15 research outputs found
Cryo-STEM-EDX spectroscopy for the characterisation of nanoparticles in cell culture media
We present a study of barium titanate nanoparticles dispersed in cell culture media. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy was undertaken on samples prepared using both conventional drop casting and also plunge freezing and examination under cryogenic conditions. This showed that drying artefacts occurred during conventional sample preparation, whereby some salt components of the cell culture media accumulated around the barium titanate nanoparticles; these were removed using the cryogenic route. Importantly, the formation of a calcium and phosphorus rich coating around the barium titanate nanoparticles was retained under cryo-conditions, highlighting that significant interactions do occur between nanomaterials and biological media
Nanoparticle corona artefacts derived from specimen preparation of particle suspensions
Progress in the implementation of nanoparticles for therapeutic applications will accelerate with an improved understanding of the interface between nanoparticle surfaces and the media they are dispersed in. We examine this interface by analytical scanning transmission electron microscopy and show that incorrect specimen preparation or analysis can induce an artefactual, nanoscale, calcium phosphate-rich, amorphous coating on nanoparticles dispersed in cell culture media. We report that this ionic coating can be induced on five different types of nanoparticles (Au, BaTiO3, ZnO, TiO2 and Fe2O3) when specimen preparation causes a significant rise in pH above physiological levels. Such a pH change reduces ionic solubility in the suspending media to permit precipitation of calcium phosphate. Finally, we demonstrate that there is no indication of a calcium-phosphorus-rich coating on BaTiO3 nanoparticles suspended in culture media when prepared without alteration of the pH of the suspending media and imaged by cryo-STEM. Therefore we recommend that future reports utilising nanoparticles dispersed in cell culture media monitor and report the pH of suspensions during sample preparation
Spray-Dried Sodium Zirconate: A Rapid Absorption Powder for CO2 Capture with Enhanced Cyclic Stability
Improved powders for capturing CO2 at high temperatures are required for H2 production using sorption-enhanced steam reforming. Here, we examine the relationship between particle structure and carbonation rate for two types of Na2ZrO3 powders. Hollow spray-dried microgranules with a wall thickness of 100â300â
nm corresponding to the dimensions of the primary acetate-derived particles gave about 75â
wtâ% theoretical CO2 conversion after a process-relevant 5â
min exposure to 15â
volâ% CO2. A conventional powder prepared by solid-state reaction carbonated more slowly, achieving only 50â% conversion owing to a greater proportion of the reaction requiring bulk diffusion through the densely agglomerated particles. The hollow granular structure of the spray-dried powder was retained postcarbonation but chemical segregation resulted in islands of an amorphous Na-rich phase (Na2CO3) within a crystalline ZrO2 particle matrix. Despite this phase separation, the reverse reaction to re-form Na2ZrO3 could be achieved by heating each powder to 900â°C in N2 (no dwell time). This resulted in a very stable multicycle performance in 40â
cycle tests using thermogravimetric analysis for both powders. Kinetic analysis of thermogravimetric data showed the carbonation process fits an AvramiâErofeyev 2âD nucleation and nuclei growth model, consistent with microstructural evidence of a surface-driven transformation. Thus, we demonstrate that spray drying is a viable processing route to enhance the carbon capture performance of Na2ZrO3 powder
Elucidating the Structural Chemistry of a Hysteretic Iron(II) SpinâCrossover Compound From its Copper(II) and Zinc(II) Congeners
Annealing [Fe L 2 ][BF 4 ] 2 â2H 2 O ( L = 2,6â bis â[5âmethylâ1 H âpyrazolâ3âyl]pyridine) affords an anhydrous material, which undergoes a spinâtransition at T Âœ = 205 K with a 65 K thermal hysteresis loop. This occurs via a sequence of phase changes, which were monitored by powder diffraction in an earlier study. [Cu L 2 ][BF 4 ] 2 â2H 2 O and [Zn L 2 ][BF 4 ] 2 â2H 2 O are not perfectly isostructural but, unlike the iron compound, they undergo singleâcrystalâtoâsingleâcrystal dehydration upon annealing. All the annealed compounds initially adopt the same tetragonal phase, but undergo a phase change near room temperature upon recooling. The lowâtemperature phase of [Cu L 2 ][BF 4 ] 2 involves ordering of its JahnâTeller distortion, to a monoclinic lattice with three unique cation sites. The zinc compound adopts a different, triclinic lowâtemperature phase with significant twisting of its coordination sphere, which unexpectedly becomes more pronounced as the crystal is cooled. Synchrotron powder diffraction data confirm the structural changes in the anhydrous zinc complex are reproduced in the highâspin iron compound, before the onset of spinâcrossover. This will contribute to the wide hysteresis in the spin transition of the iron complex. EPR spectra of copperâdoped [Fe 0.97 Cu 0.03 L 2 ][BF 4 ] 2 imply its low spin phase contains two distinct cation environments in a 2:1 ratio
