Homing peptide-conjugated gold nanorods: the effect of amino acid sequence display on nanorod uptake and cellular proliferation.

Gold nanorods (GNRs) have attracted significant interest in the field of medicine as theranostic agents for both imaging and photothermal ablation of cancerous cells/tissues. Targeting theranostic GNRs specifically to cancer cells is necessary to enhance treatment efficacy and minimize undesired side effects. In this study, targeting functionalized GNR to EphA2 receptors that are overexpressed on prostate cancer cells was investigated as a strategy to achieve enhanced GNR uptake by cancer cells. In addition, the influence of targeting peptide orientation on functionalized GNR uptake by PC-3 cells was explored. GNRs of aspect ratio 4 were functionalized with an EphA2 homing peptide, YSA, using a layer-by-layer polypeptide wrapping approach. In parallel, an analogous population of YSA-modified GNRs, which display a reversed YSA peptide, with the N- and C- termini reversed, was also prepared. GC-MS analysis of the YSA-GNRs indicated that functionalized GNRs displayed approximately 3000 peptides/GNR. The functionalized GNRs remained well-dispersed in biological media for short times (<24 h). An increase in GNRs uptake of the YSA-GNRs by PC-3 cells, compared to the reversed YSA-GNRs, was observed under identical incubation conditions. Lastly, the effect of the YSA-GNRs binding to EphA2 receptors on prostate cancer cell proliferation was also studied. The YSA-functionalized GNRs inhibit PC-3 proliferation at a significantly lower effective dose than free YSA. Overall, the polypeptide LBL deposition technique provides a facile route to target nanoparticles to overexpressed cellular receptors, with the caveat that the specific orientation and display of the targeting moiety plays a critical role in the interaction between the nanoparticle and the cell.

The Gold Nanorod-Biology Interface: From Proteins to Cells to Tissue.

Gold nanorods absorb and scatter light strongly in the near-infrared portion of the electromagnetic spectrum, making them ideal tissue contrast agents for imaging techniques such as optical coherence tomography (OCT). Strong interactions occur at the nano-bio interface, such as proteins binding to gold nanorods forming a 'corona.' To fulfill the promise of nanorods for applications such as contrast agents, we must better understand the intrinsic interactions of these nanomaterials with biological systems at the molecular, cellular and tissue level. In this paper, we briefly review the nanorod-protein interface. We then present some new fast relaxation imaging (FReI) measurements of how the presence of strongly-absorbing gold nanorods affects protein binding and folding, taking into account inner filter effects and the strong quenching effect of nanorods on fluorescent-labeled proteins. Next we show that two-photon photoluminescence of the gold nanorods can be used to image the nanorods in tissue constructs, allowing us to independently study their tissue distribution so they can be used successfully as contrast agents in optical coherence microscopy.

Nanoparticle-protein interactions: a thermodynamic and kinetic study of the adsorption of bovine serum albumin to gold nanoparticle surfaces.

Investigating the adsorption process of proteins on nanoparticle surfaces is essential to understand how to control the biological interactions of functionalized nanoparticles. In this work, a library of spherical and rod-shaped gold nanoparticles (GNPs) was used to evaluate the process of protein adsorption to their surfaces. The binding of a model protein (bovine serum albumin, BSA) to GNPs as a function of particle shape, size, and surface charge was investigated. Two independent comparative analytical methods were used to evaluate the adsorption process: steady-state fluorescence quenching titration and affinity capillary electrophoresis (ACE). Although under favorable electrostatic conditions kinetic analysis showed a faster adsorption of BSA to the surface of cationic GNPs, equilibrium binding constant determinations indicated that BSA has a comparable binding affinity to all of the GNPs tested, regardless of surface charge. BSA was even found to adsorb strongly to GNPs with a pegylated/neutral surface. However, these fluorescence titrations suffer from significant interference from the strong light absorption of the GNPs. The BSA-GNP equilibrium binding constants, as determined by the ACE method, were 10(5) times lower than values determined using spectroscopic titrations. While both analytical methods could be suitable to determine the binding constants for protein adsorption to NP surfaces, both methods have limitations that complicate the determination of protein-GNP binding constants. The optical properties of GNPs interfere with Ka determinations by static fluorescence quenching analysis. ACE, in contrast, suffers from material compatibility issues, as positively charged GNPs adhere to the walls of the capillary during analysis. Researchers seeking to determine equilibrium binding constants for protein-GNP interactions should therefore utilize as many orthogonal techniques as possible to study a protein-GNP system.

Gold nanorods: their potential for photothermal therapeutics and drug delivery, tempered by the complexity of their biological interactions.

Gold nanorods have promising applications in the fields of drug delivery and photothermal therapy. These promises arise from the nanorods' unique optical and photothermal properties, the availability of synthetic protocols that can tune the size and shape of the particles, the ability to modify the surface and conjugate drugs/molecules to the nanorods, and the relative biocompatibility of gold nanorods. In this review, current progress in using gold nanorods as phototherapeutic agents and as drug delivery vehicles is summarized. Issues of dosage, toxicity and biological interactions at three levels (biological media alone; cells; whole organisms) are discussed, concluding with recommendations for future work in this area.