Optimized Au NRs for efficient SERS and SERRS performances with molecular and longitudinal surface plasmon resonance

Abstract

Chemically stable and biocompatible gold nanorods (Au NRs) are an excellent building block for plasmonic-based applications, including surface-enhanced Raman spectroscopy (SERS). However, the quest for controlling the aspect ratio (AR) for desirable application needs an in-depth understanding of the synthesis procedure. In this article, the seed-mediated growth of Au NRs with a controlled AR is reported. Influencing reagents, including the seed concentration, are varied individually to unfurl the impact of them on AR. A subsequent optimized protocol is developed to achieve a fine-tuning in the longitudinal surface plasmonic resonance (LSPR) of Au NRs with a narrow distribution of NRs and minimal by-products. The effect of resonance of LSPR peaks closely tallying both 785 and 532 nm with laser excitations are studied for SERS applications using rhodamine 6G (R6G) dye. Furthermore, the molecular resonance of R6G analyte is achieved successfully with a 532 nm excitation laser to accomplish as high of 10−12 M, thanks to the suitable ARs and the surface-enhanced resonance Raman scatterings (SERRS) phenomenon. The enhancement factor is calculated to be 5 × 109, which allows Raman intensity mapping for a trace amount of R6G, demonstrating the potential utility of Au NRs for applications.