Mechanistic insight into the disinfection of Salmonella sp by sun-light assisted sonophotocatalysis using doped ZnO nanoparticles

The vulnerability of human life to gastrointestinal diseases of infectious origin in developing countries is increasing due to water contamination by enteric bacteria. So, there is an immediate need to search for novel techniques for the elimination of water borne pathogenic microorganisms. In this context, here we report the sun-light aided sonophotocatalytic (SPC) disinfection of a common enteric bacterium, Salmonella sp. using Iron (Fe) doped ZnO nanoparticles (ZnO:Fe NPs). ZnO:Fe NPs were found to be more effective than ZnO for SPC disinfection. Complete disinfection was not achieved with TiO2 NPs under the same experimental conditions. Fluorescence microscopy images have suggested the complete bacterial cell death after SPC. Electron microscopy has confirmed the evidences for compromised bacterial cell membrane. Our investigation has indicated that (OH)-O-center dot and O-2(center dot) radicals might be acting as the crucial component in disinfecting Salmonella Typhimurium (S. Typhimurium) in SPC process. Based on the results obtained from Resazurin assay, it is expected that reactive oxygen species (ROS) produced during SPC may have interfered with the oxido-reductase protein system of the bacteria and hence hindered its metabolic activity. Solar-SPC process using ZnO:Fe NPs demonstrated successful disinfection of S. Typhimurium in water samples collected from various sources such as river, pond, lake and municipal tap. Also, SPC treated water was found to have supportive effects on the germination of Zea mays seeds compared to that of water infected with S. Typhimurium. With high effectiveness of SPC under sunlight in disinfecting bacteria, it may have a very promising outcome as a water disinfection technique for real world applications.