Dual Polarization Interferometry: A Real‐Time Optical Technique for Measuring (Bio)molecular Orientation, Structure and Function at the Solid/Liquid Interface

The measurement of proteins, their structure, and function is a crucial step in the characterization, understanding, and utilization of many biological processes. Highly sophisticated structural and functional measurement techniques have been developed over the last 40 years as separate techniques. X-ray crystallography, nuclear magnetic resonance (NMR) and neutron reflectivity have provided structural measurements, while techniques such as surface plasmon resonance (SPR) or microcalorimetry have provided functional data. Dual polarization interferometry (DPI) is a bench-top surface analytical technique capable of providing real-time measurements of molecular (multi)layer dimensions. This enables both structural and functional aspects of biomolecular layers to be determined. Thus molecular immobilization, orientation, assembly, interactions, and stability can be probed, with applications, for example, in biomolecular interactions, drug discovery, sensor surface design, biofouling, and biocompatibility. While generally applicable to a wide range of physicochemical measurement, this chapter gives a few examples of biological applications, highlighting the complementarities of the structural and functional data, rather than mass based response alone, for which there are many other examples. Keywords: dual polarization interferometry (DPI); self-assembly; metal ion binding; molecular orientation; conformation change; protein immobilization; solid/liquid interface