In-Situ Detection of Small Biomolecule Interactions Using a Plasmonic Tilted Fiber Grating Sensor

We have proposed and experimentally demonstrated a plasmonic tilted fiber Bragg grating based biosensor for in-situ detection of the small biomolecule S-adenosyl-L-homocysteine (AdoHcy). The sensor can also monitor the molecule's interaction with the protein Set7 in real time. The biosensor is made by coating a 50-nm-thick gold film over an 18° tilted fiber Bragg grating. A spectrally dense comb of backward-propagating cladding resonance modes with Q-factor as high as 104 is excited due to the tilted grating. The spectral overlap between the excited cladding modes and the broader absorption feature of the surface plasmon makes this device a unique tool for high-accuracy measurement of small shifts of plasmon resonance wavelength. Surface biomolecular functionalization of the gold film enables us to not only detect the corresponding biomolecule but also study its interaction with other biomolecules. Our experimental results demonstrate that our biosensor can detect AdoHcy at concentration as low as 1 nM. Furthermore, we have successfully real-time monitored interaction between the protein Set7 and AdoHcy at different concentrations. Our measurements are consistent with the biological theory that the association rate of a pair of biomolecules depends on their concentrations.