Oligonucleotide loading determines cellular uptake of DNA-modified gold nanoparticles

The role radius of curvature plays in thiolated oligonucleotide loading on gold nanoparticles

We show that by correlating the radius of curvature of spherical gold nanoparticles of varying sizes with their respective thiol-terminated oligonucleotide loading densities, a mathematical relationship can be derived for predicting the loading of oligonucleotides on anisotropic gold nanomaterials. This mathematical relationship was tested with gold nanorods (radius 17.5 nm, length 475 nm) where the measured number of oligonucleotides per rod (3330 +/- 110) was within experimental error of the predicted loading of 3244 oligonucleotides from the derivation. Additionally, we show that once gold nanoparticles reach a diameter of approximately 60 nm the local surface experienced by the oligonucleotide is highly similar to that of a planar surface.

Gene regulation with polyvalent siRNA-nanoparticle conjugates

We report the synthesis and characterization of polyvalent RNA-gold nanoparticle conjugates (RNA-Au NPs), nanoparticles that are densely functionalized with synthetic RNA oligonucleotides and designed to function in the RNAi pathway. The particles were rationally designed and synthesized to be free of degrading enzymes, have a high surface loading of siRNA duplexes, and contain an auxiliary passivating agent for increased stability in biological media. The resultant conjugates have a half-life six times longer than that of free dsRNA, readily enter cells without the use of transfection agents, and demonstrate a high gene knockdown capability in a cell model.

Stability and electrostatic assembly of au nanorods for use in biological assays

The structure, stability, and aggregation potential of short Au nanorods under biological-based solution conditions have been studied. These attributes were studied using UV-vis spectroscopy, transmission electron microscopy, zeta-potential analysis, and dynamic light scattering. The stability and aggregation potential of the materials depended strongly upon both the purity and the solvent used to prepare Au nanorod solutions. When the Au nanorods were dissolved in Tris buffer at concentrations less than 10.0 mM, no aggregation was observed; however, when the solvent was comprised of Tris buffer with concentrations between 10.0 and 100 mM, significant aggregation of the materials occurred. This effect resulted in a dramatic broadening and shift in the absorbance maxima of the longitudinal surface plasmon resonance. At Tris buffer concentrations of greater than 100 mM, minimal to no aggregation of the materials in solution was observed. Such an ability is based upon electrostatic aggregation of the materials in solution mediated by the anions associated with the buffer system; at concentrations between 10.0 and 100 mM, the anions present electrostatically bind to the surfaces of the Au nanorods that are positively charged, resulting in cross-linking of the materials. At higher buffer concentrations, a sufficient number of anions are present in solution to template around the entire surface of each individual nanorod, in effect neutralizing the charge and producing an electronic double layer, which prevents aggregation. Such studies are timely as they represent an analysis of the stability and range of use of Au nanorods for biological-based applications where remarkable potential exists.

Polyvalent DNA nanoparticle conjugates stabilize nucleic acids

Polyvalent oligonucleotide gold nanoparticle conjugates have unique fundamental properties including distance-dependent plasmon coupling, enhanced binding affinity, and the ability to enter cells and resist enzymatic degradation. Stability in the presence of enzymes is a key consideration for therapeutic uses; however the manner and mechanism by which such nanoparticles are able to resist enzymatic degradation is unknown. Here, we quantify the enhanced stability of polyvalent gold oligonucleotide nanoparticle conjugates with respect to enzyme-catalyzed hydrolysis of DNA and present evidence that the negatively charged surfaces of the nanoparticles and resultant high local salt concentrations are responsible for enhanced stability.

Multifunctional Nanoparticles as Biocompatible Targeted Probes for Human Cancer Diagnosis and Therapy

The use of nanoparticles in biological application has been rapidly advancing toward practical applications in human cancer diagnosis and therapy. Upon linking the nanoparticles with biomolecules, they can be used to locate cancerous area as well as for traceable drug delivery with high affinity and specificity. In this review, we discuss the engineering of multifunctional nanoparticle probes and their use in bioimaging and nanomedicine.

Curvature-induced base pair "slipping" effects in DNA-nanoparticle hybridization

Experiments are presented that suggest DNA strands chemically immobilized on gold nanoparticle surfaces can engage in two types of hybridization: one that involves complementary strands and normal base pairing interactions and a second one assigned as a "slipping" interaction, which can additionally stabilize the aggregate structures through non-Watson-Crick type base pairing or interactions less complementary than the primary interaction. The curvature of the particles appears to be a major factor that contributes to the formation of these slipping interactions as evidenced by the observation that flat gold triangular nanoprism conjugates of the same sequence do not support them. Finally, these slipping interactions significantly stabilize nanoparticle aggregate structures, leading to large increases in T(m)'s and effective association constants as compared with free DNA and particles that do not have the appropriate sequence to maximize their contribution.

Peptide antisense nanoparticles

We have designed a heterofunctionalized nanoparticle conjugate consisting of a 13-nm gold nanoparticle (Au NP) containing both antisense oligonucleotides and synthetic peptides. The synthesis of this conjugate is accomplished by mixing thiolated oligonucleotides and cysteine-terminated peptides with gold nanoparticles in the presence of salt, which screens interactions between biomolecules, yielding a densely functionalized nanomaterial. By controlling the stoichiometry of the components in solution, we can control the surface loading of each biomolecule. The conjugates are prepared easily and show perinuclear localization and an enhanced gene regulation activity when tested in a cellular model. This heterofunctionalized structure represents a new strategy for preparing nanomaterials with potential therapeutic applications.

Size, charge and concentration dependent uptake of iron oxide particles by non-phagocytic cells

A promising new direction for contrast-enhanced magnetic resonance (MR) imaging involves tracking the migration and biodistribution of superparamagnetic iron oxide (SPIO)-labeled cells in vivo. Despite the large number of cell labeling studies that have been performed with SPIO particles of differing size and surface charge, it remains unclear which SPIO configuration provides optimal contrast in non-phagocytic cells. This is largely because contradictory findings have stemmed from the variability and imprecise control over surface charge, the general need and complexity of transfection and/or targeting agents, and the limited number of particle configurations examined in any given study. In the present study, we systematically evaluated the cellular uptake of SPIO in non-phagocytic T cells over a continuum of particle sizes ranging from 33nm to nearly 1.5microm, with precisely controlled surface properties, and without the need for transfection agents. SPIO labeling of T cells was analyzed by flow cytometry and contrast enhancement was determined by relaxometry. SPIO uptake was dose-dependent and exhibited sigmoidal charge dependence, which was shown to saturate at different levels of functionalization. Efficient labeling of cells was observed for particles up to 300nm, however, micron-sized particle uptake was limited. Our results show that an unconventional highly cationic particle configuration at 107nm maximized MR contrast of T cells, outperforming the widely utilized USPIO (<50nm).