This invention concerns the field of sample identification, in particular a method and apparatuses for identifying or discriminating 
biological species from non 
biological species, both as individual particles and as components of a composition, by pump-probe 
fluorescence spectroscopy for time-resolved detection or imaging. The method uses the finding that the UV-induced 
fluorescence of biological molecules is varied, in particular is depleted, by the addition of 
visible radiation, whereas this does not occur with non-biological 
organic molecules. The invention discriminates the 
fluorescence signals of bio and non-bio particles or species using a differential approach, i.e. the comparison. of the total fluorescence recorded with and without additional 
visible radiation. This allows to discriminate 
biological particles comprising aromatic amino-acids (AA), like peptides, proteins, 
bacteria, viruses, pollens, spores, etc., from non-
biological particles, like aromatic (AH) or polyaromatic hydrocarbons (PAH), carbonaceous aerosols, 
soot, etc.