Ultrasensitive and multiplex SERS determination of anthropogenic phenols in oil fuel and environmental samples

Abstract

Phenolic compounds are an important class of environmental pollutants to be strictly controlled. Therefore, discovering sensitive and selective approaches for their express-monitoring is of vital importance for sustainable and eco-friendly well-being. Surface-enhanced Raman spectroscopy (SERS) perfectly matches this purpose due to its capability of ultrasensitive multiplexed detection of various analytes based on their “molecular fingerprints”. Herein, we propose a unique approach of molecular immobilization and resonant Raman amplification by complex-loaded enhancers (MIRRACLE) on chitosan-coated SERS-active metallic nanostructured substrates. Selected indicator systems trap phenols into charge-transfer complexes with new absorption maxima in the 500–700 nm visible spectral range adjusted to both plasmon resonance bands of the silver nanoparticle sensor and 633 nm excitation laser wavelength. Such wavelength-matching allows the measurement of resonance SERS spectra with significantly increased sensitivity. Density functional theory analysis of the electronic structure of charge-transfer complexes aided the choice of the electron-acceptor to pair with phenolic compounds for the MIRRACLE approach. The developed strategy thus enables sensitive, rapid, yet simple on-site detection of some of the most hazardous ecotoxicants – phenol, chlorophenols, cresols, and xylenols – in complex and chemically diverse matrices like freshwater and gasoline fuel.