Photoelectroactivity of a hybrid system constructed by immobilization of avidin onto biotinylated TiO ₂ electrodes

Immobilization of avidin onto thin film nanocrystalline TiO ₂ on ITO was obtained through avidinbiotin binding. In the construction of hybrid systems, dopamine was used as the TiO ₂ surface-active ligand, providing a conductive lead to covalently linked biotin. The assembled hybrids were characterized using electrochemical techniques of chronopotentiometry, cyclic voltammetry, and photocurrent action spectroscopy. With each layer of a biomolecule (dopamine, biotin, and avidin) attached onto the TiO ₂ film, an increase in overpotential (η) for the oxidation of ferrocyanide was detected by chronopotentiometric measurements. An increase in overpotential of Δη ∼ 400 mV was measured for the monolayer of avidin bonded to biotinylated electrodes. The absorption of light by semiconductor nanocrystallites results in charge separation, holes being localized on avidin. The photoinduced charge separation and oxidation of avidin yields to the dissociation of the avidin-biotin complex, promoting changes in the photoelectro-activity of avidin-modified electrodes. The dissociation of this strong noncovalent complex was confirmed by measuring changes in chemiluminescence produced in a reaction of β-galactosidase-labeled avidin and 4-methylumbelliferyl-β-D-galactopyranoside.