Plasmonic color palettes for photorealistic printing with aluminum nanostructures.

We introduce the first plasmonic palette utilizing color generation strategies for photorealistic printing with aluminum nanostructures. Our work expands the visible color space through spatially mixing and adjusting the nanoscale spacing of discrete nanostructures. With aluminum as the plasmonic material, we achieved enhanced durability and dramatically reduced materials costs with our nanostructures compared to commonly used plasmonic materials such as gold and silver, as well as size regimes scalable to higher-throughput approaches such as photolithography and nanoimprint lithography. These advances could pave the way toward a new generation of low-cost, high-resolution, plasmonic color printing with direct applications in security tagging, cryptography, and information storage.

Crystallization of DNA-capped gold nanoparticles in high-concentration, divalent salt environments.

The multiparametric nature of nanoparticle self-assembly makes it challenging to circumvent the instabilities that lead to aggregation and achieve crystallization under extreme conditions. By using non-base-pairing DNA as a model ligand instead of the typical base-pairing design for programmability, long-range 2D DNA-gold nanoparticle crystals can be obtained at extremely high salt concentrations and in a divalent salt environment. The interparticle spacings in these 2D nanoparticle crystals can be engineered and further tuned based on an empirical model incorporating the parameters of ligand length and ionic strength.

Engineering Nanocarriers for siRNA Delivery.

The discovery of RNA interference has revitalized the long ongoing pursuit of gene therapy for the treatment of diseases. Nevertheless, despite promising results from experimental studies, there remains a pressing need for the development of nanocarriers that are clinically-relevant, biocompatible, efficient, and that can be tailored to specific disease targets. This review surveys the broad spectrum of nanomaterials and their functional add-ons, and aims to provide a guide towards engineering nanocarriers for effective siRNA delivery.

Free-standing nanoparticle superlattice sheets controlled by DNA.

Free-standing nanoparticle superlattices (suspended highly ordered nanoparticle arrays) are ideal for designing metamaterials and nanodevices free of substrate-induced electromagnetic interference. Here, we report on the first DNA-based route towards monolayered free-standing nanoparticle superlattices. In an unconventional way, DNA was used as a 'dry ligand' in a microhole-confined, drying-mediated self-assembly process. Without the requirement of specific Watson-Crick base-pairing, we obtained discrete, free-standing superlattice sheets in which both structure (inter-particle spacings) and functional properties (plasmonic and mechanical) can be rationally controlled by adjusting DNA length. In particular, the edge-to-edge inter-particle spacing for monolayered superlattice sheets can be tuned up to 20 nm, which is a much wider range than has been achieved with alkyl molecular ligands. Our method opens a simple yet efficient avenue towards the assembly of artificial nanoparticle solids in their ultimate thickness limit--a promising step that may enable the integration of free-standing superlattices into solid-state nanodevices.

Photocrosslinked DNA nanospheres for drug delivery.

DNA has been employed as both a genetic and a generic material. X-shaped DNA (X-DNA) in particular has four branched arms, providing multivalent functionalities that can allow for simultaneous multiple crosslinking. Here we report the synthesis of four acrylate-functionalized X-DNA monomers that can be further photocrosslinked to form monodisperse and tunable DNA nanospheres. In particular, the size and surface charge of these nanospheres were precisely controlled in a linear fashion, simply by tuning the monomer concentration in the reaction. The morphology and surface properties of the nanospheres were characterized using FT-IR, HPLC, TEM, AFM, zeta potential, and DLS analysis. In vitro studies in mammalian cells revealed that these DNA nanospheres demonstrated significant efficacy in the delivery of doxorubicin. These results highlight the potential of using DNA as material building blocks to design novel nanocarriers with properties tailored for the delivery of drugs in general and DNA/RNA in particular.

Surface coating directed cellular delivery of TAT-functionalized quantum dots.

