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.