DNA-based plasmonic nanoarchitectures: from structural design to emerging applications

Hierarchical Fabrication of Plasmonic Superlattice Membrane by Aspect-Ratio Controllable Nanobricks for Label-Free Protein Detection

Plasmonic superlattice membrane exhibits remarkable functional properties that are emerging from engineered assemblies of well-defined “meta-atoms,” which is featured as a conceptual new category of two-dimensional optical metamaterials. The ability to build plasmonic membranes over macroscopic surfaces but with nanoscale ordering is crucial for systematically controlling the light-matter interactions and represents considerable advances for the bottom-up fabrication of soft optoelectronic devices and circuits. Through rational design, novel nanocrystals, and by engineering the packing orders, the hybridized plasmon signature can be customized, promoting controllable near-field confinement for surface-enhanced Raman scattering (SERS) based detection. However, building such 2D architectures has proven to be remarkably challenging due to the complicated interparticle forces and multiscale interactions during self-assembly. Here, we report on the fabrication of ultralong-nanobrick-based giant plasmonic superlattice membranes as high-performance SERS substrates for ultrasensitive and label-free protein detection. Using aspect-ratio controllable short-to-ultralong nanobricks as building blocks, we construct three distinctive plasmonic membranes by polymer-ligand-based strategy in drying-mediated self-assembly at the air/water interfaces. The plasmonic membranes exhibit monolayered morphology with nanoscale assembled ordering but macroscopic lateral dimensions, inducing enhanced near-field confinement and uniform hot-spot distribution. By choosing 4-aminothiophenol and bovine serum albumin (BSA) as a model analyte, we establish an ultrasensitive assay for label-free SERS detection. The detection limit of BSA can reach 15 nM, and the enhancement factor reached 4.3 × 10⁵, enabling a promising avenue for its clinical application in ultrasensitive biodiagnostics.

DNA-Modulated Plasmon Resonance: Methods and Optical Applications

The near-field effects in the vicinity of metallic nanoparticle surfaces, as induced by electromagnetic radiation with specific wavelength, give rise to a variety of novel optical properties and attractive applications because of surface plasmons, which are the coherent oscillations of conduction electrons on a metal surface. The interdisciplinary field of plasmonics has witnessed vigorous growth, promoting research on the modulation of plasmon resonance by constructing advanced plasmonic nanoarchitectures with controllable size, morphology, or interparticle coupling. Among diversified tools, deoxyribonucleic nucleic acid (DNA) possesses prominent superiority as a result of its designability, programmability, addressability, and ease of nanomaterial modification. In this review, we focus on the methods and optical applications of plasmon resonance modulation accomplished by DNA nanotechnology. Recent developments in the construction of DNA-mediated plasmonic nanoarchitecture and key ongoing research directions utilizing unique optical features are highlighted. Obstacles and challenges in this field are pointed out, followed by preliminary suggestions on some areas of opportunity that deserve attention.

Self-assembly and characterization of 2D plasmene nanosheets

Freestanding plasmonic nanoparticle (NP) superlattice sheets are novel 2D nanomaterials with tailorable properties that enable their use for broad applications in sensing, anticounterfeit measures, ionic gating, nanophotonics and flat lenses. We recently developed a robust, yet general, two-step drying-mediated approach to produce freestanding monolayer, plasmonic NP superlattice sheets, which are typically held together by holey grids with minimal solid support. Within these superlattices, NP building blocks are closely packed and have strong plasmonic coupling interactions; hence, we termed such freestanding materials 'plasmene nanosheets'. Using the desired NP building blocks as starting material, we describe the detailed fabrication protocol, including NP surface functionalization by thiolated polystyrene and the self-assembly of NPs at the air-water interface. We also discuss various characterization approaches for checking the quality and optical properties of the as-obtained plasmene nanosheets: optical microscopy, spectrophotometry, transmission/scanning electron microscopy (TEM/SEM) and atomic force microscopy (AFM). With regard to different constituent building blocks, the key experimental parameters, including NP concentration and volume, are summarized to guide the successful fabrication of specific types of plasmene nanosheets. This protocol, from initial NP synthesis to the final fabrication and characterization, takes ~33.5 h.

