Here we systematically examined the effect of nanoparticle size (10-100 nm) and surface chemistry (i.e., poly(ethylene glycol)) on passive targeting of tumors in vivo. We found that the physical and chemical properties of the nanoparticles influenced their pharmacokinetic behavior, which ultimately determined their tumor accumulation capacity. Interestingly, the permeation of nanoparticles within the tumor is highly dependent on the overall size of the nanoparticle, where larger nanoparticles appear to stay near the vasculature while smaller nanoparticles rapidly diffuse throughout the tumor matrix. Our results provide design parameters for engineering nanoparticles for optimized tumor targeting of contrast agents and therapeutics.

Optical-based distance measurements are essential for tracking biomolecular conformational changes, drug discovery, and cell biology. Traditional Forster resonance energy transfer (FRET) is efficient for separation distances up to 100 A. We report the first successful application of a dipole-surface type energy transfer from a molecular dipole to a nanometal surface that more than doubles the traditional Forster range (220 A) and follows a 1/R(4) distance dependence. We appended a 1.4 nm Au cluster to the 5' end of one DNA strand as the energy acceptor and a fluorescein (FAM) to the 5' end of the complementary strand as the energy donor. Analysis of the energy transfer on DNA lengths (15, 20, 30, 60bp), complemented by protein-induced DNA bending, provides the basis for fully mapping the extent of this dipole surface type mechanism over its entire usable range (50-250 A). Further, protein function is fully compatible with these nanometal-DNA constructs. Significantly extending the range of optical based methods in molecular rulers is an important leap forward for biophysics.

The fluorescence behavior of molecular dyes at discrete distances from 1.5 nm diameter gold nanoparticles as a function of distance and energy is investigated. Photoluminescence and luminescence lifetime measurements both demonstrate quenching behavior consistent with 1/d(4) separation distance from dye to the surface of the nanoparticle. In agreement with the model of Persson and Lang, all experimental data show that energy transfer to the metal surface is the dominant quenching mechanism, and the radiative rate is unchanged throughout the experiment.

Interest in developing diverse nanoparticle (NP)-biological composite materials continues to grow almost unabated. This is motivated primarily by the desire to simultaneously exploit the properties of both NP and biological components in new hybrid devices or materials that can be applied in areas ranging from energy harvesting and nanoscale electronics to biomedical diagnostics. The utility and effectiveness of these composites will be predicated on the ability to assemble these structures with control over NP/biomolecule ratio, biomolecular orientation, biomolecular activity, and the separation distance within the NP-bioconjugate architecture. This degree of control will be especially critical in creating theranostic NP-bioconjugates that, as a single vector, are capable of multiple functions in vivo, including targeting, image contrast, biosensing, and drug delivery. In this review, a perspective is given on current and developing chemistries that can provide improved control in the preparation of NP-bioconjugates. The nanoscale properties intrinsic to several prominent NP materials are briefly described to highlight the motivation behind their use. NP materials of interest include quantum dots, carbon nanotubes, viral capsids, liposomes, and NPs composed of gold, lanthanides, silica, polymers, or magnetic materials. This review includes a critical discussion on the design considerations for NP-bioconjugates and the unique challenges associated with chemistry at the biological-nanoscale interface-the liabilities of traditional bioconjugation chemistries being particularly prominent therein. Select bioorthogonal chemistries that can address these challenges are reviewed in detail, and include chemoselective ligations (e.g., hydrazone and Staudinger ligation), cycloaddition reactions in click chemistry (e.g., azide-alkyne cyclyoaddition, tetrazine ligation), metal-affinity coordination (e.g., polyhistidine), enzyme driven modifications (e.g., HaloTag, biotin ligase), and other site-specific chemistries. The benefits and liabilities of particular chemistries are discussed by highlighting relevant NP-bioconjugation examples from the literature. Potential chemistries that have not yet been applied to NPs are also discussed, and an outlook on future developments in this field is given.

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The heat produced by optically excited gold nanorods is used to augment the chemotherapeutic agent cisplatin in killing tumor cells. This combined therapy kills 78% more cells than cisplatin alone, suggesting a synergistic interaction between these treatments.

Cell penetrating peptides facilitate efficient intracellular uptake of diverse materials ranging from small contrast agents to larger proteins and nanoparticles. However, a significant impediment remains in the subsequent compartmentalization/endosomal sequestration of most of these cargoes. Previous functional screening suggested that a modular peptide originally designed to deliver palmitoyl-protein thioesterase inhibitors to neurons could mediate endosomal escape in cultured cells. Here, we detail properties relevant to this peptide’s ability to mediate cytosolic delivery of quantum dots (QDs) to a wide range of cell-types, brain tissue culture and a developing chick embryo in a remarkably non-toxic manner. The peptide further facilitated efficient endosomal escape of large proteins, dendrimers and other nanoparticle materials. We undertook an iterative structure-activity relationship analysis of the peptide by discretely modifying key components including length, charge, fatty acid content and their order using a comparative, semi-quantitative assay. This approach allowed us to define the key motifs required for endosomal escape, to select more efficient escape sequences, along with unexpectedly identifying a sequence modified by one methylene group that specifically targeted QDs to cellular membranes. We interpret our results within a model of peptide function and highlight implications for in vivo labeling and nanoparticle-mediated drug delivery by using different peptides to co-deliver cargoes to cells and engage in multifunctional labeling.

Nanometal surface energy transfer (NSET), which describes an energy transfer event from optically excited organic fluorophores to small metal nanoparticles, may be used as a molecular beacon/ruler similar to FRET, but with advantages over this classical technique. Here we use NSET to measure Mg(2+)-induced conformational changes for a hammerhead ribozyme and confirm these measurements using FRET. These optical experiments enhance our understanding of the different kinetic pathways for this ribozyme.