Fabrication Of Highly Sensitive Surface-enhanced Raman Scattering Substrate And Its Application In Environmental Pollutants Detection

With the development of industry and agriculture,the problem of environmental pollution has attracted more and more attention.The pollutions will cause irreversible serious harm to human health when they were taken with the food chain and accumulate in the human body.Therefore,it is necessary to develop a highly sensitive detection technology for monitoring environmental pollutants.Surface-enhanced Raman scattering(SERS)technology,as a new type of molecular detection technology,has been widely used in environmental detection,material characterization,disease analysis due to its sensitivity,rapidity,fingerprint recognition,non-destructive testing and other characteristics.However,the application of the SERS technology critically depends on the preparation of high-performance SERS substrates.Currently,the fabrication of SERS substrates is still limited by the following three aspects:(1)The substrates materials are mainly relying on noble metal materials with plasmonic resonance feature(Au,Ag,Cu),but their stability and sensitivity need to be improved.Therefore,it is necessary to find other more suitable materials to compensate for the drawbacks of noble metal materials.(2)The formation of nanoscale rough surfaces requires simpler and more convenient micro-nano processing technology.(3)The SERS substrates produced on site limit their practical use value,the highly stable SERS substrates with long-term storage need to be developed.In this work,two highly sensitive SERS substrates were developed based on the basis of nanomaterials,electronics and micro-nano processing technology,and applied to the highly sensitive detection and analysis of heavy metal ions and antibacterial agents in water.Firstly,to improve the sensitivity of the SERS substrate,a dual-enhanced SERS substrate with integration of electromagnetic enhancement and chemical enhancement was designed and fabricated the nanoporous structured substrate by utilizing metal deposition technology and graphene wet transfer.The SERS substrate combines the electromagnetic enhancement of nanoAg/Au metal hybridization and the chemical enhancement of monolayer graphene.The SERS substrate has high sensitivity,good uniformity and reproducibility.The enhancement factor of the SERS substrate is up to 3.85×108,which is 1.63 times higher than that of ordinary metal hybrid SERS substrate.Combined with the principle of enzyme-linked reaction,the highly sensitive quantitative detection of heavy metal Pb2+was achieved on the surface of the doubleenhanced SERS substrate.The sensing mechanism was verified by FDTD simulation.The results show that the dynamic detection range of the developed Pb2+double-enhanced SERS sensor is from 1 0-11 M to 10-7 M,the lowest detection limit reaches 4.31 pM,and it has a high Pb2+specificity.The recovery rate of Pb2+in the detection of real samples is between 91.77%and 108.57%.The dual-enhanced SERS sensor can be recycled three times by reacting the Pb+enzyme on the SERS sensor.The double-enhanced SERS sensor has good stability within three weeks,which can meet the detection needs of SERS detection technology.In view of the instability of silver-based materials in SERS applications,we synthesize hydrophobic carbon/silver composite nanoparticles via combining carbon nanodot materials in one step.The carbon composite silver nano-flower like SERS substrate was formed by selfassembly hydrophobic carbon/silver composite nanoparticles on the surface of nano-flower like gallium nitride.The silver nanomaterials are encapsulated by carbon dots to isolate the oxidation conditions while still maintaining a good optical LSPR response,resulting in up to 8 months stability of SERS substrate in air.Combined with the material structure,properties and SERS properties of SERS substrates,the ultra-stability mechanism of the prepared Ag-based SERS substrates was analyzed and explained.Through a systematic research on the relationship between surface particle density and SERS performance on the surface of SERS substrate,it was found that the LSPR performance between particles was stronger with the increase of particle density.When the particles were too dense to produce dimers,the SERS performance decreased.Under the optimal conditions,the SERS substrate has good hydrophobicity.Taking the R6G molecule as target molecular,using mapping scanning and molecular statistical analysis techniques,ultra-low concentration molecular level detection can be achieved,and the lowest detection limit reaches 1pM.Finally,the practicality of the hydrophobic carbon/silver composite nanoflower-like SERS substrate was verified by the highly sensitive detection of antibacterial agents.A back-propagation neural network with a momentum-adaptive learning rate was developed for the classification of multi-type antimicrobial agents detection in water.This work will provide a reference idea for the highly sensitive classification and detection of complex substances.The technology can be explored to.detection and analysis in the fields of disease analysis and medical imaging.