a method and apparatus for enabling chemical identification of individual particles , cells of molecules by obtaining a raman spectrum of a particle , cell or molecule as it flows past a sensing point in a flow cytometer . the particles , which may be cells or molecules , are associated with a suitable noble metal colloid or colloidal aggregate . cellular particles may be associated with gold or silver colloidal particles by ultra - sonic sonification while in a sample preparation reservoir containing the gold or silver colloidal suspension . the colloid associated particles are then hydrodynamically focused into a single file by a fluid control module . the surface - enhance raman spectrum of individual particles are obtained by illuminating the particle with a laser as the particle flows past a sensing point and gathering the light that is non - elastically scattered by the particle . the surface - enhanced raman spectrum is then analyzed to identify the particle .