Design And Laser Direct Writing Fabrication Of Metal Oxide Semiconductor Gas Sensors Towards Breath Diagnosis

Healthcare is always the significant social issue associated with people's daily life,and disease diagnosis is a key part.With the rapid advance of science and technology,the health condition of human body can be well assessed by using kinds of sophisticated medical instruments and examination methods,however which is still confronted with lots of problems in the aspects of expense,efficiency,accuracy and so on.As a non-invasive diagnosis method of disease,breath diagnosis has attracted much attention in research due to its advantages in greatly reducing the side-effect in the diagnostic process and acquiring the underlying signals of some diseases effectively compared with common medical diagnostic operation.The respiration composes of thousands of organic and inorganic gases,and carries abundant information with respect to human metabolism.Up to now,various detection methods have been developed for breath analysis,including gas chromatography-mass spectrometry(GC-MS),selected ion flow tube mass spectrometry(SIFT-MS),laser-absorption spectroscopic techniques and chemical gas sensors.Due to the advantages of easy implementation,low cost,high sensitivity,and fast response,gas sensors based on metal oxide semiconductors(MOSs)have tremendous potential in the application of online breath diagnosis.However,there also exists plenty of obstacles for their partical use,arising from the complexity and high humidity condition of human respiration.At times in the past,much researches focus on developing metal oxide gas sensors with high endurance to humidity and high selectivity to specific gases such as CH3COCH3,NH3,C2H5OH and NO,which are the corresponding biomarkers of diabetes,kidney disease and asthma.On the other hand,considerable efforts have been devoted to construct gas sensor arrays for the diagnosis of diseases determined by multiple biomarkers.By taking the development tendency of MOS gas sensors into consideration,we designed and fabricated high temperature humidity sensor,ultra-fast and highly-sensitive acetone sensor and room temperature ammonia sensor based on heterostructured and ternary metal oxides to meet the demand of breath diagnosis.Notably,by overcoming the difficulty in accurate measurement of humidity,the high temperature humidity sensor provides the opportunities for real-time breath monitoring,as well as the calibration of gas sensing response affected by the humidity variation.In addition,a novel planar MOS gas sensor was realized by using laser direct writing through precursor solution.This strategy simplifies the gas sensor fabrication process compared with present ones,and forms the basis for construction of miniature gas sensor arrays.The main contents are as follows:(1)WO3-SnO2 composite hollow nanospheres were synthesized by a simple and green hydrothermal method.Interestingly,humidity sensors based on the nanospheres exhibited high performance with rapid response and recovery speed,good reversibility,high sensitivity and no hysteresis at the optimal operation temperature of 80?.The sensitivity of the humidity sensor switched between relative humidity 35%and 98%can reach up to 11,indicating its unique superiority in humidity detection.Moreover,gas sensors based on WO3-SnO2 composite nanospheres showed a temperature-dependent p-n response transition to ethanol gas.By utilizing multiple analysis method,we demonstrated the significant effect of humidity on the sensing properties at low temperature,and proposed a surface ionic and proton conduction mechanism to understand the abnormal low temperature sensing behavior.The gas sensing investigations verify the feasibility of the humidity sensor in breath humidity high-precision detection.(2)?-Fe2O3/SnO2 bilayer hollow spheres with ultra-thin inner shell were prepared via a modified template method.Gas sensors based on the ?-Fe2O3/SnO2 hollow spheres showed excellent sensing performance to acetone and ethanol with high sensitivity and selectivity,rapid response and recovery speed,revealing great potential for the real-time monitoring of breathing acetone.By comparing the sensing properties of ?-Fe2O3/SnO2 heterojunctions in different structures,we analyzed the impact of the material structures on the gas sening performance,and conclude several principles for the designing of high performance acetone sensor.(3)Bi2WO6 was adopted as room temperature ammonia sensing material for the first time.To verify the reliability of room temperature ammonia sensors in the application of breath detection,we select humidity and ethanol gas molecules which were usually present in respiration as influence factors,and demonstrate the strongly humidity-dependent and ethanol interfering ammonia sensing behaviors.Possible mechanisms were proposed to understand the unique sensing performance.Despite of the cross-sensitivity between the ammonia and ethanol,the relationships can be established between combined response and ammonia concentration,indicating the feasibility of breath ammonia gas molecules detection.(4)A novel laser direct writing method was adopted to construct planar gas sensors through an in-situ synthesis and patterning of metal oxide semiconductors from metal salt precursor solutions on a coplanar heating platform for the first time.Multiple gas sensors based on common p-type and n-type metal oxides including copper oxide,nickel oxide,and platinum doped iron oxide were successfully demonstrated,featuring the versatility and feseability of this approach.This work presents a new direction for developing metal oxide gas sensors with easy fabrication process and low cost,and paves a way for the construction of gas sensor arrays on chip.