Browsing by Author "Abtahi, Seyyed Mohammad Hossein"

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    Implications of Shape Factors on Fate, Uptake, and Nanotoxicity of Gold Nanomaterials
    Abtahi, Seyyed Mohammad Hossein (Virginia Tech, 2018-06-28)
    Noble metal nanoparticles such as gold and silver are of interest because of the unique electro-optical properties (e.g., localized surface plasmon resonance [LSPR]) that originate from the collective behavior of their surface electrons. These nanoparticles are commonly developed and used for biomedical and industrial application. A recent report has predicted that the global market for gold nanoparticles will be over 12.7 tons by year 2020. However, these surface-functionalized nanoparticles can be potential environmental persistent contaminants post-use due to their high colloidal stability in the aquatic systems. Despite, the environmental risks associated with these nanoparticles, just a few studies have investigated the effect of nanofeature factors such as size and shape on the overall fate/transport and organismal uptake of these nanomaterials in the aquatic matrices. This study presents a comprehensive approach to evaluate the colloidal stability, fate/transport, and organismal uptake of these nanoparticles while factoring in the size and shape related properties. We demonstrate the importance and effect of anisotropicity of a gold nanoparticle on the colloidal behavior and interaction with ecologically susceptible aquatic biota. We also show how readily available characterization techniques can be utilized to monitor and assess the fate/transport of this class of nanoparticles. We further describe and investigate the relationship between the aspect ratio (AR) of these elongated gold nanoparticles with clearance mechanisms and rates from the aquatic suspension columns including aggregation, deposition, and biopurification. We illustrate how a fresh water filter-feeder bivalve, Corbicula fluminea, can be used as a model organism to study the size and shape-selective biofiltration and nanotoxicity of elongated gold nanoparticles. The results suggest that biofiltration by C. fluminea increases with an increase in the size and AR of gold nanoparticle. We develop a simple nanotoxicity assay to investigate the short-term exposure nanotoxicity of gold nanoparticles to C. fluminea. The toxicity results indicate that for the tested concentration and exposure period that gold nanoparticles were not acutely toxic (i.e., not lethal). However, gold nanoparticles significantly inhibited the activities of some antioxidant enzymes in gill and digestive gland tissues. These inhibitions could directly affect the resistance of these organisms to a secondary stressor (temperature, pathogens, hypoxia etc.) and threaten organismal health.
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    Synthesis and characterization of metallic nanoparticles with photoactivated surface chemistries
    Abtahi, Seyyed Mohammad Hossein (Virginia Tech, 2013-12-19)
    During recent decades metallic nanoparticles have been found very interesting due to their unique characteristics which make them suitable for different applications. In this research, for the very first time, we tried to perform selective surface photo activation chemistry on the targeted facets of nanoparticles while they are in suspension. This technique enabled us to form desired assemblies of nanoparticles. We focused on elongated shaped gold nanorod due to its unique surface plasmon resonance and probable biomedical applications. In this research we formed a dumbbell shape assembly of nanoparticles in suspension. A probable application for these assemblies can be in vivo imaging. Initially, we reproduced gold nanorods using existing techniques in prior papers and optimized them according to our research needs. A low rpm centrifugal separation technique was developed to efficiently separate synthesized gold nanorods from other shapes. Several characterization techniques were utilized to characterize nanoparticles at each step including UV-absorbance, zeta potential, and dynamic light scattering. Different generations of oligomers were synthesized to be used as gold nanorods coating, and each coating was tested and characterized using appropriate techniques. Our two-step coating replacement method using one of these photocleavable oligomers enabled us to achieve, for the very first time, selective UV photo activation of gold nanorod tips. The photo activated tips were then exposed to oppositely charged gold nanospheres to form dumbbell shape assemblies of gold nanorods and nanospheres. Furthermore, dumbbell shape assembly of nanoparticles was investigated and characterized.