Study On Controllable Fabrication And Key Technologies Of SERS Detection Based On Gold/Silver Shell-coated Magnetic Nanoparticles And Their Hybrid SERS Substrates

Surface-enhanced Raman scattering?SERS?spectroscopy,is a new spectroscopic detection technology with high detection sensitivity.Using SERS,single cell or even single molecule detection can be achieved.And it has become an important analytical technique for biosensing and trace detection because of its enormous Raman enhancement.This technique has a very broad application prospects in the detection of pathogenic microorganisms and pesticide residues,with the advantages of less sample,almost no pre-processing,simple operation and on-site rapid detection.Based on the detection needs of pathogenic microorganisms and pesticide residues,a variety of multi-functional magnetic SERS substrates are successfully designed and synthesized.First of all,these magnetic SERS substrates have a good magnetic response capability,thus rapid magnetic enrichment and separation from the solution can be quickly achieved under external magnetic field.Secondly,these magnetic SERS substrates have good SERS performance and can enhance the Raman signal of target molecules.Finally,by using these magnetic SERS substrates,the labeled detection of bacteria and unlabeled detection of pesticide thiram are achieved.The main research work of this dissertation are as follows:1.The synthesis of magnetic microspheres are overviewed in detail.The controllable preparation methods of superparamagnetic microspheres?100³00nm in diameter?are well explored using solvent thermal method from the experimental point of view.An overview of the synthesis for magnetic microspheres and a specific elaboration of the synthesis routes for these magnetic microsphere preparation are conducted based on the published references.These synthesis methods for magnetic microspheres include physical preparation and chemical preparation.The controllable preparation methods of superparamagnetic microspheres?100³00 nm in diameter?are well explored using solvent thermal method from the experimental point of view.A good foundation is laid for the subsequent synthesis of high-performance SERS substrates including AgMNPs and AuMNPs.Successful preparation of superparamagnetic microspheres?100³00 nm?was achieved and the prepared samples were characterized by TEM,EDS,XRD,and magnetometer.2.A fast,high-sensitive,high-specific and low-cost magnetically-assisted SERS method based on aptamer recognition for single–cell detection of S.aureus is reported for the first time.First,for the demand of S.aureus detection,superparamagnetic AgMNPs?200 nm in diameter?with good SERS activity and high magnetic responsiveness,are successfully synthesized employing the PEI-interlayered seed growth method.Compared to the SiO₂ or carbon interlayered method,this method effectively improves the magnetic responsiveness and the ability to control the size of the overall structure,with a PEI layer of 1² nm thickness.Secondly,a novel SERS tag,wih good SERS activity and convenience to couple with the target recognization element,is well designed and synthesized.Finally,high-sensitive detection of S.aureus based on the sandwich structure formation of the AgMNPs/target bacteria/SERS tags,is achieved using conventional Raman and SERS imaging technology.3.A facile synthesis route,sonochemically assisted hydroxylamine seeding growth method,for the preparation of AuMNPs is reported for the first time.High-sensitive detection of S.aureus is achieved with the help of SERS tags,vertifying the practicality and great potential of AuMNPs in bioapplication.First,a sonochemically assisted hydroxylamine seeding growth method for the facile synthesis of AuMNPs is proposed for the first time.The synthesized AuMNPs are highly uniform in size and shape with good magnetic responsivity,stability and high SERS activity.Au shell of different thicknesses can be easily formed outside magnetic cores of different sizes depending on the bacteria detection demands.To the best of our knowledge,the proposed technique is the most convenient synthesis route for preparation of high-quality AuMNPs to date.Furthermore,the synthesized AuMNPs are used for bioseparation and biodetection of bacteria.High-sensitive detection of S.aureus is achieved through SERS method with the help of plasmonic SERS tags.4.A novel core–shell–satellite 3D magnetic nanocomposite is reported and synthesized for the first time,with AgMNPs as magnetic core and Au nanorods?AuNRs?as satellite NPs.High-sensitive detection of pesticide residue thiram is achieved using the newly-synthesized magnetic hybrid SERS substrate.Two synthesis routes,namely,electrostatic interaction and covalent bonding,are used for the magnetic nanocomposites.The SERS performances of AgMNP–AuNRs synthesized by these two methods are investigated through numerical simulations and experiments.For the P2VP-interlayered AgMNP–AuNRs synthesized through covalent bonding,the P2VP layer that formed outside AgMNPs is not a dense layer,with a thickness of less than 1 nm,such that target small molecules can easily adsorb in the“hotspots”to achieve a high level of SERS signal enhancement and make this SERS substrate very suitable for the detection of small molecules Finally,a high-sensitive detection of pesticide thiram with the detection limit of 10^-10 M,is achieved using AgMNP-AuNRs synthesized through P2VP-interlayered method.