An amorphous layer with high electron storage ability is uniformlygrown on the surface of MAO coatings, moreover, the greater electron storage behavior can reveal a better antibacterial effect. PL spectra can reflect the recombination of photo-induced charge carriers (electrons and holes), hence the intrinsic electron storage capability of MAO coatings was evaluated through the PL measurements. As shown in Fig.1, the PL intensity decreases remarkably after W is incorporated into the MAO coating, indicating that the enhanced amorphous layer endows the MAO-4W with electron storage capability to prevent recombination between electrons and holes. It is believed that the antibacterial activity of MAO-4W relies on its electron transfer behavior, and the electron storage capability of MAO-4W is evidenced by decreased PL signal as compared with that of MAO-0W. In fact, extracellular electron transfer is a general process in bacteria, thus the electron storage capability of MAO-4W was further visualized by a fluorescence procedure, which can track the electron extrusion process of bacterial cells. In short, the bacterial chromosome DNA,a structure that could mimic the electron extrusion process of bacterial cells, was stained by the Hoechst 33342(a blue dye with excitation light of 350nm). As shown in Fig.2(Movies S1,S2,S3,S4,S5, and S6, Supporting Information), blue fluorescence quenching and bubble formation can be observed on the surface of Ti6A14V and MAO-0W, but the fluorescence quenching and bubble formation are hardly captured on the MAO-4W surface. The above results also demonstrate that the electron storage capability of MAO-4W is superior to that of MAO-0W.
Fig. 1. PL spectra of the as-prepared MAO coatings (λEx = 300 nm).
Fig. 2. A series of photos captured with a CLSM depicting the fluctuations of fluorescence quenching and bubble growth process on the surface of samples. For details, please watch the corresponding Movies S1, S2, S3, S4, S5, S6, S7 and S8 in the Supporting Information.
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