Plasmonic Supercrystals

Abstract

CONSPECTUS: For decades, plasmonic nanoparticles have been extensively studied due to their extraordinary properties, related to localized surface plasmon resonances. A milestone in the field has been the development of the so-called seedmediated growth method, a synthetic route that provided access to an extraordinary diversity of metal nanoparticles with tailored size, geometry and composition. Such a morphological control came along with an exquisite definition of the optical response of plasmonic nanoparticles, thereby increasing their prospects for implementation in various fields. The susceptibility of surface plasmons to respond to small changes in the surrounding medium or to perturb (enhance/quench) optical processes in nearby molecules, has been exploited for a wide range of applications, from biomedicine to energy harvesting. However, the possibilities offered by plasmonic nanoparticles can be expanded even further by their careful assembly into either disordered or ordered structures, in 2D and 3D. The assembly of plasmonic nanoparticles gives rise to coupling/hybridization effects, which are strongly dependent on interparticle spacing and orientation, generating extremely high electric fields (hot spots), confined at interparticle gaps. Thus, the use of plasmonic nanoparticle assemblies as optical sensors have led to improving the limits of detection for a wide variety of (bio)molecules and ions. Importantly, in the case of highly ordered plasmonic arrays, other novel and unique optical effects can be generated. Indeed, new functional materials have been developed via the assembly of nanoparticles into highly ordered architectures, ranging from thin films (2D) to colloidal crystals or supercrystals (3D). The progress in the design and fabrication of 3D supercrystals could pave the way toward next generation plasmonic sensors, photocatalysts, optomagnetic components, metamaterials, etc. In this Account, we summarize selected recent advancements in the field of highly ordered 3D plasmonic superlattices. We first analyze their fascinating optical properties, for various systems with increasing degrees of complexity, from an individual metal nanoparticle through particle clusters with low coordination numbers, to disordered self-assembled structures and finally to supercrystals. We then describe recent progress in the fabrication of 3D plasmonic supercrystals, focusing on specific strategies but without delving into the forces governing the self-assembly process. In the last section, we provide an overview of the potential applications of plasmonic supercrystals, with a particular emphasis on those related with surface-enhanced Raman scattering (SERS) sensing, followed by a brief highlight of the main conclusions and remaining challenges.

Structural order in plasmonic superlattices

“…The polaritonic modes broaden or even vanish for a decreasing particle and crystalline quality. The large transmittance of light and small interparticle gaps lead to a strong near-field intensity enhancement at the gaps between the NPs throughout the entire supercrystal 4,54,63 . In combination with the tunability of the polaritonic excitations, this makes plasmonic supercrystals a promising platform for applications in sensing and spectroscopy 4,64,65 .…”

“…rdered arrays and superlattices of nanoparticles (NPs) have a huge potential for new materials with tuneable electrical, optical, and mechanical properties [1][2][3][4][5][6][7][8][9][10][11][12][13] . Common strategies to produce such structures include lithographybased nanofabrication [14][15][16] , and self-assembly of NPs functionalized with polymers 10 , DNA [17][18][19][20][21][22] , or dendritic molecules 23,24 .…”

Self-Assembly of Metal Nanoparticles, an Important Process to the Development of New Nanostructured Materials and Devices

“…28 De forma geral, independentemente do método empregado para a síntese de nanopartículas, pode-se dizer que o controle dos parâmetros de síntese para a geração de nanopartículas com dimensões homogêneas, i.e. partículas com baixas dispersões de tamanho e forma, é fundamental para uma correta aplicação, seja para a produção de sensores, 49,50 quanto de catalisadores, 51 53 Os sistemas coloidais são os modelos de materiais nanoestruturados mais estudados.…”

Mild Homogeneous Synthesis of Gold Nanoparticles through the Epoxide Route: Kinetics, Mechanisms, and Related One‐Pot Composites

“…[2,3,4] This wide variety of AuNP with well-controlleds izes and shapes was exploited for the production of new opticals ensors, [5,6] sensors based on surface-enhanced Raman spectroscopy, [7,8] more efficient catalysts, [9,10,11,12] and for innovative medical [13,14] and biological applications. [15,16] Depending on the chosen applications, the nanoparticles can be used directly in solution,f orming arrays ontos urfaces [17] or embedded in inorganic or polymericm atrices, in nanocomposites. [18,19,10,12] The reported methods to obtain such nanoparticles typically involve the direct mixture of the reagents and can be divided into two families:o ne-step synthesis or seedmediated approaches.…”