Methodology to evaluate the antimicrobial effectiveness of UV-activated TiO2 nanoparticle-embedded cellulose acetate film

TiO2 nanoparticle (NP)-embedded cellulose acetate (CA) films were prepared using solution casting method and found that it can inactivate Escherichia coli O157: H7 under UV-A light illumination. This study investigated the microbial inactivation efficacy of this film under several practical application scenarios: (1) direct contact with bacteria which were located either above or beneath the film; (2) with or without contact with bacteria; (3) contact with dried bacterial inoculum; and (4) submerged in contaminated water. Results showed that antimicrobial performance of TiO2 NP-embedded CA film varied depending application scenarios. For Scenario 1, the reductions were 1.1 log CFU/ml above and 0.5 log CFU/ml beneath the film after 2 h illumination. For Scenario 2, the reductions were 1 log CFU/ml with direct contact and 0.6 log CFU/ml without direct contact after 6 h exposure. For Scenario 3, the reduction was 3.5 log CFU/ml after 6 h. For scenario 4, the reduction was 5.2 log CFU/ml after 6 h. This study demonstrated the crucial role of contact between the bacterial cells and NP embedded surface to achieve microbial inactivation. Results of this study suggest that the most effective applications of TiO2 NP-embedded polymer film can be obtained when in direct contact with liquid inoculum or contaminated solutions.