Optical biosensors based on direct coupling of recognition, signal transduction, and amplification

Highly sensitive, specific and reagent-free optical signal transduction methods for detection of polyvalent proteins have been developed by directly coupling distance-dependent fluorescence self-quenching or/and resonant energy transfer to the protein-receptor binding events. The ganglioside GM1 as recognition unit for cholera toxin (CT) was covalently labeled with fluorophores, and then incorporated into a biomimetic membrane surface. In the case using fluorescence self-quenching as a signal transduction mechanism, the fluorescence intensity drops significantly due to aggregation of the fluorophore-labeled GM1 on a biomimetic surface, By labeling GM1 with a fluorescence energy transfer pair, aggregation of the labeled-GM1 results in a decrease in donor and an increase in acceptor fluorescence providing a unique signature for specific protein-receptor binding. The detection systems can reliably detect less than 0.05 nM CI with fast response (less than five minutes). This approach can easily be adapted to any biosensor scheme that relies on multiple receptors or co-receptors. The methods can also be applied to investigate the kinetics and thermodynamics of the multivalent interactions.