Fabrication Of Micro-Nanostructures Based On Self-Assembly Of Polystyrene Spheres And Their Applications In SERS

Micro-nanostructures have been widely used in many fields because of their special optical,electronic and magnetic properties,and periodic micro-nanostructures have attracted much attention in the field of Surface-Enhanced Raman Scattering（SERS）because of their good ordered structure and high controllability.However,the fabrication of SERS substrates with micro-nanostructures by photolithography requires expensive equipment and the cost is high,which limits the applications of this SERS substrates.The micro-nanostructures with periodic arrangement can be easily and accurately prepared by using low-cost and diversified colloidal sphere self-assembly technology.In this paper,polystyrene（PS）sphere self-assembly technique was used to prepare micro-nanostructures as SERS substrates.At the same time,the potential applications of SERS substrates in the field of detection was investigated.Based on this article,the main work and results are as follows:（1）Based on the air-water interface method,a set of experimental apparatus was built to prepare a large-scale close-packed PS sphere self-assembled monolayer and transfer it to the substrate stably.Non-close-packed PS sphere monolayer mask was prepared by reactive ion etching（RIE）.It was found that the diameter of PS spheres decreased linearly with the increase of etching time.So the size of the PS sphere mask and the micro-nanostructures can be accurately controlled.（2）We used etching process to roughen the surface of PS spheres and form Au nanoparticles to prepare a large-scale nanostructures SERS substrate.The fabricated SERS substrate had high reproducibility and sensitivity.The results of finite-difference time domain（FDTD）simulations proved that Au nanoparticles and clusters can provide more hot-spot,which enhance the enhancement factor（EF）to more than 10⁸ with a relative standard deviation（RSD）as low as 6.64%-13.84%.The minimum limit of detection（LDO）of the MG molecules reached 50 ng/m L.Moreover,the Raman signal of the characteristic peaks at 1175,1365 and 1617 cm^-1had a linear relationship with the logarithmic concentration of MG.（3）Large-scale and uniform Si nanorods（Si NRs）arrays were fabricated by polystyrene（PS）sphere self-assembly and nanosphere lithography technique.Then the SERS substrate was prepared by Si NRs arrays decorated with Au nanoparticles formed by Au deposition.It can detect molecules with high sensitivity and reproducibility.Au nanoparticles and clusters can provide more hot-spot,and enhance the Raman intenstiy.The EF can reach 10¹⁰ with RSD as low as 6.68%-11.68%.Finally,we applied our SERS substrate in the detection of malathion.The LDO of the malathion reached 1ng/m L,and the Raman signal the characteristic peak at 1284 cm^-1had a good linear relationship with the logarithmic concentration of malathion.The portable Raman spectrometer is also used to test the SERS substrate,and the SERS substrate has a preliminary promising applications for on-site and real-time detection.