Bioactive Titania Colloidal Particles: Preparation, Characterization and Applications

Abstract

Photocatalytic TiO2, used for oxidizing organic compounds and biological entities, has been extensively studied. However, biomolecules conjugated to photocatalytic TiO2 colloidal particles and their applications have rarely been reported. In this work, a novel platform for fabricating biomolecules conjugated to TiO2 using biotin-streptavidin/avidin bioconjugation and biotin coated photocatalytic TiO2 was developed and the properties and applications of the biomolecules conjugated photocatalytic TiO2 colloidal particles were studied. Photocatalytic TiO2 particles were treated with 3-aminopropyltriethoxysilane (APTS) and then N-hydroxysuccinimidobiotin (NHS-biotin) to give a biotin coating. The resulting aminosilanized and biotinylated TiO2 particles were characterized by a variety of methods, including nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), electrophoretic mobility, light diffraction, nitrogen adsorption, polyelectrolyte titration, conductometric titration, biotin assays, X-ray photoelectron spectroscopy (XPS), and confocal laser scanning microscopy (CLSM), giving insight into the strategies necessary to control the density of grafted amino groups, organosilane thickness, and surface charges of the resulting aminosilanized TiO2. Ultimately, the key parameters for photocatalytic performace relied on the ability to tune the surface modification reaction, and the conditions for conjugating the biotinylated TiO2 to streptavidin. The impact of UV irradiation to the aminosilanized cationic TiO2 colloidal particles was studied. The results show that an oxidization reaction occurs on TiO2 surfaces, resulting in the removal of the amino groups and the change of surface charge from positive to negative. A new light-triggered flocculation system was developed based on this surface charge conversion. Biomolecules conjugated to colloidal titania particles exhibit combined properties of the biological functions of bound biomolecules and the photocatalytic properties of titania. Two applications related to biomolecules conjugated photocatalytic TiO2 were studied in this work. One is the selective binding and killing of bacteria by using antibody coated photocatalytic TiO2 under UV irradiation. The antibody-TiO2 was prepared by coupling biotinylated TiO2 particles to biotinylated Escherichia coli (E. coli) antibody with streptavidin. In a medium containing antibody-TiO2 particles, E. coli, and Pseudomonas putida (P. putida), when UV irradiation is applied, the selective binding and killing of E. coli was confirmed by electrophoretic mobility measurement, turbidity tests, optical microscopy, scanning electron microscopy (SEM), confocal microscopy, and plate counting. The other application is the immobilization of TiO2 particles on cellulose fibers with a homogeneous distribution through multi-linker bioconjugation of CBM2a-Streptag II/streptavidin/biotinylated TiO2. The immobilized TiO2 efficiently decolorizes UV sensitive dye within about 10 hours, demonstrating the efficiency of photocatalysis of the resulting TiO2-containing paper.