Selective biomolecular photocatalytic decomposition using peptide-modified TiO2 nanoparticles

Abstract

Titanium dioxide (TiO2) is a photocatalyst widely used for the degradation of inorganic and organic contaminants in the environment; however, its lack of chemical specificity can be a particular limitation since every species in solution, including valued, innocuous, and deactivating compounds, will be degraded or deleterious to the process. Here, we describe a means to target the photocatalysis by surface modification of nanoparticulate TiO2 with a 13 amino acid streptavidin binding peptide (SBP) for the selective degradation of streptavidin, a 60kDa tetrameric protein. Modification of the TiO2 surface with the affinity peptide was confirmed by fourier transform infrared spectroscopy (FTIR), UV/Vis absorbance, and secondary ion mass spectrometry (SIMS), while streptavidin binding and affinity to bound SBP were tested using fluorescently tagged antibodies against streptavidin. Results show that the SBP retains its affinity toward streptavidin after immobilization onto TiO2. Photodegradation studies using the visible region of simulated solar radiation (≥360nm) showed rapid streptavidin degradation by SBP–TiO2 both in solution and while the photocatalyst was immobilized as a thin film on a glass substrate. In contrast, photocatalytic degradation of a non-target protein, lysozyme, was inhibited by the SBP monolayer and incompletely degraded, indicating that surface modification with biorecognition agents can control and modulate the photocatalytic process. Moreover, after extended illumination (3h), the SBP-modified TiO2 surface retained its ability to bind streptavidin demonstrating that the SBP is stable at the TiO2 surface and that the SBP–TiO2 surface is reusable. These results indicate that the modification of TiO2 with covalently bound peptide recognition moieties offers the ability to selectively degrade target proteins of interest, leaving non-target components largely unaffected.