Recent Advances in Multicomponent Particle Assembly

Particle assembly and co-assembly have been research frontiers in chemistry and material science in the past few decades. To achieve a large variety of intricate structures and functional materials, remarkable progress has been made in particle assembly principles and strategies. Essentially, particle assembly is driven by intrinsic interparticle interactions or the external control. In this article, we focus on binary or ternary particle co-assembly and review the principles and feasible strategies. These advances have led to new disciplines of microfabrication technology and material engineering. Although significant achievement on particle-based structures has been made, it is still challenging to fully develop general and facile strategies to precisely control the one-dimensional (1D) co-assembly. This article reviews the recent development on multicomponent particle co-assembly, which significantly increases structural complexity and functional diversity. In particular, we highlight the advances in the particle co-assembly of well-ordered 1D binary superstructures by liquid soft confinement. Finally, prospective outlook for future trends in this field is proposed.

Humidity-Responsive Single-Nanoparticle-Layer Plasmonic Films

2D materials possess many interesting properties, and have shown great application potentials. In this work, the development of humidity-responsive, 2D plasmonic nanostructures with switchable chromogenic properties upon wetting-dewetting transitions is reported. By exploiting DNA hybridization-directed anchoring of gold nanoparticles (AuNPs) on substrates, a series of single-nanoparticle-layer (SNL) plasmonic films is fabricated. Due to the collective plasmonic responses in SNL, these ultrathin 2D films display rapid and reversible red-blue color change upon the wetting-dewetting transition, suggesting that hydration-induced microscopic plasmonic coupling between AuNPs is replicated in the macroscopic, centimeter-scale films. It is also found that hydration finely tunes the electric field distribution between AuNPs in the SNL film, based on which responsive surface-enhanced Raman scattering substrates with spatially homogeneous hot spots are developed. Thus it is expected that DNA-mediated 2D SNL structures open new avenues for designing miniaturized plasmonic nanodevices with various applications.

Beyond quantification: in situ analysis of transcriptome and pre-mRNA alternative splicing at the nanoscale

In situ analysis offers a venue for dissecting the complex transcriptome in its natural context to tap into cellular processes that could explain the phenotypic physiology and pathology yet to be understood. Over the past decades, enormous progress has been made to improve the resolution, sensitivity, and specificity of single-cell technologies. The continued efforts in RNA research not only facilitates mechanistic studies of molecular biology but also provides state-of-the-art strategies for diagnostic purposes. The implementation of novel bio-imaging platforms has yielded valuable information for inspecting gene expression, mapping regulatory networks, and classifying cell types. In this article, we discuss the merits and technical challenges in single-molecule in situ RNA profiling. Advanced in situ hybridization methodologies developed for a variety of detection modalities are reviewed. Considering the fact that in mammalian cells the number of protein products immensely exceeds that of the actual coding genes due to pre-mRNA alternative splicing, tools capable of elucidating this process in intact cells are highlighted. To conclude, we point out future directions for in situ transcriptome analysis and expect a plethora of opportunities and discoveries in this field. WIREs Nanomed Nanobiotechnol 2017, 9:e1443. doi: 10.1002/wnan.1443 For further resources related to this article, please visit the WIREs website.

Tuning the Drug Loading and Release of DNA-Assembled Gold-Nanorod Superstructures

The use of DNA to assemble inorganic nanoparticles into superstructures is an emerging strategy to build non-toxic delivery vehicles for targeting diseases in the body. The impact of the core-satellite nanosystem design in mediating drug storage, drug release (via heat), and killing of HeLa cells in culture is investigated.

