Agglomerate settling impacts nanotoxicology and nanomedicine as well as the stability of engineered nanofluids. Here, the mobility of nanostructured fractal-like SiO2 agglomerates in water is investigated and their settling rate in infinitely dilute suspensions is calculated by a Brownian dynamics algorithm tracking the agglomerate translational and rotational motion. The corresponding friction matrices are obtained using the HYDRO++ algorithm [J. G. de la Torre, G. del Rio Echenique, and A. Ortega, J. Phys. Chem. B 111, 955 (2007)] from the Kirkwood-Riseman theory accounting for hydrodynamic interactions of primary particles (PPs) through the Rotne-Prager-Yamakawa tensor, properly modified for polydisperse PPs. Agglomerates are generated by an event-driven method and have constant mass fractal dimension but varying PP size distribution, mass, and relative shape anisotropy. The calculated diffusion coefficient from HYDRO++ is used to obtain the agglomerate mobility diameter dm and is compared with that from scaling laws for fractal-like agglomerates. The ratio dm/dg of the mobility diameter to the gyration diameter of the agglomerate decreases with increasing relative shape anisotropy. For constant dm and mean dp, the agglomerate settling rate, us, increases with increasing PP geometric standard deviation σp,g (polydispersity). A linear relationship between us and agglomerate mass to dm ratio, m/dm, is revealed and attributed to the fast Brownian rotation of such small and light nanoparticle agglomerates. An analytical expression for the us of agglomerates consisting of polydisperse PPs is then derived, us=1-ρfρpg3πμmdm (ρf is the density of the fluid, ρp is the density of PPs, μ is the viscosity of the fluid, and g is the acceleration of gravity), valid for agglomerates for which the characteristic rotational time is considerably shorter than their settling time. Our calculations demonstrate that the commonly made assumption of monodisperse PPs underestimates us by a fraction depending on σp,g and agglomerate mass mobility exponent. Simulations are in excellent agreement with deposition rate measurements of fumed SiO2 agglomerates in water.
The delivered nanoparticle dose to cells in vitro may depend on nanoparticle sedimentation rate. Here, the conditions under which optical absorption spectroscopy can be used to quantify the deposited nanoparticle dose in vitro are investigated.Nanoparticle cytotoxicity in both upright and inverted cell culture orientations is studied in the presence and absence of serum.Dissolvable nanoparticles, such as ZnO, exhibit no difference in upright and inverted cultures due to dissolved Zn(2+) ions that dominate cytotoxicity. Insoluble nanoparticles, however, exhibit different sedimentation rates and deposited doses that are linked to the observed cytotoxicity.The combined use of upright-inverted cell orientations and optical absorption spectroscopy can provide a simple experimental approach to interpret in vitro nano-biointeractions.
Abstract Background Amorphous silica nanoparticles (SiO2 NPs) have been regarded as relatively benign nanomaterials, however, this widely held opinion has been questioned in recent years by several reports on in vitro and in vivo toxicity. Surface chemistry, more specifically the surface silanol content, has been identified as an important toxicity modulator for SiO2 NPs. Here, quantitative relationships between the silanol content on SiO 2 NPs, free radical generation and toxicity have been identified, with the purpose of synthesizing safer-by-design fumed silica nanoparticles. Results Consistent and statistically significant trends were seen between the total silanol content, cell membrane damage, and cell viability, but not with intracellular reactive oxygen species (ROS), in the macrophages RAW264.7. SiO 2 NPs with lower total silanol content exhibited larger adverse cellular effects. The SAEC epithelial cell line did not show any sign of toxicity by any of the nanoparticles. Free radical generation and surface reactivity of these nanoparticles were also influenced by the temperature of combustion and total silanol content. Conclusion Surface silanol content plays an important role in cellular toxicity and surface reactivity, although it might not be the sole factor influencing fumed silica NP toxicity. It was demonstrated that synthesis conditions for SiO 2 NPs influence the type and quantity of free radicals, oxidative stress, nanoparticle interaction with the biological milieu they come in contact with, and determine the specific mechanisms of toxicity. We demonstrate here that it is possible to produce much less toxic fumed silicas by modulating the synthesis conditions.
Nanoalloying Ag with Au minimizes nanoparticle surface oxidation and subsequent toxic Ag+ ion release rendering such nanoparticles safer for theranostic applications.
The effect of dynamic shape switching of hydrogel bilayers on the performance of self-folding microrobots is investigated for navigation in body orifices and drug release on demand. Tubular microrobots are fabricated by coupling a thermoresponsive hydrogel nanocomposite with a poly(ethylene glycol)diacrylate (PEGDA) layer, to achieve spontaneous and reversible folding from a planar rectangular structure. Graphene oxide (GO) or silica-coated superparamagnetic iron oxide nanoparticles are dispersed in the thermoresponsive hydrogel matrix to provide near-infrared (NIR) light sensitivity or magnetic actuation, respectively. The NIR light-responsive microstructures are fabricated for triggered drug delivery while magnetic nanocomposite-based microrobots are used to analyze the role of shape in locomotion. Experimental analysis and computational simulations of tubular structures show that drug release and motility can be optimized through controlled shape change. These concepts are finally applied to helical microrobots to show a possible way to achieve autonomous behavior.
Abstract Reliable ammonia quantification assays are essential for monitoring ammonemia in patients with liver diseases. In this study, we describe the development process of a microplate-based assay for accurate, precise, and robust ammonia quantification in biological fluids, following regulatory guidelines on bioanalytical method validation. The assay is based on transmembrane pH-gradient polymersomes that encapsulate a pH-sensitive ratiometric fluorophore, the fluorescence signal of which correlates with the ammonia concentration in the sample. Using four-parameter logistic regression, the assay had a large quantification range (30–800 µM ammonia). As for selectivity, the presence of amino acids or pyruvate (up to clinically relevant concentrations) showed no assay interference. In samples with low bilirubin levels, polymersomes containing the fluorophore pyranine provided accurate ammonia quantification. In samples with high bilirubin concentrations, billirubin’s optical interference was alleviated when replacing pyranine with a close to near-infrared hemicyanine fluorophore. Finally, the assay could correctly retrieve the ammonia concentration in ammonia-spiked human plasma samples, which was confirmed by comparing our measurements with the data obtained using a commercially available point-of-care device for ammonia.
Optically stable nanophosphors coated with a nanothin amorphous SiO2layer allow for dynamic imaging of cell host–pathogen interactions. The SiO2layer facilitates the functionalization of the nanoprobes with antibodies for selective cell targeting.
Abstract Reliable ammonia quantification assays are essential for monitoring ammonemia in patients with liver diseases. In this study, we describe the development process of a microplate-based assay for accurate, precise, and robust ammonia quantification in biological fluids, following regulatory guidelines on bioanalytical method validation. The assay is based on transmembrane pH-gradient polymersomes that encapsulate a pH-sensitive ratiometric fluorophore, the fluorescence signal of which correlates with the ammonia concentration in the sample. Using a four-parameter logistic regression, the assay had a large quantification range (30–800 μM ammonia). As for selectivity, the presence of amino acids or pyruvate (up to clinically relevant concentrations) showed no assay interference. In samples with low bilirubin levels, polymersomes containing the fluorophore pyranine provided accurate ammonia quantification. In samples with high bilirubin concentrations, billirubin’s optical interference was alleviated when replacing pyranine with a close to near-infrared hemicyanine fluorophore. Finally, the assay could correctly retrieve the ammonia concentration in ammonia-spiked human plasma samples, which was confirmed by comparing our measurements with the data obtained using a commercially available point-of-care device for ammonia.
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