An assay stick 7 includes a transparent reaction vessel or tube 14 having one or more microbeads 8 disposed therein. The microbeads 8 have a plurality of unique identification digital codes based on a diffraction grating 12 disposed therein that are detected when illuminated by incident light 24. The...http://www.google.es/patents/US7901630?utm_source=gb-gplus-sharePatente US7901630 - Diffraction grating-based encoded microparticle assay stick
