We present a biosensor using a photonic crystal slab (PCS) surface-functionalized with aptamers (thus aptasensor) and a label-free photometric detection scheme. Resonances in the optical transmission spectrum of the PCS are highly sensitive to mass changes on the surface of the PCS. We align the resonance's spectral position to the falling edge of a light emitting diode's (LED) spectrum and use two crossed polarization filters before and after the PCS. Thus, we may detect a molecular binding process on the surface of the PCS with a simple photometric intensity measurement. Using a CMOS camera, we determine the signal and reference intensity at different positions on the PCS. The functionality of this aptasensor is demonstrated by applying a 125 nM thrombin-solution to the PCS bio-functionalized with anti-thrombin aptamers. A significant signal was obtained and the reaction kinetic was observed.
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