Nanomanufacturing: A Perspective

Nanomanufacturing, the commercially scalable and economically sustainable mass production of nanoscale materials and devices, represents the tangible outcome of the nanotechnology revolution. In contrast to those used in nanofabrication for research purposes, nanomanufacturing processes must satisfy the additional constraints of cost, throughput, and time to market. Taking silicon integrated circuit manufacturing as a baseline, we consider the factors involved in matching processes with products, examining the characteristics and potential of top-down and bottom-up processes, and their combination. We also discuss how a careful assessment of the way in which function can be made to follow form can enable high-volume manufacturing of nanoscale structures with the desired useful, and exciting, properties.

Two-Dimensional Bipyramid Plasmonic Nanoparticle Liquid Crystalline Superstructure with Four Distinct Orientational Packing Orders

Anisotropic plasmonic nanoparticles have been successfully used as constituent elements for growing ordered nanoparticle arrays. However, orientational control over their spatial ordering remains challenging. Here, we report on a self-assembled two-dimensional (2D) nanoparticle liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles (BNPs), which showed four distinct orientational packing orders, corresponding to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent particle building elements. These packing orders are characteristic of the unique shape of BNPs because all four packing modes were observed for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS packing orders were observed for the free-standing ordered array nanosheets formed from a drying-mediated self-assembly at the air/water interface of a sessile droplet. This is due to strong surface tension and the absence of particle-substrate interaction. In addition, we found the collective plasmonic coupling properties mainly depend on the packing type, and characteristic coupling peak locations depend on particle sizes. Interestingly, surface-enhanced Raman scattering (SERS) enhancements were heavily dependent on the orientational packing ordering. In particular, V-NLCS showed the highest Raman enhancement factor, which was about 77-fold greater than the H-NLCS and about 19-fold greater than C-NLCS. The results presented here reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays.

Linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic nanoantennas

We study the linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic gap nanoantennas. Using a two-step-aligned electron beam lithography process, we demonstrate the ability to selectively and reproducibly fill the gap region of nanoantennas with dielectric nanoparticles made of lithium niobate (LiNbO3) with high efficiency. The linear optical properties of the antennas are modified due to the large refractive index of the material. This leads to a change in the coupling strength as well as an increase of the effective refractive index of the surrounding. The combination of these two effects causes a red- or blue-shift of the plasmonic modes, respectively. We find that the nonlinear optical properties of the combined system are only modified in the range of one order of magnitude. The observed changes in our experiments in the nonlinear emission can be traced to the changed dielectric environment and thus the modified linear optical properties. The intrinsic nonlinearity of the dielectric used is in fact small when compared to the nonlinearity of the metallic part of the hybrid antennas. Thus, the nonlinear signals generated by the antenna itself are dominant in our experiments. We demonstrate that the well-known nonlinear response of bulk dielectric materials cannot always straightforwardly be used to boost the nonlinear response of nanoscale antenna systems. Our results significantly deepen the understanding of these interesting hybrid systems and offer important guidelines for the design of nanoscale, nonlinear light sources.

Helical silver(I)-glutathione biocoordination polymer nanofibres

Helical nanofibres of silver(I)-glutathione (Ag-GSH) biocoordination polymer (BCP) are fabricated by introducing dimethyl sulfoxide into the mixture solution of Ag⁺ ions and L-GSH molecules. The prepared BCP nanofibres show hierarchical helical structures, which are constructed via twisting of small fibres. Water-soluble helices could be further cross-linked with Ca²⁺ ions to form a well-dispersed aqueous suspension. When gold nanorods are adsorbed onto these helical nanofibres, the unique plasmon-induced circular dichroism characteristic is observed in the region of the local surface plasmon resonance of gold nanorods. This type of chiroptical metamaterials may have promising applications in nonlinear optics, negative refraction and biosensing.

DNA patchy particles

A simple and effective way to make DNA patchy particles is reported. A small patch of DNA strands is "stamped" from a gold surface onto colloidal particles of different sizes by streptavidin-biotin bonds. These DNA patchy particles provide direction-selective and thermoreversible interactions, and hence can lead to unique assembly protocols and structures controlled by temperature.