Role of toll-like receptors 3, 4 and 7 in cellular uptake and response to titanium dioxide nanoparticles

Innate immune response is believed to be among the earliest provisional cellular responses, and mediates the interactions between microbes and cells. Toll-like receptors (TLRs) are critical to these interactions. We hypothesize that TLRs also play an important role in interactions between nanoparticles (NPs) and cells, although little information has been reported concerning such an interaction. In this study, we investigated the role of TLR3, TLR4 and TLR7 in cellular uptake of titanium dioxide NP (TiO₂ NP) agglomerates and the resulting inflammatory responses to these NPs. Our data indicate that TLR4 is involved in the uptake of TiO₂ NPs and promotes the associated inflammatory responses. The data also suggest that TLR3, which has a subcellular location distinct from that of TLR4, inhibits the denaturation of cellular protein caused by TiO₂ NPs. In contrast, the unique cellular localization of TLR7 has middle-ground functional roles in cellular response after TiO₂ NP exposure. These findings are important for understanding the molecular interaction mechanisms between NPs and cells.     

Structural features of bionanocomposite derived from novel designed poly(ester-imide) based on natural amino acids with hydroxyl segments tailored for better dispersion of TiO 2 nanofiller

Deliberately inorganic nanoparticles (NP)s in polymer matrices significantly affect their characteristics and therefore their applications, but key factor to achieve the expected efficiency is well dispersion of the NPs in polymer matrix. The work presented here deals with the polymerization of amino acid-based monomer to synthesize optically active poly(ester-imide) (PEI) with hydroxyl terminated groups, using tosyl chloride/pyridine/N,N-dimethylformamide system as a condensing agent. The synthesized polymer was used for the preparation of bionanocomposite (BNC) containing modified titanium dioxide (TiO₂) NPs using ultrasonic irradiation. With the aim of γ-amidopropyl-triethoxylsilicane as a coupling agent, the surface of nanoscale TiO₂ was modified to decrease aggregation of the NPs in polymer matrix. The obtained PEI/TiO₂ BNCs were characterized with fourier transfer infrared (FT–IR), thermogravimetric analysis, field emission scanning electron microscopy (FE–SEM), X-ray diffraction and transmission electron microscopy (TEM) techniques. Morphology study of resulting PEI/TiO₂ BNCs by FE–SEM and TEM analyses demonstrated that the hydroxyl-terminated polymer chains reduced aggregation of the NPs and thus lead to better dispersion of the NPs in the polymer matrix.     

Absorption spectra and photocurrent densities of Ag nanoparticle/TiO2 composite thin films with various amounts of Ag

To study the absorption spectra and photocurrent densities of metallic Ag nanoparticle/titania (Ag NP)/TiO₂ composite thin films, COMP-Agn, with various amounts of Ag (10 mol% ≤n ≤80 mol%) were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. Apart from a surface plasmon resonance (SPR) peak around 400 nm, additional wide-range absorption spread in the wide vis-region at wavelengths greater than 400 nm was observed in the composite thin films. The wide-range absorption is due to a tip–tip plasmon mode, intraparticle plasmonic coupling of tip and cavity resonances (LSPR). The absorption spectral patterns could be categorized into three types, depending on the Ag NP content. The photocurrent density of the TiO₂ thin film and COMP-Agn was measured under natural potential by a conventional three-electrode method using a Ag plate as a counter electrode. The photocurrent densities of COMP-Agn were comparable to those of the three patterns categorized according to their absorption spectra. The cathodic photocurrent densities generated by COMP-Agn with Ag content greater than 45 mol% could be observed under both UV- and visible (vis-) light irradiation. The enhanced photocurrent density was observed till the Ag content was increased up to 70 mol%. Under dark conditions, cathodic current densities were 1/5–1/20 of those under vis-light irradiation probable due to chemical redox reactions that may occur to the system. On the basis of photoexcited electron transfer from Ag NPs to the TiO₂ conduction band and the electrical conductivity of COMP-Agn, the excellent response to vis-light and major factors affecting the photoresponse and photocurrent polarity were clarified by LSPR.     

