Detection and characterization of single atmospheric bioaerosols using optical trapping-surface enhanced Raman spectroscopy (OT-SERS)

A rapid and precise method for detecting and characterizing airborne bioaerosol particles is in high demand. Surface-enhanced Raman spectroscopy (SERS) is a promising method, as it merges the molecular fingerprints of Raman spectroscopy with enhanced sensitivity. This study presents the integration of optical trapping (OT) with SERS to analyze single bioaerosol particles in air and showcases the first demonstration of OT-SERS for studying the enhanced Raman spectra from common airborne bioaerosols. We measured five different airborne bioaerosols: three pollens (English oak, ragweed, and Arizona ash) and two fungal spores (Bermuda grass smut and Johnson grass smut). The results showed that the enhanced Raman spectra from optically trapped particles achieved an approximate 100 times enhancement and are free from fluorescence interference. Additionally, the intensity of the enhanced Raman signals, with an integration time of 3 seconds, is equivalent to the regular Raman spectra requiring 60 seconds of integration time. Furthermore, Raman bands in the 500-1000 cm⁻¹ range, which are often overwhelmed by fluorescence or challenging to resolve in regular Raman spectroscopy, were clearly resolved in the spectra captured through the OT-SERS.