Photocatalytic Titanium Dioxide P25 Antifungal Properties And Mechanisms Preliminary Study

Objective1. To evaluate the Candida albicans inactivation performance with P25 nano titanium dioxide (TiO2) under two different wavelengths of ultraviolet (UV) irradiation, and preliminary exploration of possible mechanisms of antifungal.2. Assess the impact of nano-titanium dioxide P25 onset time and UV sterilization effect.Methods1. The monoclonal of Candida albicans was cultured aerobically into 3 ml modified Martin medium at 37℃ thermostatic incubation. The C.albicans albicans suspension were collected then centrifuged at 4000×g min-1 for 3 min at 4℃ for three times and formulated as about 107 CFU/ml concentration of C.albicans albicans suspension. Each group was pipetted 100μl fungal suspension with different concentrations of P25 nanometer TiO2 (Sigma-Aldrich, USA) under UV irradiation until measured emission of long-wave UV light (UVA) and short-wave ultraviolet light (UVC) wavelength by ultraviolet radiation meter. Group Ⅰ (0.2 mg/ml P25 100 μl, UVA irradiation), Group Ⅱ (0.4 mg/ml P25 100 μl, UVA irradiation), Group Ⅲ (0.2 mg/ml P25 100 μl, UVC irradiation), Group Ⅳ (0.4 mg/ml P25 100 μl, UVC irradiation), Group Ⅴ (sterilization ddH2O 100 μl, UVA irradiation), Group Ⅵ (sterilization ddH2O 100 μl, UVC irradiation), Group Ⅶ (37℃ 150 ml sterilization ddH2O complete dissolution a piece of Polident then had been pipetted 100μl into the well of 96-well plate). The first four groups were for the experimental and the control group were the later three groups. Preparation for each group pipetted suspension of 200 μl into each of 96 well plates were for preparation.2. Detection the type of reactive oxygen species from Group Ⅰ to Ⅳ photocatalytic reaction produced with electron paramagnetic resonance spectroscopy (EPR EMX-plus) and the absolute number spins. In Group Ⅰ and Group Ⅲ, adding radical scavengers (DMPO) formulated as the final concentration was 100 mmol/L at the suspension final concentration, Group Ⅱ and Group VI got the final concentration for 150 mmol/L, then EPR detection at 0 min,5 min,10 min and 15 min were taken.3. Take Candida albicans suspension by centrifugation, fixed, dehydrated, and dried, then thin layer of gold-palladium was coated by sputtered for scanning electron microscope (Scanning electron microscope, SEM) observation. The observation of Group Ⅰ and Group Ⅱ adsorption situation between P25 TiO2 and Candida albicans, SEM observation until selection for natural drying method and later spraying thin layer of gold-palladium coated.4. The antifungal photocatalyst activity were taken in 96 well plate after 0 min,5 min, 10 min, and 15 min pipetted 100 μl from the suspension then 10- fold serial dilutions from each group, extracted 100 μl onto modified Martin agar medium 37℃,24 h incubation, colony forming units were counted culture (Colony forming unit, CFU). The experiment was repeated for three times. Candida albicans viability is calculated as followed:Percentage of survival (%)= surviving colonies of different irradiation time number/initial number of colonies ×100%.Results1. Except for Group Ⅶ, the photocatalytic reaction of P25 TiO2 in each group produced hydroxyl radical (HO·), there did not detected the superoxide anion and other type of reactive oxygen radicals signals. Absolute numbers of spins experimental was observed in the concentration at 0.4 mg/ml P25 TiO2 group generated more HO signal than 0.2 mg/ml P25 (Group Ⅰ and Group Ⅲ produced more HO· signal than Group Ⅱ and Group Ⅳ), there was no P25 TiO2-Group Ⅴ and Group Ⅵ also could detect the HO· signal were lower than others.2. The adsorbent between Candida albicans and P25 was associated with the concentration of P25, The higher the concentration, the more obvious agglomeration.3. The percentage of survival of Candida albicans 15 min at each group were as followed:in the experimental group, the Group Ⅰ was higher than Group Ⅱ respectively,94.8% and 82.45%; Group Ⅲ and Group IV percentage of survival were 1.18%and 20%. In the control group, the percentage of survival Candida albicans at 15 min were:Group Ⅴ and Group Ⅶ display 79.75% and 18.5%, while Group Ⅵ was zero at 5min.Conclusion1. Hydroxyl radicals (HO·) was detected in the suspension at 5 min,10 min and 15 min points under UVA or UVC irradiation in the presence or of P25 TiO2.2. After receiving UVA irradiation, P25 TiO2 Candida albicans suspension does not have antifungal activity while UVC irradiation P25 TiO2 have significantly reduced the amount of fungal, yet it did not exclude the antifungal properties UVC itself.3. There were no additive antifungal effects of P25 TiO2 under UVA or UVC irradiation observed.