Protein binding detection using on-chip silicon gratings.

We demonstrate a silicon gratings-based biosensor to detect functionalized protein binding on its surface. The designed silicon gratings have sensitivities up to 197 nm/RIU in detecting refractive index change and 1.61 nm per nanometer of thickness change of bio-material on the surface of silicon gratings. Functionalizing proteins on gratings surface by eliminating unspecific binding makes this device more selective and efficient. Streptavidin at a concentration of 0.016 μmol/mL was functionalized on silicon substrate and biotin of 12 μmol/mL concentration was used as a target molecule in our detection experiments. Normal transmission measurements of gratings are made in air at different stages of immobilization, bare silicon grating, after attaching streptavidin and after trapping biotin. Total shifts in resonant peak wavelength of ∼15 nm in normal transmission were observed after immobilizing biotin with ∼7 nm of shift in resonant peak wavelength after functionalizing streptavidin to silicon substrate.