Sterilization effects of a TiO<Subscript>2</Subscript> photocatalytic film against a<Emphasis Type="Italic">Streptococcus mutans</Emphasis> culture

Streptococcus mutans is one of the more significant pathogens involved in the development of dental caries in humans. The purpose of this research was to design a TiO₂-coated dental instrument and to determine the bactericidal effects of the instrument onS. mutants. TiO₂ photocatalytic films were prepared by the low-pressure metal-organic chemical vapor deposition (LPMOCVD) method using titanium tetraisopropoxide (TTIP) as precursor. The photocatalytic reaction was carried out on a TiO₂-coated pyrex petri dish with an ultraviolet (UV) light emitting diode (LED) illuminator or a fluorescent lamp light source. Our data indicates that the relative survival ratio ofS. mutans when plated onto TiO₂ photocatalytic films and under exposure to UV-A light for 15 min was 0.01%. In addition, a fluorescent lamp light source also had bactericidal effects on theS. mutans plated TiO₂ photocatalytic films. These results indicate that TiO₂-coated dental materials or devices may be useful in dental treatments for the prevention of carious or enamel demineralization.     

Photoinduced bactericidal activity of TiO2 films

A decline in CFU of gram-positive and gram-negative bacteria on the surface of UV illuminated TiO2 films (wavelength of 380 nm) is shown. A 29, 45, and 47% decrease in bacterial viability of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, respectively, was seen following a 12-min exposition. It was first discovered that the reuse of TiO2 films to test a bacterial suspension for viability removes UV-induced bactericidal activity. However, annealing of TiO2 at a temperature above 400 degrees C restores the photoinduced bactericidal activity to its initial state.     

The effects of the bacterial interaction with visible-light responsive titania photocatalyst on the bactericidal performance

Bactericidal activity of traditional titanium dioxide (TiO₂) photocatalyst is effective only upon irradiation by ultraviolet light, which restricts the potential applications of TiO₂ for use in our living environments. Recently carbon-containing TiO₂ was found to be photoactive at visible-light illumination that affords the potential to overcome this problem; although, the bactericidal activity of these photocatalysts is relatively lower than conventional disinfectants. Evidenced from scanning electron microscopy and confocal Raman spectral mapping analysis, we found the interaction with bacteria was significantly enhanced in these anatase/rutile mixed-phase carbon-containing TiO₂. Bacteria-killing experiments indicate that a significantly higher proportion of all tested pathogens including Staphylococcus aureus, Shigella flexneri and Acinetobacter baumannii, were eliminated by the new nanoparticle with higher bacterial interaction property. These findings suggest the created materials with high bacterial interaction ability might be a useful strategy to improve the antimicrobial activity of visible-light-activated TiO₂.     

Visible-Light-Induced Bactericidal Activity of a Nitrogen-Doped Titanium Photocatalyst against Human Pathogens

The antibacterial activity of photocatalytic titanium dioxide (TiO₂) substrates is induced primarily by UV light irradiation. Recently, nitrogen- and carbon-doped TiO₂ substrates were shown to exhibit photocatalytic activities under visible-light illumination. Their antibacterial activity, however, remains to be quantified. In this study, we demonstrated that nitrogen-doped TiO₂ substrates have superior visible-light-induced bactericidal activity against Escherichia coli compared to pure TiO₂ and carbon-doped TiO₂ substrates. We also found that protein- and light-absorbing contaminants partially reduce the bactericidal activity of nitrogen-doped TiO₂ substrates due to their light-shielding effects. In the pathogen-killing experiment, a significantly higher proportion of all tested pathogens, including Shigella flexneri, Listeria monocytogenes, Vibrio parahaemolyticus, Staphylococcus aureus, Streptococcus pyogenes, and Acinetobacter baumannii, were killed by visible-light-illuminated nitrogen-doped TiO₂ substrates than by pure TiO₂ substrates. These findings suggest that nitrogen-doped TiO₂ has potential application in the development of alternative disinfectants for environmental and medical usages.     

