Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO₂-Ag nanowires with a diameter of 200 nm and a length of 6-20 µm were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO₂ phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO₂-Ag nanowires, a TiO₂ gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO₂ gel resulted in the formation of crystalline TiO₂ nanotubes. A subsequent Ag electrodeposition step inside the TiO₂ nanotubes resulted in formation of coaxial TiO₂-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO₂) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H₂ gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min of illumination, approximately 0.2 vol% H₂ gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.     

TiO2 Nanocrystals Synthesized by Laser Pyrolysis for the Up‐Scaling of Efficient Solid‐State Dye‐Sensitized Solar Cells

A crucial issue regarding emerging nanotechnologies remains the up‐scaling of new functional nanostructured materials towards their implementation in high performance applications on a large scale. In this context, we demonstrate high efficiency solid‐state dye‐sensitized solar cells prepared from new porous TiO₂ photoanodes based on laser pyrolysis nanocrystals. This strategy exploits a reduced number of processing steps as well as non‐toxic chemical compounds to demonstrate highly porous TiO₂ films. The possibility to easily tune the TiO₂ nanocrystal physical properties allows us to demonstrate all solid‐state dye‐sensitized devices based on a commercial benchmark materials (organic indoline dye and molecular hole transporter) presenting state‐of‐the‐art performance comparable with reference devices based on a commercial TiO₂ paste. In particular, a drastic improvement in pore infiltration, which is found to balance a relatively lower surface area compared to the reference electrode, is evidenced using laser‐synthesized nanocrystals resulting in an improved short‐circuit current density under full sunlight. Transient photovoltage decay measurements suggest that charge recombination kinetics still limit device performance. However, the proposed strategy emphasizes the potentialities of the laser pyrolysis technique for up‐scaling nanoporous TiO₂ electrodes for various applications, especially for solar energy conversion.     

The Photocatalytic Activity of TiO<Subscript>2</Subscript> Thin Film Deposited on Al Plate Together with Cu(II) and Ag(I)

Cu (II) and Ag(I) together with TiO₂ powder were deposited on conducting support substrates to enhance the photocatalytic ability. The catalytic efficiency was tested by monitoring the photocatalytic degradation and detriment of methylene blue (MB) and bovine serum albumin (BSA). The conformational change of BSA induced by catalysts was also observed by circular dichroism spectroscopy.The antibacterial activities were studied by Escherichia coli. Both MB and BSA could be degraded more efficiently than pure TiO₂. After treatment with catalyst, the morphology of cells became twisted and rougher. Regular wrinkles were damaged and groove-like rift appeared on the surface. The fluorescence polarization has shown a significant decrease in membrane fluidity and the increase of permeability of cell membrane. Changes of the spectral profile of E. coli were observed, which suggested the damages of surface groups on the cell membrane.     

High‐Energy,High‐Rate,Lithium–Sulfur Batteries: Synergetic Effect of Hollow TiO2‐Webbed Carbon Nanotubes and a Dual Functional Carbon‐Paper Interlayer

A novel nanocomposite cathode consisting of sulfur and hollow‐mesoporous titania (HMT) embedded within carbon nanotubes (CNT), which is designated as S‐HMT@CNT, has been obtained by encapsulating elemental sulfur into the pores of hollow‐mesoporous, spherical TiO₂ particles that are connected via CNT. A carbon‐paper interlayer, referred to as dual functional porous carbon wall (DF‐PCW), has been obtained by filling the voids in TiO₂ spheres with carbon and then etching the TiO₂ template with a chemical process. The DF‐PCW interlayer provides a medium for scavenging the lithium polysulfides and suppressing them from diffusing to the anode side when it is inserted between the sulfur cathode and the separator. Lithium–sulfur cells fabricated with the thus prepared S‐HMT@CNT cathode and the DF‐PCW interlayer exhibit superior performance due to the containment of sulfur in TiO₂ and improved lithium–ion and electron transports. The Li–S cells display high capacity with excellent capacity retention at rates as high as 1C, 2C, and 5C rates.     

