Immobilization of streptavidin on titania-coated cellulose fibers

Protein immobilization on cellulose nanofibers was achieved by surface sol-gel process using filter paper as substrate, and the resulted protein sheet was bioactive. First, 5-nm thick titania gel layer was uniformly deposited on each cellulose nanofiber in a piece of commercial filter paper, and then monolayer of biotin molecules was adsorbed onto the titania layer to give a bioactive biotinylated surface. Streptavidin (SAv) molecules were thereafter immobilized on the fiber surface via formation of biotin-SAv conjugate. The resulted paper sheet was composed of cellulose fibers coated with streptavidin molecules, which fully retained their biological activity. Hence the protein sheet was applied for the separation and detection of biotin-tagged species. The detection limitation was found to be ∼1 nM for analyte biotin-4- fluorescein, which was clearly visualized by its characteristic green fluorescence on the cellulose fiber.