Kinetic analysis of biomolecular interactions by surface plasmon enhanced ellipsometry

We present the application of ellipsometry to the phase measurement of surface plasmon resonance (SPR) in biomolecular detection. In this work, the experimental setup for the SPR sensor was based on a custom-built rotating analyzer ellipsometer, which was equipped with a SPR cell and a microfluidic system. We investigate the sensitivity of SPR sensor which is dependent on the thickness and roughness of metal film, alignment of optical system, and stability of microfluidics. In the drug discovery process, to directly monitor the interaction of small molecule-protein, it is necessary to design a high-sensitivity SPR sensor with a sensitivity of greater than 1 pg/mm2. Our sensor demonstrates a much better sensitivity in comparison to other SPR sensors based on reflectometry or phase measurements. The results of calibration indicate that the phase change, δ▵, had an almost linear response to the concentration of ethanol in the double-distilled water solutions. A quantitative analysis of refractive index variation was possible using the results of the ellipsometric model fits for the multilayered thin film on the gold film. Thus, this method is applicable not only to sensor applications, such as affinity biosensors, but also to highly sensitive kinetics for drug discovery. In this paper, we demonstrate how a custom-built rotating analyzer ellipsometer in the SPR condition can be used to directly obtain the interactions and binding kinetics of analytes (biotins, peptides) with immobilized ligand (streptavidin, antibody). We achieved a detection limit of lower than 1.0 x10-7 RIU, which is the equivalent of 0.1 pg/mm2.