Response of bacteriorhodopsin thin films to ammonia

The optical response of optical fibres end-coated with bacteriorhodopsin-containing films to ammonia vapour was investigated. Both static absorptance changes and changes in the dynamic parameters of the actinic light-induced photocycle were determined. Simple optical adsorption measurements can be used to detect ammonia with a detection limit of 5 ppm and a dynamic range of 10-10,000 ppm, over which the response is logarithmic. By analysing the modulation of the photocycle response by ammonia, the limit of detection can be decreased to 0.9 ppm. The incorporation of chemicals with an amine functionality, such as triethanolamine, in the film suppresses the ammonia response, and is therefore useful for referencing.