Rapid Dissolution of ZnO Nanoparticles Induced by Biological Buffers Significantly Impacts Cytotoxicity.

Zinc oxide nanoparticles (nZnO) are one of the most highly produced nanomaterials and are used in numerous applications including cosmetics and sunscreens despite reports demonstrating their cytotoxicity. Dissolution is viewed as one of the main sources of nanoparticle (NP) toxicity; however, dissolution studies can be time-intensive to perform and complicated by issues such as particle separation from solution. Our work attempts to overcome some of these challenges by utilizing new methods using UV/vis and fluorescence spectroscopy to quantitatively assess nZnO dissolution in various biologically relevant solutions. All biological buffers tested induce rapid dissolution of nZnO. These buffers, including HEPES, MOPS, and PIPES, are commonly used in cell culture media, cellular imaging solutions, and to maintain physiological pH. Additional studies using X-ray diffraction, FT-IR, X-ray photoelectron spectroscopy, ICP-MS, and TEM were performed to understand how the inclusion of these nonessential media components impacts the behavior of nZnO in RPMI media. From these assessments, we demonstrate that HEPES causes increased dissolution kinetics, boosts the conversion of nZnO into zinc phosphate/carbonate, and, interestingly, alters the structural morphology of the complex precipitates formed with nZnO in cell culture conditions. Cell viability experiments demonstrated that the inclusion of these buffers significantly decrease the viability of Jurkat leukemic cells when challenged with nZnO. This work demonstrates that biologically relevant buffering systems dramatically impact the dynamics of nZnO including dissolution kinetics, morphology, complex precipitate formation, and toxicity profiles.

Chronic fine particulate matter exposure induces systemic vascular dysfunction via NADPH oxidase and TLR4 pathways.

RATIONALE: Chronic exposure to ambient air-borne particulate matter of < 2.5 µm (PM2.5) increases cardiovascular risk. The mechanisms by which inhaled ambient particles are sensed and how these effects are systemically transduced remain elusive. OBJECTIVE: To investigate the molecular mechanisms by which PM2.5 mediates inflammatory responses in a mouse model of chronic exposure. METHODS AND RESULTS: Here, we show that chronic exposure to ambient PM2.5 promotes Ly6C(high) inflammatory monocyte egress from bone-marrow and mediates their entry into tissue niches where they generate reactive oxygen species via NADPH oxidase. Toll-like receptor (TLR)4 and Nox2 (gp91(phox)) deficiency prevented monocyte NADPH oxidase activation in response to PM2.5 and was associated with restoration of systemic vascular dysfunction. TLR4 activation appeared to be a prerequisite for NAPDH oxidase activation as evidenced by reduced p47(phox) phosphorylation in TLR4 deficient animals. PM2.5 exposure markedly increased oxidized phospholipid derivatives of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (oxPAPC) in bronchioalveolar lavage fluid. Correspondingly, exposure of bone marrow-derived macrophages to oxPAPC but not PAPC recapitulated effects of chronic PM2.5 exposure, whereas TLR4 deficiency attenuated this response. CONCLUSIONS: Taken together, our findings suggest that PM2.5 triggers an increase in oxidized phospholipids in lungs that then mediates a systemic cellular inflammatory response through TLR4/NADPH oxidase-dependent mechanisms.

Site-specific stamping of graphene micro-patterns over large areas using flexible stamps.

Site-specific stamping has the potential of becoming a low-cost, high-throughput method for depositing specific-shaped graphene micro-patterns over large areas on a wide variety of substrates. The use of an approach involving flexible stamps presented here represents an important advance towards reaching that potential. This approach entails lithographic creation (dry etching) of high-quality micro-pillar arrays of highly oriented pyrolytic graphite (HOPG) over large areas. This is followed by embedding the micro-pillar arrays in polydimethylsiloxane (PDMS), and detaching them from the HOPG base. This results in flexible stamps containing embedded HOPG micro-pillar arrays with freshly cleaved stamping surfaces. The flexible HOPG/PDMS stamps are then brought into contact with substrate surfaces to site-specifically stamp graphene or few-layer graphene (FLG) arrays over large areas. The freshly cleaved nature of the micro-pillar surfaces in the flexible stamps, the low elastic modulus of the flexible stamps and the elimination of sidewall deposits on the micro-pillars allow for more uniform stamping, relative to the use of stiff HOPG stamps from earlier studies. This approach has the potential to expand the substrate choice for graphene or FLG stamping to include curved and/or flexible substrates that could have an impact on the burgeoning field of flexible/stretchable electronics.

Defect Engineering of ZnO Nanoparticles for Bioimaging Applications.

Many promising attributes of ZnO nanoparticles (nZnO) have led to their utilization in numerous electronic devices and biomedical technologies. nZnO fabrication methods can create a variety of intrinsic defects that modulate the properties of nZnO, which can be exploited for various purposes. Here we developed a new synthesis procedure that controls certain defects in pure nZnO that are theorized to contribute to the n-type conductivity of the material. Interestingly, this procedure created defects that reduced the nanoparticle band gap to ∼3.1 eV and generated strong emissions in the violet to blue region while minimizing the defects responsible for the more commonly observed broad green emissions. Several characterization techniques including thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, Raman, photoluminescence, and inductively coupled plasma mass spectrometry were employed to verify the sample purity, assess how modifications in the synthesis procedure affect the various defects states, and understand how these alterations impact the physical properties. Since the band gap significantly decreased and a relatively narrow visible emissions band was created by these defects, we investigated utilizing these new nZnO for bioimaging applications using traditional fluorescent microscopy techniques. Although most nZnO generally require UV excitation sources to produce emissions, we demonstrate that reducing the band gap allows for a 405 nm laser to sufficiently excite the nanoparticles to detect their emissions during live-cell imaging experiments using a confocal microscope. This work lays the foundation for the use of these new nZnO in various bioimaging applications and enables researchers to investigate the interactions of pure nZnO with cells through fluorescence-based imaging techniques.