14 research outputs found
A Directional Entropic Force Approach to Assemble Anisotropic Nanoparticles into Superlattices
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102143/1/14230_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102143/2/ange_201306009_sm_miscellaneous_information.pd
DNA-nanoparticle superlattices formed from anisotropic building blocks
Directional bonding interactions in solid-state atomic lattices dictate the unique symmetries of atomic crystals, resulting in a diverse and complex assortment of three-dimensional structures that exhibit a wide variety of material properties. Methods to create analogous nanoparticle superlattices are beginning to be realized, but the concept of anisotropy is still largely underdeveloped in most particle assembly schemes. Some examples provide interesting methods to take advantage of anisotropic effects, but most are able to make only small clusters or lattices that are limited in crystallinity and especially in lattice parameter programmability. Anisotropic nanoparticles can be used to impart directional bonding interactions on the nanoscale, both through face-selective functionalization of the particle with recognition elements to introduce the concept of valency, and through anisotropic interactions resulting from particle shape. In this work, we examine the concept of inherent shape-directed crystallization in the context of DNA-mediated nanoparticle assembly. Importantly, we show how the anisotropy of these particles can be used to synthesize one-, two- and three-dimensional structures that cannot be made through the assembly of spherical particles.
Includes Supplementary Information (44 pp.)
Anisotropic Nanoparticles as Shape-Directing Catalysts for the Chemical Etching of Silicon
Anisotropic
Au nanoparticles have been used to create a library
of complex features on silicon surfaces. The technique provides control
over feature size, shape, and depth. Moreover, a detailed study of
the etching rate as a function of the nanoparticle surface facet interfaced
with the silicon substrate suggested that the etching is highly dependent
upon the facet surface energy. Specifically, the etching rate for
Au nanocubes with {100}-terminated facets was ∼1.5 times higher
than that for triangular nanoprisms with {111} facets. Furthermore,
this work gives fundamental insight into the mechanism of metal-catalyzed
chemical etching
Linking Hydrophilic Macromolecules to Monodisperse Magnetite (Fe3O4) Nanoparticles via Trichloro-s-triazine
Counting the Number of Magnesium Ions Bound to the Surface-Immobilized Thymine Oligonucleotides That Comprise Spherical Nucleic Acids
Label-free
studies carried out under aqueous phase conditions quantify
the number of Mg<sup>2+</sup> ions binding to surface-immobilized
T<sub>40</sub> sequences, the subsequent reordering of DNA on the
surface, and the consequences of Mg<sup>2+</sup> binding for DNA–DNA
interactions. Second harmonic generation measurements indicate that,
within error, 18–20 Mg<sup>2+</sup> ions are bound to the T<sub>40</sub> strand at saturation and that the metal–DNA interaction
is associated with a near 30% length contraction of the strand. Structural
reordering, evaluated using vibrational sum frequency generation,
atomic force microscopy, and dynamic light scattering, is attributed
to increased charge screening as the Mg<sup>2+</sup> ions bind to
the negatively charged DNA, reducing repulsive Coulomb forces between
nucleotides and allowing the DNA single strands to collapse or coil
upon themselves. The impact of Mg<sup>2+</sup> binding on DNA hybridization
and duplex stability is assessed with spherical nucleic acid (SNA)
gold nanoparticle conjugates in order to determine an optimal working
range of Mg<sup>2+</sup> concentrations for DNA–DNA interactions
in the absence of NaCl. The findings are consistent with a charge
titration effect in which, in the absence of NaCl, (1) hybridization
does not occur at room temperature if an average of 17.5 or less Mg<sup>2+</sup> ions are bound per T<sub>40</sub> strand, which is not reached
until the bulk Mg<sup>2+</sup> concentration approaches 0.5 mM; (2)
hybridization proceeds, albeit with low duplex stability having an
average <i>T</i><sub>m</sub> of 31(3)°C, if an average
of 17.5–18.0 Mg<sup>2+</sup> ions are bound; and (3) highly
stable duplexes having a <i>T</i><sub>m</sub> of 64(2)°C
form if 18.5–19.0 Mg<sup>2+</sup> ions are bound, corresponding
to saturation of the T<sub>40</sub> strand
Hollow Spherical Nucleic Acids for Intracellular Gene Regulation Based upon Biocompatible Silica Shells
Cellular transfection of nucleic acids is necessary for
regulating
gene expression through antisense or RNAi pathways. The development
of spherical nucleic acids (SNAs, originally gold nanoparticles functionalized
with synthetic oligonucleotides) has resulted in a powerful set of
constructs that are able to efficiently transfect cells and regulate
gene expression without the use of auxiliary cationic cocarriers.
The gold core in such structures is primarily used as a template to
arrange the nucleic acids into a densely packed and highly oriented
form. In this work, we have developed methodology for coating the
gold particle with a shell of silica, modifying the silica with a
layer of oligonucleotides, and subsequently oxidatively dissolving
the gold core with I<sub>2</sub>. The resulting hollow silica-based
SNAs exhibit cooperative binding behavior with respect to complementary
oligonucleotides and cellular uptake properties comparable to their
gold-core SNA counterparts. Importantly, they exhibit no cytotoxicity
and have been used to effectively silence the eGFP gene in mouse endothelial
cells through an antisense approach
Cross-linked Heterogeneous Nanoparticles as Bifunctional Probe
Cross-linked Heterogeneous
Nanoparticles as Bifunctional
Prob