Ellipsometry-Based Biosensor for Label-Free Detection of Biomolecular Interactions in Microarray Format

Microarrays of biological molecules are useful tools for discovery and functionality characterization in fundamental and applied research of genomics, proteomics, glycomics, and cytomics. They provide a high-throughput platform that enables parallel studies of hundreds to tens of thousands of distinct biomolecular reactions. Usually, the characterization of binding reactions between surface-immobilized targets and solution- phase analytes involves fluorescence-based detection methods. However, labeling analytes inevitably changes innate properties of the molecules and, in turn, modifies analyte-target interactions often in an uncharacterized manner. As a result, label-free microarray detection is desirable. In this study, optical microscopes based on the oblique- incidence reflectivity difference (OI-RD) technique are developed and used to detect biomolecular interactions in microarray format. OI-RD, a most sensitive form of optical elliposometry, measures the difference in reflectivity change (both magnitude and phase) between two polarized components of an optical beam. Such a difference is related to the thickness and dielectric constant of surface-immobilized biomolecules. Here, we report the use of such microscopes to study novel protein-protein, oligosaccharide-protein, and small molecule-protein interactions. These experimental results demonstrate that the OI- RD microscopes can serve as powerful tools in biosensing, high-throughput screening, and other applications in biophysics, biochemistry, and biomedical engineering.