Toxicological Aspects of Long‐Term Treatment of Keratinocytes with ZnO and TiO2 Nanoparticles

Sunscreens containing ZnO and TiO₂ nanoparticles (NPs) are increasingly applied to skin over long time periods to reduce the risk of skin cancer. However, long‐term toxicological studies of NPs are very sparse. The in vitro toxicity of ZnO and TiO₂ NPs on keratinocytes over short‐ and long‐term applications is reported. The effects studied are intracellular formation of radicals, alterations in cell morphology, mitochondrial activity, and cell‐cycle distribution. Cellular response depends on the type of NP, concentration, and exposure time. ZnO NPs have more pronounced adverse effects on keratinocytes than TiO₂. TiO₂ has no effect on cell viability up to 100 μg mL^?1, whereas ZnO reduces viability above 15 μg mL^?1 after short‐term exposure. Prolonged exposure to ZnO NPs at 10 μg mL^?1 results in decreased mitochondrial activity, loss of normal cell morphology, and disturbances in cell‐cycle distribution. From this point of view TiO₂ has no harmful effect. More nanotubular intercellular structures are observed in keratinocytes exposed to either type of NP than in untreated cells. This observation may indicate cellular transformation from normal to tumor cells due to NP treatment. Transmission electron microscopy images show NPs in vesicles within the cell cytoplasm, particularly in early and late endosomes and amphisomes. Contrary to insoluble TiO₂, partially soluble ZnO stimulates generation of reactive oxygen species to swamp the cell redox defense system thus initiating the death processes, seen also in cell‐cycle distribution and fluorescence imaging. Long‐term exposure to NPs has adverse effects on human keratinocytes in vitro, which indicates a potential health risk.     

Synthesis and characterization of photocatalytic polyurethane and poly(methyl methacrylate) microcapsules for the controlled release of methotrexate

Abstract

The aim of this work is to prepare ultraviolet (UV) triggered controlled release of compounds from microcapsule systems (MCs). Polyurethane (PU) and poly(methyl methacrylate) (PMMA) microcapsules were studied with/without chemical functionalization using photocatalytic TiO₂ nanoparticles (NPs) on their surface. Once TiO₂ nanoparticles are illuminated with UV light (λ?=?370?nm), they initiate the rupture of the polymeric bonds of the microcapsule and subsequently initiate the encapsulated compound release, methotrexate (MTX) or rhodamine (Rh), in the present work. The size, polydispersity, charge, and yield of all MCs were measured, being the methotrexate drug release for all systems determined and compared with and without functionalization with TiO₂ NPs, under dark, visible light and UV illumination in vitro. Finally, the Rh release was characterized using fluorescence microscopy. The TiO₂ NPs size is around 10?nm, as determined by X-ray diffraction experiments. The PU MCs average size is around 60?µm, its electric charge +3.11?mV and yield around 85%. As for the PMMA MCs, the average size is around 280?µm, its electric charge ?7.2?mV and yield around 25% and 30% for both MTX and Rh, respectively. In general, adding TiO₂ NPs or the encapsulated products to the MCs does not affect the size but functionalization with TiO₂ NPs lowers the electric charge. Microcapsules functionalized with TiO₂ nanoparticles and irradiated with UV light presented the highest release of MTX and Rh. All other samples showed lower drug release levels when studied under the same conditions.     

