A system and method are disclosed for the simultaneous optical disinfection and detection of biological particles in a flowing fluid, such as air or water, medium. A light source for irradiating the flowing medium is a dual wavelength laser element simultaneously emitting a visible laser beam and an ultraviolet laser beam. In particular, a laser diode may generate a first visible laser light beam, and a second ultraviolet laser light beam may be generated by passing the first laser light beam through a frequency doubling crystal. Optical detectors measure scattering, fluorescence and/or transmission of the laser light beams from the air or water medium to determine the presence of biological particles in real-time.