A surface plasmon resonance sensor has been designed using a rotating optic
al disk coated with a silver film and a transparent dielectric film with a
thickness gradient. A pH indicator, bromocresol purple, was used as a recep
tor on the surface to demonstrate the technique by detecting ammonia, Ammon
ia concentrations in the few ppb range could be detected with relatively si
mple and inexpensive electronics. (C) 1999 Elsevier Science S.A. All rights
reserved.