Photochemistry and Photobiology, 2014, 90: 1099–1107 Photoactive Titania Float for Disinfection of Water; Evaluation of Cell Damage by Bioanalytical Techniques R. Shwetharani, M. S. Jyothi, P. D. Laveena and R. Geetha Balakrishna* Center for Nano and Material Sciences, Jain University, Ramanagaram, Bangalore, India Received 9 February 2013, accepted 19 March 2014, DOI: 10.1111/php.12277 ABSTRACT A photoactive float was fabricated with the modified titania to cause a feasible disinfection of water, contaminated with E. coli. The commercially available titania was doped with neodymium by pulverization technique to enhance its activity in sunlight and a multiapproach technique was used to evalu- ate the extended efficiency of the doped sample. X-ray dif- fraction patterns depicted the retention of anatase phase on doping and the existence of neodymium was confirmed by the energy dispersive atomic X-ray analysis and the X-ray photoelectron spectroscopy. Transmission electron micros- copy and Bruner–Emmett–Teller analysis depicted a mar- ginal increase in the particle size and a decrease in the surface area, respectively. Doping induces semiconductor behavior with lower band energy that could respond to visi- ble light and exhibit better disinfection activity. The “f” and “d” transitions of the lanthanide in doped sample caused new electronic behavior of trapping/detrapping effect together with bandgap narrowing. The amount of malondialdehyde, protein, DNA and RNA released on destruction of E. coli was observed to be 0.915 3 10 À3 lg mL À1 , 859.912 lg mL À1 , 20.173 lg mL À1 and 1146.073 lg mL À1 , respectively. The above analytical methods along with standard plate count method substantiated the enhanced disinfection efficiency of the doped sample in sunlight. INTRODUCTION The availability of decontaminated water is a serious problem in rural areas of developing countries. A total of 37.7 million Indi- ans are affected by waterborne diseases annually, 1.5 million children are estimated to die of diarrhea and 73 million working days are lost due to waterborne disease each year (1). The classi- cal techniques such as ultraviolet light irradiation, ozone treat- ment, low frequency ultrasonic irradiation and reverse osmosis processes have their disadvantages and advantages. A simple dis- infection method which can work in sunlight and without usage of nonrenewable source of energy is interesting (2). The major pathogenic organisms responsible for waterborne diseases in India are bacteria (E. coli, Shigella, V. cholera), viruses (Hepati- tis A, Poliovirus, Rotavirus) and parasites (E. histolytica, Giardia Hook worm). E. coli is a gram-negative microorganism and is used as an indicator organism of fecal contamination. Water- borne diseases caused from this organism involve flu-like symp- toms such as diarrhea, nausea, fever and vomiting (3–5). The present study investigates a feasible and effective method for inactivation of this pathogenic microbe using a photoactive float. Titania is a well known photocatalyst for its use in oxidative, photodestructive and disinfection processes (6). TiO 2 due to its large band energy absorbs in the near UV and utilizes only a very small fraction of the solar spectrum and generate excess electrons in the conduction band and positive holes in the valence band. At the TiO 2 particle surface, the holes react with either adsorbed H 2 O or surface OH À groups to form HO . radicals. Excess electrons in the conduction band react with molecular oxygen to form superoxide ions, which further disproportionate to form more HO . radicals. Hence, the photocat- alyst-mediated reactions cause the generation of a number of reactive oxygen species (ROS) and hydroxyl radicals (HO . ). The generated ROS interacts with the cell wall components like pep- tidoglycan, amino acids and lipids, and causes the damage of the bacterial cell wall. TiO 2 utilizes only a small fraction of the solar spectrum and this led to the search of a photocatalyst which could utilize the most abundant energy source—the sunlight. Sul- fur and nitrogen have been doped into titania to enhance the absorption of visible light (7–9). The positive and adverse effects of doping transition metal ions like Au, Ag and Mo into the TiO 2 lattice for sunlight-mediated catalytic activity have also been reported (10–13). The special electronic structure 4f x , 5d y in lanthanide (Ln) ions, having a redox couple of Ln n+ /Ln (nÀ1)+ are able to form labile oxygen vacancy of high mobility of bulk oxygen species which would result in a dissimilar catalytic prop- erty and different optical property. This influences the photocata- lytic activity and photocurrent intensity of Ln n+ -TiO 2 greatly. Also Ln n+ is proposed to replace Ti 4+ inside the octahedral inter- stitial site to impose an unbalanced charge. Therefore, Ti-O-Ln bond and the charge imbalance are expected to change the sur- face chemical state of Ln n+ - TiO 2 greatly (14). We thus have investigated the doping effect of inner transition metal, neodym- ium into TiO 2 by solid state technique to induce changes in its electronic structure for the effective absorption of a broader spec- trum of sunlight, which results in a higher amount of reactive oxygen species for an improved and feasible photoinactivation of E. coli in sunlight. Different biochemical assays have been used as analytical tools to measure the extent of antibacterial activity. Titania and its doped analogues were investigated in powder form for bactericidal activity with respect to both gram-positive and gram-negative bacteria (15,16). But the suspended powders *Corresponding author email: geethabalakrishna@yahoo.co.in (R. Geetha Bala krishna) © 2014 The American Society of Photobiology 1099