SRU Biosystems of Woburn, Mass., has received US Patent No. 7,935,520, "Optical detection of label-free biomolecular interactions using microreplicated plastic sensor elements." A biosensor is described that includes an optical grating with a first and a second surface. The optical grating includes an optically transparent material that conducts electricity. The grating is replicated from a master grating structure by causing a liquid to harden after dispensing the liquid between the master grating structure and a substrate layer.