Probing the effect of stoichiometry on structural, optical and bacterial growth inhibition properties of ZnO thin films against <i>E. coli</i>

Abstract

The spray pyrolysis technique was employed to deposit In, Fe-In and Sn-In doped zinc oxide thin films on borosilicate glass substrates with two different precursor solutions prepared using deionized water and methanol-deionized water. The samples were probed for their antibacterial properties against Escherechia coli, along with characterisation of their structural and optical properties. X-ray diffraction patterns depicted the zincite phase of the deposited ZnO nanoparticles in all cases. However, in the thin films deposited using methanol-water, a preferential orientation along the (002) plane was favoured with the evolution of typical nanoparticle morphologies, e.g. nanospheres in undoped and In doped ZnO, nanoflakes in Fe-In doped ZnO and nanospindles in Sn-In doped ZnO thin films. Deionized water did not lead to any typical transformation in morphology other than the change in nanoparticle size. The particle size varied in the range 26�110?nm for methanol-deionised water derived ZnO samples, whereas it varied in the range 22�37?nm for water derived samples. The optical band gap of ZnO was found to be narrowed by doping with In, Fe-In and Sn-In. The antibacterial action against E. coli is attributed to the excess oxygen present in the film, which directly generates reactive oxygen species. Zn2+ ions are found to have a minimal role in the bactericidal action. Accordingly, Fe-In doping results in optimum antibacterial properties in ZnO and the resulting films could be a promising candidate for food processing industries.