Carbohydrate-protein interactions characterized by dual polarization hybrid plasmonic waveguide

Optical biosensors present good performance for the affinity analysis of a molecular binding event. However, most of those excited with single optical mode are "blind" to the conformational change of bound molecules. We theoretically demonstrate a dual polarization hybrid plasmonic (DPHP) waveguide with nano-slots. By addressing the structure with dual polarizations, the optogeometrical properties (density and thickness) of protein layers have been determined without ambiguity. Differences in the hybrid mode dispersion between the transverse electric (TE) and transverse magnetic (TM) modes allow to separately determine the thickness and the density at all stages during the molecular interaction. In addition, nano-slots can be equated with an effective optical capacitance resulting in a strong field confinement; thereby, subtle changes in the ambient medium can be sensed. A proof of concept is conducted by analyzing the conformational change of HepV, a recombinant fragment of collagen V, during complicated molecular interaction. Integrated with adlayer thickness and density, we can conclude that a thick sparse layer formed after heparin capture and a thin dense layer arising from HepV bound. Accordingly, HepV undergoing conformational change has been traced and verified as molecular interaction occurs.