SurroMed's Nanobarcodeâ„¢ technology uses cylindrically-shaped colloidal metal nanoparticles, in which the metal composition can be alternated along the length and the size of each metal segment can be controlled. Intrinsic differences in reflectivity between the metal segments allow individual particles to be identified by conventional optical microscopy. See SurroMed and Penn State Publish Pioneering Work in the Journal Science Describing Nanobarcodeâ„¢ Particles