Characterization,Cytotoxicity, and Genotoxicity of TiO<Subscript>2</Subscript> and Folate-Coupled Chitosan Nanoparticles Loading Polyprenol-Based Nanoemulsion

The structure and bioactivity of Ginkgo biloba leaves polyprenol (GBP) are similar to that of dolichol which widely exists in human and mammalian organs. GBP possesses potential pharmacological activities against cancer. This study involved oil-in-water type nanoemulsion (NE) loading GBP was prepared by dissolving polyprenol in nanoemulsion of sodium tripolyphosphate (TPP)/TiO₂ solution, Triton X-100, and 1-octanol by inversed-phase emulsification (EIP) and ultrasonic emulsification (UE) method. Folic acid (FA)-coupled chitosan (CS) nanoparticles (NPs), GBP-FA-CS-NPs and GBP-TiO₂-FA-CS-NPs, were fabricated by ionic cross-linking of positively charged FA-CS conjugates and negatively charged nanoemulsion with TPP/TiO₂. And characterizations of them were investigated by TEM, SEM, FTIR, particle size, and zeta potential. The cytotoxic and genotoxic effects of GBP-TiO₂-FA-CS-NP treatment were higher than GBP-NE, GBP-FA-CS-NPs, TiO₂-NE, GBP-TiO₂-NE, TiO₂-FA-CS-NPs, and GBP-TiO₂-FA-CS-NP treatment at the same tested concentrations in HepG2 cells. GBP-TiO₂-FA-CS-NPs at low TiO₂ concentration (from 1 to 2.5 μg/ml) showed good inhibition capacity on HepG2 cells and low cytotoxic and genotoxic effects on HL-7702 cells. The possible mechanism of cytotoxicity on GBP-TiO₂-FA-CS-NPs against HepG2 cells is by preventing excessive intracellular Ca²⁺ into extracellular spaces via inhibiting Ca²⁺-ATPase and Ca²⁺/Mg²⁺-ATPase.     

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.     

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.     

Cellulose/carrageenan/TiO<Subscript>2</Subscript> nanocomposite for adsorption and photodegradation of cationic dye

Cellulose/carrageenan/TiO₂ nanocomposites were simply prepared by the co-dissolution of cellulose and carrageenan, and the dispersion of TiO₂ in 1-ethyl-3- methylimidazolium acetate, followed by reconstitution with anti-solvents. The cellulose/carrageenan/TiO₂ composite showed a much higher adsorption capacity for methylene blue (MB) than the cellulose and cellulose/TiO₂ composite. The cellulose/carrageenan/TiO₂ composite also degraded MB more efficiently in aqueous solution than the cellulose/ TiO₂ composite. The MB adsorption capacity of the cellulose/carrageenan/TiO₂ composite increased linearly with increasing carrageenan content in the composites.     

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.     

Efficient Plastic Perovskite Solar Cell with a Low‐Temperature Processable Electrodeposited TiO2 Compact Layer and a Brookite TiO2 Scaffold

Recent research on fabricating scaffold‐type perovskite solar cells on plastic substrates has reported noteworthy progress in replacing the high‐temperature processing of TiO₂ scaffolds and compact layers with various low‐temperature processes. Herein, recent progress in the laboratory is reported regarding the development of electrodeposited TiO_x compact layers and brookite TiO₂ scaffolds, both of which can be processed under 150 °C without greatly sacrificing their photovoltaic performance. Through systematic characterization of device properties and careful optimization of the fabrication conditions, a record‐high 15.76% power conversion efficiency of a plastic TiO₂ scaffold‐type perovskite solar cell is demonstrated. In addition, bending durability and preliminary stability tests on this plastic perovskite solar cell show promising results and indicate clear directions for future improvement.     

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.     

Impact of Bulk and Nanosized Titanium Dioxide (TiO<Subscript>2</Subscript>) on Wheat Seed Germination and Seedling Growth

The impacts of different concentrations of bulk and nanosized TiO₂ on seed germination and seedling growth of wheat were studied in a randomized completely design with four replications in the College of Agriculture, Ferdowsi University of Mashhad, Iran, in 2011. The experimental treatments included five concentrations of bulk (1, 2, 10, 100, and 500 ppm), five concentrations of nanosized TiO₂ (1, 2, 10, 100, and 500 ppm), and control (without any TiO₂). Results indicated that among the wheat germination indices, only mean germination time was affected by treatments. The lowest and the highest mean germination time (0.89 vs. 1.35 days) were obtained in 10 ppm concentration of nanosized TiO₂ and control treatments, respectively. In addition, shoot length, seedling length, and root dry matters were affected by bulk and nanosized TiO₂ concentrations, significantly. Shoot and seedling lengths at 2 and 10 ppm concentrations of nanosized TiO₂ were higher than those of the untreated control and bulk TiO₂ at 2 and 10 ppm concentrations. Employing nanosized TiO₂ in suitable concentration could promote the seed germination of wheat in comparison to bulk TiO₂ but in high concentrations had inhibitory or any effect on wheat.     

