Sarah J. Hurst

Colloidal Gold and Silver Triangular Nanoprisms

It is now well-known that the size, shape, and composition of nanomaterials can dramatically affect their physical and chemical properties, and that technologies based on nanoscale materials have the potential to revolutionize fields ranging from catalysis to medicine. Among these materials, anisotropic particles are particularly interesting because the decreased symmetry of such particles often leads to new and unusual chemical and physical behavior. Within this class of particles, triangular Au and Ag nanoprisms stand out due to their structure- and environment-dependent optical features, their anisotropic surface energetics, and the emergence of reliable synthetic methods for producing them in bulk quantities with control over their edge lengths and thickness. This Review will describe a variety of solution-based methods for synthesizing Au and Ag triangular prismatic structures, and will address and discuss proposed mechanisms for their formation.

Antibody-Linked Spherical Nucleic Acids for Cellular Targeting

Spherical nucleic acid (SNA) constructs are promising new single entity gene regulation materials capable of both cellular transfection and gene knockdown, but thus far are promiscuous structures, exhibiting excellent genetic but little cellular selectivity. In this communication, we describe a strategy to impart targeting capabilities to these constructs through noncovalent functionalization with a complementary antibody-DNA conjugate. As a proof-of-concept, we designed HER2-targeting SNAs and demonstrated that such structures exhibit cell type selectivity in terms of their uptake, and significantly greater gene knockdown in cells overexpressing the target antigen as compared to the analogous antibody-free and off-target materials.

Three-dimensional hybridization with polyvalent DNA-gold nanoparticle conjugates

We have determined the minimum number of base pairings necessary to stabilize DNA-Au NP aggregates as a function of salt concentration for particles between 15 and 150 nm in diameter. Significantly, we find that sequences containing a single base pair interaction are capable of effecting hybridization between 150 nm DNA-Au NPs. While traditional DNA hybridization involves two strands interacting in one dimension (1D, Z), we propose that hybridization in the context of an aggregate of polyvalent DNA-Au NP conjugates occurs in three dimensions (many oligonucleotides oriented perpendicular to the X, Y plane engage in base pairing), making nanoparticle assembly possible with three or fewer base pairings per DNA strand. These studies enabled us to compare the stability of duplex DNA free in solution and bound to the nanoparticle surface. We estimate that 4-8, 6-19, or 8-33 additional DNA bases must be added to free duplex DNA to achieve melting temperatures equivalent to hybridized systems formed from 15, 60, or 150 nm DNA-Au NPs, respectively. In addition, we estimate that the equilibrium binding constant (K(eq)) for 15 nm DNA-Au NPs (3 base pairs) is approximately 3 orders of magnitude higher than the K(eq) for the corresponding nanoparticle free system.

Matrix‐Assisted Dip‐Pen Nanolithography and Polymer Pen Lithography

The controlled patterning of nanomaterials presents a major challenge to the field of nanolithography because of differences in size, shape and solubility of these materials. Matrix-assisted dip-pen nanolithography and polymer pen lithography provide a solution to this problem by utilizing a polymeric matrix that encapsulates the nanomaterials and delivers them to surfaces with precise control of feature size.

Synthetically Programmable DNA Binding Domains in Aggregates of DNA-Functionalized Gold Nanoparticles†

Polyvalent DNA-functionalized gold nanoparticle conjugates (DNA–Au NPs) have proven useful in a variety of assembly,[1–3] biodiagnostic,[4–6] and nanotherapeutic[7–10] applications. Their widespread use is a consequence of: 1) their novel hybridization properties and 2) straightforward methods for synthesizing macroscopic quantities of them in relatively monodisperse form.[1,11,12] In some applications, the utility of DNA–Au NPs relies on their ability to assemble via DNA hybridization into polymeric aggregates (Scheme 1A).[1] This reaction is accompanied by a concomitant red-to-blue color change, a consequence of the dampening and red-shifting of the nanoparticle surface plasmon resonance (SPR) band at ~520 nm (for a 15-nm nanoparticle).[13] As the temperature is increased above the melting temperature of the duplex DNA linkages connecting the gold nanoparticles, the polymeric structure dehybridizes, the spectroscopic signature associated with the dispersed particles is restored, and a single, highly cooperative melting transition is observed. The melting transition occurs at a higher temperature and over a more narrow temperature range than free duplex DNA of the same sequence.[1,14,15]