UV-Induced Antibacterial Activity of Green-Synthesized TiO2 Nanoparticles for the Potential Reuse of Raw Surface and Underground Water

The pollution of raw surface and underground water with pharmaceutical compounds has an impact on increasing the resistance of pathogenic microorganisms. Environmental challenges include investigating a novel and cost-effective therapeutic approach for the bactericidal treatment of water supplies. Ethyl acetate extracts from three marine algae (Caulerpa racemosa, Codium fragile, and Cystoseira myrica) obtained from the Red Sea (Hurghada, Egypt) were used for the green synthesis of TiO₂ nanoparticles (TiO₂-NPs). A highly crystalline nanoparticle structure with a stable tetragonal anatase structure was obtained; the mean concentrations were 2.43 to 6.09?×?10⁸ NPs/mL and the average particle size was 125–131 nm. In ultrapure water, the TiO₂-NPs were confirmed to be a stable solution following zeta potential analysis. UV light (λ?=?350 nm) for 2 h was used to activate the TiO₂-NPs before the antibacterial activity tests. The application of UV-activated TiO₂-NPs for 4 h treatments demonstrated promising bactericidal activity, with a 73.08% reduction in Salmonella typhi and a 91.51% reduction in Enterobacter ludwigii. Antibiofilm activities against the reference strains Salmonella typhi NCTC 12023/ATTC and Morganella morganii ATCC25829 and the bacterial isolates Klebsiella pneumoniae, Enterobacter ludwigii, and Enterococcus faecium were tested. The TiO₂-NPs were nontoxic against the human normal cell line RPE1. Regarding the treatment of total and fecal coliform, in addition to fecal streptococci, in raw surface and underground water, the UV-activated TiO₂-NPs prepared from the ethyl acetate extracts of Caulerpa racemosa showed high applicability. The present study offered insights into the nature and development of nontoxic and green TiO₂-NP formulations for use as modern antibacterial alternatives against coliforms in aquatic systems.

     

Chitosan films are NOT antimicrobial

Chitosan is a promising biomaterial for biomedical applications and is currently applied as wound dressings. While chitosan solutions demonstrate strong bactericidal activity against a range of medically important bacteria, the study here reports a loss of this beneficial property in thin films cast from the same solutions. Chitosan films (20 μm) showed no inhibitory effects against Escherichia coli, Staphylococcus aureus or S. epidermidis species. In contrast, solutions used to prepare the films showed almost complete inhibition (~98 ± 2%) when tested on bacterial lawns and in liquid cultures. Increased acidity of the chitosan solutions (pH 5) was shown to promote the bactericidal effects of this biopolymer. The concept that devices fabricated from chitosan have an inherent antimicrobial activity is suggested as an important misconception.     

The effect of thermal treatment on antibacterial properties of nanostructured TiO<Subscript>2</Subscript>(N) films illuminated with visible light

This work focuses on the photocatalytic performances and antibacterial activity of nitrogen doped TiO₂ nanosystems with three and five layers obtained by a sol-gel route, followed by thermal treatment in oxygen or ammonia atmosphere at temperatures between 400 and 1000°C. Subsequently, the antibacterial activity of the obtained nanosystems on the Escherichia coli cells are determined and discussed. The obtained results show a significant dependence of the functional performances on the system’s composition. In particular, the antimicrobial activity of nitrogen-doped TiO₂ films is correlated with the temperature of thermal treatment and illumination time with visible artificial light.     

Evaluation of the antibacterial activity and treatment of acne with SiO<Subscript>2</Subscript>-ionized loess

SiO₂-ionized loess was prepared from the reaction of loess and sodium hydroxide at 1,400°C for 2 h. The antibacterial activity of SiO₂-ionized loess against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aerusinosa, and Propionobacterium acnes causing acne was examined by comparing the results against those of untreated loess, and treatment efficacy was examined for treating acne using soap containing SiO₂-ionized loess. The minimum inhibitory concentration value of SiO₂-ionized loess against S. aureus, P. aerusinosa, B. subtilis, E. coli, and P. acne was 10.0, 10.0, 2.5, 5.0, and 2.5 mg/mL, respectively. However, medium containing untreated loess had no antimicrobial activity. A treatment efficacy test revealed that acne symptoms decreased as the duration of using soap containing SiO₂-ionized loess increased.     

