Ian Y. Goon

Controlled Fabrication of Polyethylenimine-Functionalized Magnetic Nanoparticles for the Sequestration and Quantification of Free Cu2+

Presented herein is a detailed study into the controlled adsorption of polyethylenimine (PEI) onto 50 nm crystalline magnetite nanoparticles (Fe(3)O(4) NPs) and how these PEI-coated Fe(3)O(4) NPs can be used for the magnetic capture and quantification of ultratrace levels of free cupric ions. We show the ability to systematically control the amount of PEI adsorbed onto the Fe(3)O(4) magnetic nanoparticle surfaces by varying the concentration of polymer during the adsorption process. This in turn allows for the tailoring of important colloidal properties such as the electrophoretic mobility and aggregation stability. Copper adsorption tests were carried out to investigate the effectiveness of PEI-coated Fe(3)O(4) NPs in copper remediation and detection. The study demonstrated that the NPs ability to bind with copper is highly dependent on the amount of PEI adsorbed on the NP surface. It was found that PEI-coated Fe(3)O(4) NPs were able to capture trace levels (approximately 2 ppb) of free cupric ions and concentrate the ions to allow for detection via ICP-OES. More importantly, it was found that due to the amine-rich structure of PEI, the PEI-coated Fe(3)O(4) NPs selectively adsorb toxic free cupric ions but not the less toxic EDTA complexed copper. This unique property makes PEI-coated Fe(3)O(4) NPs a novel solution for the challenge of separating and quantifying toxic cupric ions as opposed to the total copper concentration of a sample.

Bi-functional gold-coated magnetite composites with improved biocompatibility.

The effect of gold attachment on the physical characteristics, cellular uptake, gene expression efficiency, and biocompatibility of magnetic iron oxide (MNP) vector was investigated in vitro in BHK21 cells. The surface modification of magnetite with gold was shown to alter the morphology and surface charge of the vector. Nonetheless, despite the differences in the surface charge with and without gold attachment, the surface charge of all vectors were positive when conjugated with PEI/DNA complex, and switched from positive to negative when suspended in cell media containing serum, indicating the adsorption of serum components onto the composite. The cellular uptake of all MNP vectors under the influence of a magnetic field increased when the composite loadings increased, and was higher for the MNP vector that was modified with gold. Both bare magnetite and gold-coated magnetite vectors gave similar optimal gene expression efficiency, however, the gold-coated magnetite vector required a 25-fold higher overall loading to achieve a comparable efficiency as the attachment of gold increased the particle size, thus reducing the surface area for PEI/DNA complex conjugation. The MNP vector without gold showed optimal gene expression efficiency at a specific magnetite loading, however further increases beyond the optimum loading decreased the efficiency of gene expression. The drop in efficiency at high magnetite loadings was attributed to the significant reduction in cellular viability, indicating the bare magnetite became toxic at high intracellular levels. The gene expression efficiency of the gold-modified vector, on the other hand, did not diminish with increasing magnetite loadings. Intracellular examination of both bare magnetite and gold-coated magnetite vectors at 48h post-magnetofection using transmission electron microscopy provided evidence of the localization of both vectors in the cell nucleus for gene expression and elucidated the nuclear uptake mechanism of both vectors. The results of this work demonstrate the efficacy of gold-modified vectors to be used in cellular therapy research that can function both as a magnetically-driven gene delivery vehicle and an intracellular imaging agent with negligible impact on cell viability.

The Biochemiresistor: An Ultrasensitive Biosensor for Small Organic Molecules

New sensation: A resistance-based biosensor uses gold-coated magnetic nanoparticles (Au@MNPs) functionalized with the antibiotic enrofloxin (see picture; purple), which bind to anti-enrofloxin as analyte (blue). The Au@MNPs can be magnetically assembled between electrodes, and the measured resistance R is a function of analyte concentration.

Thiol functionalisation of gold-coated magnetic nanoparticles: Enabling the controlled attachment of functional molecules

Gold-coated magnetite nanoparticles (Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs) have recently become the focus of research efforts which exploit the novel nano-architecture of these nanoparticles as platforms for magnetically controlled biomedical and analytical applications. To effectively utilise the Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs, thiol molecules can be bound onto the gold coating to provide a predictable surface for controlled attachment of functional molecules. Herein we present a facile process by which thiols with different moieties are attached to Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs. Dynamic light scattering and zeta-potential measurements were performed to study the effect of different thiols on the aggregation stability and surface charge of the Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs. The controlled attachment of an electroactive osmium complex is then demonstrated via voltammetric measurements. This work highlights importance of thiol molecule selection in enabling the fabrication of functional Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs.

DNA hybridization for nanocube functionalization

It is shown that silver nanocubes, functionalised with single stranded oligonucleotide sequences, can be decorated with smaller oligonucleotide functionalized gold nanoparticles via hybridization. This work demonstrates the suitability of silver nanocubes for DNA-mediated self-assembly and is an important advance for future work on face-specific modification of silver nanocubes.