Biological analysis device having improved contamination prevention

A device for conducting biological analysis, such as cell culture, is disclosed having improved contamination prevention features. In a preferred embodiment, a microwell membrane plate for cell analysis is adapted to be inserted into a shallow rectangular tray with elevated side walls which form a single large reservoir for holding an appropriate liquid used in cell growth and analysis. The side surfaces of the tray include a raised ridge extending about the entire periphery of the tray. A series of uniform-height steps formed on the ridge serve as support for the microwell membrane plate when inserted into the tray and also create a narrow capillary gap between the plate and the tray. A ledge extending laterally from the base of the ridge forms a second, wider gap when the microwell membrane plate is inserted into the tray. The height of the first capillary gap is less than the height of the second gap formed within the zone of space extending to the exterior of the device, thus when the tray and plate are tilted, as when jostled during handling, liquid from the reservoir will preferentially remain in the space formed by the first capillary gap. Liquid which does spill into the second gap will run back into the reservoir when the device is leveled.