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1. Plasmon-Coupled Gold Nanoparticles in Stretched Shape-Memory Polymers for Mechanical/Thermal Sensing

   https://doi.org/10.1021/acsanm.1c00309  

   Yadav, Prachi R.; Rizvi, Mehedi H.; Kuttich, Björn; Mishra, Sumeet R.; Chapman, Brian S.; Lynch, Brian B.; Kraus, Tobias; Oldenburg, Amy L.; Tracy, Joseph B. (March 2021, ACS Applied Nano Materials)

   null (Ed.)

   The organization of plasmonic nanoparticles (NPs) determines the strength and polarization dependence of coupling of their surface plasmons. In this study, plasmon coupling of spherical Au NPs with an average diameter of 15 nm was investigated in shape-memory polymer films before and after mechanical stretching and then after thermally driving shape recovery. Clusters of Au NPs form when preparing the films that exhibit strong plasmon coupling. During stretching, a significant polarization-dependent response develops, where the optical extinction maximum corresponding to the surface plasmon resonance is redshifted by 19 nm and blueshifted by 7 nm for polarization parallel and perpendicular to the stretching direction, respectively. This result can be explained by non-uniform stretching on the nanoscale, where plasmon coupling increases parallel to the shear direction as Au NPs are pulled into each other during stretching. The polarization dependence vanishes after shape recovery, and structural characterization confirms the return of isotropy consistent with complete nanoscale recovery of the initial arrangement of Au NPs. Simulations of the polarized optical responses of Au NP dimers at different interparticle spacings establish a plasmon ruler for estimating the average interparticle spacings within the experimental samples. An investigation of the temperature-dependent recovery behavior demonstrates an application of these materials as optical thermal history sensors. 

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2. Nanoscale goldbeating: Solid-state transformation of 0D and 1D gold nanoparticles to anisotropic 2D morphologies

   https://doi.org/10.1093/pnasnexus/pgad267  

   Tanjil, Md Rubayat-E; Gupta, Tanuj; Gole, Matthew T; Suero, Keegan P; Yin, Zhewen; McCleeary, Donald J; Douglas, Ossie R; Kincanon, Maegen M; Rudawski, Nicholas G; Anderson, Alissa B; et al (August 2023, PNAS Nexus)

   Walters, Keisha (Ed.)

   Abstract Goldbeating is the ancient craft of thinning bulk gold (Au) into gossamer leaves. Pioneered by ancient Egyptian craftsmen, modern mechanized iterations of this technique can fabricate sheets as thin as ∼100 nm. We take inspiration from this millennia-old craft and adapt it to the nanoscale regime, using colloidally synthesized 0D/1D Au nanoparticles (AuNPs) as highly ductile and malleable nanoscopic Au ingots and subjecting them to solid-state, uniaxial compression. The applied stress induces anisotropic morphological transformation of AuNPs into 2D leaf form and elucidates insights into metal nanocrystal deformation at the extreme length scales. The induced 2D morphology is found to be dependent on the precursor 0D/1D NP morphology, size (0D nanosphere diameter and 1D nanorod diameter and length), and their on-substrate arrangement (e.g., interparticle separation and packing order) prior to compression. Overall, this versatile and generalizable solid-state compression technique enables new pathways to synthesize and investigate the anisotropic morphological transformation of arbitrary NPs and their resultant emergent phenomena. 

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3. Substrate-immobilized noble metal nanoplates: a review of their synthesis, assembly, and application

   https://doi.org/10.1039/d1tc01494c  

   Neal, Robert D.; Hughes, Robert A.; Preston, Arin S.; Golze, Spencer D.; Demille, Trevor B.; Neretina, Svetlana (January 2021, Journal of Materials Chemistry C)

   null (Ed.)