Antibacterial effect of hydrogen peroxide-titanium dioxide suspensions in the decontamination of rough titanium surfaces

The chemical decontamination of infected dental implants is essential for the successful treatment of peri-implantitis. The aim of this study was to assess the antibacterial effect of a hydrogen peroxide-titanium dioxide (H₂O₂–TiO₂) suspension against Staphylococcus epidermidis biofilms. Titanium (Ti) coins were inoculated with a bioluminescent S. epidermidis strain for 8 h and subsequently exposed to H₂O₂ with and without TiO₂ nanoparticles or chlorhexidine (CHX). Bacterial regrowth, bacterial load and viability after decontamination were analyzed by continuous luminescence monitoring, live/dead staining and scanning electron microscopy. Bacterial regrowth was delayed on surfaces treated with H₂O₂–TiO₂ compared to H₂O₂. H₂O₂-based treatments resulted in a lower bacterial load compared to CHX. Few viable bacteria were found on surfaces treated with H₂O₂ and H₂O₂–TiO₂, which contrasted with a uniform layer of dead bacteria for surfaces treated with CHX. H₂O₂–TiO₂ suspensions could therefore be considered an alternative approach in the decontamination of dental implants.     

Comparative effects of TiO2-immobilized photocatalytic supporters on the bactericidal efficiency of a novel photoreactor

A novel and highly effective UV-TiO₂ photocatalytic reactor was developed for killing microorganisms, including Escherichia coli. Among tested four types of TiO₂-immobilized photocatalytic supporters (glass bead, muscovite bead, alginate bead, and TiO₂ thin film coated quartz tube), the muscovite bead had a 99.9% percent bactericidal activity within 5 min along with permanent longevity. Adding air bubbles or H₂O₂ (<50 mg l^–1) to the sample solution significantly enhanced the killing activity in that 100% percent of bacterial cells were killed within 3 min.     

Interaction Between Nanoparticulate Anatase TiO<Subscript>2</Subscript> and Lactate Dehydrogenase

In order to study the mechanisms underlying the effects of TiO₂ nanoparticles on lactate dehydrogenase (LDH, EC1.1.1.27), Institute of Cancer Research region mice were injected with nanoparticulate anatase TiO₂ (5 nm) of various doses into the abdominal cavity daily for 14 days. We then examined LDH activity in vivo and in vitro and direct evident for interaction between nanoparticulate anatase TiO₂ and LDH using spectral methods. The results showed that nanoparticulate anatase TiO₂ could significantly activate LDH in vivo and in vitro; the kinetics constant (Km) and Vmax were 0.006 μM and 1,149 unit mg⁻¹ protein min⁻¹, respectively, at a low concentration of nanoparticulate anatase TiO₂, and 3.45 and 0.031 μM and 221 unit mg⁻¹ protein min⁻¹, respectively, at a high concentration of nanoparticulate anatase TiO₂. By fluorescence spectral assays, the nanoparticulate anatase TiO₂ was determined to be directly bound to LDH, and the binding constants of the binding site were 1.77 × 10⁸ L mol⁻¹ and 2.15 × 10⁷ L mol⁻¹, respectively, and the binding distance between nanoparticulate anatase TiO₂ and the Trp residue of LDH was 4.18 nm, and nanoparticulate anatase TiO₂ induced the protein unfolding. It was concluded that the binding of nanoparticulate anatase TiO₂ altered LDH structure and function.     

