Real-time detection of multiple biomolecular reactions on a functionalized glass surface using a scanning oblique-incidence optical reflectivity difference (an ellipsometric technique).

One of the enabling platforms in proteomic research is parallel (high-throughput) detection of multiple biomolecular interactions on a microarray. To keep conformational and in turn functional integrity of protein molecules, label-free detection is desirable. We have developed an oblique-incidence optical reflectivity difference (OI-RD) technique for label-free measurements of protein reactions with molecular targets in microarray format immobilized on functionalized glass surface. As an ellipsometric technique, OI-RD measures changes in thickness and/or optical dielectric response instead of fluorescence. By incorporating total internal refection geometry and a multi-element photodiode array detector, we demonstrate how such the OI-RD technique can be efficiently used to measure multiple protein reactions in real time with surface-immobilized molecules or molecular groups on a glass substrate.