Preparation Of Silver Based SERS Substrate By Surface Molecular Imprinting And Used For Environmental And Biological Molecule Detection

The combination of molecular imprinting technique(MIT)and surface-enhanced Raman scattering(SERS)has been using to prepare a new SERS substrate with specific recognition performance.The new SERS substrate has not only a high sensitivity of SERS detection but also an excellent selectivity of MIT.These outstanding properties make it exhibit a broad application prospect in the field of SERS.The environment that human beings live in has been polluting by different pollutants from medicine,industry,agriculture,and other fields.Bisphenol A has estrogenic activity,and it is highly toxic to aquatic organisms.Glibenclamide is an antidiabetic drug that can use to treat type II diabetes.It is dependent on hydroxylation metabolized by the cyclohexyl part in the molecule.And its excretion rate as a parent compound is fair to low.Biomolecules,as biomarkers of disease diagnosis,have become more and more vital in many aspects.For example,specific proteins have been used as biomarkers to achieve the detection of a variety of diseases and environmental monitoring.Lysozyme,a kind of protein biomarker,is a single-chain protein composed of 129 types of amino acids.Lysozyme can decompose bacteria by hydrolyzing the main components of the bacterial cell wall.It is described as a human antibiotic and plays a vital physiological role in the innate immune system.In this paper,Ag-based molecular imprinted polymer(MIPs)has been prepared as a new SERS substrate for the detection of organic molecules and biomolecules.Not only the morphology and structure of the prepared materials were analyzed by a series of characterization methods,but also the experiment on the SERS performance of prepared materials shows it can achieve sensitive and selective detection of the target analyte.The Ag@MIPs has parpared by surface imprinting technique,and we chose bisphenol A as the template molecule,4-vinylpyridine as the functional monomer,and Ag particles modified by 3-aminopropyltriethoxysilane as the assisted functional monomer.Characterization technologies have been using to characterize the morphology and crystal phase of Ag@MIPs.The average thickness of the MIPs layer was 15 nm.The SERS signal from Ag@MIPs for bisphenol A was better than that from Ag particles.The detection of bisphenol A can obtain the satisfactory SERS signal within the concentration range from 1.0×10^-9mol·L^-1to 1.0×10^-3mol·L^-1.The lowest detection concentration of Ag@MIPs for bisphenol A was1.0×10^-9mol·L^-1.The Ag@MIPs has synthesized using glibenclamide as the template molecule and acrylamide as the functional monomer.The existence of the MIPs layer can effectively protect the flower-like Ag from being oxidized and improve the stability of the SERS substrate.Repeated use studies have shown that the SERS intensity of glibenclamide can maintain 87%of the initial value after repeated use four times.The Ag@MIPs has been fabricating by using lysozyme as the template molecule.Both methacrylic acid and acrylamide are used as functional monomers.The density functional theory(DFT)has been utilizing to calculate the optimal structure and molecular electrostatic potential of amino acid residues.Also,the active sites between template molecule lysozyme and functional monomers have been calculating by DFT.Based on the DFT simulation,a MIPs layer with a thickness of less than 15 nm was coated on the surface of Ag microspheres by surface imprinting technique.Besides,the DFT calculation has been applying to simulate the SERS spectra for amino acid residues of lysozyme.The detection by Ag@MIPs for lysozyme has shown high selectivity and reusability.The relative standard deviation was less than 10%after repeated use five times.Compared with the Ag microspheres,Ag@MIPs as a SERS substrate has a higher SERS enhancement effect for lysozyme.TiO₂ nanoparticles grow on Ag microspheres in situ to form the Ag-Ti O₂.It was used as a matrix to be coated by MIPs.Ag-Ti O₂has self-cleaning characteristics,and the residual template molecules in the MIPs layer can efficiently degrade by photocatalysis.As a result,the interference of background noise to the SERS signal weakened,and the detection sensitivity is improved.The Ag-Ti O₂@MIPs sandwich structure has prepared by using sulfamethazine as the template molecule.The DFT calculation has been utilizing to select the optimal functional monomer and simulate the SERS spectrum of sulfamethazine.The SERS enhancement of Ag-Ti O₂@MIPs attributed to the synergistic effect of Ag-Ti O₂and MIPs layer.The selective experiment suggested that Ag-Ti O₂@MIPs had a specific recognition ability to sulfamethazine and the detection limit was as low as 3.6×10^-9mol·L^-1.The reusability result showed that the intensity of the characteristic peak remained above 65%after repeated use for four times at low concentration.It shown that Ag-Ti O₂@MIPs as a SERS substrate can be used for the selectivity and reliability detection of sulfamethazine.