Metal–complex assisted resonant SERS for trace-level detection of hazardous gaseous pyridine

Abstract

Pyridine and its derivatives are highly toxic and strictly regulated class of compounds, making their sensitive monitoring essential for human health and environmental safety. Despite the high sensitivity of surface-enhanced Raman scattering (SERS) for detecting various analytes, analysing volatile compounds remains difficult due to the inability to retain the analyte on noble metal nanoparticle surfaces. Herein, we demonstrate for the first time that SERS enables the sensitive, rapid and simple detection of the toxicant pyridine in gaseous form. We introduce a novel strategy that provides SERS analysis of volatile analytes, thereby expanding the scope of molecules accessible to this method. Trapping pyridine in stable transition metal–pyridine complexes enables shifting the absorption maximum from ultraviolet to the visible spectral range (500–660 nm), which is closer in energy to the plasmon absorption band of the silver nanostructured substrate and the laser energy of the Raman spectrometer. Thus, we observed sensitivity down to 5.7 mg/m³ using benchtop Raman spectrometer with a 638 nm laser wavelength, achieving detection limits below the permissible exposure limit for gaseous pyridine, due to the additional resonant enhancement. The immobilisation of transition metal ions in a porous chitosan layer on the plasmonic surface efficiently captures and retains pyridine vapours near the surface. This approach demonstrates broad potential for the trace-level monitoring of a wide class of volatile analytes by SERS.