Photonic crystal surface waves for optical biosensing

A high-precision optical biosensor technique capable of independently determining the refractive index (RI) of liquids is presented. Photonic crystal surface waves (PC SWs) were used to detect surface binding events, while an independent registration of the critical angle was used for accurate determination of the liquid RI. This technique was tested using binding of biotin molecules to a streptavidin monolayer at various biotin concentrations. The attained baseline noise is 2×10^-13 m/Hz^1/2 for adlayer thickness changes and 8×10^-8 RIU/Hz^1/2 for RI changes.