Progressive depositions of cerebral amyloid are primary neuropathologic features of Alzheimer's disease (AD). The amyloid is composed of a 39-42 amino acid peptide called the amyloid beta-protein (A beta). Repeated investigation suggests that the conformational transition of A beta from a-helix or random coil to beta-sheet structure plays a key role in the inappropriate accumulation of cerebral amyloid plaques. In this manuscript, we describe a fluorescence-based immunoassay technology to investigate the conformation and topology of A beta peptides interacting with peptide-tethered planar lipid bilayers. Dual monoclonal antibodies (mAbs) labelled with fluorophores were employed to recognise a linear N- and a beta-sheet C-terminus of A beta peptides on the model membrane, respectively. Kinetics of antibody-A beta binding were determined by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The conformational transition of A beta by melatonin, a defined beta-sheet breaker, was probed using paired monoclonal antibodies. The A beta interaction with the membrane was evaluated by carefully analyzing the change in kinetic/affinity parameters in the presence or absence of melatonin. These results show that SPFS can be used to examine conformational transition of A beta on an artificial membrane, providing a novel and versatile platform for conveniently monitoring protein-membrane interaction and screening for new beta-sheet breakers. (C) 2009 Elsevier Inc. All rights reserved.