Photoinduced bactericidal activity of TiO<Subscript>2</Subscript> films

A decrease 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 after 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°C restores the photoinduced bactericidal activity to its initial state.     

Both Enhanced Biocompatibility and Antibacterial Activity in Ag-Decorated TiO2 Nanotubes

In this study, Ag is electron-beam evaporated to modify the topography of anodic TiO₂ nanotubes of different diameters to obtain an implant with enhanced antibacterial activity and biocompatibility. We found that highly hydrophilic as-grown TiO₂ nanotubes became poorly hydrophilic with Ag incorporation; however they could effectively recover their wettability to some extent under ultraviolet light irradiation. The results obtained from antibacterial tests suggested that the Ag-decorated TiO₂ nanotubes could greatly inhibit the growth of Staphylococcus aureus. In vitro biocompatibility evaluation indicated that fibroblast cells exhibited an obvious diameter-dependent behavior on both as-grown and Ag-decorated TiO₂ nanotubes. Most importantly, of all samples, the smallest diameter (25-nm-diameter) Ag-decorated nanotubes exhibited the most obvious biological activity in promoting adhesion and proliferation of human fibroblasts, and this activity could be attributed to the highly irregular topography on a nanometric scale of the Ag-decorated nanotube surface. These experimental results demonstrate that by properly controlling the structural parameters of Ag-decorated TiO₂ nanotubes, an implant surface can be produced that enhances biocompatibility and simultaneously boosts antibacterial activity.     

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.     

PHBV‐TiO2 mats prepared by electrospinning technique: Physico‐chemical properties and cytocompatibility

One of the most important challenges in tissue engineering research is the development of biomimetic materials. In this present study, we have investigated the effect of the titanium dioxide (TiO₂) nanoparticles on the properties of electrospun mats of poly (hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), to be used as scaffold. The morphology of electrospun fibers was observed by scanning electron microscopy (SEM). Both pure PHBV and nanocomposites fibers were smooth and uniform. However, there was an increase in fiber diameter with the increase of TiO₂ concentration. Thermal properties of PHBV and nanocomposite mats were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis showed that the crystallization temperature for PHBV shifts to higher temperature in the presence of the nanoparticles, indicating that TiO₂ nanoparticles change the process of crystallization of PHBV due to heterogeneous nucleation effect. TGA showed that in the presence of the nanoparticles, the curves are shifted to lower temperatures indicating a decreasing in thermal stability of nanocomposites compared to pure PHBV. To produce scaffolds for tissue engineering, it is important to evaluate the biocompatibility of the material. Cytotoxicity assay showed that TiO₂ nanoparticles were not cytotoxic for cells at the concentration used to synthesize the mats. The proliferation of cells on the mats was evaluated by the MTT assay. Results showed that the nanocomposite samples increased cell proliferation compared to the pure PHBV. These results indicate that continuous electrospun fibrous scaffolds may be a good substrate for tissue regeneration.     

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.     

Self-assembly and photocatalytic activity of branched silicatein/silintaphin filaments decorated with silicatein-synthesized TiO<Subscript>2</Subscript> nanoparticles