Induction of cytotoxicity by photoexcitation of TiO<Subscript>2</Subscript> can prolong survival in glioma-bearing mice

We have investigated the possibility that photoexcited titanium dioxide (TiO₂) could inhibit the growth of malignant cells. We studied the anti-glioma effects of nano-TiO₂ excited with ultraviolet A (UVA) irradiation both in vitro and in vivo. Transmission electron microscopy demonstrated that glioma cells take up TiO₂ by phagocytosis, and vital staining revealed that TiO₂ alone has no effect on glioma cell proliferation. However, if TiO₂ was combined with UVA irradiation the proliferation rate was decreased significantly compared to controls (P < 0.05). RT–PCR suggested that TiO₂ induction of glioma cell apoptosis is associated with changes in the expression of genes encoding Bcl-2 family members. We then investigated the in vivo antitumor effects of combined TiO₂ plus UVA treatment of established glioma tumors. TiO₂ plus UVA led to pronounced areas of necrosis, elevated indices of apoptosis, delayed tumor growth, and increased survival compared with the TiO₂-alone control group (P < 0.001). Log-rank survival analysis showed that median survival duration was prolonged (P < 0.001). These findings suggest that nano-TiO₂ based photodynamic therapy has potential in the treatment of glioma.     

Symbiotic Antimicrobial Effects of Cellulose-Based Bio-Nanocomposite for Disease Management of Agricultural Crops

In the present work, a bionanocomposite for plant crop protection was prepared by non-toxic biocompatible & biodegradable nanomaterials (Cellulose & TiO₂) to utilize its synergistic effects against antimicrobial pathogens. The commercially available microcrystalline cellulose has been reduced to a nanometric scale regime using acid hydrolysis, while the standard TiO₂ nano-powder of particle size ~20 nm has been used to prepare their nanocomposite (NC). The antibacterial studies via agar well diffusion method demonstrated that after 72 h of incubation, parent nanomaterials Ncell and TiO₂ were not showing any activity against phytopathogens X. campestris pv. campestris, and Clavibacter while the nanocomposite's NC's were still effective depicting both bacteriostatic and bactericidal actions. However, the bacterial growth of biocontrol P. fluorescence was not affected by Ncell, TiO₂ NPs and NC after 72 h of incubation. The antifungal testing results via poison food agar assay method suggest that the nanocomposite, along with Ncell and TiO₂ NPs, exhibited strong inhibition of fungal growth of Phytophthora Spp at 0.125 mg/ml concentration while for F. graminearum, similar effect was observed at 0.25 mg/ml concentration. The nanocomposite has proved its potential by exhibiting longer & stronger synergistic effects against plant pathogens as a good antimicrobial agent for protection of agricultural crops.     

The Regulation of TiO<Subscript>2</Subscript> Nanoparticles on the Expression of Light-Harvesting Complex II and Photosynthesis of Chloroplasts of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Recent studies demonstrated that titanium dioxide nanoparticles (TiO₂ NPs) could significantly promote photosynthesis and plant growth, but its mechanism is still unclear. In this article, we studied the mechanism of light absorption and transfer of chloroplasts of Arabidopsis thaliana caused by TiO₂ NPs treated. The results showed that TiO₂ NPs could induce significant increases of light-harvesting complex II (LHCII) b gene expression and LHCII II content on the thylakoid membrane in A. thaliana, and the increases in LHCII were higher than the non-nano TiO₂ (bulk-TiO₂) treatment. Meanwhile, spectroscopy assays indicated that TiO₂ NPs obviously increased the absorption peak intensity of the chloroplast in red and blue region, the fluorescence quantum yield near 680 nm, the excitation peak intensity near 440 and 480 nm and/or near 650 and 680 nm of the chloroplast. TiO₂ NPs treatment could reduce F ₄₈₀/F ₄₄₀ ratio and increase F ₆₅₀/F ₆₈₀ ratio and accelerate the rate of whole chain electron transport and oxygen evolution of the chloroplast. However, the photosynthesis improvement of the non-nanoTiO₂ treatment was far less effective than TiO₂ NPs treatment. Taken together, TiO₂ NPs could promote the light absorption of chloroplast, regulate the distribution of light energy from PS I to PS II by increasing LHCII and accelerate the transformation from light energy to electronic energy, water photolysis, and oxygen evolution.     

