Soheyl Tadjiki - Academia.edu (original) (raw)

Papers by Soheyl Tadjiki

Langmuir, Sep 17, 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.

$Research paper thumbnail of Studies on the characterisation and behavior of soil colloids using field-flow fractionation$

This thesis was scanned from the print manuscript for digital preservation and is copyright the a... more This thesis was scanned from the print manuscript for digital preservation and is copyright the author. Researchers can access this thesis by asking their local university, institution or public library to make a request on their behalf. Monash staff and postgraduate students can use the link in the References field.

Journal of Radioanalytical and Nuclear Chemistry, Mar 1, 1995

Nanoparticles (NPs) are defi ned as ultrafi ne particles with one dimension between 1–100 nm [1].... more Nanoparticles (NPs) are defi ned as ultrafi ne particles with one dimension between 1–100 nm [1]. Because of their small size, they have a very large surface area relative to their weight, so they often react quite differently from a bulk solid or dissolved material of the same composition. For this reason they may offer novel and interesting properties for a broad range of applications. Current and potential applications for NPs range from food additives, cosmetics and pharmaceuticals, to biocidal packaging, fuel cell technology and electronics. But while their use is constantly increasing, questions and concerns have been raised about their safety and their health impact. For this reason, there is an urgent need to develop analytical methods that are suitable for the particular evaluation of NPs. These methods need to be appropriate to the specifi c properties of nanoparticles, Single particle analysis using the Agilent 7700x ICP-MS

TechConnect Briefs, Jun 15, 2014

A methodology has been developed to measure mass, size and density of the core and the shell of S... more A methodology has been developed to measure mass, size and density of the core and the shell of Silver-shelled Gold nanoparticles for the first time. The FFF-based methodology allows for the measurement of the mass of the nanoparticle using Centrifugal Field-Flow Fractionation and the volume by Asymmetrical Flow Field-Flow Fractionation. The nanoparticle density can then be calculated from the obtained mass and volume data. Mass of the core was measured either by Single-Particle ICP-MS or by the FFF analysis of the uncoated core nanoparticle. The nanoparticle diameter was measured as 56 nm with the core diameter and shell thickness of 30 nm and 13 nm respectively. The nanoparticle mass was measured as 8.76×10-19 kg with a shell/core mass ratio of 3.5. The densities of the core, shell and core-shell nanoparticle were measured as 12800 kg/m 3 , 8900 kg/m 3 , and 9500 kg/m 3 respectively.

A novel method to detect unlabeled inorganic nanoparticles and submicron particles in tissue by s... more A novel method to detect unlabeled inorganic nanoparticles and submicron particles in tissue by sedimentation field-flow fractionation

Frontiers in Toxicology, 2021

Plastics have long been an environmental contaminant of concern as both large-scale plastic debri... more Plastics have long been an environmental contaminant of concern as both large-scale plastic debris and as micro- and nano-plastics with demonstrated wide-scale ubiquity. Research in the past decade has focused on the potential toxicological risks posed by microplastics, as well as their unique fate and transport brought on by their colloidal nature. These efforts have been slowed by the lack of analytical techniques with sufficient sensitivity and selectivity to adequately detect and characterize these contaminants in environmental and biological matrices. To improve analytical analyses, microplastic tracers are developed with recognizable isotopic, metallic, or fluorescent signatures capable of being identified amidst a complex background. Here we describe the synthesis, characterization, and application of a novel synthetic copolymer nanoplastic based on polystyrene (PS) and poly(2-vinylpyridine) (P2VP) intercalated with gold, platinum or palladium nanoparticles that can be capped...

$Research paper thumbnail of Development of a field-flow fractionation method for separation of natural clay particles using FLFFF and SDFFF$

Biophysical Journal, 2018

Ankara : Department of Chemistry and Institute of Engineering and Sciences, Bilkent Univ., 1992.

$Research paper thumbnail of Combining centrifugal and flow field-flow fractionation with ICPAES to characterize the size and elemental composition of soil clay minerals$

Applied Clay Science, 2020

In this work a method was developed for determining the mass and element-based size distributions... more In this work a method was developed for determining the mass and element-based size distributions of submicron sized soil particles. The method used field-flow fractionation (FFF) to separate the particles and inline UV and inductively coupled plasma atomic emission spectrometry (ICPAES) detectors to evaluate the mass and element concentrations in the eluent respectively. The data was used to plot strategic element molar ratios versus particle diameter which greatly simplifies interpretation of the trends in terms of soil processes. The method was tested using samples collected from the A and B horizon matrix material and cutans of the Camel Hill sand near Monarto in South Australia, a soil with strongly contrasting texture. The major findings were that the size of the clay mineral components (particles < 2 μm) decreased in the order A horizon > B horizon > cutans and that the mineralogy was almost identical in all soil samples. A possible implication would be that the clays in the B horizon matrix and cutans have been physically translocated from the A horizon with little chemical weathering but this does not fit the photoimages of the soil horizon. However, this study strongly indicated that the information obtained by FFF-UV-ICPAES, when combined with data derived from other analytical techniques, will be a powerful tool in understanding the mechanisms of soil formation and weathering.

