Dynamics of E. coli membrane cell peroxidation during TiO2 photocatalysis studied by ATR-FTIR spectroscopy and AFM microscopy

Escherichia coli (E. coli) photokilling due to the TiO2 under light irradiation in a batch reactor was studied by using of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and atomic force microscopy (AFM). The ATR-FTIR spectral features and AFM images were analyzed in relation to E. coli viability data. ATR-FTIR is shown to be a suitable technique to follow the structural changes of the E. coli cell membranes during TiO2 photocatalysis. Formation of the peroxidation products due to the photocatalysis of E. coli cell is reported by this technique. Time dependent ATR-FTIR experiments provides the evidence for the changes in the E. coli cell wall membranes as the precursor events leading to bacterial lysis. Under the same experimental conditions used by ATR-FTIR spectroscopy, AFM microscopy was carried out to provide direct evidence for the E. coli lysis taking place under light irradiation after about 1 h in the presence of TiO2. By transmission electron microscopy (TEM), the aggregated TiO2 Degussa P-25 in aqueous solution is shown to interact with the bacteria surface and partly to remain in the aqueous solution at the concentration of 1 mg/ml.