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ABSTRACT: We report the first method for synthesizing binary semiconductor materials by scanning probe block copolymer lithography (SPBCL) in desired locations on a surface. In this work, we utilize SPBCL to create polymer features containing a desired amount of Cd(2+), which is defined by the feature volume. When they are subsequently reacted in H(2)S in the vapor phase, a single CdS nanoparticle is formed in each block copolymer (BCP) feature. The CdS nanoparticles were shown to be both crystalline and luminescent. Importantly, the CdS nanoparticle sizes can be tuned since their diameters depend on the volume of the originally deposited BCP feature.
Nano Letters 02/2012; 12(2):1022-5. · 13.20 Impact Factor
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ABSTRACT: We report the development of the multiplexed nanoflare, a nanoparticle agent that is capable of simultaneously detecting two distinct mRNA targets inside a living cell. These probes are spherical nucleic acid (SNA) gold nanoparticle (Au NP) conjugates consisting of densely packed and highly oriented oligonucleotide sequences, many of which are hybridized to a reporter with a distinct fluorophore label and each complementary to its corresponding mRNA target. When multiplexed nanoflares are exposed to their targets, they provide a sequence specific signal in both extra- and intracellular environments. Importantly, one of the targets can be used as an internal control, improving detection by accounting for cell-to-cell variations in nanoparticle uptake and background. Compared to single-component nanoflares, these structures allow one to determine more precisely relative mRNA levels in individual cells, improving cell sorting and quantification.
Analytical Chemistry 01/2012; 84(4):2062-6. · 5.86 Impact Factor
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ABSTRACT: A historical perspective of the development of spherical nucleic acid (SNA) conjugates and other three-dimensional nucleic acid nanostructures is provided. This Perspective details the synthetic methods for preparing them, followed by a discussion of their unique properties and theoretical and experimental models for understanding them. Important examples of technological advances made possible by their fundamental properties spanning the fields of chemistry, molecular diagnostics, gene regulation, medicine, and materials science are also presented.
Journal of the American Chemical Society 01/2012; 134(3):1376-91. · 9.91 Impact Factor
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ABSTRACT: The ability to observe intermediate structures as part of coarsening processes that lead to the formation of single nanoparticles (NPs) is important in gaining fundamental insight pertaining to nanostructure growth. Here, we use scanning probe block copolymer lithography (SPBCL) to create "nanoreactors" having attoliter volumes, which confine Au NP nucleation and growth to features having diameters <150 nm on a substrate. With this technique, one can use in situ TEM to directly observe and study NP coarsening and differentiate Ostwald ripening from coalescence processes. Importantly, the number of metal atoms that can engage in coarsening can be controlled with this technique, and TEM "snapshots" of particle growth can be taken. The size of the resulting nanostructures can be controlled in the 2-10 nm regime.
Journal of the American Chemical Society 01/2012; 134(1):158-61. · 9.91 Impact Factor
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ABSTRACT: Freeze-frame: Octahedral and square-planar structural isomers, representing the two "end states" in a hemilabile ligand bond-breaking isomerization reaction, have been characterized in solution by spectroscopic methods and in the solid state by X-ray crystallography (see picture: Ni green, C gray, P orange, N blue, S yellow).
Angewandte Chemie International Edition 12/2011; 51(6):1469-72. · 13.45 Impact Factor
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ABSTRACT: Nanopods functionalized with anti-HER2 antibodies (ImmunoPods, see scheme) have been synthesized by adsorbing the proteins onto gold nanoparticles and catalytically cross-linking them with a coadsorbed polymer through pendant propargyl ether groups. Upon dissolution of the gold template, the hollow polymer nanopod-protein conjugates remain. ImmunoPods are bioactive and can target cancer cells that express the HER2 antigen.
Angewandte Chemie International Edition 12/2011; 51(5):1169-72. · 13.45 Impact Factor
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ABSTRACT: Crystalline nanoparticle arrays and superlattices with well-defined geometries can be synthesized by using appropriate electrostatic, hydrogen-bonding or biological recognition interactions. Although superlattices with many distinct geometries can be produced using these approaches, the library of achievable lattices could be increased by developing a strategy that allows some of the nanoparticles within a binary lattice to be replaced with 'spacer' entities that are constructed to mimic the behaviour of the nanoparticles they replace, even though they do not contain an inorganic core. The inclusion of these spacer entities within a known binary superlattice would effectively delete one set of nanoparticles without affecting the positions of the other set. Here, we show how hollow DNA nanostructures can be used as 'three-dimensional spacers' within nanoparticle superlattices assembled through programmable DNA interactions. We show that this strategy can be used to form superlattices with five distinct symmetries, including one that has never before been observed in any crystalline material.
