The hybrid methylene blue–zeolite system: a higher efficient photocatalyst for photoinactivation of pathogenic microorganisms

Abstract

The composite system can be prepared by incorporation of methylene blue (MB) into the channels of zeolite and by adsorption on the surface of the crystals. The composite photosensitizer effectively absorbs the red light (k max = 648 nm) and upon illumination with light-emitting diode at a fluence rate of 1.02 mW cm -2 generates effectively reactive singlet oxygen in aqueous solution, which was proved by EPR spectroscopy. To test efficiency for inactivation of pathogenic microorganisms, we measured photokilling of bacteria Escherichia coli and Staphylococcus aureus and yeasts Candida albicans. We found out that after the microorganisms have been adsorbed at the surface of such modified zeolite, the photogenerated singlet oxygen quickly penetrates their cell walls, bringing about their effective photoinactivation. The growth inhibition reached almost 50 % at 200 and 400 mg modified zeolite in 1 ml of medium in E. coli and C. albicans, respectively. On the other hand, the growth inhibition of S. aureus reached 50 % at far smaller amount of photocatalyst (30 lg per 1 ml of medium). These results demonstrate differences in sensitivities of bacteria and yeast growth. The comparison revealed that concentration required for IC 50 was in case of C. albicans several orders of magnitude lower for a zeolite-immobilized dye than it was for a freely dissolved dye. In S. aureus, this concentration was even lower by four orders of magnitude. Thus, our work suggested a new possibility to exploitation of zeolite and MB in the protection of biologically contaminated environment, and in photodynamic therapy.

Bactericidal Efficacy of High Irradiance Ultraviolet A Photoactivation of Riboflavin Versus Standard Corneal Cross-Linking Protocol In Vitro

“…33 In particular, the outer wall of Gram-positive bacteria has a high level of porosity and thus does not act as a barrier for frequently used photosensitizers. 34 However, we were unable to reduce the bacterial load with the ultrarapid and rapid photochemical protocols. Photoactivated riboflavin must take time to distribute, link, and exert its action allowing the 1 O 2 to reach targets on microorganisms.…”