Shoeleh Assemi - Academia.edu (original) (raw)

Papers by Shoeleh Assemi

$Research paper thumbnail of Characterization of water-soluble fullerene C60 nanoparticles using asymmetrical flow field-flow fractionation and atomic force microscopy$

Clays and Clay Minerals, 2015

$Research paper thumbnail of Investigation of stability of nanoparticles using asymmetrical flow field-flow fractionation and atomic force microscopy$

$Research paper thumbnail of Characterization of water-soluble C60 (OH) 24 fullerol nanoparticles using asymmetrical flow field-flow fractionation and atomic force microscopy$

Methods in Molecular Biology, 2012

Engineered nanomaterials (ENMs) have become increasingly prevalent in the past two decades in aca... more Engineered nanomaterials (ENMs) have become increasingly prevalent in the past two decades in academic, medical, commercial, and industrial settings. The unique properties imbued with nanoparticles, as the physiochemical properties change from the bulk material to the surface atoms, present unique and often challenging characteristics that larger macromolecules do not possess. While nanoparticle characteristics are indeed exciting for unique chemistries, surface properties, and diverse applications, reports of toxicity and environmental impacts have tempered this enthusiasm and given cause for an exponential increase for concomitant nanotoxicology assessment. Currently, nanotoxicology is a steadily growing with new literature and studies being published more frequently than ever before; however, the literature reveals clear, inconsistent trends in nanotoxicological assessment. At the heart of this issue are several key problems including the lack of validated testing protocols and models, further compounded by inadequate physicochemical characterization of the nanomaterials in question and the seminal feedback loop of chemistry to biology back to chemistry. Zebrafish (Danio rerio) are emerging as a strong nanotoxicity model of choice for ease of use, optical transparency, cost, and high degree of genomic homology to humans. This review attempts to amass all contemporary nanotoxicology studies done with the zebrafish and present as much relevant information on physicochemical characteristics as possible. While this report is primarily a physicochemical summary of nanotoxicity studies, we wish to strongly emphasize that for the proper evolution of nanotoxicology, there must be a strong marriage between the physical and biological sciences. More often than not, nanotoxicology studies are reported by groups dominated by one discipline or the other. Regardless of the starting point, nanotoxicology must be seen as an iterative process between chemistry and biology. It is our sincere hope that the future will introduce a paradigm shift in the approach to nanotoxicology with multidisciplinary groups for data analysis to produce predictive and correlative models for the end goal of rapid preclinical development of new therapeutics into the clinic or insertion into environmental protection.

Langmuir, 2010

The effects of solution pH and 1:1 electrolyte concentration on the aggregation behavior of fulle... more The effects of solution pH and 1:1 electrolyte concentration on the aggregation behavior of fullerol C 60 (OH) 24 nanoparticles were investigated using flow field-flow fractionation (FlFFF). Particle separations were confirmed by examining FFF fractions using atomic force microscopy (AFM). Results showed that fullerol C 60 (OH) 24 nanoparticles remain stable at low salt concentration (0.001 M NaCl) and basic pH (pH 10). Changing the pH did not affect the size significantly, but increasing the salt concentration promoted some aggregation. Fullerol C 60 (OH) 24 nanoparticles did not form large clusters and reached a maximum size of at most several nanometers. Particle interaction analysis using the colloid interaction theory as described by the energetics of electrostatic repulsion and van der Waals attraction explained the differences in the colloidal stability of the fullerol C 60 (OH) 24 nanoparticles under different solution conditions.

ACS Nano, 2012

Poly(amidoamine) (PAMAM) dendrimers are increasingly studied as model nanoparticles for a variety... more Poly(amidoamine) (PAMAM) dendrimers are increasingly studied as model nanoparticles for a variety of biomedical applications, notably in systemic administrations. However, with respect to blood-contacting applications, amine-terminated dendrimers have recently been shown to activate platelets and cause a fatal, disseminated intravascular coagulation (DIC)-like condition in mice and rats. We here demonstrate that, upon addition to blood, cationic G7 PAMAM dendrimers induce fibrinogen aggregation, which may contribute to the in vivo DIC-like phenomenon. We demonstrate that amine-terminated dendrimers act directly on fibrinogen in a thrombin-independent manner to generate dense, high-molecular-weight fibrinogen aggregates with minimal fibrin fibril formation. In addition, we hypothesize this clot-like behavior is likely mediated by electrostatic interactions between the densely charged cationic dendrimer surface and negatively charged fibrinogen domains. Interestingly, cationic dendrimers also induced aggregation of albumin, suggesting that many negatively charged blood proteins may be affected by cationic dendrimers. To investigate this further, zebrafish embryos were employed to more specifically determine the speed of this phenomenon and the pathway- and dose-dependency of the resulting vascular occlusion phenotype. These novel findings show that G7 PAMAM dendrimers significantly and adversely impact many blood components to produce rapid coagulation and strongly suggest that these effects are independent of classic coagulation mechanisms. These results also strongly suggest the need to fully characterize amine-terminated PAMAM dendrimers in regard to their adverse effects on both coagulation and platelets, which may contribute to blood toxicity.

