The invention disclosed herein provides biosensors and methods which increase the sensitivity of assays of optically labelled molecules fluorescently tagged polypeptides and polynucleotides while decreasing the sample volume required for detection. By integrating reflective sidewalls into the receptacles used in such assays, the signal-to-noise ratio of the optical signal is increased significantly. Typically the receptacles are microchannels. In addition, the geometry of the receptacles can be controlled to further optimize the signal-to-noise ratio of the optical signal. The invention disclosed herein further provides methods and devices involving integrated electronics, wherein an element such as a diode, a transistor, an integrated circuit etc., is integrated with a bio-reactor/channel in order to facilitate the detection or fabrication of bio-materials.