Tuning the Optical Coupling between Molecular Dyes and Metal Nanoparticles by the Templated Silica Mineralization of J‑Aggregates

Supramolecular porphyrin aggregates are used as a template for the higher-order assembly of fluorophore–dielectric–metal hybrid nanostructures in which the optical properties of the molecules are modulated by the finely tuned coupling to localized plasmons. First, J-aggregates are encapsulated inside a dielectric silica shell of well-controlled thickness, which reinforces mechanically the template and serves as a precise optical coupling spacer. The silicified J-aggregates are then decorated with gold or silver nanoparticles. UV–visible and fluorescence spectroscopies show that the presence of metal nanoparticles induces a marked enhancement of the J-aggregate fluorescence when the silica thickness is tuned to 7–12 nm, whereas a significant quenching is measured when the dielectric thickness is sub-2 nm. Interestingly, the enhancement is maximized when oxidized silver nanoparticles are placed very close to the J-aggregates

Novel Bioinorganic Nanostructures Based on Mesolamellar Intercalation or Single-Molecule Wrapping of DNA Using Organoclay Building Blocks

Nanosheets or nanoclusters of aminopropyl-functionalized magnesium phyllosilicate (AMP) were prepared in water by exfoliation and used as structural building blocks for the preparation of DNA-based hybrid nanostructures in the form of ordered mesolamellar nanocomposites or highly elongated nanowires, respectively. The former consisted of alternating layers of single sheets of AMP interspaced with intercalated monolayers of intact double-stranded DNA molecules of relatively short length (∼700 base pairs) that were accessible to small molecules such as ethidium bromide. In contrast, the nanowires comprised isolated micrometer-long molecules of λ-DNA or plasmid DNA that were sheathed in an ultrathin organoclay layer and which were either protected from or remained accessible to endonuclease-mediated clipping depending on the extent of biomolecule wrapping. Both types of hybrid nanostructures showed a marked increase in the DNA melting (denaturation) temperature, indicating significant thermal stabilization of the confined biomolecules. Our results suggest that nanoscale building blocks derived from organically modified inorganic clays could be useful agents for enhancing the chemical, thermal, and mechanical stability of isolated molecules or ensembles of DNA. Such constructs should have increased potential as functional components in bionanotechnology and nonviral gene transfection

Plasmonic Hot Printing in Gold Nanoprisms

The raster-scanned irradiation of ultrathin sub-micrometer crystalline gold colloidal prisms with the tightly focused spot of a femtosecond, near-infrared laser triggers the deterministic deformation and partial melting of nanometer-sized areas of the nanoprisms. The morphological modification of the Au nanoprisms evidences extremely localized sources of heat, the in-plane distribution of which varies with the particle shape and laser polarization. We demonstrate for the first time the direct relationship between heat source density and surface plasmon local density of states (SP-LDOS), which describes quantitatively the rich modal structure of the surface plasmons sustained by the 2D metallic platelets, independently of the knowledge of the illumination configuration. Green’s Dyadic numerical simulations confirm that the optical excitation of the 2D SP modes results in the subwavelength hot imprinting of the SP modal pattern onto the metal surface

Plasmonic Nanoparticle Networks for Light and Heat Concentration

Self-assembled plasmonic nanoparticle networks (PNN) composed of chains of 12 nm diameter crystalline gold nanoparticles exhibit a longitudinally coupled plasmon mode centered at 700 nm. We have exploited this longitudinal absorption band to efficiently confine light fields and concentrate heat sources in the close vicinity of these plasmonic chain networks. The mapping of the two phenomena on the same superstructures was performed by combining two-photon luminescence and fluorescence polarization anisotropy imaging techniques. Besides the light and heat concentration, we show experimentally that the planar spatial distribution of optical field intensity can be simply modulated by controlling the linear polarization of the incident optical excitation. On the contrary, the heat production, which is obtained here by exciting the structures within the optically transparent window of biological tissues, is evenly spread over the entire PNN. This contrasts with the usual case of localized heating in continuous nanowires, thus opening opportunities for these networks in light-induced hyperthermia applications. Furthermore, we propose a unified theoretical framework to account for both the nonlinear optical and thermal near-fields around PNN. The associated numerical simulations, based on a Green's function formalism, are in excellent agreement with the experimental images. This formalism therefore provides a versatile tool for the accurate engineering of optical and thermodynamical properties of complex plasmonic colloidal architectures

Selection of Arginine-Rich Anti-Gold Antibodies Engineered for Plasmonic Colloid Self-Assembly

Antibodies are affinity proteins with a wide spectrum of applications in analytical and therapeutic biology. Proteins showing specific recognition for a chosen molecular target can be isolated and their encoding sequence identified in vitro from a large and diverse library by phage display selection. In this work, we show that this standard biochemical technique rapidly yields a collection of antibody protein binders for an inorganic target of major technological importance: crystalline metallic gold surfaces. Twenty-one distinct anti-gold antibody proteins emerged from a large random library of antibodies, and they were sequenced. The systematic statistical analysis of all the protein sequences reveals a strong occurrence of arginine in anti-gold antibodies, which corroborates recent molecular dynamics predictions on the crucial role of arginine in protein/gold interactions. Once tethered to small gold nanoparticles using histidine tag chemistry, the selected antibodies could drive the self-assembly of the colloids onto the surface of single crystalline gold platelets as a first step toward programmable protein-driven construction of complex plasmonic architectures. Electrodynamic simulations based on the Green Dyadic Method suggest that the antibody-driven assembly demonstrated here could be exploited to significantly modify the plasmonic modal properties of the gold platelets. Our work shows that molecular biology tools can be used to design the interaction between fully folded proteins and inorganic surfaces with potential applications in the bottom-up construction of plasmonic hybrid nanomaterials

