Research Into Exhaled Gas Detection Based On High Performance Moisture-resistant Gas Sensor

Exhaled air is mainly composed of more than 200 kinds of organic and inorganic molecules,which contains a wealth of information closely related to human metabolism.However,the exhaled air also contains water molecules with a relative humidity of 65-88%.This brings great challenges to the selectivity and precision of traditional exhaled gas analysis devices,such as gas chromatographs:Hundreds of interfering gases and high concentrations of water molecules can block the target molecular signals,making it difficult to make high selectivity,real-time diagnosis of disease.Based on this,the emerging metal oxide semiconductor based sensors,characterized by fast detection,small size,light weight and durability,provide a very attractive solution for portable health monitoring.However,there are still some problems consisted in this kind of sensor,such as the detection limit,selectivity and stability of exhaled gas in a high humidity environment.Therefore,for the detection of the main components of respiratory gas in disease,this paper systematically studied its sensitivity to volatile organic compounds in exhaled air from the design and synthesis of composite gas sensitive material and the preparation of sensor parts,and optimized and improved the moisture resistance of the material.It has important theoretical significance for solving the problem of real-time detection and health warning of human diseases.The main research contents of this paper are as follows.（1）N-n type Zn In₂S₄@In₂O₃nanospheric heterostructures supported by 2D Zn In₂S₄nanosheets are prepared by solvothermal-water bath in situ-conversion method.It is found that the addition of 2D Zn In₂S₄sheets have a great effect on the morphology and microstructure of Zn In₂S₄@In₂O₃nanospheres.The gas sensitivity test shows that,the Zn In₂S₄@In₂O₃-1.0 sensor shows good selectivity for ethanol,high sensitivity（R_a/R_g=58 for 100 ppm of ethanol）,certain humidity resistance（8 sensitivity at 60%R.H.）and good long-term stability.This lays a technical foundation for the anti-humidity sensor for human exhaled gas monitoring.（2）The N-C@Sn O₂-Co₃O₄hollow nanoboxes with the organic-inorganic composite structure are prepared by a vapor deposition method.The introduction of organic coating can construct abundant oxygen vacancies.And because of its special structure,it can preferentially adsorb the target molecule acetone,which can play a role of de-selectivity/shielding for water molecules.According to the results of gas sensing test,the sensitivity of the N-C@Sn O₂-Co₃O₄sensor to 50ppm of acetone is 9 at the optimum working temperature of 160^oC.And when the relative humidity is 90%,the sensitivity of the N-C@Sn O₂-Co₃O₄sensor is still kept at 14 to 50 ppm of acetone,showing excellent humidity resistance.This provides an important strategic support for the application of acetone gas sensor array in human exhaled gas detection;（3）On the basis of previous vapor deposition technology,the surface modified C@Sn O₂-Co O nanoboxes are obtained by chemical modification.The alcohol gas sensitivity of the modified C@Sn O₂-Co O has been comprehensively improved,especially in the sensitivity and moisture resistance,which are greatly improved in the range of 50-90%R.H.（R_g/R_a=58）.At the same time,the C@Sn O₂-Co O sensor demonstrated good repeatability in simulating the humidity level of the exhaled air（65-88%R.H.）.And it can quickly measure low concentration alcohol gas in 5 consecutive sensing cycles.The carbon coating can effectively screen the target gas molecules,and the response signal does not decline.Based on the above results,C@Sn O₂-Co O material is expected to be a candidate material for preparing an anti-moisture alcohol sensor.