Femtosecond laser pulses distinguish bacteria from background urban aerosols.

The fluorescence from living bacteria (Bacillus subtilis, Enteroccocus and Escherichia coli), induced by a ultrashort 270 nm pump pulse is depleted up to 50% by an optically delayed ultrafast 810 nm probe pulse in a pump-probe arrangement. The fast (subpicosecond) fluorescence decrease occurs for a pump-probe delay of Δt>2 ps. Depletion is also observed for tryptophan in water in contrast with organic cyclic molecules such as naphtalene or diesel fuel, despite similar absorption and fluorescence spectra. This remarkable difference allows us to propose a new remote sensing method able to efficiently discriminate organic from biological aerosols in highly populated urban areas. [ABSTRACT FROM AUTHOR]