DMPS reverts morphologic and mitochondrial damage in OK cells exposed to toxic concentrations of HgCl<Subscript>2</Subscript>

Mercuric chloride (HgCl₂) is a highly toxic compound, which can cause nephrotoxic damage. In the present study effects of HgCl₂ on mitochondria integrity and energy metabolism, as well as antidotal effects of 2,3-dimercaptopropane-1-sulfonate (DMPS) were investigated in the opossum kidney derived cell line (OK). OK cell monolayers were incubated during 0, 1, 3, 6, and 9 h in serum-free culture medium containing 15 μM HgCl₂, either in the absence or in the presence of 60 μM DMPS in a 1:4 ratio. Intracellular ATP content, MTT reduction, and HSP70/HSP90 induction were studied; confocal, transmission electron microscopy, and light microscopy studies were also performed. For confocal analysis, a mitochondrial selective probe (MitoTracker Red CMXH2Ros) was used. Antioxidant activity of DMPS was also studied by the scavenging of the free radical 2, 2-diphenyl-1-picrylhydrazyl (DPPH) technique. A decrease of ATP content, an impaired ability to reduce tetrazolium, and dramatic changes on cellular and mitochondrial morphology, and energetic levels were found after either 6 or 9 h of HgCl₂ exposure. Increased expression of HSP90 and HSP70 were also seen. When OK cells were co-incubated with HgCl₂ and DMPS, cellular morphology, viability, intracellular ATP, and mitochondrial membrane potential were partially restored; a protective effect on mitochondrial morphology was also seen. DMPS also showed potent antioxidant activity in vitro. Mitochondrial protection could be the cellular mechanism mediated by DMPS in OK cells exposed to a toxic concentration of HgCl₂.     

Bactericidal Performance of Visible-Light Responsive Titania Photocatalyst with Silver Nanostructures

Background

Titania dioxide (TiO₂) photocatalyst is primarily induced by ultraviolet light irradiation. Visible-light responsive anion-doped TiO₂ photocatalysts contain higher quantum efficiency under sunlight and can be used safely in indoor settings without exposing to biohazardous ultraviolet light. The antibacterial efficiency, however, remains to be further improved.

Methodology/Principal Findings

Using thermal reduction method, here we synthesized silver-nanostructures coated TiO₂ thin films that contain a high visible-light responsive antibacterial property. Among our tested titania substrates including TiO₂, carbon-doped TiO₂ [TiO₂ (C)] and nitrogen-doped TiO₂ [TiO₂ (N)], TiO₂ (N) showed the best performance after silver coating. The synergistic antibacterial effect results approximately 5 log reductions of surviving bacteria of Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus and Acinetobacter baumannii. Scanning electron microscope analysis indicated that crystalline silver formed unique wire-like nanostructures on TiO₂ (N) substrates, while formed relatively straight and thicker rod-shaped precipitates on the other two titania materials.

Conclusion/Significance

Our results suggested that proper forms of silver on various titania materials could further influence the bactericidal property.     

The influence of nanoscopically thin silver films on bacterial viability and attachment

The physicochemical and bactericidal properties of thin silver films have been analysed. Silver films of 3 and 150 nm thicknesses were fabricated using a magnetron sputtering thin-film deposition system. X-ray photoelectron and energy dispersive X-ray spectroscopy and atomic force microscopy analyses confirmed that the resulting surfaces were homogeneous, and that silver was the most abundant element present on both surfaces, being 45 and 53 at.% on the 3- and 150-nm films, respectively. Inductively coupled plasma time of flight mass spectroscopy (ICP-TOF-MS) was used to measure the concentration of silver ions released from these films. Concentrations of 0.9 and 5.2 ppb were detected for the 3- and 150-nm films, respectively. The surface wettability of the films remained nearly identical for both film thicknesses, displaying a static water contact angle of 95°, while the surface free energy of the 150-nm film was found to be slightly greater than that of the 3-nm film, being 28.8 and 23.9 mN m⁻¹, respectively. The two silver film thicknesses exhibited statistically significant differences in surface topographic profiles on the nanoscopic scale, with R _a, R _q and R _max values of 1.4, 1.8 and 15.4 nm for the 3-nm film and 0.8, 1.2 and 10.7 nm for the 150-nm film over a 5 × 5 μm scanning area. Confocal scanning laser microscopy and scanning electron microscopy revealed that the bactericidal activity of the 3-nm silver film was not significant, whereas the nanoscopically smoother 150-nm silver film exhibited appreciable bactericidal activity towards Pseudomonas aeruginosa ATCC 9027 cells and Staphylococcus aureus CIP 65.8 cells, obtaining up to 75% and 27% sterilisation effect, respectively.     

