
The conventional direct absorption spectroscopy (DAS) technique has been plagued by the difficulty of obtaining accurate baseline, which is caused by photoelectric drift and the absence of non-absorbing regions in the transmitted light intensity signal. An inverse fitting direct absorption spectroscopy (IF-DAS) technique has been proposed to address this difficulty. The technique leverages the intrinsic nonlinear intensity response of tunable lasers to achieve baseline-free concentration measurements. It offers the advantages of being straightforward to implement, baseline-free, calibration-free, and resistant to photoelectric signal drift. Its efficacy was validated using an example under ambient temperature and atmospheric pressure conditions. The performance of the IF-DAS technique was compared with that of the conventional DAS technique through standard experimental tests. The results demonstrate that the IF-DAS technique is less susceptible to fluctuations in light intensity, exhibits superior linearity and accuracy, with an R2 value of 0.99986 and an overall error of less than 2%. This technique shows potential for application in harsh scenarios such as reactive flow fields and long-term engineering applications.
RESUMO
The advent of dual-atom nanozymes (DAzymes) featuring distinctive bimetallic active sites garnered significant attention, representing enhanced iterations of conventional single-atom nanozymes. The quest for an effective and universal strategy to modulate the catalytic activity of DAzymes posed a formidable challenge, yet few published reports addressed this. Herein, we designed and synthesized S-doped Fe/Co DAzymes (S-FeCo-NC) under theoretical guidance and revealed their excellent oxidase-like activity. Experimental and theoretical calculations indicated that the superior oxidase-like activity exhibited by S-FeCo-NC was attributed to the S-doping, which modulated the local electronic structure of the dual-atom active site. This modulation of the local electronic structure significantly optimizes oxygen adsorption energy, thereby accelerating the rate of enzyme-catalyzed reactions. As a proof-of-concept, this study integrated S-FeCo-NC with the cascade inhibition reaction of acetylcholinesterase (AChE) to devise a sensitive analytical platform for detecting organophosphorus pesticides. This study paved the way for elucidating the correlation between the local electronic structure of the active site and enzyme activity, offering novel methodologies and insights for the rational design of DAzymes.
RESUMO
Taking advantages of distributed feedback laser diode a technique is described to achieve high-sensitive measurement for water vapor concentration. This technique, with a modified balanced ratio metric detection system, has improved the accuracy of measured absorption spectrum by two main aspects. Improvement by matching equivalent conductivity of signal or reference photo detector (PD) is presented, and with the additional matched resistance suppression for the power variation in the signal-beam has been improved from 53 to 88 dB. The importance of integrating amplifier bandwidth design from the circuit to the measured absorption spectrum has been demonstrated in our experiment. For a scan rate of 32 Hz with an optimal corresponding bandwidth of 15.9 kHz, the absorption spectrum is well described by Voigt profile, with a difference of 1% at an atmosphere pressure of 1 atm and a room temperature of 296 K. With the application of averaging and filtering, absorption sensitivity of 1.093×10(-6) for water vapor at 1368.597 nm has been demonstrated, and the corresponding concentration is 71.8 ppb in just a 10 cm path length.
RESUMO
Water vapor existing inside internal end-face gaps of optical components of an optical fiber H2O sensing system makes it possible to influence the measurement accuracy and stability. The influence principle has been briefly analyzed based on the structure of three main optical components: a distributed feedback laser diode (DFB-LD), a collimator, and a photoelectric diode (PD). With application of a differential technique, the influence of water vapor inside the DFB-LD can be removed. With reasonable recombination of the collimator and the PD in a dual-beam detection system, the influence of water vapor inside the collimator and the PD's end-face gaps has been suppressed from more than 1.57×10(-3) to as low as -2.175×10(-5) in absorbance. After H2O isolation processing water vapor inside the end-face gaps of the DFB-LD, the collimator, and the PD can be utilized as a reference to design a simple but feasible H2O sensor. As a result, good linearity with an R2 of 0.9964 has been realized in a concentration range of 39-2110 ppm during an application test, and a long-term test of the designed H2O sensor against the S8000 with a difference of 10 ppm has been achieved.
RESUMO
Subtraction, division, and balanced ratiometric detection (BRD) are three extensively used demodulation methods for dual-beam wavelength-modulation trace gas detection. However, reliability comparisons among these methods under changing environmental conditions were rarely researched. In this paper, the influences of ambient temperature and bend loss of fibers are analyzed in detail, and the reliabilities of the subtraction, division, and BRD methods are quantitatively compared for the first time to our knowledge. When the ambient temperature is increased by 1°C, the deviation of the division method is only 0.29%, which obviously outperforms the subtraction method (2.90%) and the BRD method (0.55%). Furthermore, a concept, "power fluctuation rejection ratio," is introduced to compare the suppression effects of the subtraction, division, and BRD methods on the laser light source power fluctuation. The study results demonstrate that the division method provides better reliability when the ambient temperature or bending loss is varied. The validity and reliability are fully verified by the fact that the experimental results give good agreement with the theoretical simulation.