This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce ∼4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applica...

Anisotropic metal nanoparticles: Synthesis, assembly, and optical applications

Plasmons in strongly coupled metallic nanostructures.

The design and realization of metallic nanostructures with tunable plasmon resonances has been greatly advanced by combining a wealth of nanofabrication techniques with advances in computational electromagnetic design. Plasmonics — a rapidly emerging subdiscipline of nanophotonics — is aimed at exploiting both localized and propagating surface plasmons for technologically important applications, specifically in sensing and waveguiding. Here we present a brief overview of this rapidly growing research field.

https://dsl.nju.edu.cn/litao/res/Plasmonic%20review/%5bReview%20article%5d%20nphoton.2007%20Photonic-Nano-optics%20from%20sensing%20to%20waveguiding.pdf

Nano-optics from sensing to waveguiding

J-aggregates are of significant interest for organic materials conceived by supramolecular approaches. Their discovery in the 1930s represents one of the most important milestones in dye chemistry as well as the germination of supramolecular chemistry. The intriguing optical properties of J-aggregates (in particular, very narrow red-shifted absorption bands with respect to those of the monomer and their ability to delocalize and migrate excitons) as well as their prospect for applications have motivated scientists to become involved in this field, and numerous contributions have been published. This Review provides an overview on the J-aggregates of a broad variety of dyes (including cyanines, porphyrins, phthalocyanines, and perylene bisimides) created by using supramolecular construction principles, and discusses their optical and photophysical properties as well as their potential applications. Thus, this Review is intended to be of interest to the supramolecular, photochemistry, and materials science communities.

J-aggregates: from serendipitous discovery to supramolecular engineering of functional dye materials.

A 1,340-fold increase in single-molecule fluorescence has been observed from a lithographically fabricated gold bowtie nanoantenna — approximately an order of magnitude greater than that achieved in previous reports on such structures. The improvement results from an estimated ninefold increase in quantum efficiency, caused by enhanced absorption and an increased radiative emission rate.

Large single-molecule fluorescence enhancements produced by a bowtie nanoantenna

We have investigated the optical response of periodic arrays of metallic (gold) nanoparticles composed of a pair of particles on each lattice site. By varying the interparticle separation within the pairs from dielectric proximity to conductive contact on a nanometer scale, we observe an abrupt, large renormalization as well as a splitting of the surface plasmon polariton energy. These spectral anomalies are ascribed to a transition whereupon the interparticle dipole−dipole interaction is shunted and the plasmon polaritons exhibit multipolar behavior, including a very high local concentration of electromagnetic energy in the vicinity of their conductive contact.

Strongly Interacting Plasmon Nanoparticle Pairs: From Dipole−Dipole Interaction to Conductively Coupled Regime

Nanoengineered fluorescent response is reported from semiconductor core-shell (CdSe/ZnS) quantum dots in proximity to the surface plasmon polariton field of periodic Ag nanoparticle arrays. Tuning the surface plasmon polariton resonance to the quantum dot exciton emission band results in an enhancement of up to approximately 50-fold in the overall fluorescence efficiency, in a design where each Ag nanoparticle is interconnected by a continuous Ag thin film. Propagating modes of surface plasmon resonances have a direct impact on the fluorescence enhancement.

Large enhancement of fluorescence efficiency from CdSe/ZnS quantum dots induced by resonant coupling to spatially controlled surface plasmons.

Highly efficient resonant coupling of optical excitations in hybrid organic/inorganic semiconductor nanostructures

Solid state cavity QED: Strong coupling in organic thin films

Metal nanoparticles are being actively explored for applications that use localized surface plasmon (LSP) resonance for optical sensing. Here we report an electrostatic field sensing technique which has been applied to detection of mammalian brain cell activity, by optically measuring the cellular potential induced shift in the SP resonance mode of an adjacent planar gold nanoparticle array. An experimental scheme was first devised which enables a quantitative calibration of the field-induced plasmon resonance modulation in air. Hippocampal (brain) neural cells were then grown onto the nanoparticle template and cellular level individual transient signals were detected optically when the chemically triggered neurons switched their potential. Experimental data are compared with calculations using the Drude model for the dielectric response of gold and the Stern model for the metal-electrolyte junction, with good agreement.

/pdf/optical-detection-of-brain-cell-activity-using-plasmonic-1z00k3h2ki.pdf

T. Atay

Papers

Strongly Interacting Plasmon Nanoparticle Pairs: From Dipole−Dipole Interaction to Conductively Coupled Regime

Large enhancement of fluorescence efficiency from CdSe/ZnS quantum dots induced by resonant coupling to spatially controlled surface plasmons.

Highly efficient resonant coupling of optical excitations in hybrid organic/inorganic semiconductor nanostructures

Solid state cavity QED: Strong coupling in organic thin films

Optical Detection of Brain Cell Activity Using Plasmonic Gold Nanoparticles