SERS detection of polyciclic aromatic hydrocarbons using coral-like nanostructured Ag-films

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants mainly originating from the incomplete combustion of fossil fuels. Health and cancer risk arising from these compounds makes it quite urgent to monitor them in air, soil, and water. Since their concentrations in the environment are usually low (order of ng/L in water), highly sensitive techniques are required. Thanks to the large amount of structural information that it can offer, Surface Enhanced Raman Spectroscopy (SERS) has proven to be an effective alternative to traditional chromatographic techniques for the detection of PAHs. By exploiting the plasmonic properties of metallic nanostructures, this technique allows the detection of very low analyte concentration (nano-and pico-molar range), achieving even the limit of single-molecule detection. However, due to the ineffective adsorption of PAHs onto metallic SERS-active substrates, these surfaces are generally functionalized to increase their adhesion. Such chemical modifications can surely improve the selectivity of selected compounds but might hinder the effective direct contact of analytes to the substrate surface contributing to the background SERS signal. Herein, we propose a simple and effective nanofabrication procedure to produce large-scale 3D nanoporous Ag-based SERS substrates which exhibit excellent spatial reproducibility and EF of about 107. Our substrates can detect polycyclic aromatic hydrocarbons dispersed in water without any functionalization of the surface, reaching a limit of detection (LOD) of ~20 nM for pyrene (PYR). As matter of fact, the nanoporous nature combines a high density of hotspots with the capacity to trap PAH molecules through not covalent bonding, facilitating their adhesion to the metallic surface. In perspective, our outcomes demonstrate the high potentiality of our approach for chemical sensing and environmental control applications.