Aptamers as Functional Modules for DNA Nanostructures.

Watson-Crick base-pairing of DNA allows the nanoscale fabrication of biocompatible synthetic nanostructures for diagnostic and therapeutic biomedical purposes. DNA nanostructure design elicits exquisite control of shape and conformation compared to other nanoparticles. Furthermore, nucleic acid aptamers can be coupled to DNA nanostructures to allow interaction and response to a plethora of biomolecules beyond nucleic acids.

Optimization of on-bead emulsion polymerase chain reaction based on single particle analysis.

Emulsion polymerase chain reaction (ePCR) enables parallel amplification of millions of different DNA molecules while avoiding bias and chimeric byproducts, essential criteria for applications including next generation sequencing, aptamer selection, and protein-DNA interaction studies. Despite these advantages, ePCR remains underused due to the lack of optimal starting conditions, straightforward methods to evaluate success, and guidelines for tuning the reaction. This knowledge has been elusive for bulk emulsion generation methods, such as stirring and vortexing, the only methods that can emulsify libraries of ≥10 sequences within minutes, because these emulsions have not been characterized in ways that preserve the heterogeneity that defines successful ePCR.

Patterning of supported gold monolayers via chemical lift-off lithography.

The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au-alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au-alkanethiolate thin films lack a measurable optical signature.

Polymer-Pen Chemical Lift-Off Lithography.

We designed and fabricated large arrays of polymer pens having sub-20 nm tips to perform chemical lift-off lithography (CLL). As such, we developed a hybrid patterning strategy called polymer-pen chemical lift-off lithography (PPCLL). We demonstrated PPCLL patterning using pyramidal and v-shaped polymer-pen arrays.

Plasmonic polymers unraveled through single particle spectroscopy.

Plasmonic polymers are quasi one-dimensional assemblies of nanoparticles whose optical responses are governed by near-field coupling of localized surface plasmons. Through single particle extinction spectroscopy correlated with electron microscopy, we reveal the effect of the composition of the repeat unit, the chain length, and extent of disorder on the energies, intensities, and line shapes of the collective resonances of individual plasmonic polymers constructed from three different sizes of gold nanoparticles. Our combined experimental and theoretical analysis focuses on the superradiant plasmon mode, which results from the most attractive interactions along the nanoparticle chain and yields the lowest energy resonance in the spectrum.

Turning the corner: efficient energy transfer in bent plasmonic nanoparticle chain waveguides.

For integrating and multiplexing of subwavelength plasmonic waveguides with other optical and electric components, complex architectures such as junctions with sharp turns are necessary. However, in addition to intrinsic losses, bending losses severely limit plasmon propagation. In the current work, we demonstrate that propagation of surface plasmon polaritons around 90° turns in silver nanoparticle chains occurs without bending losses.

Toward plasmonic polymers.

We establish the concept of a plasmonic polymer, whose collective optical properties depend on the repeat unit. Experimental and theoretical analyses of the super- and sub- radiant plasmon response of plasmonic polymers comprising repeat units of single nanoparticles or dimers of gold nanoparticles show that (1) the redshift of the lowest energy coupled mode becomes minimal as the chain approaches the infinite chain limit at a length of ∼10 particles, (2) the presence and energy of the modes are sensitive to the geometries of the constituents, that is, repeat unit, but (3) spatial disorder and nanoparticle heterogeneity have only small effects on the super-radiant mode.

Radiative and nonradiative properties of single plasmonic nanoparticles and their assemblies.

A surface plasmon is the coherent oscillation of the conduction band electrons. When a metal nanoparticle is excited to produce surface plasmons, incident light is both scattered and absorbed, giving rise to brilliant colors. One available technique for measuring these processes, ensemble extinction spectroscopy, only measures the sum of scattering and absorption.

Electromagnetic energy transport in nanoparticle chains via dark plasmon modes.

Using light to exchange information offers large bandwidths and high speeds, but the miniaturization of optical components is limited by diffraction. Converting light into electron waves in metals allows one to overcome this problem. However, metals are lossy at optical frequencies and large-area fabrication of nanometer-sized structures by conventional top-down methods can be cost-prohibitive.

Low absorption losses of strongly coupled surface plasmons in nanoparticle assemblies.

Coupled surface plasmons in one-dimensional assemblies of metal nanoparticles have attracted significant attention because strong interparticle interactions lead to large electromagnetic field enhancements that can be exploited for localizing and amplifying electromagnetic radiation in nanoscale structures. Ohmic loss (i.e.

Seeing double: coupling between substrate image charges and collective plasmon modes in self-assembled nanoparticle superstructures.

The interaction between adjacent metal nanoparticles within an assembly induces interesting collective plasmonic properties. Using dark-field imaging of plasmon scattering, we investigated rings of gold nanoparticles and observed that the images were dependent on the substrate. In particular, for nanoparticles assembled on carbon and gold substrates, intensity line sections perpendicular to the ring revealed a significant broadening beyond the optical resolution accompanied by an intensity dip in the middle of the line profile.

Effects of symmetry breaking and conductive contact on the plasmon coupling in gold nanorod dimers.

We have explored the consequences of symmetry breaking on the coupled surface plasmon resonances in individual dimers of gold nanorods using single-particle dark-field scattering spectroscopy and numerical simulations. Pairs of chemically grown nanorods can exhibit wide variation in sizes, gap distances, and relative orientation angles. The combination of single-particle spectroscopy and theoretical analysis allowed us to discern the effects of specific asymmetry-inducing parameters one at a time.

Plasmonic nanorod absorbers as orientation sensors.

Nanoparticles are actively exploited as biological imaging probes. Of particular interest are gold nanoparticles because of their nonblinking and nonbleaching absorption and scattering properties that arise from the excitation of surface plasmons. Nanoparticles with anisotropic shapes furthermore provide information about the probe orientation and its environment.

One-dimensional coupling of gold nanoparticle plasmons in self-assembled ring superstructures.

Plasmon coupling in ordered metal nanoparticle assemblies leads to tunable collective surface plasmon resonances that strongly depend on the interparticle distance. Here we report on the surface plasmon scattering of polystyrene-functionalized 40 nm gold nanoparticles self-assembled into close-packed rings. Using single particle dark-field scattering spectroscopy, we observed strong near-field coupling between neighboring nanoparticles, which results in red-shifted multipolar plasmon modes highly polarized along the ring circumference.

Ordered mesoporous materials from metal nanoparticle-block copolymer self-assembly.

The synthesis of ordered mesoporous metal composites and ordered mesoporous metals is a challenge because metals have high surface energies that favor low surface areas. We present results from the self-assembly of block copolymers with ligand-stabilized platinum nanoparticles, leading to lamellar CCM-Pt-4 and inverse hexagonal (CCM-Pt-6) hybrid mesostructures with high nanoparticle loadings. Pyrolysis of the CCM-Pt-6 hybrid produces an ordered mesoporous platinum-carbon nanocomposite with open and large pores (>/=10 nanometers).