Plasmonic Shaping in Gold Nanoparticle Three-Dimensional Assemblies

When a large number of similar gold particles are organized into complex architectures, the dipolar plasmon spectrum of the individual plasmonic entities gives rise to a broader, red-shifted feature centered around 750 nm. In this work, we show that superstructures fabricated using the convective assisted capillary force assembly method (CA-CFA) and excited at that wavelength display a subwavelength patterning of their optical field intensity that results from the self-consistent coupling between the colloidal nanoparticles. First, we demonstrate the fabrication of shape-controlled three-dimensional assemblies of metallic nanocrystals using the CA-CFA method. In a second step, the absorption band resulting from the mutual coupling between the metallic building blocks is exploited to excite a coupled plasmon mode and map the two-photon luminescence (TPL) by scanning a tightly focused light beam. Highly resolved TPL images show that the morphology of the plasmonic particle assemblies has a strong impact on their optical response. A model based on a rigorous optical Gaussian beam implementation inside a generalized propagator derived from a three-dimensional Green dyadic function accurately reproduces the TPL maps revealing the influence of interparticle separation and thus coupling between the individual particles. Finally, we show that the spatial distribution of the electric field intensity can be controlled by tuning the linear polarization of the optical excitation

Designing plasmonic eigenstates for optical signal transmission in planar channel devices

On-chip optoelectronic and all-optical information processing paradigms require compact implementation of signal transfer for which nanoscale surface plasmons circuitry offers relevant solutions. This work demonstrates the directional signal transmittance mediated by 2D plasmonic eigenmodes supported by crystalline cavities. Channel devices comprising two mesoscopic triangular input and output ports and sustaining delocalized, higher-order plasmon resonances in the visible to infra-red range are shown to enable the controllable transmittance between two confined entry and exit ports coupled over a distance exceeding 2 $\mu$m. The transmittance is attenuated by > 20dB upon rotating the incident linear polarization, thus offering a convenient switching mechanism. The optimal transmittance for a given operating wavelength depends on the geometrical design of the device that sets the spatial and spectral characteristic of the supporting delocalized mode. Our approach is highly versatile and opens the way to more complex information processing using pure plasmonic or hybrid nanophotonic architectures

Elucidation of the Self-Assembly Pathway of Lanreotide Octapeptide into β-Sheet Nanotubes: Role of Two Stable Intermediates

Nanofabrication by molecular self-assembly involves the design of molecules and self-assembly strategies so that shape and chemical complementarities drive the units to organize spontaneously into the desired structures. The power of self-assembly makes it the ubiquitous strategy of living organized matter and provides a powerful tool to chemists. However, a challenging issue in the self-assembly of complex supramolecular structures is to understand how kinetically efficient pathways emerge from the multitude of possible transition states and routes. Unfortunately, very few systems provide an intelligible structure and formation mechanism on which new models can be developed. Here, we elucidate the molecular and supramolecular self-assembly mechanism of synthetic octapeptide into nanotubes in equilibrium conditions. Their complex hierarchical self-assembly has recently been described at the mesoscopic level, and we show now that this system uniquely exhibits three assembly stages and three intermediates: (i) a peptide dimer is evidenced by both analytical centrifugation and NMR translational diffusion experiments; (ii) an open ribbon and (iii) an unstable helical ribbon are both visualized by transmission electron microscopy and characterized by small angle X-ray scattering. Interestingly, the structural features of two stable intermediates are related to the final nanotube organization as they set, respectively, the nanotube wall thickness and the final wall curvature radius. We propose that a specific self-assembly pathway is selected by the existence of such preorganized and stable intermediates so that a unique final molecular organization is kinetically favored. Our findings suggests that the rational design of oligopeptides can encode both molecular- and macro-scale morphological characteristics of their higher-order assemblies, thus opening the way to ultrahigh resolution peptide scaffold engineering

Compact Implementation of a 1‑Bit Adder by Coherent 2‑Beam Excitation of a Single Plasmonic Cavity

We demonstrate experimentally the dual beam optical drive of an interconnect-free 2-input, 2-output 1-bit adder implemented inside a single gold plasmonic cavity, focused ion milled in an ultrathin single crystalline gold microplate. To obtain this result, we have set a coherent 2-beam excitation scheme up that allows us to independently and arbitrarily choose the intensity, polarization, and relative phase shift of two femtosecond-pulsed laser spots. The spots are focused on any chosen location of the micrometer-sized plasmonic cavity. The nonlinear photoluminescence (NPL) response of the cavity encodes the Boolean output, while the Boolean inputs are borne by the linear polarizations of the excitation. A generic map analysis tool is developed to pinpoint the realized Boolean functions and to assess their robustness. This tool is used to demonstrate the experimental implementation of the elusive XOR gate and its combination with an AND gate in the same cavity to perform the full 1-bit adder. The analysis of 160,000 instances of the 1-bit adder clearly shows the soundness of our approach and reveals some underlying mechanistic features of the remotely generated NPL. These results establish the first practical step of a general approach to cascade-free all-optical arithmetic and logic units