The fundamental mechanisms of biomineralization and their translation into innovative synthetic approaches have yielded promising perspectives for the fabrication of biomimetic and bioinspired organic–inorganic hybrid materials. In siliceous sponges, the enzyme silicatein catalyzes the polycondensation of molecular precursors to nano-structured SiO₂ that is deposited on self-assembled filaments consisting of the two silicatein isoforms (silicatein-α and -β) and the scaffold protein silintaphin-1. Due to its broad substrate specificity silicatein is also able to convert in vitro various other precursors to non-biogenic materials (e.g., hydrolysis of titanium bis(ammonium lactato)-dihydroxide [TiBALDH] and subsequent polycondensation to titania [TiO₂]). In the present approach, silicatein was bioengineered to carry a protein tag (Arg-tag) that confers binding affinity to TiO₂. Then, by combining Arg-tagged silicatein-α with silicatein-β and silintaphin-1, self-assembled branched hybrid protein microfilaments were fabricated. Upon subsequent incubation with TiBALDH the filaments were decorated with TiO₂ and assayed for photocatalytic activity through photodegradation of the dye methylene blue. This is the first approach that considers concomitant application of two silicatein isoforms for the synthesis of bioinspired organic–inorganic hybrid materials. It is also the first time that the biocatalytic activity of the enzymes has been combined with both the structure-providing properties of silintaphin-1 and a TiO₂ affinity protein tag to fabricate self-assembled branched protein filaments as template for a silicatein-synthesized TiO₂ photocatalyst. The TiO₂-decorated filaments might be explored as a practical alternative to approaches where biotemplates have to be laboriously isolated from their original biological source prior to TiO₂ immobilization.     

H<Subscript>2</Subscript>O<Subscript>2</Subscript>-induced changes in mitochondrial activity in isolated mouse pancreatic acinar cells

This study employed confocal laser scanning microscopy to monitor the effect of H₂O₂ on cytosolic as well as mitochondrial calcium (Ca²⁺) concentrations, mitochondrial inner membrane potential (_m) and flavine adenine dinucleotide (FAD) oxidation state in isolated mouse pancreatic acinar cells. The results show that incubation of pancreatic acinar cells with H₂O₂, in the absence of extracellular Ca²⁺ ([Ca²⁺]_o) led to an increase either in cytosolic and in mitochondrial Ca²⁺ concentration. Additionally, H₂O₂ induced a depolarization of mitochondria and increased oxidized FAD level. Pretreatment of cells with the mitochondrial inhibitors rotenone or cyanide inhibited the response induced by H₂O₂ on mitochondrial inner membrane potential but failed to block oxidation of FAD in the presence of H₂O₂. However, the H₂O₂-evoked effect on FAD state was blocked by pretreatment of cells with the mitochondrial uncoupler, carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP). On the other hand, perfusion of cells with thapsigargin (Tps), an inhibitor of the SERCA pump, led to an increase in mitochondrial Ca²⁺ concentration and in oxidized FAD level, and depolarized mitochondria. Pretreatment of cells with thapsigargin inhibited H₂O₂-evoked changes in mitochondrial Ca²⁺ concentration but not those in membrane potential and FAD state. The present results have indicated that H₂O₂ can evoke marked changes in mitochondrial activity that might be due to the oxidant nature of H₂O₂. This in turn could represent the mechanism of action of ROS to induce cellular damage leading to cell dysfunction and generation of pathologies in the pancreas. (Mol Cell Biochem 269: 165–173, 2005)     

Aqueous Synthesis and Concentration-Dependent Dermal Toxicity of TiO<Subscript>2</Subscript> Nanoparticles in Wistar Rats

A number of dermal toxicological studies using TiO₂ nanoparticles exist which are based on the study of various animal models like mice, rabbits etc. However, a well-defined study is lacking on the dermal toxic effects of TiO₂ nanoparticles on rats, which are the appropriate model for systemic absorption study of nanoparticles. Furthermore, toxicity of TiO₂ nanoparticles varies widely depending upon the size, concentration, crystallinity, synthesis method etc. This study was conducted to synthesize TiO₂ nanoparticles of different sizes (∼15 to ∼30 nm) by aqueous method, thereby evaluating the concentration-dependent toxicological effects of the ∼20-nm sized nanoparticles on Wistar rats. Characterization of the particles was done by transmission electron microscope, dynamic light scattering instrument, X-ray diffractrometer, and ultraviolet spectrophotometer. The toxicity study was conducted for 14 days (acute), and it is observed that TiO₂ nanoparticles (∼20 nm) at a concentration of 42 mg/kg, when applied topically showed toxicity on rat skin at the biochemical level. However, the histopathological studies did not show any observable effects at tissue level. Our data suggest that well-crystallized spherical-shaped ∼20 nm anatase TiO₂ nanoparticles synthesized in aqueous medium can induce concentration-dependent biochemical alteration in rat skin during short-term exposure.