The present disclosure relates to microfluidic devices adapted for facilitating cytometry analysis of particles flowing therethrough. In certain embodiments, the microfluidic devices allow light collection from multiple directions. In certain other embodiments, the microfluidic devices use spatial intensity modulation. In certain other embodiments, the microfluidic devices have magnetic field separators. In certain other embodiments, the microfluidic devices have the ability to stack. In certain other embodiments, the microfluidic devices have 3-D hydrodynamic focusing to align sperm cells. In certain other embodiments, the microfluidic devices have acoustic energy couplers. In certain other embodiments, the microfluidic devices have phase variation producing lenses. In certain other embodiments, the microfluidic devices have transmissive and reflective lenses. In certain other embodiments, the microfluidic devices have integrally-formed optics. In certain other embodiments, the microfluidic devices have non-integral geographically selective reagent delivery structures. In certain other embodiments, the microfluidic devices have optical waveguides incorporated into their flow channels. In certain other embodiments, the microfluidic devices have optical waveguides with reflective surfaces incorporated into their flow channels. In certain other embodiments, the microfluidic devices have virus detecting and sorting capabilities. In certain other embodiments, the microfluidic devices display a color change to indicate use or a result.