After incubation and perhaps application of additional reagents, the zones with biological activity are identified and some-times quantified by using a charged-coupled device or scanning densitometer. The materials and instrumentation for the general toxicity screen employing the luminescent bacteria Alivibrio fischeri is commercially available as the Bioluminizer (Camag, Muttenz,Switzerland) or MicroChemi (Biostep, Jahnsdouf, Germany). The Bioluminizer is shown in Fig. 21, and consists of a tray for holding the thin-layer plate, a procedure to humidify the coated layer to stabilize the bacterium, a light-tight housing, and a charge-coupled device camera for detection. After a short incubation time toxic sub-stances are indicated as “dark” spots or bands due to in habitation of cellular respiration on a green background. The thermoelectrically cooled cameras used for this application are optimized for low light detection with a wide linear response range. Sequential captured images can be presented in film format to displaychanges in the bacteria metabolism correlating with the toxicity of the compounds.