Three differently sized, highly dispersed platinum nanoparticle (Pt-NP) preparations were generated by supercritical fluid reactive deposition (SFRD) and deposited on a β-cyclodextrin matrix. The average particle size and size distribution were steered by the precursor reduction conditions, resulting in particle preparations of <20, <100 and >100 nm as characterised by TEM and SEM. As reported previously, these Pt-NPs were found to cause DNA strand breaks in human colon carcinoma cells (HT29) in a concentration- and time-dependent manner and a distinct size dependency. Here, we addressed the question whether Pt-NPs might affect directly DNA integrity in these cells and thus behave analogous to platinum-based chemotherapeutics such as cisplatin. Therefore, DNA-associated Pt as well as the translocation of Pt-NPs through a Caco-2 monolayer was quantified by ICP-MS. STEM imaging demonstrated that Pt-NPs were taken up into HT29 cells in their particulate and aggregated form, but appear not to translocate into the nucleus or interact with mitochondria. The platinum content of the DNA of HT29 cells was found to increase in a time- and concentration-dependent manner with a maximal effect at 1,000 ng/cm(2). ICP-MS analysis of the cell culture medium indicated the formation of soluble Pt species, although to a limited extent. The observations suggest that DNA strand breaks mediated by metallic Pt-NPs are caused by Pt ions forming during the incubation of cells with these nanoparticles.
Supercritical fluid reactive deposition was used for the deposition of highly dispersed platinum nanoparticles with controllable metal content and particle size distribution on beta-cyclodextrin. The average particle size and size distribution were steered by the precursor reduction conditions, resulting in particle preparations <20, <100, and >100 nm as characterized by transmission electron microscopy and scanning electron microscopy (SEM). These particle preparations of different size distributions were used to address the question as to whether metallic platinum particles are able to invade cells of the gastrointestinal tract as exemplified for the human colon carcinoma cell line HT29 and thus affect the cellular redox status and DNA integrity. Combined focused ion beam and SEM demonstrated that platinum nanoparticles were taken up into HT29 cells in their particulate form. The chemical composition of the particles within the cells was confirmed by energy-dispersive X-ray spectroscopy. The potential influence of platinum nanoparticles on cellular redoxsystems was determined in the DCF assay, on the translocation of Nrf-2 and by monitoring the intracellular glutathione (GSH) levels. The impact on DNA integrity was investigated by single cell gel electrophoresis (comet assay) including the formation of sites sensitive to formamidopyrimidine-DNA-glycosylase. Platinum nanoparticles were found to decrease the cellular GSH level and to impair DNA integrity with a maximal effect at 1 ng/cm(2). These effects were correlated with the particle size in an inverse manner and were enhanced with increasing incubation time but appeared not to be based on the formation of reactive oxygen species.
The hysteresis in the CO oxidation
profile over Pt/Al2O3 catalysts has been intensively
studied, but its origin
is still controversial. In this work, the influence of the Pt particle
size and size distribution was systematically investigated. By the
application of conventional and advanced preparation methods, such
as flame spray pyrolysis and supercritical fluid reactive deposition,
a series of catalysts containing homogeneous distributions of Pt particles
were obtained. An optimal Pt particle size of 2–3 nm was identified
for the CO oxidation light-off on Pt/Al2O3 catalysts.
The CO oxidation results show a clear correlation between the Pt nanoparticle
size and the ignition/extinction profile, including the switch of
the hysteresis loop. On the basis of high-angle annular dark-field
scanning transmission electron microscopy characterization combined
with in situ diffuse reflectance infrared Fourier transform spectroscopy
and operando X-ray absorption spectroscopy measurements, the appearance
of inverse hysteresis for catalysts containing very small Pt nanoparticles
(<2 nm) and typical hysteresis for larger Pt nanoparticles could
be related to the different CO adsorption strengthd, to surface/bulk
oxidation of Pt particles, and to the ability of the catalyst to regenerate
the active sites, considering also the exothermicity of the CO oxidation
reaction.
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