Optical Immunosensor Based on Photoluminescent TiO2 Nanostructures for Determination of Bovine Leucosis Proteins. Model of Interaction Mechanism

The main aspects of the interaction mechanism between nanostructured TiO2 layer and BLV proteins gp51 have been evaluated during the formation of photoluminescence-based immunosensor. Bovine leucosis protein gp51 was adsorbed on the surface of a nanostructured TiO2 thin film, formed on glass substrates. A photoluminescence (PL) peak shift from 517 to 499 nm was observed after modification of TiO2 surface by adsorbed gp51 (i.e. formation of the biosensitive layer gp51/TiO2). An incubation of gp51/TiO2 in a solution containing anti-gp51 antibodies resulted in the formation a of a new structure (anti-gp51/gp51/TiO2) and the backward PL peak shift from 499 nm to 516 nm. The PL shifts are attributed to the variations in the self-trapped exciton energy level, which were induced by the changes of electrostatic interaction between positively charged atoms and groups, provided by the adsorbed gp51 protein and negatively charged surface of TiO2. The charge–charge-based interaction in the double charged layers gp51/TiO2 can also be interpreted as a model based on ‘imaginary capacitor’, formed as a result of the electrostatic interaction between oppositely charged protein gp51 layer and the TiO2 surface.