The Study Of NH₃ Sensor For The Breath Detection Of Helicobacter Pylori

It has been identified that ammonia（NH₃）in human breath can be used as a biomarker for Helicobacter pylori（Hp）stomach,owing to the fact that the concentration of NH₃in the breath of patients is much higher than in the general population（0.8-0.9 ppm）.Therefore,the utilization of the rapid and efficient ammonia detection technique for the accurate detection of NH₃in human breath is of great importance in disease prevention and clinical diagnosis,etc.In recent years,chemiresistive gas sensors based on oxide semiconductor have gained widespread attention in ammonia detection benefiting from their simple device structure,low cost,ease of miniaturisation and integration.However,the present oxide semiconductor-based chemiresistive ammonia sensors have generally been characterised by low sensitivity,poor selectivity,lack of stability and high power consumption,which cannot meet the requirements of exhaled breath detection for disease.Therefore,this study intends to improve the sensitivity and selectivity of the sensor for low concentrations of ammonia through nano-structure modulation and noble metal loading modification of oxide semiconductor sensing materials.Meanwhile,in order to further reduce the power consumption of the sensors,an AlOOH-based chemiresistive ammonia sensor that can operate at room temperature has been constructed by creating a new ion-conducting nanostructured AlOOH sensing material and utilizing its humidity boosting mechanism in this paper.The sensor has excellent resistance to humidity interference and preliminarily enables the detection of extremely low concentrations of ammonia in human Human exhalation.The main studies are as follows:1.Highly dispersed Pt-loaded SnO₂nanoparticle-sol were prepared by hydrothermal and photochemical reduction methods.By means of the PS spheres template method and a spin coating process,the porous Pt-loaded SnO₂sensing films on the substrate surface（test electrode side）of planar sensor devices were fabricated.Test results showed that gas sensors based on Pt-loaded SnO₂porous films exhibited high sensitivity（S=1.15）to low concentrations of NH₃（500 ppb）at 200℃and high selectivity,which was attributable to the chemical and electronic sensitization of the noble metal Pt and the high sensing body utilization efficiency of the porous structure.In addition,on the basis of the above study,Pt Ru@SnO₂thin sensing films were prepared by loading bimetallic Pt Ru nanoclusters in the process of photochemical reduction to further enhance the gas-sensitive performance of SnO₂-based sensors.The test results showed that the ammonia sensor based on Pt Ru@SnO₂thin films had high sensitivity,low limit of detection（100 ppb）and high selectivity（with a sensitivity of NH₃（S=1.32,100 ppb）greater than that of interfering gases such as acetone（1.26,5 ppm）and H₂S（1.13,5 ppm））at the optimum operating temperature（200℃）.The sensitization mechanism study showed that this was not only attributed to the chemical and electronic sensitization of the nano-bimetal to semiconductor sensing materials,but also benefited from the catalytic regulation of Ru to NH₃decomposition reaction.The high level of water vapour in human exhalation can seriously affect the performance of the oxide semiconductor sensors.Therefore,new-type ammonia-sensitive materials working at room temperature are urgently required for the accurate detection of low concentrations of ammonia in this harsh environment and to further reduce the power consumption of the sensors.The mesoporous structure of AlOOH hollow microspheres was prepared by modulation of the micro-nano structure using in situ etching and hydrothermal methods,which improved the utilization efficiency of sensing body(specific surface area:150.2 m~2g^-1)and gas adsorption/desorption rates.The test results showed that the response of mesoporous AlOOH-based sensors to NH₃increased with the increase of humidity,exhibited low detection limit（500 ppb）,high sensitivity and great selectivity under 98%relative humidity.The direct current analysis,complex impedance plot and the test of NH₃-TPD were employed to prove that the humidity-activated sensing mechanism of the new-type mesoporous AlOOH ammonia sensing material was attributed to the Bronsted acid adsorption,and the formation of ionic conduction involving the strongly polar nature of NH₃and its well ionization ability in water molecule.