Biosynthesis of titanium dioxide nanoparticles using a probiotic from coal fly ash effluent

The synthesis of titanium dioxide nanoparticle (TiO₂ NP) has gained importance in the recent years owing to its wide range of potential biological applications. The present study demonstrates the synthesis of TiO₂ NPs by a metal resistant bacterium isolated from the coal fly ash effluent. This bacterial strain was identified on the basis of morphology and 16s rDNA gene sequence [KC545833]. The physico-chemical characterization of the synthesized nanoparticles is completely elucidated by energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and transmission and scanning electron microscopy (TEM, SEM). The crystalline nature of the nanoparticles was confirmed by X-RD pattern. Further, cell viability and haemolytic assays confirmed the biocompatible and non toxic nature of the NPs. The TiO₂ NPs was found to enhance the collagen stabilization and thereby enabling the preparation of collagen based biological wound dressing. The paper essentially provides scope for an easy bioprocess for the synthesis of TiO₂ NPs from the metal oxide enriched effluent sample for future biological applications.     

Effect of particle size on in vitro cytotoxicity of titania and alumina nanoparticles

Aluminium oxide (Al₂O₃) and titanium dioxide (TiO₂) nanoparticles (NPs) have been widely used in nanotechnology-based products. Recently, researchers and the public have raised concerns about the adverse effects of these NPs in biological systems, particularly in humans. The aim of this study was to investigate the possible adverse effects of these two common metal oxide NPs on human lung epithelium cells (A549) and to investigate NP size-dependent effects on these cells, considering both the primary and hydrodynamic particle size. NPs were found to inhibit cell viability and proliferation at the highest concentration level (10?mg/mL) included in this study, as measured by a clonogenic assay. Moreover, cell viability, proliferation and metabolism were impaired to a greater extent by the smaller NPs (5?nm TiO₂ and 10?nm Al₂O₃) relative to the larger particles (200?nm TiO₂ and 50?nm Al₂O₃) included in this study, as measured by cell proliferation and metabolism. Notably, the observed cytotoxic effects correlated to the primary size, rather than the hydrodynamic size. Similarly, NP cytotoxicity was found to be correlated with the NP surface area. These findings highlight the importance of including primary size and surface area information in NP characterisation in cytotoxicity studies.     

Resistive Switching of Individual,Chemically Synthesized TiO2 Nanoparticles

Resistively switching devices are considered promising for next‐generation nonvolatile random‐access memories. Today, such memories are fabricated by means of “top–down approaches” applying thin films sandwiched between nanoscaled electrodes. In contrast, this work presents a “bottom–up approach” disclosing for the first time the resistive switching (RS) of individual TiO₂ nanoparticles (NPs). The NPs, which have sizes of 80 and 350 nm, respectively, are obtained by wet chemical synthesis and thermally treated under oxidizing or vacuum conditions for crystallization, respectively. These NPs are deposited on a Pt/Ir bottom electrode and individual NPs are electrically characterized by means of a nanomanipulator system in situ, in a scanning electron microscope. While amorphous NPs and calcined NPs reveal no switching hysteresis, a very interesting behavior is found for the vacuum‐annealed, crystalline TiO_2–x NPs. These NPs reveal forming‐free RS behavior, dominantly complementary switching (CS) and, to a small degree, bipolar switching (BS) characteristics. In contrast, similarly vacuum‐annealed TiO₂ thin films grown by atomic layer deposition show standard BS behavior under the same conditions. The interesting CS behavior of the TiO_2–x NPs is attributed to the formation of a core–shell‐like structure by re‐oxidation of the reduced NPs as a unique feature.     

Reduced graphene oxide and CdTe nanoparticles co-decorated TiO2 nanotube array as a visible light photocatalyst

TiO₂ nanotube array (TiO₂ NT) was co-decorated by reduced graphene oxide (RGO) and CdTe nanoparticles (NPs) through a simple one-step electrodeposition process. RGO film was formed on the top surface of TiO₂ NT and CdTe NPs homogeneously dispersed within the RGO sheets and on the inner/outer walls of TiO₂ NT. Resulting from the synergetic effect of RGO and CdTe, the photocatalytic activity of the ternary RGO/CdTe–TiO₂ NT photocatalyst far exceeded those of bare TiO₂ NT, RGO-TiO₂ NT, and CdTe–TiO₂ NT photocatalysts in the degradation of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under simulated solar light or visible light irradiation. After 180-min UV–Vis (or visible light) irradiation, almost 100 % (or 96 %) 2,4-D removal efficiency was achieved on RGO/CdTe–TiO₂ NT, much higher than 42 % (or 2 %) on bare TiO₂ NT, 58 % (or 10 %) on RGO–TiO₂ NT, and 52 % (or 41 %) on CdTe–TiO₂ NT. This study will inspire better design of advanced photocatalysts with high visible-light photocatalytic activity.     