Journal of Radioanalytical and Nuclear Chemistry, 1994

Batch method was used to investigate the sorption behavior of radioiodine on organic rich soil, a... more Batch method was used to investigate the sorption behavior of radioiodine on organic rich soil, alumina, chlorite-illite clay mixture and bentonite.131I was used as tracer. The grain sizes of the samples used were all below 38 μm. A rather slow kinetics was observed for the adsorption of radioiodine on organic rich soil. The distribution ratio increased with increasing solution/solid (V/m) ratio, and the contact time. The pH of the synthetic groundwater did not change the distribution ratio appreciably. The soil biomass however, showed a striking effect on the adsorption of radioiodine. Among the clay minerals, the highest distribution ratio value was found for chlorite-illite clay mixture. All the values were however well below those of the organic rich soil. The sorption data were fitted to Freundlich and Dubinin-Radushkevich types isotherms. Means energies of adsorption, as well as the affinity ratios of the sorption sites to iodine and chlorine were calculated.

Advances in Water Resources, 2007

This paper examines the non-perturbed deposition and re-entrainment dynamics of biological and no... more This paper examines the non-perturbed deposition and re-entrainment dynamics of biological and non-biological colloids in porous media in the presence of an energy barrier to deposition at the grain surface. Deposition and re-entrainment rate coefficients were determined from numerical simulation of breakthrough-elution behavior and the profiles of retained colloids. We present composite trends from original and previously published data for biological and non-biological colloids which demonstrate that hydrodynamic drag mitigates deposition and drives re-entrainment of both biological and non-biological colloids in the presence of an energy barrier under nonperturbed conditions. Original data is presented for two sizes of colloids (1.1 and 5.7 lm microspheres) under a variety of ionic strength and fluid velocity conditions to examine the torque balance governing re-entrainment of colloids attached to the grain surfaces. The analysis indicates that in the presence of an energy barrier to deposition, hydrodynamic drag may influence deposition and re-entrainment of colloids associated directly with the grain surface via primary energy minima. However, the hydrodynamic field would also be expected to influence deposition and re-entrainment of colloids associated with the surface via secondary energy minima. Hence, the observed influences of fluid velocity are consistent with colloid association via either mechanism. These results call for the development of colloid transport theories that explicitly account for the influence of the hydrodynamic field at the grain surface.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2006

Depths of colloid-surface interaction energy minima have been sometimes utilized for estimation o... more Depths of colloid-surface interaction energy minima have been sometimes utilized for estimation of the force holding a colloid to the surface upon contact. Since this approach assumes that non-contact forces prevail following attachment, a comparison of this approach to direct measurement via atomic force microscopy is warranted. Interaction and adhesion forces between 1.0-m diameter carboxylate-modified polystyrene latex microspheres and a glass surface were measured directly with an atomic force microscope using the colloidal probe technique. Measurements were conducted as a function of ionic strength in NaCl with and without added MOPS (3-(N-morpholino)-propanesulfonic acid) buffer, at pH 6.8-6.9. Theoretical DLVO force curves were fit to the AFM approach curves by varying the surface potential of the microspheres. The depths of the primary minima of the theoretical DLVO curves fitted to AFM approach curves, were used to estimate adhesion forces according to previously published approaches, and were compared to the pull-off forces measured by AFM. Pull-off forces measured by AFM in both electrolytes were consistently a factor of about 20-30 lower than the pull-off forces estimated from theoretical adhesion forces obtained from DLVO curves. AFMmeasured pull-off forces decreased with increasing the ionic strength in both electrolytes, whereas the adhesion forces calculated from DLVO showed either no change or a slight increase with increasing the ionic strength. Possible reasons for these discrepancies include roughness on one or both surfaces, which would presumably reduce the adhesion force via reduced contact area and presence of hydration forces that could reduce adhesion via strong short-range repulsion in the neighborhood of the contact points. These observations demonstrate that DLVO-based approach for determining adhesion force overestimates actual adhesion force, likely because a DLVO-based approach neglects interactions that manifest at very close separation distances and upon contact.

