Local pH Gradient Initiated by Light on TiO2 for Light-Triggered Modulation of Polyhistidine-Tagged Proteins

A new principle of photo-assisted spatial desorption of (poly)histidine-tagged (His-Tag) proteins on a TiO2 surface is suggested. A semiconductor TiO2 surface is decorated by layer-by-layer (LbL) assembly of a strong polyelectrolyte, namely, polystyrene sulfonate (PSS), and nickel–nitrilotriacetic acid (NTA). The PSS/NTA multilayer architecture provides n-fold (n×NTA) binding efficiency for more precise protein recognition in comparison to existing molecular His-Tag protein recognition with one- and threefold multiplication (1×NTA, 3×NTA). Spatially resolved desorption of proteins is regulated by non- photodestructive short-term low-intensity light irradiation (<5 mW cm−2). The local pH shift on irradiated TiO2 selectively affects the pH-sensitive NTA/protein complex, but not the LbL assembly of PSS and NTA, which is stable in a broad pH range.