| With the development of human medical technology,the clinical diagnosis and therapeutic management of human exhaled compounds have become an emerging research field.Human exhaled breath analysis,as an emerging noninvasive medical diagnostic tool,may in the near future be incorporated into routine clinical care used today,such as screening,diagnosis,prognosis,and monitoring of inflammatory activity for disease.The development of trace gas sensor technology is a key factor driving the advancement of exhaled gas analysis.Ideally,a method for clinical monitoring should be non-invasive,costeffective,reliable,fast,reproducible,and understandable.So far,the demand for highly sensitive,fast-response,portable exhaled gas sensors that can measure continuously has been strong.Among them,the sensor based on the new photoacoustic spectroscopy technology has the characteristics of good anti-interference ability,zero background,fast response,no wavelength selectivity,small size,and high detection sensitivity,making it very suitable for the development of sensors for exhaled gas analysis.This paper designed and researched a variety of sensors for human exhaled gas detection around the relevant theories and characteristics of the new photoacoustic spectroscopy technology,and achieved the following research results:1.Focusing on the relevant theories and characteristics of beat-frequency quartzenhanced photoacoustic spectroscopy technology,using a quantum cascade laser with a central wavelength of 10.359 μm as the excitation light source,a human exhaled ammonia detector that can be used for clinical diagnosis is designed and studied.The instrument has the characteristics of being calibration-free,having high sensitivity,and having a fast response.Based on the theory of gas viscosity,the viscosity problem of exhaled ammonia is solved by making the instrument work at 42 degrees Celsius,and the respiration front end was designed by combining the pressure sensor and the end-expiratory carbon dioxide detector to realize the detection of the expiratory stage of the subjects.The design of the front end of the breath quantifies the strength of the subject’s exhalation,making the measurement results more intuitive and eliminating the interference from oral ammonia.2.Based on the low-noise differential photoacoustic cell and combined with the beat frequency detection algorithm,a new type of photoacoustic heterodyne gas sensor is developed,which eliminates the need for frequency calibration and wavelength locking during the working process of the sensor.With rapid response and high sensitivity,it can realize real-time human exhaled carbon monoxide monitoring.Clinically,it can provide valuable information about diseases related to oxidative stress and respiratory inflammation in humans.In addition,the principle of the photoacoustic heterodyne sensors is explained in detail,which provides a reference for future research on the photoacoustic heterodyne sensors and photoacoustic cells.3.Based on quartz-enhanced photoacoustic spectroscopy technology,a DFB laser with a 2 μm central band and 3D printing technology were used to design and develop a sensor that can be used for quantitative online analysis of the carbon dioxide content eliminated by human skin.The sensor can be directly carried on the surface of human skin,which solves the problems of frequent sample replacement and skin irritation associated with traditional transcutaneous carbon dioxide monitors.It provides a new possibility for clinical monitoring of carbon dioxide transcutaneous partial pressure.Its reliability was demonstrated by the real-time measurement and analysis of the rate and concentration of carbon dioxide excreted by the skin of subjects during exercise.4.The advantages and disadvantages of quartz enhanced photoacoustic spectroscopy(QEPAS)and beat frequency QEPAS(BF-QEPAS)for environmental monitoring were compared.A spectrophotometer consisting of a T-shaped quartz tuning fork(QTF)and a resonant tube was used as the detection module.The interband cascade laser is used as the excitation source,achieving the lowest detection limits for NO at 90 ppb(QEPAS)and 180ppb(BF-QEPAS). |
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