High Performance Surface-enhanced Raman Substrate Based On Using Silver Nanocube Self-assembly Method

Surface-enhanced Raman scattering（SERS）is a commonly used micro molecule detection technology,which has a series of advantages such as simple method,high detection sensitivity,and fingerprint analysis.Additionally,SERS has already widely used in environmental detection,food safety,medical diagnosis and many other fields.According to the electromagnetic field enhancement theory,the signal enhancement of SERS substrate mainly came from the hot spot density and intensity of the substrate.The self-assembly method was an efficient and simple method for constructing excellent SERS substrates.However,its application in actual SERS detection was limited by a series of deficiencies,such as insufficient strength,and uneven density distribution in SERS hotspots constructed by the traditional self-assembly method.In this paper,silver nanocubes with excellent plasma properties and easy preparation were used as the basic material for self-assembly.And then we used the prepared silver nanocubes to assemble a series of SERS substrates with high-performance such as silver nanocube assembled single layer,silver nanocube self-assembly array,and paper based-MIP-SERS silver nanocube assembled substrate.The specific research included the following three parts:Firstly,ordered Ag nanocubes were assembled on a thiolated Si substrate as SERS substrate.The combination of thiolated groups and Ag makes the dense Ag nanocube monolayer fixed on the Si substrate to form a high-density hot spot.The detection limit of Rhodamine 6G can be reduced to 1.0×10^-15 M,which indicates that the substrate has a high detection sensitivity.At the same time,a wide linear detection range(10^-7～10^-13 M)and a low relative standard deviation（RSD,6.48%）both indicate that the substrate has good detection repeatability.In addition,the assembled substrate can be used to detect crystal violet and malachite green molecules in lake water samples.This preparation method provides a way to increase the hot spot density of SERS substrate and achieve high sensitivity detection.Secondly,a method of patterned substrates as templates was adopted to assemble Ag nanocubes further preparing SERS substrates with patterned array structure.Patterned limited domain templates are prepared by lithography.Under the action of the spatial limit of the template,the Ag nanocubes are tightly assembled at each point of the pattern,reducing the assembly defects and increasing the hot spot density.The detection limit of Rhodamine 6G on the self-assembled array is as low as 1.0×10^-15 M,and the enhancement factor is as high as 3.4×10¹⁰.The RSD of different substrates was 8.75%.These results indicate that the self-assembled array structure as SERS substrate has high detection sensitivity and repeatability.The assembled substrate can be used for the detection of trace melamine in milk,and the detection limit is 7.9×10^-7 M,the RSD is6.91%,demonstrating that it has great application potential in food and environmental monitoring.Thirdly,in situ polymerization method was used to polymerize the molecularly imprinted polymer（MIP）on the paper base modified by 3-（isobutylloxy）propyl trimethoxysilane,and then Ag nanocubes were assembled on the MIP layer as SERS substrate.The prepared paper based-MIP-SERS substrate not only has the ability of MIP specific adsorption of malachite green molecules,but also has the high-density hot spot of Ag nanocube assembly structure.The detection limit of malachite green in the prepared substrate was 1.0×10^-11 M,and the RSD was 4.66%.Moreover,the substrate can detect malachite green specifically in the mixed solution with methylene blue and crystal violet.Meanwhile,the substrate can quantitatively detect malachite green molecules in shrimp extract,which has the potential to accurately detect malachite green in a variety of complex environments.