Design,Preparation And Application Of Metal-Dielectric Nanocomposites

The rational combination of dielectric and metallic nanoparticles?NPs?brings novel optical properties to conventional subwavelength structures.In contrast to solely metal or dielectric particle arrays,this type of material not only enhances the near electric field intensity within the metal nano cluster hot spots,but also expands the overall volume of enhanced electric field.Plasmonic molecules and NP clusters are of great interest for the implementation in optical signal transmission,chemical sensing,and a broad range of other applications.In particular,the electric?E-?field enhancement is widely utilized in surface enhanced Raman spectroscopy?SERS?where the strong electromagnetic field enhancement is crucial for Raman signal amplification.In this work,the metal-dielectric nanocomposite is fabricated through deposition of dielectric SiO₂ microspheres on self-assembled monolayers of gold nanoparticles?AuNPs?,the finite-difference time-domain?FDTD?simulations are chosen to capture the essential structural aspects of this system,and the self-assembled nanocomposite is used as the SERS substrate to achieve highly sensitive detection of methamphetamine.First,the FDTD simulation proves that the self-assembly of the SiO₂ dielectric microspheres to the self-assembled monolayers of AuNPs will greatly enhance the E-field in the"hot spot"area between metal nanoparticles.In addition,the E-field in the area where the dielectric microsphere and nanoparticle contact is also increased.And the E-field enhancement displays size dependence on the SiO₂ microsphere.As the size of the microsphere increasing,the E-field enhancement gradually increases,this trend is more obvious in 500 nm³?m SiO₂ microspheres.For SiO₂ microspheres larger than 4?m,the E-field enhancement trend slows down.AuNPs were then prepared via a seeded-growth approach in aqueous solution,and a monolayer AuNPs was prepared by electrostatic adsorption,solvent evaporation and interface methods.Among them,the interfacial strategy is simple in operation,short in experiment time,and does not require complicated equipment and reagents.The achieved monolayer AuNPs array is dense and highly uniform,confirm interfacial strategy is suitable for quickly preparing monolayer AuNPs array.The application of the metal-dielectric hybrid in SERS detection was studied.The silane coupling agent Silane-PEG-COOH was used to modify the surface of the SiO₂microspheres,the surface of the SiO₂ microspheres will be negatively charged after the modification,therefore,it can capture the analytes via electrostatic adsorption.The inclined drop coating method was used to assemble SiO₂ microspheres capturing analytes on the substrate containing a monolayer AuNPs,to synthtesis metal-dielectric hybrids and explore its SERS performance.SERS detection for methamphetamine solution was carried out by capture method,results shows the detection limit of methamphetamine in aqueous solution can reach 1 nM,proved this composite material has highly efficient SERS performance.In addition,it has been verified in subsequent interference experiments that this SERS substrate can still have outstanding sensing performance in complex environments such as human body fluids?urine,saliva?,and reach detection limits of 10 nM?urine?and 5 nM?saliva?,respectively.These results demonstrate that metal-dielectric hybrid nano structure is a promising candidate as a high sensitivity platform for specifically capture and rapid detection for illicit compounds.