$Research paper thumbnail of A novel method to detect unlabeled inorganic nanoparticles and submicron particles in tissue by sedimentation field-flow fractionation$

Particle and Fibre Toxicology, 2008

A novel methodology to detect unlabeled inorganic nanoparticles was experimentally demonstrated... more A novel methodology to detect unlabeled inorganic nanoparticles was experimentally demonstrated using a mixture of nano-sized (70 nm) and submicron (250 nm) silicon dioxide particles added to mammalian tissue. The size and concentration of environmentally relevant inorganic particles in a tissue sample can be determined by a procedure consisting of matrix digestion, particle recovery by centrifugation, size separation by sedimentation field-flow fractionation (SdFFF), and detection by light scattering. Background Laboratory nanoparticles that have been labeled by fluorescence, radioactivity, or rare elements have provided important information regarding nanoparticle uptake and translocation, but most nanomaterials that are commercially produced for industrial and consumer applications do not contain a specific label. Methods Both nitric acid digestion and enzyme digestion were tested with liver and lung tissue as well as with cultured cells. Tissue processing with a mixture of protease enzymes is preferred because it is applicable to a wide range of particle compositions. Samples were visualized via fluorescence microscopy and transmission electron microscopy to validate the SdFFF results. We describe in detail the tissue preparation procedures and discuss method sensitivity compared to reported levels of nanoparticles in vivo. Conclusion Tissue digestion and SdFFF complement existing techniques by precisely identifying unlabeled metal oxide nanoparticles and unambiguously distinguishing nanoparticles (diameter<100 nm) from both soluble compounds and from larger particles of the same nominal elemental composition. This is an exciting capability that can facilitate epidemiological and toxicological research on natural and manufactured nanomaterials.

$Research paper thumbnail of Detection, separation, and quantification of unlabeled silica nanoparticles in biological media using sedimentation field-flow fractionation$

Journal of Nanoparticle Research, 2009

A rapid, high-resolution methodology for characterization, separation, and quantification of unla... more A rapid, high-resolution methodology for characterization, separation, and quantification of unlabeled inorganic nanoparticles extracted from biological media, based on sedimentation field-flow fractionation and light scattering detection is presented. Silica nanoparticles were added to either human endothelial cell lysate or rat lung tissue homogenate and incubated. The nanoparticles were extracted by acid digestion and then separated and characterized by sedimentation field-flow fractionation. Fractions collected at the peak maxima were analyzed by transmission electron microscopy (TEM) to verify the size and shape of the isolated nanoparticles. Using the linear relationship between the particle number and the area under the fractogram, the recoveries of particles from the tissue homogenate and cell lysate were calculated as 25% and 79%, respectively. The presented methodology facilitates detection, separation, size characterization, and quantification of inorganic nanoparticles in biological samples, within one experimental run.

Journal of Adhesion Science and Technology, 2011

Interaction and adhesion forces between polymer and mineral fillers are key factors in controllin... more Interaction and adhesion forces between polymer and mineral fillers are key factors in controlling their affinity during the preparation of high-quality nanobiocomposites. In this work, the compatibility between polymer (alginate) and mineral filler (mica, borax or bentonite) surfaces was characterized by direct force measurements using atomic force microscopy (AFM). Direct force measurements, using a single spherical alginate particle prepared by the spinning disc atomization method and attached to a cantilever, have been employed to characterize adhesion forces between alginate and several mineral filler surfaces in air. The free energies of adhesion for alginate-mica, alginate-bentonite and alginate-borax systems were compared. The experimental adhesion forces for these systems were compared with those predicted using the Johnson-Kendall-Roberts (JKR) approximation and the Liftshitz-van der Waals and Lewis acid-base interaction theory. The discrepancies between the experimental values and theoretical predictions were discussed on the basis of the surface roughness effect on the measured adhesion forces.

