Spherical and Rod-shaped Gold Nanoparticles for Surface Enhanced Raman Spectroscopy

Raman Spectroscopy offers an in-situ, rapid, and non-destructive characterization tool for the chemical analysis of diverse samples with minimal or no preparation. However, due to the inherent weak signal of conventional Raman spectroscopy, surface plasmon resonance features of various nanostructures have been utilized to conduct Surface Enhanced Raman Spectroscopy (SERS) in detecting trace-level contaminants in foods and foodstuffs. In this effort, we synthesized gold nanoparticles (AuNPs) by reducing chloroauric acid (HAuCl 4 ) using sodium citrate dihydrate. We prepared different sizes of AuNPs at a fixed temperature (100 °C) but with two different pHs, 4 and 8. UV-Vis spectroscopy, Dynamic Light Scattering (DLS), and Field Emission Scanning Electron Microscopy (FE-SEM) were used to analyze the synthesized AuNPs. FE-SEM micrographs revealed spherical AuNPs with an average diameter of ~55 ± 13 nm and rod-shaped AuNPs with an average length of ~170 ± 36 nm for samples synthesized at pH 8 and 4, respectively. The effectiveness of the as-prepared AuNPs for SERS is tested by detecting Rhodamine 6G (R6G) diluted at a trace level. This study suggests that plasmonic nanoparticles coupled with SERS have great potential for broad applications in detecting other trace amounts of hazardous elements in foods and foodstuffs.