The OCR measurements were performed on a custom experimental platform built around an inverted microscope [Eclipse TE2000, Nikon, Melville, NY; Fig. 2(b)]. All experiments were performed at 37°C, controlled by means of an environmental chamber enclosing the microscope. The sensor was excited using a narrow-band LED with an emission maximum of 396 nm (Lumibright, Innovations in Optics, Woburn, MA) coupled to the epi-illumination port of the microscope. A diffuser was placed in front of the LED to produce uniform illumination of the field of view. The sensor was excited and emission photons were collected utilizing a , 0.45 NA Plan Apochromat objective lens (Nikon) and a dichroic mirror (440 dclp, Chroma Corp., Bellows Falls, VT) mounted in the filter turret of the microscope. The emission signal was passed through one of two band-pass filters (BP595/70 and BP650/50, Omega Optical, Brattleboro, VT) for SiOEP and PtOEP emissions, respectively. These filters were mounted on a motorized filter wheel rotating in an infinity plane outside the microscope. Sensor emission images were collected using a cooled, electron multiplying, charge-coupled device camera (Cascade II 512, Photometrics, Tucson, AZ). The LED was operated in a pulsed mode synchronized to the camera exposure time to ensure that sensor excitation occurred only during image acquisition. Sensor data was captured every 5 sec with an exposure time of 20 ms per spectral channel. Alignment of well and lid arrays and the production of an air-tight seal between them, were accomplished using a high precision XYZ translation stage and a motorized rotation stage mounted on the microscope stage (Fig. 6).