Highly sensitive user friendly thrombin detection using emission light guidance from quantum dots-aptamer beacons in 3-dimensional photonic crystal

In this paper, we present a highly sensitive biosensor for thrombin detection using emission light guidance by 3-dimensional (3D) photonic (PC) crystals. The emission light guidance is induced by optical resonances at the specific wavelength that can be engineered by modifying the pore size of the nanoporous PC structures, and it results in enhancing the fluorescent signals from quantum dots (Qdot)-aptamer beacons. For easy to use, we introduce a fluorescence based 'On-Off-On' detection protocol: first, the immobilization of Qdot-aptamer beacons on the surface of PC turns biosensor to 'On' state with an original fluorescent intensity; then, the conjugation between the beacons and dark quencher-labeled guard-DNA (G-DNA) quenches the fluorescent signals and turns biosensor to 'Off' state; finally, in presence of target protein (thrombin), the thrombin-aptamer binding and the release of G-DNA induce the restoration of fluorescent signals and turns biosensor back to 'On' state and the recovery efficiency ratio of fluorescent signal varies quantitatively with the concentration of the target protein. Owing to emission light guidance of the artificially designed 3D nanoporous PC structure, as far as we know, this proposed thrombin detection biosensor shows the highest sensitivity with a detection limit of 3.8 pM compared to other existing fluorescent based detection techniques.