The colloidal stability of gold nanoparticles (AuNPs) cap-exchanged with either monothiol- or dithiolane-terminated PEG-OCH(3) ligands was investigated. Three distinct aspects were explored: (1) effects of excess salt concentration; (2) ligation competition by dithiothreitol (DTT); and (3) resistance to sodium cyanide digestion. We found that overall ligands presenting higher coordination numbers (dithiolane) exhibit much better stability to excess added salt and against competition from DTT compared to their monodentate counterparts. Resistance to NaCN digestion indicated that there is a balance between coordination number and density of ligand packing on the NP surface. For smaller NPs, where a larger surface curvature reduces the ligand packing density, a higher coordination number is clearly beneficial. In comparison, a higher ligand density allowed by the smaller curvature for larger nanocrystals makes monothiol-PEG-capped NPs more resistant to cyanide digestion. The present study indicates that balance between the coordination number and surface packing density is crucial to enhancing the colloidal stability of AuNPs.

For luminescent quantum dots (QDs) to realize their full potential as intracellular labeling, imaging and sensing reagents, robust noninvasive methods for their delivery to the cellular cytosol must be developed. Our aim in this study was to explore a range of methods aimed at delivering QDs to the cytosol. We have previously shown that QDs functionalized with a polyarginine 'Tat' cell-penetrating peptide (CPP) could be specifically delivered to cells via endocytic uptake with no adverse effects on cellular proliferation. We began by assessing the long-term intracellular fate and stability of these QD-peptide conjugates. We found that the QDs remained sequestered within acidic endolysosomal vesicles for at least three days after initial uptake while the CPP appeared to remain stably associated with the QD throughout this time. We next explored techniques designed to either actively deliver QDs directly to the cytosol or to combine endocytosis with subsequent endosomal escape to the cytosol in several eukaryotic cell lines. Active delivery methods such as electroporation and nucleofection delivered only modest amounts of QDs to the cytosol as aggregates. Delivery of QDs using a variety of transfection polymers also resulted in primarily endosomal sequestration of QDs. However, in one case the commercial PULSin reagent did facilitate a modest cytosolic dispersal of QDs, but only after several days in culture and with significant polymer-induced cytotoxicity. Finally, we demonstrated that an amphiphilic peptide designed to mediate cell penetration and vesicle membrane interactions could mediate rapid QD uptake by endocytosis followed by a slower efficient endosomal release which peaked at 48 h after initial delivery. Importantly, this QD-peptide bioconjugate elicited minimal cytotoxicity in the cell lines tested.

Fe nanoparticles prepared by iron carbonyl decomposition using different methods are compared structurally, chemically, and magnetically. The specific magnetization of the particles was determined from the magnetic moment, the particle size observed by transmission electron microscopy, and the total iron concentration found from calibrated X-ray fluorescence. The volume fraction of oxide is reported for particles of different sizes and for particles made by slightly different techniques.

Remarkable progress has recently been made in the synthesis and characterization of engineered nanoparticles for imaging and treatment of cancers, resulting in several promising candidates in clinical trials. Despite these advances, clinical applications of nanoparticle-based therapeutic/imaging agents remain limited by biological, immunological, and translational barriers. In order to overcome the existing status quo in drug delivery, there is a need for open and frank discussion in the nanomedicine community on what is needed to make qualitative leaps toward translation. In this Nano Focus, we present the main discussion topics and conclusions from a recent workshop: “Mechanisms and Barriers in Nanomedicine”. The focus of this informal meeting was on biological, toxicological, immunological, and translational aspects of nanomedicine and approaches to move the field forward productively. We believe that these topics reflect the most important issues in cancer nanomedicine.

No abstract

We describe the magnetic properties of gold-coated iron nanoparticles, and the effects of low pH and heat treatment. Acicular iron and spherical iron based nanoparticles were coated with a thin layer of gold. The morphology and magnetic properties of magnetic particles were examined using transmission electron microscopy and alternative gradient magnetometry. While the small spherical particles had relatively uniform layers coatings, the larger acicular particles had many gold clusters decorating the surface. The original acicular iron nanoparticles had a specific magnetic moment of 145 emu/g and a coercivity of 1664 Oe. Corrosion tests showed good corrosion resistance for gold-coated commercial iron particles even in a 1.0×10−3 M HCl solution at 80 °C for 12 h, compared with uncoated particles.

We characterized the resonance energy transfer interactions for conjugates consisting of QD donors self-assembled with three distinct fluorescent protein acceptors: two monomeric fluorescent proteins, the dsRed derivative mCherry or yellow fluorescent protein and the multi-chromophore bphycoerythrin light harvesting complex. Using steady-state and time-resolved fluorescence, we showed that nonradiative transfer of excitation energy in these conjugates can be described within the Förster dipole-dipole formalism, with transfer efficiencies that vary with the degree of spectral overlap, donor-acceptor separation distance and the number of acceptors per QD. Comparison between the quenching data and simulation of the conjugate structures indicated that while energy transfer to monomeric proteins was identical to what was measured for QD-dye pairs, interactions with b-phycoerythrin were more complex. For the latter, the overall transfer efficiency results from the cumulative contribution of individual channels between the central QD and the chromophores distributed throughout the protein structure. Due to the biocompatible nature of fluorescent proteins, these QD-assemblies may have great potential for use in intracellular imaging and sensing.

Multicolor fluorescent labeling of both intra- and extracellular structures is a powerful technique for simultaneous monitoring of multiple complex biochemical processes. This approach remains extremely challenging, however, as it often necessitates the combinatorial use of numerous targeting probes (e.g., antibodies), multistep bioconjugation chemistries, different delivery strategies (e.g., electroporation or transfection reagents), cellular fixation coupled with membrane permeabilization, and complex spectral deconvolution. Here, we present a nanoparticle-based fluorescence labeling strategy for the multicolor labeling of distinct subcellular compartments within live cells without the need for antibody conjugation or cellular fixation/permeabilization. This multipronged approach incorporates an array of delivery strategies, which localize semiconductor quantum dots (QDs) to various subcellular structures. QD uptake is implemented in a spaciotemporal manner by staggering the delivery of QD-peptide composites and exploiting various innate (peptide-mediated endocytosis, peptide-membrane interaction, polymer-based transfection) along with physical (microinjection) cellular delivery modalities to live cells growing in culture over a 4 day period. Imaging of the different intracellular labels is simplified by the unique photophysical characteristics of the QDs in combination with Förster resonance energy transfer sensitization, which allow for multiple spectral windows to be accessed with one excitation wavelength. Using this overall approach, QDs were targeted to both early and late endosomes, the cellular cytosol, and the plasma membrane in live cells, ultimately allowing for simultaneous five-color fluorescent imaging.