  Raman Spectroscopy offers an in-situ, rapid, and non-destructive
characterization tool for chemical analysis of diverse samples with no or
minimal preparation. However, due to the inherent weak signal of conventional
Raman spectroscopy, surface plasmon resonance features of noble metal
nanoparticles have been utilized to conduct Surface Enhanced Raman Spectroscopy
(SERS) in detecting trace label contaminants in foods and foodstuffs. In this
effort, we synthesized gold nanoparticles (AuNPs) by reduction of chloroauric
acid (HAuCl4) with sodium citrate dehydrate. We prepared different sizes of
AuNPs at a fixed temperature (100 oC) but with varying pHs of 4 and 8. The
as-synthesized AuNPs were characterized by UV-Vis spectroscopy, dynamic light
scattering (DLS), and Field Emission Scanning Electron Microscopy (FE-SEM).
FE-SEM micrographs revealed spherical AuNPs with an average diameter of approx.
55 nm and rod-shaped AuNPs with an average length of approx. 170 nm for sample
synthesis at pH 8 and 4, respectively. The effectiveness of the as-prepared
AuNPs for SERS is tested by detecting Rhodamine 6G 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
chemicals in foods and foodstuffs.
