The Mechanism Study And Applications Of Metal/Semiconductor Composite Materials In Surface-assisted Laser Desorption/ionization Mass Spectrometry

In recent years,surface-assisted laser desorption/ionization mass spectrometry(SALDI-MS)has been widely applied in the fields of environmental,biological and clinical analysis due to its advantages of high sensitivity,high repeatability,low molecular weight without background peak interference.Desorption/ionization mechanisms remain to be futher explored,the charge transfer and energy transfer mechanism have been widely recognized.Generally,materials with high surface area,strong ultraviolet absorption are favorable for SALDI-MS substrates.During the SALDI process,the substrate absorbs laser energy and transfers it to analytes for desorption and ionization.Based on the mechanism,SALDI-MS materials with excellent performance have been widely developed and applied,such as carbon-based materials,silicon-based materials,metal-based materials and composite materials.Semiconductor material also has been widely applied in SALDI-MS detection,the most representative semiconductor ZnO is considered as an excellent substrate material in SALDI-MS due to its high electron mobility,large bandgap width,and good light absorption performance in the ultraviolet wavelength band.However,the photoelectron-hole recombination rate of pure semiconductor materials is extremely fast,resulting in the extremely low utilization efficiency of photoelectric charge.Therefore,improving the utilization rate of photogenic charge is very important for highly sensitive SALDI-MS detection,and it is of great significance to explore the mechanism of charge transfer.The development and application of composite substrate materials can well solve this problem.Comparing with pure semiconductor material,the metal/semiconductor composite material can transfer electrons in conduction band on the semiconductor surface to the metal nanoparticles under ultraviolet laser irradiation,so that it has higher electron-hole separation efficiency.Thereby,the sensitivity of SALDI-MS detection is improved.In addition,the absence of internal standard quantitation of SALDI-MS and the rapid analysis of actual samples are of great significance in modern testing.Therefore,it is necessary to prepare a large-area uniform substrate to ensure the repeatability of mass spectrometry detection;On the other hand,direct detection of complex samples can be realized by interaction of the substrate with the analyte.To solve the above problems,firstly uniform ZnO nanorods(ZnO NRs)were prepared,and then metal/semiconductor composite structures were prepared by vacuum thermal evaporation or ice water bath synthesis method,and their photoelectric properties were studied.The synthesis conditions were optimized to improve detection performance of SALDI-MS.This paper includes the following two aspects:Firstly,combining hydrothermal synthesis method and thermal evaporation technology,we optimized the synthesis conditions of ZnO NRs and the amount of silver nanoparticles(Ag NPs)deposited on ZnO NRs to ensure good light absorption performance.The introduction of Ag NPs enables electrons in ZnO NRs conduction band to transfer to its surface,and the surface photovoltage can characterize this separation phenomenon.The electron-hole separation efficiency of Ag NPs/ZnO NRs composite substrate material improves,thus the utilization rate of charge increases in LDI-MS.Hydrophobic modification on the surface of the structure can enrich the analyte.Therefore,the detection limit of arginine is as low as 3 zmol,and quantitative analysis of malachite green in lake water,methadone in urine,verapamil and bradykinin in serum is achieved.Secondly,ZnO NRs was prepared according to the above method,and then ZnO NRs composite substrate loaded with gold nanoparticles(Au NPs)was synthesized by ice water bath method.The substrate selectively detected sulfhydryl compounds by Au-S interaction,and achieved quantitative analysis of GSH in altamolan drugs and cherry tomato.In addition,the substrate can also be used as a universal substrate material for the analysis of dye molecules,carbohydrates,peptides,drugs,and amino acid mixtures.FDTD simulates the surface electromagnetic field distribution of Au NPs/ZnO NRs substrate.The surface plasmon effect between Au NPs transfers more energy and electrons to the analyte molecules,which improves the detection sensitivity of SALDI-MS.