   Noble metal nanoplates are a unique class of two-dimensional (2D) nanomaterials whose planar geometry serves as one of the most important nanoscale building blocks. Referred to by names such as nanoplates, nanodisks, nanoprisms, and nanotriangles, they offer a distinct and compelling set of physicochemical properties renowned for their plasmonic response and catalytic activity. When immobilized on substrates, these same structures are empowered with new capabilities triggered by synergistic interactions with their support and coupling phenomena activated when adjacent nanostructures are held in place with nanometer-scale spacings. In this review, we bring together an impressive literature dedicated to the synthesis, assembly, and application of substrate-immobilized noble metal nanoplates where we highlight the interplay between the nanostructures and their support as a means for deriving a distinct and diverse product. Methods for obtaining substrate-bound nanoplates rely on colloid-to-substrate transfers or syntheses occurring directly on the substrate-surface and span a wide range of techniques including chemisorption, solvent evaporation assembly, air–liquid interfacial assembly, substrate- and seed-mediated syntheses, electrochemical syntheses, vapor-phase depositions, DNA-assisted assembly, and capillary assembly. Collectively, these techniques realize nanoplate formations that are random, close-packed assemblies, periodic arrays, and three-dimensional superlattices. Nanoplate functionality is demonstrated in sensor applications with a broad range of analytes that include explosives, environmentally persistent pollutants, illicit drugs, and microRNA biomarkers for cancer and cardiovascular disease, with proof-of-concept demonstrations as active plasmonics, skin-mountable sensors, point-of-care diagnostics, and electrochemical reactors. Together, this work demonstrates substrate-immobilized nanoplates as a powerful platform for realizing photo- and chemically-active surfaces of technological relevance. 

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4. Tunable Orientation and Assembly of Polymer-Grafted Nanocubes at Fluid–Fluid Interfaces

   https://doi.org/10.1021/acsnano.1c10416  

   Zhou, Yilong; Tang, Tsung-Yeh; Lee, Brian Hyun-jong; Arya, Gaurav (April 2022, ACS Nano)

   Self-assembly of faceted nanoparticles is a promising route for fabricating nanomaterials; however, achieving low-dimensional assemblies of particles with tunable orientations is challenging. Here, we demonstrate that trapping surface-functionalized faceted nanoparticles at fluid–fluid interfaces is a viable approach for controlling particle orientation and facilitating their assembly into unique one- and two-dimensional superstructures. Using molecular dynamics simulations of polymer-grafted nanocubes in a polymer bilayer along with a particle-orientation classification method we developed, we show that the nanocubes can be induced into face-up, edge-up, or vertex-up orientations by tuning the graft density and differences in their miscibility with the two polymer layers. The orientational preference of the nanocubes is found to be governed by an interplay between the interfacial area occluded by the particle, the difference in interactions of the grafts with the two layers, and the stretching and intercalation of grafts at the interface. The resulting orientationally constrained nanocubes are then shown to assemble into a variety of unusual architectures, such as rectilinear strings, close-packed sheets, bilayer ribbons, and perforated sheets, which are difficult to obtain using other assembly methods. Our work thus demonstrates a versatile strategy for assembling freestanding arrays of faceted nanoparticles with possible applications in plasmonics, optics, catalysis, and membranes, where precise control over particle orientation and position is required. 

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5. Open and Close‐Packed, Shape‐Engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances

   https://doi.org/10.1002/adma.202301323  

   Cai, Yi‐Yu; Fallah, Asma; Yang, Shengsong; Choi, Yun Chang; Xu, Jun; Stein, Aaron; Kikkawa, James M.; Murray, Christopher B.; Engheta, Nader; Kagan, Cherie R. (August 2023, Advanced Materials)

   Abstract A top‐down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well‐defined sizes, shapes, and compositions that are often not accessible by wet‐chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template‐assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size‐ and shape‐engineered templates and organize into open or close‐packed multi‐NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal‐shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open and close‐packed architectures highlights that introduction of a center NP to form close‐packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation‐dependent scattering response. 

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