Label-free detection of glycoproteins using reflectometric interference spectroscopy-based sensing system with upright episcopic illumination

A reflectometric interference spectroscopy (RIfS)-based sensing was demonstrated on the detection of glycoproteins using concanavalin A (Con A)-immobilized silicon nitride sensing chips. When ovalbumin (OVA), a model glycoprotein, was injected, the sensor response increased due to the spectral change in interference reflectance caused by the increase in optical thickness on the sensor chip after the binding of OVA. In contrast, such response was not observed when bovine serum albumin was injected, suggesting that the molecular recognition events such as specific binding of OVA toward the immobilized Con A can be detected by the present sensing system. An apparent dissociation constant was estimated to be 5.4 x 10(-6) M from Scatchard analysis, which was a similar order of magnitude to previously reported values. Consequently, the RIfS system appeared to be a tool for the label-free detection of protein recognition events in real time and could provide quantitative information on the binding.