Surface-enhanced Raman scattering effect of silver nanoparticles array

Abstract

The Raman signal of adsorbed Raman probe molecule can be significantly enhanced by using metallic nanostructures with high-density hot spots as surface enhanced Raman scattering (SERS) substrates. A great effort has been devoted to the improving of the SERS detection sensitivity and reproducibility by preparing ordered metal nanostructure arrays with controlled particle size, shape and hot spot position, which are used as SERS substrates. In this paper, we prepare high-density Ag nanoparticle arrays by electrochemical deposition in anodic aluminum oxide (AAO) templates. The particle size and the nanogap between the adjacent particles can be adjusted by changing the deposition time. The structures and surface plasmons of Ag nanoparticle arrays are characterized by scanning electron microscopy and reflectance spectra. The size of the gap between the particles significantly affects the plasmon resonance and the plasmon coupling between the particles. The SERS properties of Ag nanoparticle arrays are investigated by using 1, 4-benzenedithiol (1, 4-BDT) as Raman probe molecule. The Ag nanoparticle arrays with high SERS detection sensitivity and high reproducibility (uniformity) are prepared by optimizing the deposition time (the nanogap between the adjacent particles), and the detection limit of the 1, 4-BDT can reach 10-13 mol/L. The relative standard deviation of the SERS signal intensity randomly measured from 20 spots on the Ag nanoparticle array substrate is 5.35%. The finite-difference time domain simulations confirm that the plasmon coupling between nanoparticles is strong, and that the coupling between the nanoparticles will increase as the nanogap decreases. Additionally, the local field is enhanced at the bottom of the nanoparticle and the gap between the Ag nanoparticle and the AAO template is larger. These results show that Ag nanoparticle array can be used as a high-efficiency SERS substrate.