Structural Transformations and SpinâCrossover in [FeL2]2+ Salts (L = 4â{tertbutylsulfanyl}â2,6âdi{pyrazolâ1âyl}pyridine) â the Influence of Bulky Ligand Substituents
4â(Tertâbutylsulfanyl)â2,6âdi(pyrazolâ1âyl)pyridine (L) was obtained in low yield from a oneâpot reaction of 2,4,6âtrifluoropyridine with 2âmethylpropaneâ2âthiolate and sodium pyrazolate in a 1:1:2 ratio. The materials [FeL2][BF4]2·solv (1[BF4]2·solv) and [FeL2][ClO4]2·solv (1[ClO4]2·solv; solv = MeNO2, MeCN or Me2CO) exhibit a variety of structures and spinâstate behaviors including thermal spinâcrossover (SCO). Solvent loss on heating 1[BF4]2·xMeNO2 (x â 2.3) occurs in two steps. The intermediate phase exhibits hysteretic SCO around 250 K, involving a âreverseâSCOâ step in its warming cycle at a scan rate of 5 Kminâ1. The reverseâSCO is not observed in a slower 1 Kminâ1 measurement, however, confirming its kinetic nature. The final product [FeL2][BF4]2·0.75MeNO2 was crystallographically characterized, and shows abrupt but incomplete SCO at 172 K which correlates with disorder of an L ligand. The asymmetric unit of 1[BF4]2·yMe2CO (y â 1.6) contains five unique complex molecules, four of which undergo gradual SCO in at least two discrete steps. Lowâspin 1[ClO4 ]2·0.5Me2CO is not isostructural with its BF4â congener, and undergoes singleâcrystalâtoâsingleâcrystal solvent loss with a tripling of the crystallographic unit cell volume, while retaining the P â1 space group. Three other solvate salts undergo gradual thermal SCO. Two of these are isomorphous at room temperature, but transform to different lowâtemperature phases when the materials are fully lowâspin
Hydrothermal Synthesis of Silver Nanoparticles for High Throughput Biosensing Applications
Metallic silver nanoparticles were synthesized using a hydrothermal route for use in high throughput biosensing applications. Particle shape was engineered by varying polyvinyl pyrollidone (PVP) concentration in the precursor mixture, resulting in the emergence of flat triangular shaped nanoparticles with increasing PVP content. The hydrothermal method was found to yield particles with better particle size distribution and longer shelf life relative to polyol synthesis particles
Low-Temperature Preparation of Undoped ZnO Films with High Transparency and Conductivity by Ion Beam Deposition
Systematic investigation of the physicochemical factors that contribute to the toxicity of ZnO nanoparticles.
ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn(2+) or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco's modified Eagle's medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO2, and pH 7.68) and by systematic comparison of cell-NP interaction for three different ZnO NP preparations. For NPs at concentrations up to 5.5 Όg ZnO/mL, dissolution is complete (with the majority of the soluble zinc complexed to dissolved ligands in the medium), taking ca. 1 h for uncoated and ca. 6 h for polymer coated ones. Above 5.5 Όg/mL, the results are consistent with the formation of zinc carbonate, keeping the solubilized zinc fixed to 67 ΌM of which only 0.45 ΌM is as free Zn(2+), i.e., not complexed to dissolved ligands. At these relatively high concentrations, NPs with an aliphatic polyether-coating show slower dissolution (i.e., slower free Zn(2+) release) and reprecipitation kinetics compared to those of uncoated NPs, requiring more than 48 h to reach thermodynamic equilibrium. Cytotoxicity (MTT) and DNA damage (Comet) assay dose-response curves for three epithelial cell lines suggest that dissolution and reprecipitation dominate for uncoated ZnO NPs. Transmission electron microscopy combined with the monitoring of intracellular Zn(2+) concentrations and ZnO-NP interactions with model lipid membranes indicate that an aliphatic polyether coat on ZnO NPs increases cellular uptake, enhancing toxicity by enabling intracellular dissolution and release of Zn(2+). Similarly, we demonstrate that needle-like NP morphologies enhance toxicity by apparently frustrating cellular uptake. To limit toxicity, ZnO NPs with nonacicular morphologies and coatings that only weakly interact with cellular membranes are recommended