Shape-dependent bactericidal activity of TiO2 for the killing of Gram-negative bacteria Agrobacterium tumefaciens under UV torch irradiation.

This paper demonstrated the relative bactericidal activity of photoirradiated (6W-UV Torch, λ > 340 nm and intensity = 0.64 mW/cm(2)) P25-TiO2 nanoparticles, nanorods, and nanotubes for the killing of Gram-negative bacterium Agrobacterium tumefaciens LBA4404 for the first time. TiO2 nanorod (anatase) with length of 70-100 nm and diameter of 10-12 nm, and TiO2 nanotube with length of 90-110 nm and diameter of 9-11 nm were prepared from P-25 Degussa TiO2 (size, 30-50 nm) by hydrothermal method and compared their biocidal activity both in aqueous slurry and thin films. The mode of bacterial cell decomposition was analyzed through transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR), and K(+) ion leakage. The antimicrobial activity of photoirradiated TiO2 of different shapes was found to be in the order P25-TiO2 > nanorod > nanotube which is reverse to their specific surface area as 54 < 79 < 176 m(2) g(-1), evidencing that the highest activity of P25-TiO2 nanoparticles is not due to surface area as their crystal structure and surface morphology are entirely different. TiO2 thin films always exhibited less photoactivity as compared to its aqueous suspension under similar conditions of cell viability test. The changes in the bacterial surface morphology by UV-irradiated P25-TiO2 nanoparticles was examined by TEM, oxidative degradation of cell components such as proteins, carbohydrates, phospholipids, nucleic acids by FT-IR spectral analysis, and K(+) ion leakage (2.5 ppm as compared to 0.4 ppm for control culture) as a measure of loss in cell membrane permeability.