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

TL;DR

This study synthesizes spherical and rod-shaped gold nanoparticles at different pH levels and evaluates their effectiveness in surface-enhanced Raman spectroscopy for detecting trace contaminants in food samples.

Contribution

It demonstrates how pH-controlled synthesis of gold nanoparticles influences their shape and enhances SERS detection capabilities for food safety applications.

Findings

Spherical AuNPs (~55 nm) synthesized at pH 8.

Rod-shaped AuNPs (~170 nm) synthesized at pH 4.

Both shapes effectively detect trace Rhodamine 6G.

Abstract

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.