Controllable synthesis and photocatalytic activities of water-soluble TiO2 nanoparticles

Water-soluble anatase, mixed-phase (anatase and rutile) and rutile TiO₂ nanoparticles (NPs) or nanorods were synthesized under mild solution conditions using polyethylene glycol 400 (PEG 400) as a stabilizer and HCl as a phase controlling reagent. The photocatalytic properties of these NPs with different crystal phases were evaluated by photocatalytic degradation experiments of methyl orange (MO). As-prepared pure anatase TiO₂ NPs show a higher photocatalytic activity than other samples and commercial P25, which may be related to the high crystallinity, the pure anatase phase, small size and the enhanced absorbability associated with the existence of PEG 400 on the NP surface.     

CdSe quantum dot-sensitized Au/TiO2 hybrid mesoporous films and their enhanced photoelectrochemical performance

Novel CdSe quantum dot (QD)-sensitized Au/TiO₂ hybrid mesoporous films have been designed, fabricated, and evaluated for photoelectrochemical (PEC) applications. The Au/TiO₂ hybrid structures were made by assembly of Au and TiO₂ nanoparticles (NPs). A chemical bath deposition method was applied to deposit CdSe QDs on TiO₂ NP films with and without Au NPs embedded. We observed significant enhancements in photocurrent for the film with Au NPs, in the entire spectral region we studied (350–600 nm). Incident-photon-to-current efficiency (IPCE) data revealed an average enhancement of 50%, and the enhancement was more significant at short wavelength. This substantially improved PEC performance is tentatively attributed to the increased light absorption of CdSe QDs due to light scattering by Au NPs. Interestingly, without QD sensitization, the Au NPs quenched the photocurrent of TiO₂ films, due to the dominance of electron trapping over light scattering by Au NPs. The results suggest that metal NPs are potentially useful for improving the photoresponse in PEC cells and possibly in other devices such as solar cells based on QD-sensitized metal oxide nanostructured films. This work demonstrates that metal NPs can serve as light scattering centers, besides functioning as photo-sensitizers and electron traps. The function of metal NPs in a particular nanocomposite film is strongly dependent on their structure and morphology.      

Removal of nitrophenols from water using cellulose derived nitrogen doped graphitic carbon material containing titanium dioxide

Nitrophenols (NPs) and their derivatives are highly toxic, mutagenic and bio-refractory pollutants commonly present in natural water resources and industrial wastewater. To remove NPs from water, N-doped graphitic carbon (NGC) and NGC adsorbent containing titanium dioxide (NGC–TiO₂) were synthesized by pyrolysis of microcrystalline cellulose and dopamine mixture, and the mixture along with TiO₂ at 500°C, respectively. NCG-TiO₂ was thoroughly characterized using various analytical techniques. NP adsorption on the NGC–TiO₂ adsorbent surface was studied by varying the pH, initial concentration of NP, and adsorbent dose. The results showed that the most efficient adsorption was achieved at pH 3. After 4?h sonication at pH 3, 80% 4-NP adsorption was achieved using NGC–TiO₂ compared to 74% with NGC adsorbent. The percentage removal of 4-NP was higher than 3-NP which was also higher than 2,4-DNP using NGC–TiO₂. 4-NP adsorption best fitted to the Langmuir isotherm plot with R² value of 0.9981 and adsorption capacity of 52.91?mg?g^?1. The adsorption process of NP was found to follow a pseudo-second-order kinetic model. The rate constant value for the adsorption of 10^?4?M 4-NP at pH 3 using 10?mg of NGC–TiO₂ adsorbent was found to be 3.76?×?10^?5?g.mg^?1.min^?1     

Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO₂ (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO₂ in anatase structure in both pure and Co doped TiO₂ NPs. The most intense Raman active E_g peak of TiO₂ NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.     

