In-Situ Single-Particle Sensing of Carbonaceous Aerosols in Freshly Generated Smoke Using Optical Trapping–Raman Spectroscopy

Carbonaceous aerosols represent a major component of atmospheric particulate matter. However, current characterization methods have limitations in sensing these particles because they either measure only one type of aerosol property or rely on offline measurement from collected samples. In-situ sensing is crucial for characterizing the physical and chemical properties of carbonaceous aerosols while they remain airborne. In this work, optical trapping–Raman spectroscopy (OT–RS) was applied for in-situ sensing of single carbonaceous aerosol particles in freshly generated smoke. Nylon rope and plastic fiber were ignited inside an open chamber using the trapping laser itself. The resulting particles were captured directly in air by the optical trap and immediately analyzed using Raman spectroscopy and real-time imaging within seconds. The optically trapped particles had spatial dimensions of several micrometers and estimated masses on the order of ~10 pg. We demonstrate that this minute amount of material is sufficient to obtain detailed Raman spectral fingerprints. Furthermore, analysis of the Raman bands allowed two types of particles to be clearly distinguished based on their distinct Raman features. Spatially resolved Raman spectra further resolved that individual trapped particles are chemically heterogeneous, with organic carbon and soot located in different regions within the same particle. These results demonstrate that OT–RS provides an effective platform for in-situ characterization of single carbonaceous aerosol particles and possesses strong potential for future on-site atmospheric sensing and monitoring.