John W. Stone

Uptake, distribution and toxicity of gold nanoparticles in tobacco (Nicotiana xanthi) seedlings

Abstract Understanding plant interactions with nanoparticles is of increasing importance for assessing their toxicity and trophic transport. The primary objective of this study was to assess uptake, biodistribution and toxicity associated with exposure of tobacco plants (Nicotiana xanthi) to gold nanoparticles (AuNPs). We employed synchrotron-based X-ray microanalysis with X-ray absorption near-edge microspectroscopy and high resolution electron microscopy to localize AuNPs within plants. Results from these experiments reveal that AuNPs entered plants through the roots and moved into the vasculature. Aggregate bodies were also detected within root cell cytoplasm. Furthermore, AuNP uptake was size selective as 3.5 nm AuNP spheres were detected in plants but 18 nm AuNPs remained agglomerated on the root outer surfaces. Finally, leaf necrosis was observed after 14 days of exposure to 3.5 nm AuNPs. Overall, results of this work show the potential for AuNPs to enter plants through size-dependent mechanisms, translocate to cells and tissues and cause biotoxicity.

Iron Oxide Coated Gold Nanorods: Synthesis, Characterization, and Magnetic Manipulation

We report a simple process to generate iron oxide coated gold nanorods. Gold nanorods, synthesized by our three-step seed mediated protocol, were coated with a layer of polymer, poly(sodium 4-styrenesulfonate). The negatively charged polymer on the nanorod surface electrostatically attracted a mixture of aqueous iron(II) and iron(III) ions. Base-mediated coprecipitation of iron salts was used to form uniform coatings of iron oxide nanoparticles onto the surface of gold nanorods. The magnetic properties were studied using a superconducting quantum interference device (SQUID) magnetometer, which indicated superparamagnetic behavior of the composites. These iron oxide coated gold nanorods were studied for macroscopic magnetic manipulation and were found to be weakly magnetic. For comparison, premade iron oxide nanoparticles, attached to gold nanorods by electrostatic interactions, were also studied. Although control over uniform coating of the nanorods was difficult to achieve, magnetic manipulation was improved in the latter case. The products of both synthetic methods were monitored by UV-vis spectroscopy, zeta potential measurements, and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the oxidation state of iron in the gold nanorod-iron oxide composites, which is consistent with Fe2O3 rather than Fe3O4. The simple method of iron oxide coating is general and applicable to different nanoparticles, and it enables magnetic field-assisted ordering of assemblies of nanoparticles for different applications.

Colloidal Stability of Citrate and Mercaptoacetic Acid Capped Gold Nanoparticles upon Lyophilization: Effect of Capping Ligand Attachment and Type of Cryoprotectants

For various applications of gold nanotechnology, long-term nanoparticle stability in solution is a major challenge. Lyophilization (freeze-drying) is a widely used process to convert labile protein and various colloidal systems into powder for improved long-term stability. However, the lyophilization process itself may induce various stresses resulting in nanoparticle aggregation. Despite a plethora of studies evaluating lyophilization of proteins, liposomes, and polymeric nanoparticles, little is known about the stability of gold nanoparticles (GNPs) upon lyophilization. Herein, the effects of lyophilization and freeze-thaw cycles on the stability of two types of GNPs: Citrate-capped GNPs (stabilized via weakly physisorbed citrate ions, Cit-GNPs) and mercaptoacetic acid-capped GNPs (stabilized via strongly chemisorbed mercaptoacetic acid, MAA-GNPs) are investigated. Both types of GNPs have similar core size and effective surface charge as evident from transmission electron microscopy and zeta potential measurements, respectively. Plasmon absorption of GNPs and its dependence on nanoparticle aggregation was employed to follow stability of GNPs in combination with dynamic light scattering analysis. Plasmon peak broadening index (PPBI) is proposed herein for the first time to quantify GNPs aggregation using nonlinear Gaussian fitting of GNPs UV-vis spectra. Our results indicate that Cit-GNPs aggregate irreversibly upon freeze-thaw cycles and lyophilization. In contrast, MAA-GNPs exhibits remarkable stability under the same conditions. Cit-GNPs exhibit no significant aggregation in the presence of cryoprotectants (molecules that are typically used to protect labile ingredients during lyophilization) upon freeze-thaw cycles and lyophilization. The effectiveness of the cyroprotectants evaluated was on the order of trehalose or sucrose > sorbitol > mannitol. The ability of cryoprotectants to prevent GNPs aggregation was dependent on their chemical structure and their ability to interact with the GNPs as assessed with zeta potential analysis.

Age-dependent expression of collagen receptors and deformation of type I collagen substrates by rat cardiac fibroblasts.

Little is known about how age influences the ways in which cardiac fibroblasts interact with the extracellular matrix. We investigated the deformation of collagen substrates by neonatal and adult rat cardiac fibroblasts in monolayer and three-dimensional (3D) cultures, and quantified the expression of three collagen receptors [discoidin domain receptor (DDR)1, DDR2, and β1 integrin] and the contractile protein alpha smooth muscle actin (α-SMA) in these cells. We report that adult fibroblasts contracted 3D collagen substrates significantly less than their neonate counterparts, whereas no differences were observed in monolayer cultures. Adult cells had lower expression of β1 integrin and α-SMA than neonate cultures, and we detected significant correlations between the expression of α-SMA and each of the collagen receptors in neonate cells but not in adult cells. Consistent with recent work demonstrating age-dependent interactions with myocytes, our results indicate that interactions between cardiac fibroblasts and the extracellular matrix change with age.