Biotin modified polycationic polymers are capable of penetrating the Au overlayer of poly(N-isopropylacrylamide)-co-acrylic acid microgel-based etalons. Once penetrated, the polycations crosslink the polyanionic microgels, causing them to collapse, resulting in a concomitant blue shift of the spectral peaks in the reflectance spectrum. We show that the magnitude of the blue shift depends on the concentration of the biotinylated polycation solution exposed to the etalon. This behavior is subsequently used for biosensing applications.