Quantitative Proteomics Study Reveals Changes in the Molecular Landscape of Human Embryonic Stem Cells with Impaired Stem Cell Differentiation upon Exposure to Titanium Dioxide Nanoparticles

The increasing number of nanoparticles (NPs) being used in various industries has led to growing concerns of potential hazards that NP exposure can incur on human health. However, its global effects on humans and the underlying mechanisms are not systemically studied. Human embryonic stem cells (hESCs), with the ability to differentiate to any cell types, provide a unique system to assess cellular, developmental, and functional toxicity in vitro within a single system highly relevant to human physiology. Here, the quantitative proteomics approach is adopted to evaluate the molecular consequences of titanium dioxide NPs (TiO₂ NPs) exposure in hESCs. The study identifies ≈328 unique proteins significantly affected by TiO₂ NPs exposure. Proteomics analysis highlights that TiO₂ NPs can induce DNA damage, elevated oxidative stress, apoptotic responses, and cellular differentiation. Furthermore, in vivo analysis demonstrates remarkable reduction in the ability of hESCs in teratoma formation after TiO₂ NPs exposure, suggesting impaired pluripotency. Subsequently, it is found that TiO₂ NPs can disrupt hESC mesoderm differentiation into cardiomyocytes. The study unveils comprehensive changes in the molecular landscape of hESCs by TiO₂ NPs and identifies the impact which TiO₂ NPs can have on the pluripotency and differentiation properties of human stem cells.     

Improvement of cement-based mortars by application of photocatalytic active Ti–Zn–Al nanocomposites

Photocatalytic active TiO₂ has been extensively applied in construction material science due to its ability to remove pollutants from material surfaces. New inorganic–inorganic nanocomposite photocatalyst based on layered double hydroxides (LDHs) associated to TiO₂ were introduced in order to increase the compatibility of photocatalyst with cement-based mortars. Different materials were prepared and characterized: cement paste with Ti–Zn–Al powder, mortar with cement paste finishing layer containing Ti–Zn–Al LDH and mortar with Ti–Zn–Al coatings. Degradation of methylene blue under UV light was selected as photocatalytic test reaction. The correlation between surface properties and photocatalytic activity was analyzed. The synergetic effect between TiO₂ and Zn–Al-LDH contributes to pronounced photocatalytic performances, improving at the same time mortar performances as an important indicator of the compatibility of photocatalyst with mortar. The photocatalyst introduction procedure influences the active sites surface concentration, giving preference to surface coating method. However, introduction of photocatalyst into the bulk, having lower photocatalytic activity, results in an overall more stable system for prolonged application.     

Growth of ZnO nanorods on TiO2 nanoparticles films and their application to the electrode of dye-sensitized solar cells

A ZnO nanorods (NRs)/TiO₂ nanoparticles (NPs) film has been prepared by electrochemical deposition of ZnO NRs growth on P25 TiO₂ NPs film surfaces. It was found that ZnO NRs/TiO₂ NPs could significantly improve the efficiency of dye-sensitized solar cells owing to its relatively enhanced light-scattering capability and efficient charge transport efficiency. The overall energy-conversion efficiency (η) of 3.48 % was achieved by the formation of ZnO NRs/TiO₂ NPs film, which is 33 % higher than that formed by TiO₂ NPs alone (η = 2.62 %). The charge recombination behavior of cells was investigated by electrochemical impedance spectra, and the results showed that ZnO NRs/TiO₂ NPs film has the longer electron lifetime than TiO₂ NPs alone, which could facilitate the reduction of recombination processes and thus would promote the photocatalysis and solar cell performance.     