Nature Nanotechnology 12/2011; 7(1):24-8. · 27.27 Impact Factor
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ABSTRACT: The development of a novel method for functionalizing nanopatterned surfaces with catalytically active proteins is reported. This method involves using dip-pen nanolithography (DPN) and polymer pen lithography (PPL) to generate nanoscale patterns of coenzyme A, followed by a phosphopantetheinyl transferase-mediated coupling between coenzyme A and proteins fused to the ybbR-tag. By exploiting the ability to generate protein features over large areas afforded by DPN and PPL, it was now possible to measure protein activity directly on these surfaces. It was found that proteins immobilized on the nanoscale features not only display higher activity per area with decreasing feature size, but are also robust and can be used for repeated catalytic cycles. The immobilization method is applicable to a variety of proteins and gives rise to superior activity compared to proteins attached in random orientations on the surface.
Nanoscale 12/2011; 4(2):659-66. · 5.91 Impact Factor
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ABSTRACT: Gold nanoparticles (Au NPs) were employed as templates to synthesize spherical, high-density lipoprotein (HDL) biomimics (HDL Au NPs) of different sizes and surface chemistries. The effect of size and surface chemistry on the cholesterol binding properties and the ability of the HDL Au NPs to efflux cholesterol from macrophage cells were measured. Results demonstrate that Au NPs may be utilized as templates to generate nanostructures with different physical characteristics that mimic natural HDL. Furthermore, the properties of the HDL Au NPs may be tailored to modulate the ability to bind cholesterol in solution and efflux cholesterol from macrophages. From the conjugates tested, the optimum size and surface chemistry for preparing functional Au NP-templated HDL biomimics were identified.
ACS Nano 11/2011; 6(1):276-85. · 10.77 Impact Factor
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ABSTRACT: The ability to control the placement of individual protein molecules on surfaces could enable advances in a wide range of areas, from the development of nanoscale biomolecular devices to fundamental studies in cell biology. Such control, however, remains a challenge in nanobiotechnology due to the limitations of current lithographic techniques. Herein we report an approach that combines scanning probe block copolymer lithography with site-selective immobilization strategies to create arrays of proteins down to the single-molecule level with arbitrary pattern control. Scanning probe block copolymer lithography was used to synthesize individual sub-10-nm single crystal gold nanoparticles that can act as scaffolds for the adsorption of functionalized alkylthiol monolayers, which facilitate the immobilization of specific proteins. The number of protein molecules that adsorb onto the nanoparticles is dependent upon particle size; when the particle size approaches the dimensions of a protein molecule, each particle can support a single protein. This was demonstrated with both gold nanoparticle and quantum dot labeling coupled with transmission electron microscopy imaging experiments. The immobilized proteins remain bioactive, as evidenced by enzymatic assays and antigen-antibody binding experiments. Importantly, this approach to generate single-biomolecule arrays is, in principle, applicable to many parallelized cantilever and cantilever-free scanning probe molecular printing methods.
Proceedings of the National Academy of Sciences 11/2011; 108(49):19521-5. · 9.68 Impact Factor
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ABSTRACT: We report on the modification of the properties of surface-confined ligands in nanoparticle systems through the introduction of shape anisotropy. Specifically, triangular gold nanoprisms, densely functionalized with oligonucleotide ligands, hybridize to complementary particles with an affinity that is several million times higher than that of spherical nanoparticle conjugates functionalized with the same amount of DNA. In addition, they exhibit association rates that are 2 orders of magnitude greater than those of their spherical counterparts. This phenomenon stems from the ability of the flat, extended facets of nonspherical nanoparticles to (1) support more numerous ligand interactions through greater surface contact with complementary particles, (2) increase the effective local concentration of terminal DNA nucleotides that mediate hybridization, and (3) relieve the conformational stresses imposed on nanoparticle-bound ligands participating in interactions between curved surfaces. Finally, these same trends are observed for the pH-mediated association of nanoparticles functionalized with carboxylate ligands, demonstrating the generality of these findings.
Journal of the American Chemical Society 11/2011; 133(46):18865-9. · 9.91 Impact Factor
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ABSTRACT: A current limitation in nanoparticle superlattice engineering is that the identities of the particles being assembled often determine the structures that can be synthesized. Therefore, specific crystallographic symmetries or lattice parameters can only be achieved using specific nanoparticles as building blocks (and vice versa). We present six design rules that can be used to deliberately prepare nine distinct colloidal crystal structures, with control over lattice parameters on the 25- to 150-nanometer length scale. These design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (5 to 60 nanometers), periodicity, and interparticle distance. As such, this work represents an advance in synthesizing tailorable macroscale architectures comprising nanoscale materials in a predictable fashion.