$Research paper thumbnail of Experimental verification of the steric-entropic mode of retention in centrifugal field-flow fractionation using illite clay plates$

Journal of Chromatography A, 2018

The commonly used theory to describe the normal Brownian mode of field-flow fractionation (FFF) a... more The commonly used theory to describe the normal Brownian mode of field-flow fractionation (FFF) assumes the particles to be point masses and hence the shape is ignored. Beckett and Giddings extended this theory to include the effect of thin rods and discs being forced very close to the accumulation wall. By including the decrease in the entropy this causes, they derived new expressions for the retention of such nonspherical particles in FFF. The steric-entropic theory predicts that when the sample cloud thickness is less than the major dimension of the rods or discs then particles elute earlier than predicted by the Brownian mode theory. This leads to an underestimation of the buoyant mass and equivalent spherical diameter calculated from FFF data. In this paper we report for the first time experimental data for the retention of thin illite particles in centrifugal FFF that agrees well with these steric-entropic predictions. Not only do the size distributions calculated using the Brownian mode theory shift to lower size when the field is increased but the shift in the retention ratio of the peak maxima of the FFF fractograms could be predicted fairly accurately by the steric-entropic equations.

Biophysical Journal, 2017

Fusion and fission of cellular membranes involve dramatic, precisely regulated changes in membran... more Fusion and fission of cellular membranes involve dramatic, precisely regulated changes in membrane curvature mediated by a number of proteins. The mechanisms by which proteins influence membrane curvature are not well understood, and current methods for investigating curvature changes using well-controlled systems are limited. We have developed a system based on supported lipid bilayers in which lipid tubules spontaneously form in a manner that can be tuned by varying the ionic character and strength used during bilayer deposition and imaging. Using this supported tubulated bilayer system, which we term ''STuBS,'' we have investigated membrane-targeting C2 domains from synaptotagmin-7, a member of the synaptotagmin protein family that triggers exocytosis in neurons and neuroendocrine cells. We find that addition of purified synaptotagmin-7 C2AB domains, but not synaptotagmin-1 C2A, leads to a Ca 2þ-dependent disappearance of tubules with concomitant formation of vesicles. These studies demonstrate that synaptotagmin-7 can alter membrane morphology by driving changes in membrane curvature. STuBS is a novel experimental system useful for monitoring soluteand protein-mediated effects on membrane topology in aqueous media and in real time.

$Research paper thumbnail of Field-flow fractionation method and apparatus$

Analytical Chemistry, 2016

The presence of silver nanoparticles (AgNPs) in aquatic environments could potentially cause adve... more The presence of silver nanoparticles (AgNPs) in aquatic environments could potentially cause adverse impacts on ecosystems and human health. However, current understanding of the environmental fate and transport of AgNPs is still limited because their properties in complex environmental samples cannot be accurately determined. In this study, the feasibility of using asymmetric flow field-flow fractionation (AF4) connected online with single particle inductively coupled plasma mass spectrometry (spICPMS) to detect and quantify AgNPs at environmentally relevant concentrations was investigated. The AF4 channel had a thickness of 350 μm and its accumulation wall was a 10 kDa regenerated cellulose membrane. A 0.02% FL-70 surfactant solution was used as an AF4 carrier. With 1.2 mL/min AF4 cross-flow rate, 1.5 mL/min AF4 channel flow rate, and 5 ms spICPMS dwell time, the AF4-spICPMS can detect and quantify 40-80 nm AgNPs, as well as Ag-SiO2 core-shell nanoparticles (51.0 nm diameter Ag core and 21.6 nm SiO2 shell), with good recovery within 30 min. This system was not only effective in differentiating and quantifying different types of AgNPs with similar hydrodynamic diameters, such as in mixtures containing Ag-SiO2 core-shell nanoparticles and 40-80 nm AgNPs, but also suitable for differentiating between 40 nm AgNPs and elevated Ag(+) content. The study results indicate that AF4-spICPMS is capable of detecting and quantifying AgNPs and other engineered metal nanomaterials in environmental samples. Nevertheless, further studies are needed before AF4-spICPMS can become a routine analytical technique.

