Joshua I. Cutler

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.

Spherical Nucleic Acids

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.

Polyvalent Nucleic Acid Nanostructures

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.

Polyvalent Oligonucleotide Iron Oxide Nanoparticle "Click" Conjugates

We have utilized the copper-catalyzed azide-alkyne reaction to form a dense monolayer of oligonucleotides on a superparamagnetic nanoparticle core. These particles exhibit the canonical properties of materials densely functionalized with DNA, which can be controlled by modulating the density of oligonucleotides on the surface of the particles. Furthermore, like their Au analogues, these particles can easily cross HeLa (cervical cancer) cell membranes without transfection agents due to their dense DNA shell. Importantly, this approach should be generalizable to other azide-functionalized particles.

Transitioning DNA‐Engineered Nanoparticle Superlattices from Solution to the Solid State

In the assembly and crystallization of nanoparticles into ordered lattices, DNA is a powerful structure-directing ligand because its programmability allows for a priori control over the lattice symmetries and lattice constants of the nanoparticle superstructures. [ 1–8 ] Practically, however, characterization and processing of superlattices made from DNA-modifi ed particles is limited because the morphology and programmability of these structures exhibited in solution are either distorted or lost entirely when they are removed from their assembly medium (aqueous saline solution). Because these superlattices are held together via cooperative DNA duplexes, they rapidly collapse or dissociate where these interactions are unfavorable, such as in distilled water, in common organic solvents, at high temperatures, or under vacuum. Therefore, the development of a method for improving the mechanical stability and solution processability of the nanoparticle lattices is a necessary step as studies of these materials shift from understanding the parameters that govern their assembly to pursuing fundamental properties and useful applications. [ 9–11 ] In this work, we report a method for stabilizing DNA-assembled three-dimensional superlattices in the solid state by silica encapsulation, where both the symmetries and lattice spacings of the solution-phase lattices are preserved. Once encapsulated, superlattice morphologies are no longer dictated by DNA interactions, and as such remain stable against distortion, collapse, or dissociation under many previously inaccessible conditions. Silica encapsulation is a technique commonly used to stabilize inorganic nanoparticles of varying chemical compositions and morphologies against aggregation or oxidation. [ 12–17 ]

Nanopod formation through gold nanoparticle templated and catalyzed cross-linking of polymers bearing pendant propargyl ethers

A novel method for synthesizing polymer nanopods from a linear polymer bearing pendant propargyl ether groups, using gold nanoparticles as both the template and the catalyst for the cross-linking reaction, is reported. The transformations involved in the cross-linking process are unprecedented on the surface of a gold particle. A tentative cross-linking mechanism is proposed.

In-wire conversion of a metal nanorod segment into an organic semiconductor.

The development of chemical and physical methods for modifying the structure and composition of nanowires or nanorods[1–10] is necessary to expand the utility and function (e.g. electronic, optical, and magnetic properties) of one-dimensional nanomaterials. For instance, on-wire lithography (OWL) is based on a facile three-step process (1) electrochemical deposition of multisegmented nanowires,[11,12] 2) physical coating of one wire face with a material that can hold the rod segments together (post etching), and 3) selective chemical etching of sacrificial wire segments) and allows the rational preparation of a wide variety of structures with nanoscale control over compositional and architectural features along the longitudinal axis of the wires.[6] This includes nanogaps,[13,14] electrical nanotraps,[15] plasmonic disk arrays,[16] optimized Raman “hot spots”,[17] and heterostructures that behave as catalytic nanorotors.[18] Organic semiconductor materials have recently attracted significant interest for their potential application in the context of functional nanoscale electronic devices[19–21] owing to their many unique properties such as their structural and compositional diversity and physical flexibility.[22,23] There are a variety of ways of making nanowire-based structures consisting of metal segments sandwiching an organic segment. For instance, methods to synthesize structures in which both the metal and conductive polymer segments are electrically deposited have been developed.[24,25] Also, a monolayer of organic molecules can be chemisorbed to the surface of electrochemically deposited rods followed by electroless deposition of a metal segment (which can be further lengthened by electrochemical methods).[26,27] Additionally, assembly of an organic layer within gaps formed by two metal nanowires has been reported.[6,13]

ImmunoPods: Polymer Shells with Native Antibody Cross‐Links

Recently, we described the discovery of a novel gold nano-particle (AuNP) catalyzed reaction, which allows one to make heavily cross-linked polymer shells on the surface of the NP.[1] With this reaction, the NP acts both as a scaffold and catalyst to facilitate the cross-linking of linear polymers with propargyl ether side chains. Specifically, it has been postulated that hydroxy groups, formed from the hydrolysis of the propargyl ethers, add to the alkynes adsorbed on the gold surface, leading to cross-linking of the polymer.[2] Importantly, the NP core can be subsequently removed to form hollow polymer nanopods. These structures, which are highly adaptable through choice of polymer and AuNP template, show promise for many applications, spanning molecular diagnostics,[3] drug delivery,[4] materials synthesis, and colloidal crystal design.[5] However, before they can be fully utilized, methods for functionalizing them with bioactive structures must be developed. In this regard, we have devised methods for making nanopods from oligonucleotides with modified bases to generate polyvalent oligonucleotide nanostructures, which now constitute an entire class of single-entity intracellular gene regulation agents.[6] Herein, we address the challenge of creating nanopods functionalized with antibodies (Abs) by creating a class of materials, termed immunopods (IPs), structures that can be made from Abs and the appropriate linear polymers with propragyl ether side chains in a one-pot fashion, and then explore their ability to selectively target cells. IPs are important entries in the class of structures that can be made by gold-particle surface-templated and catalyzed approaches since they can enable a wide variety of pharmaceutical studies and potential applications.