Laser-Patterned Cu–Ag Alloy Micropillars Incorporated with Laser-Ablated AgAu Bimetallic Nanoparticles for Label-free Detection of Water Pollutants

Abstract

Water pollution is always a threat for all organisms, which has detrimental impacts on their health and the ecosystem. The goal of this study is to identify and quantify even the tiniest amounts of surfactant pollutants and heavy metals in water using surface-enhanced Raman spectroscopy (SERS). For making SERS substrates, thin layers of copper (Cu) and silver (Ag) were sequentially deposited on silicon wafer (Si) by thermal evaporation. Following this, laser patterning of Si/Cu/Ag immersed in a AgAu bimetallic nanocolloid produced microstructure features of CuAg-alloyed micropillars embellished with AgAu bimetallic nanoparticles on their surface. The nanocolloids composed of spherical AgAu nanoparticles of an average size of 13.4 ± 2.7 nm having a plasmonic peak at 449 nm were synthesized by pulsed laser ablation in liquid (PLAL). The surface morphology and chemical states of elements present on the SERS substrates were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy. The SERS sensors present remarkable sensitivity, measuring 1 pM for rhodamine 6G, 10⁻¹⁰ M for surfactant molecules, and 1 nM for heavy metal compounds in water. The sensor’s signal homogeneity is shown by a comparatively minimal relative standard deviation (RSD) of 11.07% for 1 nM. A linearity plot of signal intensity to concentration demonstrating R² = 0.994 validates the quantitative identification of contaminants. The sensors are stable and could reproduce SERS spectra for about a month of storage time. Above all, their reusability after a simple microwave treatment and scribing in AgAu nanocolloids is their advantage.