Langmuir, 2006

Interaction forces between a fluorite (CaF 2 ) surface and colloidal silica were measured by atom... more Interaction forces between a fluorite (CaF 2 ) surface and colloidal silica were measured by atomic force microscopy (AFM) in 1 × 10 -3 M NaNO 3 at different pH values. Forces between the silica colloid and fluorite flat were measured at a range of pH values above the isoelectric point (IEP) of silica so that the forces were mainly controlled by the fluorite surface charge. In this way, the IEP of the fluorite surface was deduced from AFM force curves at pH ∼9.2. Experimental force versus separation distance curves were in good agreement with theoretical predictions based on long-range electrostatic interactions, allowing the potential of the fluorite surface to be estimated from the experimental force curves. AFM-deduced surface potentials were generally lower than the published zeta potentials obtained from electrokinetic methods for powdered samples. Differences in methodology, orientation of the fluorite, surface carbonation, and equilibration time all could have contributed to this difference.

International Journal of Mineral Processing, 2008

Interaction forces between a hydrophilic silica particle and an air bubble were measured by atomi... more Interaction forces between a hydrophilic silica particle and an air bubble were measured by atomic force microscopy using simplified model systems with deionized water and dilute KCl solutions. Contributions from the hydrodynamic force were minimized by using a low piezo speed. Particle-bubble separation distance and the bubble spring constant were calculated from linear regression of the piezo extension versus cantilever deflection. The bubble surface potential was then estimated from fitting the AFM-measured forces to the Hogg-Healy-Fuerstenau (HHF) model, using the surface element integration (SEI) method. Surface potentials obtained for the bubble at a low applied force were comparable with the literature data, suggesting that the simplified model used here can give a reasonable estimation of the bubble surface potential under moderate applied forces. Interaction forces between a silica particle and an air bubble were also measured at different locations on the air bubble surface. The force curves obtained at the edges of the bubble fitted very well to the theoretical force curves regardless of the applied force, while curves obtained at the center and halfway to the center, were more difficult to fit, in particular at higher applied forces , suggesting that force curves obtained at the edges of the air bubble might be less prone to deformation effects.

Environmental Science & Technology, 2000

Diffusion coefficients of the Suwannee River fulvic acid (SRFA) obtained using fluorescence corre... more Diffusion coefficients of the Suwannee River fulvic acid (SRFA) obtained using fluorescence correlation spectroscopy (FCS), pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR), and flow field-flow fractionation (FlFFF) were compared as a function of pH (4.0-8.5) and ionic strength (5-500 mM). Diffusion coefficients of the SRFA ranged between 1.9 and 3.5 × 10 -10 m 2 s -1 . These values were fairly constant as a function of both pH and ionic strength and comparable to the limited literature values available. Polydispersity data are shown indicating that there is some degree of size and chemical heterogeneity for this humic sample including a small fraction of SRFA components with a diffusion coefficient smaller than 1 × 10 -10 m 2 s -1 . The results imply that the majority of SRFA components have hydrodynamic diameters between 1.5 and 2.5 nm.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2004

Atomic force microscopy (AFM) was used to study the effect of adsorption of humic substances onto... more Atomic force microscopy (AFM) was used to study the effect of adsorption of humic substances onto a goethite-coated mica surface, on the forces between the goethite surface and a silica colloidal probe. The positively charged goethite surface (at pH < 7) resulted in strong adsorption of humic substances. The adsorption process could be controlled by altering the solution concentration, pH and exposure time. Force versus distance curves were measured directly by AFM between a silica sphere colloidal probe and the planar goethite-coated mica surface, with and without the presence of humic substances. The thickness of the adsorbed layer was estimated to be about 5 nm from the force curves. These experiments demonstrate the influence of adsorbed humic substances on the surface charge of goethite, which has direct relevance to the colloid stability of natural aquatic particles.

Water Research, 1997

Natural organic material (NOM) from Myponga Reservoir in South Australia was concentrated and fra... more Natural organic material (NOM) from Myponga Reservoir in South Australia was concentrated and fractionated using ultrafiltration into nominal molecular weight fractions < 500, 500--3000, 3000-10,000, 10,000-30,000 and > 30,000. The fractions were characterised using flow field-flow fractionation, ~3C NMR, colour determination and potentiometric titration. The ultrafiltration fractions displayed a gradual transformation from highly coloured, highly branched, high carbohydrate structures to compounds with a prevalence of long chain aliphatic carbon with much lower carbohydrate content and colour. There were no clear trends in the carboxyl content of the fractions, as determined by both NMR and titration. Analysis of the titration data showed evidence of three distinct types of carboxyl groups and the same types of groups were present in each fraction. © 1997 Elsevier Science Ltd