Two-photon excited fluorescence from biological aerosol particles

We used a 40 MHz mode-locked 524 nm laser source to evaluate the utility of sub-picosecond excitation of fluorescence from 2-photon absorption in biological aerosols. Individual particles of biological composition, as well as other calibration particles, suspended in an inlet air flow were illuminated and measured as they passed through an optical chamber. To our knowledge, this was the first demonstration of 2-photon excited fluorescence from micron-sized particles composed of micro-organisms. We also observed a high fluorescence signal at visible wavelengths, which was not present with single-photon excitation.

Research highlights► First 2-photon excited fluorescence from micron-sized particles of micro-organisms. ► Discrimination between biological aerosol particles based on 2-photon fluorescence. ► Biological particle emission proportional to the square of excitation intensity. ► Volume dependence of fluorescent emission on particle size for bio-aerosols.