Engineering plasmonic nanochain for optical sensor via regulating electric field

Surface-enhanced Raman scattering (SERS) has a great application potential for ultra-sensitive detection of biological and chemical molecules. However, the preparation of assembly nanostructure often requires expensive processing equipment, long preparation cycle, and the yield is relatively low, thus its application is limited. It is found that adjusting the Brownian motion of the colloid via electric field can control the distribution of nanoparticles (NPs) and provide potential capabilities for assembled nanostructures. This study aimed to demonstrate the production of remarkable SERS activity of large-area gold nanochain array(AuNCR) substrates through a simple, cost-effective, and nanofabrication-free method. The substrates were prepared by controlling the voltage and frequency of the alternating current (AC) electric field so that the NPs form a chain structure on an Indium Tin Oxide glass substrate. We selected Rhodamine 6G as the Raman probe molecule, the enhancement factor (EF) improved by five orders of magnitude. Besides, a wet chemical transfer method is used to transfer single-layer graphene to AuNCR (SG/AuNCR), and it is found that the SERS EF of SG/AuNCR is 1.5 times higher than that of AuNCR substrate. Based on the finite element method(FEM), a strong plasmon coupling was found between the AuNCR and graphene. It is also found that the local electromagnetic field of SG/AuNCR is 1.4 times stronger than that of AuNCR, which is consistent with experimental observation. Therefore, the obtained results show that the AuNCR nanostructure has great potential in the field of SERS detection.