Potentiation of bacterial killing activity of zinc chloride by pyrrolidine dithiocarbamate

Zinc has antimicrobial activity and zinc salts including zinc chloride (ZnCl₂) have been used for the control of oral malodor. In this study, we hypothesized that pyrrolidine dithiocarbamate (PDTC), a zinc ionophore, may enhance antimicrobial efficacy of ZnCl₂. The bactericidal effectiveness of ZnCl₂ alone (0.5–8 mM) or in combination with PDTC (1 or 10 μM) was evaluated by in vitro short (1 h) time-killing assays against Fusobacterium nucleatum and Porphyromonas gingivalis. Only a slight viability decrease was observed with ZnCl₂ or PDTC alone after 1-h incubation. By contrast, combination of ZnCl₂ and PDTC could achieve a more than 100-fold viability reduction compared with ZnCl₂ or PDTC alone in F. nucleatum and P. gingivalis. Therefore, PDTC greatly enhanced the bactericidal activity of ZnCl₂ against the oral malodor-producing bacteria. These results suggest that use of PDTC may be useful for enhancing bactericidal activity of antimalodor regimens of zinc salts.     

The Improvement of Spinach Growth by Nano-anatase TiO<Subscript>2</Subscript> Treatment Is Related to Nitrogen Photoreduction

The improvement of spinach growth is proved to relate to N₂ fixation by nano-anatase TiO₂ in this study. The results show that all spinach leaves kept green by nano-anatase TiO₂ treatment and all old leaves of control turned yellow white under culture with N-deficient solution. And the fresh weight, dry weight, and contents of total nitrogen, , chlorophyll, and protein of spinach by nano-anatase TiO₂ treatment presented obvious enhancement compared with control. Whereas the improvements of yield of spinach were not as good as nano-anatase TiO₂ treatment under N-deficient condition, confirming that nano-anatase TiO₂ on exposure to sunlight could chemisorb N₂ directly or reduce N₂ to NH₃ in the spinach leaves, transforming into organic nitrogen and improving the growth of spinach. Bulk TiO₂ effect, however, was not as significant as nano-anatase TiO₂. A possible metabolism of the function of nano-anatase TiO₂ reducing N₂ to NH₃ was discussed.     

Promotion of Energy Transfer and Oxygen Evolution in Spinach Photosystem II by Nano-anatase TiO<Subscript>2</Subscript>

Being a proven photocatalyst, nano-anatase is capable of undergoing electron transfer reactions under light. In previous studies we had proven that nano-anatase improved photosynthesis and greatly promoted spinach growth. The mechanisms by which nano-anatase promotes energy transfer and the conversion efficiency of the process are still not clearly understood. In the present paper, we report the results obtained with the photosystem II (PSII) isolated from spinach and treated by nano-anatase TiO₂ and studied the effect of nano-anatase TiO₂ on energy transfer in PSII by spectroscopy and on oxygen evolution. The results showed that nano-anatase TiO₂ treatment at a suitable concentration could significantly change PSII microenvironment and increase absorbance for visible light, improve energy transfer among amino acids within PSII protein complex, and accelerate energy transport from tyrosine residue to chlorophyll a. The photochemical activity of PSII (fluorescence quantum yield) and its oxygen-evolving rate were enhanced by nano-anatase TiO₂. This is viewed as evidence that nano-anatase TiO₂ can promote energy transfer and oxygen evolution in PSII of spinach.