DNA damaging potential of photoactivated p25 titanium dioxide nanoparticles.

Titanium dioxide nanoparticles (TiO2 NPs) are found in numerous commercial and personal care products. Thus, it is necessary to understand and characterize their potential environmental health and safety risks. It is well-known that photoactivated TiO2 NPs in aerated aqueous solutions can generate highly reactive hydroxyl radicals ((•)OH), which can damage DNA. Surprisingly, recent in vitro studies utilizing the comet assay have shown that nonphotoactivated TiO2 NPs kept in the dark can also induce DNA damage. In this work, we utilize stable isotope-dilution gas chromatography/tandem mass spectrometry to quantitatively characterize the levels and types of oxidatively generated base lesions in genomic DNA exposed to NIST Standard Reference Material TiO2 NPs (Degussa P25) under precisely controlled illumination conditions. We show that DNA samples incubated in the dark for 24 h with TiO2 NPs (0.5-50 µg/mL) do not lead to the formation of base lesions. However, when the same DNA is exposed to either visible light from 400 to 800 nm (energy dose of ∼14.5 kJ/m(2)) for 24 h or UVA light at 370 nm for 30 min (energy dose of ∼10 kJ/m(2)), there is a significant formation of lesions at the 50 µg/mL dose for the visible light exposure and a significant formation of lesions at the 5 and 50 µg/mL doses for the UVA light exposure. These findings suggest that commercial P25 TiO2 NPs do not have an inherent capacity to oxidatively damage DNA bases in the absence of sufficient photoactivation; however, TiO2 NPs exposed to electromagnetic radiation within the visible portion of the light spectrum can induce the formation of DNA lesions. On the basis of these findings, comet assay processing of cells exposed to TiO2 should be performed in the dark to minimize potential artifacts from laboratory light.

Photofading in cotton fibers dyed using red, yellow, and blue direct dyes during examination with microspectrophotometry (MSP).

Microspectrophotometry (MSP) is a rapid, nondestructive technique for the analysis of color in textile fibers. This technique combines microscopy and ultraviolet (UV)/visible (Vis) spectroscopy, allowing for very small colored samples, like dyed textile fibers, to be analyzed directly and thereby eliminates the need for time consuming and destructive extractions. While MSP is generally accepted to be a nondestructive evaluation method, a loss of color during analysis, or photofading can occur. In this work, cotton fabric dyed with blue, yellow, and red direct dyes at different concentrations. Dye photofading during MSP examination was investigated by measuring the absorbance at a specific position on the fibers from these fabrics, periodically over the course of 30 minutes. Visible color loss and a reduction in absorbance was observed for all three colors, but was most pronounced for the fibers dyed red. A major goal of this study is to increase awareness of the photofading phenomenon when analyzing cotton fibers using MSP.

Biophysical characterization of functionalized titania nanoparticles and their application in dental adhesives.

It is demonstrated that carboxylic acid-functionalized titanium dioxide (TiO2) NPs produce significantly higher levels of reactive oxygen species (ROS) after visible light irradiation (400-800nm, 1600mW/cm2) in comparison to nonfunctionalized TiO2 NPs. The level of ROS produced under these irradiation conditions was not capable of generating oxidatively induced DNA damage in a cell-free system for TiO2 concentrations of 0.5mg/L or 5mg/L. In addition, specific incorporation of the acrylic acid-functionalized TiO2 NPs into dental composites allowed us to utilize the generated ROS to enhance photopolymerization (curing and degree of vinyl conversion (DC)) of resin adhesives and create mechanically superior and biocompatible materials for dental applications. Incorporation of the TiO2 NPs into selected dental composites increased the mean DC values by ≈7%. The modified TiO2 materials and dental composite materials were extensively characterized using thermogravimetric analysis, electron microscopy, Fourier transform infrared spectroscopy, and electron paramagnetic resonance. Notably, dental adhesives incorporated with acrylic acid-functionalized TiO2 NPs produced stronger bonds to human teeth following visible light curing in comparison to traditional dental adhesives not containing NPs with an increase in the shear bond strength of ≈29%. In addition, no leaching of the incorporated NPs was detectable from the dental adhesives after 2500 thermal cycles using inductively coupled plasma-optical emission spectroscopy, indicating that biocompatibility of the adhesives was not compromised after extensive aging. These findings suggest that NP-induced ROS may be useful to produce enhanced nanocomposite materials for selected applications in the medical device field. STATEMENT OF SIGNIFICANCE: Titanium dioxide nanoparticles (TiO2 NPs) have unique photocatalytic, antibacterial and UV-absorbing properties that make them beneficial additives in adhesives and composites. However, there is concern that the reactive oxygen species (ROS) produced by photoactivated TiO2 NPs might pose toxicological risks. We demonstrate that it is possible to incorporate acid-functionalized TiO2 NPs into dental resins which can be applied as dental adhesives to human teeth. The ROS generated by these NPs through visible-light irradiation may be utilized to increase the degree of vinyl conversion of resins, leading to adhesives that have an enhanced shear-bond strength to human teeth. Investigation into the potential genotoxicity of the NPs and their potential for release from dental composites indicated a low risk of genotoxic effects.