TAT peptide functionalized shell-core ZnS-CdSe quantum dots (QDs) have been prepared by three different methods, direct ligand exchange with cysteine-terminated TAT (TAT-QD(lig exch)), and covalent conjugation to QDs coated with silanes (TAT-QD(silica)) and polyacrylate derivatives (TAT-QD(polyacrylate)). The silica and polyacrylate coatings incorporated multiple primary and secondary amines, introducing positive surface charges onto the QDs, providing high water solubility and sites for peptide conjugation, while inducing the "proton sponge effect". The different coating methods produced particles of different sizes, surface charges, and colloidal stability; these factors jointly influenced the cellular uptake and subcellular localization of these particles. As the particle size increased, (TAT-QD(lig exch) (6 nm) < TAT-QD(silica) (10 nm) < QD(polyacrylate) (25 nm)), both the particle surface charge and cellular uptake increased. The smaller TAT-QD(lig exch) and TAT-QD(silica) particles were localized mainly in the perinuclear regions, while the larger TAT-QD(polyacrylate) particles were localized in both the perinuclear regions and the lysosomes. Compared to the other TAT-QDs, TAT-QD(lig-exch) has a lower colloidal stability and was more cytotoxic due to the weak binding of the ligands.

Accurate Modeling of Dark-Field Scattering Spectra of Plasmonic Nanostructures.

Dark-field microscopy is a widely used tool for measuring the optical resonance of plasmonic nanostructures. However, current numerical methods for simulating the dark-field scattering spectra were carried out with plane wave illumination either at normal incidence or at an oblique angle from one direction. In actual experiments, light is focused onto the sample through an annular ring within a range of glancing angles. In this paper, we present a theoretical model capable of accurately simulating the dark-field light source with an annular ring. Simulations correctly reproduce a counterintuitive blue shift in the scattering spectra from gold nanodisks with a diameter beyond 140 nm. We believe that our proposed simulation method can be potentially applied as a general tool capable of simulating the dark-field scattering spectra of plasmonic nanostructures as well as other dielectric nanostructures with sizes beyond the quasi-static limit.

Three-dimensional plasmonic stereoscopic prints in full colour.

Metal nanostructures can be designed to scatter different colours depending on the polarization of the incident light. Such spectral control is attractive for applications such as high-density optical storage, but challenges remain in creating microprints with a single-layer architecture that simultaneously enables full-spectral and polarization control of the scattered light. Here we demonstrate independently tunable biaxial colour pixels composed of isolated nanoellipses or nanosquare dimers that can exhibit a full range of colours in reflection mode with linear polarization dependence. Effective polarization-sensitive full-colour prints are realized. With this, we encoded two colour images within the same area and further use this to achieve depth perception by realizing three-dimensional stereoscopic colour microprint. Coupled with the low cost and durability of aluminium as the functional material in our pixel design, such polarization-sensitive encoding can realize a wide spectrum of applications in colour displays, data storage and anti-counterfeiting technologies.

Building plasmonic nanostructures with DNA.

Plasmonic structures can be constructed from precise numbers of well-defined metal nanoparticles that are held together with molecular linkers, templates or spacers. Such structures could be used to concentrate, guide and switch light on the nanoscale in sensors and various other devices. DNA was first used to rationally design plasmonic structures in 1996, and more sophisticated motifs have since emerged as effective and versatile species for guiding the assembly of plasmonic nanoparticles into structures with useful properties. Here we review the design principles for plasmonic nanostructures, and discuss how DNA has been applied to build finite-number assemblies (plasmonic molecules), regularly spaced nanoparticle chains (plasmonic polymers) and extended two- and three-dimensional ordered arrays (plasmonic crystals).

Crystalline Gibbs monolayers of DNA-capped nanoparticles at the air-liquid interface.

Using grazing-incidence small-angle X-ray scattering in a special configuration (parallel SAXS, or parSAXS), we mapped the crystallization of DNA-capped nanoparticles across a sessile droplet, revealing the formation of crystalline Gibbs monolayers of DNA-capped nanoparticles at the air-liquid interface. We showed that the spatial crystallization can be regulated by adjusting both ionic strength and DNA sequence length and that a modified form of the Daoud-Cotton model could describe and predict the resulting changes in interparticle spacing. Gibbs monolayers at the air-liquid interface provide an ideal platform for the formation and study of equilibrium nanostructures and may afford exciting routes toward the design of programmable 2D plasmonic materials and metamaterials.

DNA nanomedicine: Engineering DNA as a polymer for therapeutic and diagnostic applications.

Nanomedicine, the application of nanotechnology to medicine, encompasses a broad spectrum of fields including molecular detection, diagnostics, drug delivery, gene regulation and protein production. In recent decades, DNA has received considerable attention for its functionality and versatility, allowing it to help bridge the gap between materials science and biological systems. The use of DNA as a structural nanoscale material has opened a new avenue towards the rational design of DNA nanostructures with different polymeric topologies. These topologies, in turn, possess unique characteristics that translate to specific therapeutic and diagnostic strategies within nanomedicine.