ZnO nanowire/TiO2 nanoparticle photoanodes prepared by the ultrasonic irradiation assisted dip-coating method

Hybrid ZnO/TiO₂ photoanodes for dye-sensitized solar cells were prepared by combining ZnO nanowire (NW) arrays and TiO₂ nanoparticles (NPs) with the assistance of the ultrasonic irradiation assisted dip-coating method. Results show that the ultrasonic irradiation was an efficient way to promote the gap filling of TiO₂ NPs in the interstices of ZnO NWs. Hybrid ZnO NW/TiO₂ NP electrodes prepared with ultrasonic treatment exhibited better gap filling efficiency and higher visible absorptance. The overall conversion efficiency of the hybrid electrode was 0.79%, representing 35% improvement compared with that of the traditional one (0.58%). The enlarged surface area and improved attachments of TiO₂ NPs onto the walls of ZnO NWs induced by the application of ultrasonic irradiation may be the underlying reason. Electrochemical impedance spectroscopy measurements indicated that hybrid electrodes combined the advantages of improved electron transport along the ZnO NWs and increased surface area provided by infiltrated TiO₂ NPs, both of which are responsible for the improved cell efficiency.     

Improvements of transparent electrode materials for GaN metal–semiconductor–metal photodetectors

Metal–semiconductor–metal (MSM) photodetectors based on GaN grown on (0 0 0 1) sapphire were fabricated and characterized. The responsivity of the Pt/GaN MSM device is low due to the blocking of incoming light by Pt electrodes. Although this problem can be partly solved by the transparent indium–tin oxide (ITO) contact, the range of operation voltage for ITO/GaN MSM devices is limited by the internal gain. Transparent multilayered electrode is proposed in this work by incorporating various intermediate layers (Ti, TiO₂, and Ti/TiO₂). The dark current of the ITO/TiO₂/GaN contact is two orders of magnitude lower than that of the ITO/Ti/GaN contact. The thin TiO₂ barrier also contributes the lower responsivity of the ITO/TiO₂/GaN structure. By introducing a thin Ti/TiO₂ interlayer at the ITO–GaN interface, a significant decrease in the dark current and an increase in responsivity can be achieved simultaneously. The photo-to-dark current contrast can reach 6×l0⁵, and the responsivity shows no discernible internal gain under a bias between 2.5 and 7.5 V.     

Hybrid photoelectrode by using vertically aligned rutile TiO2 nanowires inlaid with anatase TiO2 nanoparticles for dye-sensitized solar cells

We report a hybrid photoelectrode fabricated by using single crystalline rutile TiO₂ nanowires (NWs) inlaid with anatase TiO₂ nanoparticles (NPs) for efficient dye-sensitized solar cells. For this purpose, ∼4-μm-thick vertically aligned NWs were synthesized on the FTO glass substrate through a solvothermal treatment. Then, as-prepared NW film was treated with the NP colloidal dispersion to construct the NW–NP film. In particular, the NWs offer a fast pathway for electron transport as well as light scattering effect. On the other hand, the inlaid NPs give an extra amount of space for the dye-uptake. Accordingly, the present NW–NP electrode exhibited 6.2% of the conversion efficiency, which corresponds to ∼48% improvement over the efficiency of the NP-DSC. We attribute this notable result to the synergetic effects of the enhanced light confinement, charge collection, and dye-loading.     

Dye-sensitized solar cells using TiO<Subscript>2</Subscript> nanoparticles transformed from nanotube arrays

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ mesoporous layers obtained by very simple method—transformation of TiO₂ nanotube (NT) films grown by electrochemical oxidation to nanoparticle (NP) films. This transformation is based on thermal annealing of TiO₂ NT arrays formed by anodization of titanium foil in fluorine ambient. Performance of DSSCs fabricated with different size NPs was studied in the range from 35 to 350 nm. Highest nominal efficiency (9.05%) was achieved for DSSC with NP size 65 nm while the lowest nominal efficiency (1.48%) was observed for DSSCs with NP size 350 nm. The dependence of the solar cell parameters with NP size is discussed.