RESUMO
The discoloration of methylene blue in aqueous solution was studied under illumination by a fluorescent lamp, LEDs of red, green, and blue light, and a UV-A black light bulb. Overall results showed that methylene blue was discolored with and without the presence of any photoactive semiconductor. Outcomes depended on the combination substrate-light source employed. Photosensitization was assumed as the discoloration mechanism followed upon visible light irradiation. Fluorescence spectroscopy and high-performance liquid chromatography were used to investigate the possible intermediates formed in the irradiated solutions. The detailed nature of formed species was not stablished, but it was proved that the dye molecule photo-bleached and partially defragmented in several intermediates including leuco dyes, demethylated phenothiazine dyes, and probably humic substances. Since the fluorescence intermediates found were similar for most of the irradiated solutions, it was assumed that comparable reactive species were responsible for the discoloration of the molecule in solution. Results proved the misconception of discoloration experiments found in the literature when employing visible light near the absorption region of the dye.
RESUMO
The antibacterial efficiency of longwave UV-irradiated TiO(2) thin films as well as the ultrastructural damage on bacterial cells was evaluated using Pseudomonas aeruginosa as a model. The quantitative antibacterial efficiency assays showed a bacterial inhibition in the range of 32-72% at different times of irradiation. Transmission electron microscopy (TEM) was used to detect the effect of irradiation of TiO(2) thin films on the ultrastructure of the bacterial cell in order to reveal possible cellular damage. After 40 min irradiation, an abnormal cellular division was observed: instead of a normal septum, an 'elongated bridge' was formed. At a longer irradiation time, wavy structures all around the outer cell membrane were observed, and also some bubble-like protuberances, which expelled inner material. The mechanism of irreversible bacterial cell damage caused by the photocatalytic effect of TiO(2) could be related to abnormal cell division, aside from the reported physicochemical alteration of the cell membrane.
Assuntos
Pseudomonas aeruginosa/efeitos da radiação , Pseudomonas aeruginosa/ultraestrutura , Protetores Solares/farmacologia , Titânio/farmacologia , Raios Ultravioleta , Divisão Celular/efeitos dos fármacos , Divisão Celular/efeitos da radiação , Relação Dose-Resposta a Droga , Microscopia Eletrônica , Modelos Biológicos , Pseudomonas aeruginosa/efeitos dos fármacosRESUMO
The photoinduced bactericidal capacity of TiO(2) based films was evaluated, using as model organism Pseudomonas aeruginosa. Thin films were obtained by spray pyrolysis; they included undoped, Cu doped, and Al doped TiO(2). Scanning electron microscopy was used to observe the final effect of the irradiated films upon the bacteria. Depending on the composition and characteristics of the films, quantitative experiments show that bacterial inhibition varies between 28 and 96%. The order of magnitude of the average quantum yield of the films was determined between 10(-9) and 10(-11) inhibited bacterial per photon.