Microscopic 'Alphabet Soup'

In a process that brings to mind the sorcerer's apprentice, two UCLA chemists have designed and mass-produced billions of fluorescent microscopic particles in the shape of the letters of the alphabet (shown) and other complex three-dimensional forms. Thomas G. Mason and Carlos J. Hernandez used high-throughput lithography to create particles with virtually any desired shape and with dimensions of just a few micrometers. The particles are made by coating a silicon wafer with a water-soluble layer topped by a photosensitive epoxy layer. Exposure to UV light through a mask cross-links the regions not hidden by the mask. The unreacted material is then removed, and an aqueous solution lifts the particles off the wafer to form a colloidal dispersion dubbed "alphabet soup" (J. Phys. Chem. C 2007, 111, 4477). Because each letter is smaller than a single cell, the particles could be used to literally label individual cells. The technology could also be used in security applications.