A fuel injector for the direct injection of fuel into the combustion chamber of a mixture-compressing internal combustion engine having external ignition includes a valve housing formed by a nozzle body, and a seal which seals the fuel injector from a cylinder head of the internal combustion engine. The bacteria may be Desulforomonas sp. Laser induced breakdown spectroscopic processing is employed and spectra attributable to known collection tape materials is subtracted to derive particle spectra for comparison to known hazardous agent spectra.