Clays and Clay Minerals, 2015

The swelling properties of smectite-type clay particles (including montmorillonite) are of intere... more The swelling properties of smectite-type clay particles (including montmorillonite) are of interest in various industries. A fundamental understanding of the surface properties of smectite particles at the sub-micron level would facilitate investigation of the effect of distributed properties such as charge and elemental composition. Swelling and delamination of SWy-2 Na-montmorillonite (Na-Mnt) nano-clay particles were studied here using size distributions obtained by sedimentation field-flow fractionation (SdFFF). Fractions were examined by electron microscopy and inductively-coupled optical emission spectroscopy (ICP-OES). Two distinct populations were observed in the size distribution of SWy-2 Na-Mnt particles (bimodal size distribution), with mean equivalent spherical diameters of ~60 nm and 250 nm, respectively. In contrast, the size distribution of STx-1 Ca-montmorillonite (Ca-Mnt) particles showed only one peak with a mean equivalent spherical diameter of ~410 nm, which changed to 440 nm after 4 days of hydration. Analyses of the fractions by ICP-OES obtained along the size distribution of Na-Mnt showed an abundance of Ca and Mg in the fractions below 250 nm, and confirmed the presence of Fe and Mg as isomorphous substituents. Electron micrographs of the fractions obtained from Na-Mnt size distributions were used to calculate the thickness of the clay particles. Bridging forces between pure orMgsubstituted montmorillonite and either Ca2+ or Na+ were calculated using semi-empirical methods. The results demonstrated that swelling and delamination of Na-Mnt clay particles are dictated by properties such as elemental composition and surface charge which are distributed along the size distribution.

Acta hydrochimica et hydrobiologica, 2003

ABSTRACT Pore water samples from sediment cores of the rivers Saale and Elbe were examined for va... more ABSTRACT Pore water samples from sediment cores of the rivers Saale and Elbe were examined for variations of colloidal heavy metal associations during transition from anoxic to oxic conditions. Asymmetric flow-field flow fractionation coupled to ICP-MS was used to collect size distributions and element-size distributions simultaneously. The data obtained reveal an increasing amount of colloidal bound main and trace elements in the pore waters during oxidation. Although there was a significant trend to increasing colloid concentrations and colloidal bound heavy metals over the observed 48 hour period of oxidation, differences between both samples were obvious.Kolloidale Partikel in Sedimentporenwässern: Partikelgrößenverteilungen und Elementverteilungen assoziierter Metalle in anoxischen und reoxidierten Proben, ermittelt mit einer FFF-ICP-MS-KopplungPorenwässer in Sedimentkernen aus Saale und Elbe wurden auf Änderungen der Gehalte kolloidassoziierter Metalle untersucht, wobei die Porenwässer über 48 Stunden aus dem ursprünglich anoxischen in den oxischen Zustand überführt wurden. Eine Kopplung von asymmetrischer Fluss-Feld-Fluss-Fraktionierung mit ICP-MS wurde verwendet, um Partikelgrößen- und Elementverteilungen zu erhalten. Die Ergebnisse zeigen einen Anstieg der kolloidassoziierten Haupt- und Spurenelemente während der Oxidation. Obwohl es einen einheitlichen Trend zu ansteigenden Konzentrationen von Kolloiden und kolloidgebundenen Metallen gab, wurden auch Unterschiede zwischen den Proben aus Saale und Elbe deutlich.

$Research paper thumbnail of Soil colloid analysis by flow field-flow fractionation$

Field-Flow Fractionation (FFF) is emerging as an essential piece in the toolkit of the colloid an... more Field-Flow Fractionation (FFF) is emerging as an essential piece in the toolkit of the colloid analyst. Of all the chameleon-like forms that FFF can assume, Flow FFF appears the most versatile, not least because of its capability, in theory, of separating particles, colloids and macromolecules in a range of 15 orders of magnitude in molecular weight. Another key attribute is that separation is independent of particle density. Here we demonstrate, for the first time, that Flow FFF is capable of separating very fine illitic colloids <80nm, isolated from the lower B horizon of a soil profile. We show that marked decreases in the K/Si ratio with decrease in particle size are caused by the presence of very fine kaolinite. The theory of Flow FFF, and the linkage of a Flow FFF channel to Inductively Coupled Plasma Atomic Emission and Mass Spectrometers to produce rapid elemental concentrations as a function of particle size, is explained.