Detection and characterization of chemical and biological aerosols using laser-trapping single-particle Raman spectroscopy

Abstract

Detection and characterization of the presence of chemical and biological agent aerosols in various complex atmospheric environments is essential. Raman spectroscopy has the ability to identify chemical molecules, but there are a limited number of photons detectable from each single airborne aerosol particle as it flows through a detecting system. Here, we report a single-particle Raman spectrometer that can measure strong spontaneous, stimulated, and resonance Raman spectra from a single laser-trapped airborne aerosol particle. Samples such as the VX nerve agent chemical simulant diethyl phthalate and various pollens were tested. A particular optical trap using two focusing counter-propagating hollow beams was able to stably trap both absorbing and non-absorbing particles in air for long observation times. Using this system, time-resolved Raman spectra and elastic scattered intensities were recorded to monitor the chemical properties and size variation of the trapped particle. Specifically, the developed technology was able to measure the Raman spectra from different submicron positions within a single laser-trapped airborne particle. Such a system provides a new approach for the detection and characterization of single airborne chemical- and biological-agent aerosol particles, as well as.to detect and monitor the molecules and molecular reactions located in different positions within a micron-sized particle as it responds to various micro-local environments.