Science 10/2011; 334(6053):204-8. · 31.20 Impact Factor
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Small 09/2011; 7(22):3158-62. · 8.35 Impact Factor
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ACS Nano 08/2011; · 10.77 Impact Factor
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ABSTRACT: Paclitaxel, a potent chemotherapeutic utilized in a variety of cancers, can be limited in its effectiveness due to inherent insolubility in aqueous media and acquired chemoresistance within certain cells. An approach has been developed for increasing Paclitaxel solubility and effectiveness by covalent attachment to gold nanoparticles via DNA linkers. The resulting conjugates are highly soluble in aqueous buffer, exhibiting greater than a 50-fold increase in solubility over the unconjugated drug. DNA linkers are labeled with a fluorophore, which affords a convenient means of visualizing resultant conjugates within cells. Internalized conjugates demonstrate increased activity as compared with free drug across a variety of cell types, including a Paclitaxel-resistant cell line. Attachment to DNA-nanoparticle conjugates may become a general strategy for solubilizing and enhancing a wide variety of therapeutic agents in aqueous media.
ACS Nano 08/2011; 5(9):6962-70. · 10.77 Impact Factor
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ABSTRACT: Polyvalent oligonucleotide-functionalized gold nanoparticles are remarkably stable in a cellular environment against degradation by nucleases, a property that was recently attributed to the local high concentration of mono- and divalent ions. To evaluate this hypothesis in more detail, we investigate the composition of the ion cloud around spherical nanoparticles that are functionalized by stiff, highly charged polyelectrolyte chains by means of classical density functional theory and molecular dynamics simulations. We present a cell model that includes ligands explicitly and both applies over the entire relevant parameter space and is in excellent quantitative agreement with simulations. We study the ion cloud for varying oligonucleotide grafting densities and bulk ionic concentrations, as well as different sizes of nanoparticles and chains, and distinguish a parameter regime where many-body interactions between the ligands have a dominant effect on the local environment. For small particles with high oligonucleotide surface densities, we find strongly enhanced local salt concentrations, a large radial component of the electric field between the ligands, and a pronounced localization of divalent ions near the surface of the nanoparticle, thus providing multiple supporting arguments for the hypothesis.
08/2011;
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ABSTRACT: Four different gold nanostructures: octahedra, rhombic dodecahedra, truncated ditetragonal prisms, and concave cubes, have been synthesized using a seed-mediated growth method by strategically varying the Ag(+) concentration in the reaction solution. Using X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy, we provide quantitative evidence that Ag underpotential deposition is responsible for stabilizing the various surface facets that enclose the above nanoparticles. Increasing concentrations of Ag(+) in the growth solution stabilize more open surface facets, and experimental values for Ag coverage on the surface of the particles fit well with a calculated monolayer coverage of Ag, as expected via underpotential deposition.
Nano Letters 07/2011; 11(8):3394-8. · 13.20 Impact Factor
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ABSTRACT: Polyvalent oligonucleotide-nanoparticle conjugates possess several unique emergent properties, including enhanced cellular uptake, high antisense bioactivity, and nuclease resistance, which hypothetically originate from the dense packing and orientation of oligonucleotides on the surface of the nanoparticle. In this Communication, we describe a new class of polyvalent nucleic acid nanostructures (PNANs), which are comprised of only cross-linked and oriented nucleic acids. We demonstrate that these particles are capable of effecting high cellular uptake and gene regulation without the need of a cationic polymer co-carrier. The PNANs also exhibit cooperative binding behavior and nuclease resistance properties.
Journal of the American Chemical Society 06/2011; 133(24):9254-7. · 9.91 Impact Factor
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Angewandte Chemie International Edition 06/2011; 50(33):7482-5. · 13.45 Impact Factor
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ABSTRACT: Gold octahedra with hollow features have been synthesized in high yield via the controlled overgrowth of preformed concave cube seeds. This Ag(+)-assisted, seed-mediated synthesis allows for the average edge length of the octahedra and the size of the hollow features to be independently controlled. We propose that a high concentration of Ag(+) stabilizes the {111} facets of the octahedra through underpotential deposition while the rate of Au(+) reduction controls the dimensions of the hollow features. This synthesis represents a highly controllable bottom-up approach for the preparation of hollow gold nanostructures.
Journal of the American Chemical Society 06/2011; 133(27):10414-7. · 9.91 Impact Factor