Tuning photo-catalytic activities of TiO2 nanoparticles using dimethacrylate resins.

OBJECTIVE: The unique photo-catalytic activities (PCAs) of titanium dioxide nanoparticles (TiO2 NPs) made them attractive in many potential applications in medical devices. The objective of this study is to optimize the benefits of PCAs of TiO2 NPs through varying chemical structures of dimethacrylate resins. METHODS: TiO2 NPs were functionalized to improve the PCAs and bonding to the resins. The PCAs of TiO2 NPs were evaluated using electron paramagnetic resonance (EPR) and UV-vis spectroscopy to determine the amount of the radicals generated and the energy required for their production, respectively. The beneficial effects of the radicals were assessed through: (1) the improvement of degree of vinyl conversion (DC) and (2) modification of resin hydrophilicity. One-way ANOVA with a 95% confidence interval was used to indicate the significant differences between the experimental groups. RESULTS: EPR and UV-vis results clearly showed that the functionalization of TiO2 NPs enhanced PCAs in terms of generating radicals under visible light irradiation. The presence of hydroxyl and carboxylic acid functionalities played an important role in DC enhancement and hydrophilicity modification. The DC could be increased up to 22% by adding only 0.1wt% TiO2 NPs. Viscosity of the resins had minimal or no role in DC improvement through TiO2 NPs. In resins with abundant hydroxyl groups, radicals were more effective in making the resin more hydrophilic. SIGNIFICANCE: Knowledge learned from this study will help formulating nano-composites with optimized use of TiO2 PCAs as co-initiators for photo-polymerization, additives for making super-hydrophilic materials and/or antibacterial agents.

NIST gold nanoparticle reference materials do not induce oxidative DNA damage.

One primary challenge in nanotoxicology studies is the lack of well-characterised nanoparticle reference materials which could be used as positive or negative nanoparticle controls. The National Institute of Standards and Technology (NIST) has developed three gold nanoparticle (AuNP) reference materials (10, 30 and 60 nm). The genotoxicity of these nanoparticles was tested using HepG2 cells and calf-thymus DNA. DNA damage was assessed based on the specific and sensitive measurement of four oxidatively-modified DNA lesions (8-hydroxy-2´-deoxyguanosine, 8-hydroxy-2´-deoxyadenosine, (5´S)-8,5´-cyclo-2´-deoxyadenosine and (5´R)-8,5´-cyclo-2´-deoxyadenosine) using liquid chromatography/tandem mass spectrometry. Significantly elevated, dose-dependent DNA damage was not detected at concentrations up to 0.2 µg/ml, and free radicals were not detected using electron paramagnetic resonance spectroscopy. These data suggest that the NIST AuNPs could potentially serve as suitable negative-control nanoparticle reference materials for in vitro and in vivo genotoxicity studies. NIST AuNPs thus hold substantial promise for improving the reproducibility and reliability of nanoparticle genotoxicity studies.

Comparing methods for detecting and characterizing metal oxide nanoparticles in unmodified commercial sunscreens.

AIMS: To determine if commercial sunscreens contain distinct nanoparticles and to evaluate analytical methods for their ability to detect and characterize nanoparticles in unmodified topical products using commercial sunscreens as a model. METHODS: A total of 20 methods were evaluated for their ability to detect and characterize nanoparticles in unmodified commercial sunscreens. RESULTS: Variable-pressure scanning-electron microscopy, atomic-force microscopy, laser-scanning confocal microscopy and X-ray diffraction were found to be viable and complementary methods for detecting and characterizing nanoparticles in sunscreens. CONCLUSIONS: It was determined that several of the commercial sunscreens contained distinct nanoparticles. No one method was able to completely characterize nanoparticles in the unmodified products but the viable methods provided complementary information regarding the nanoparticles and how they were interacting with the sunscreen matrix.