Method and apparatus for detecting microparticles in fluid samples

A device for detecting a microparticle in a fluid, the microparticle being tagged with a fluorescent substance, the fluorescent substance emitting fluorescent light of predetermined wavelengths when exposed to electromagnetic radiation, the device comprising:

• a capillary tube having an internal diameter configured to admit the microparticles one at a time;
• a fluid delivery system coupled to the capillary tube, the fluid delivery system capable of causing the microparticle and the fluid to flow through the capillary tube;
• a source of electromagnetic radiation for projecting a beam of electromagnetic radiation of predetermined wavelength and size of the capillary tube through said capillary tube whereby the beam size and the interior of the capillary tube define a test volume which exposes the fluorescent substance in the test volume to the electromagnetic radiation to cause emission of fluorescent light by said fluorescent microparticles in said volume;
• a detection device configured and disposed to detect fluorescent light emitted from the fluorescent substance in the volume when the microparticle is in the capillary volume and provide an output signal;
• and
• means disposed between said fluorescent substance in said volume and the detector to pass light at said predetermined wavelengths.