Detection and Classification of Aerosolized Biowarfare Agent Surrogates by The Single-Particle Optical Trapping-Raman Spectroscopy System

The biowarfare agents (BWAs) are the biological materials used with the intention to cause diseases to humans, animals, and plants. Because of the potential threat, the detection of BWAs has become increasingly important. We built a single-particle optical-trapping Raman spectroscopy (OT-RS) system and applied it for the detection of BWAs. The system can levitate a single particle in air from minutes to hours and capture the time-resolved Raman spectra from the single particle. Simultaneously, an associated image system can provide the position, shape, and size of the trapped particle in real time. The trapped particle in air is free from the noise of the substrate, and the interference from fluorescence can be effectively quenched by the photo-bleaching process. Four different BWA surrogates: Bacillus globigii (BG), Yersinia rhodei (Yr), MS2, and Bacillus subtilis (BS) with some bioaerosol particles which are commonly presented in air were tested in the experiment. The single particle spectra show some similarities and distinguishable Raman peaks. We monitored the time evolution of the spectra for the trapped particle. The intensity change of some Raman bands indicates that some particle experienced a chemical or physical property change during the trapping period. The classification was processed by the principle component analyses (PCA). The PCA results suggest that the spectra of the single BWA surrogates can be identified and can also be clearly distinguished from the common bioaerosols in air.