We investigate the fluorescence from dyes coupled to individual DNA-functionalized metal nanoparticles. We use single-particle darkfield scattering and fluorescence microscopy to correlate the fluorescence intensity of the dyes with the localized surface plasmon resonance (LSPR) spectra of the individual metal nanoparticles to which they are attached. For each of three different dyes, we observe a strong correlation between the fluorescence intensity of the dye and the degree of spectral overlap with the plasmon resonance of the nanoparticle. On average, we observe the brightest fluorescence from dyes attached to metal nanoparticles that have a LSPR scattering peak approximately 40-120 meV higher in energy than the emission peak of the fluorophore. These results should prove useful for understanding and optimizing metal-enhanced fluorescence.

Silver nanobars with rectangular side facets and an average aspect ratio of 2.7 have been synthesized by modifying the concentration of bromide added to a polyol synthesis. Subsequent rounding of nanobars transformed them into nanorice. Due to their anisotropy, nanobars and nanorice exhibit two plasmon resonance peaks, scattering light both in the visible and in the near-infrared regions. With a combination of discrete-dipole approximation calculations and single-nanoparticle spectroscopy, we explored the effect of nanostructure aspect ratio and corner sharpness on the frequency of plasmon resonance. Near-field calculations and surface-enhanced Raman scattering measurements on single particles were performed to show how local field enhancement changes with both the wavelength and polarization of incident light.

The near-field effects of plasmonic optical antennas are being explored in applications ranging from biosensors to solar cells. We demonstrate that photoluminescence emission enhancement from CdSe quantum dots (QDs) can be obtained in the absence of any excitation enhancement near single silver nanoprisms. The spectral dependence of the radiative and nonradiative decay rate of the QDs closely follows the silver nanoparticle plasmon scattering spectrum. Using both experiment and theory we show that, in the absence of excitation enhancement, the ratio of radiative to nonradiative decay rate enhancement is proportional to the silver nanoparticle scattering efficiency. These results provide guidelines both for separating excitation and emission enhancement effects in sensing and device applications and for tailoring emission enhancement effects using plasmonic nanostructures.

We introduce a new sensing modality based on the actuation of discrete gold nanoparticle dimers. Binding of the target DNA leads to a geometrical extension of the dimer, thereby yielding a spectral blue shift in the hybridized plasmon mode as detected by single nanostructure scattering spectroscopy. The magnitude and opposite direction of this shift enabled us to spectroscopically distinguish the target from nonspecific binding and to detect the target in complex media like serum.

We study plasmon-enhanced fluorescence from CdSe∕CdS∕CdZnS∕ZnS core/shell quantum dots near a variety of Ag and Au nanoparticles. The photoluminescence excitation (PLE) spectrum of quantum dots closely follows the localized surface plasmon resonance (LSPR) scattering spectrum of the nanoparticles. We measure excitation enhancement factors of ∼3 to 10 for different shapes of single metal nanoparticles.

We study the homogeneous line width of the plasmon resonance scattering peaks of anisotropic silver nanoparticles using single particle darkfield scattering spectroscopy. We correlate the scattering spectra with scanning electron microscopy images of the particles to investigate the effects of nanoparticle size on the plasmon line width. We observe that the scattering line widths of silver nanoprisms increase both as the particle volume increases and as the plasmon resonance energy increases. We attribute the size dependence to radiation damping and compare our data both to simple dipole-limit approximations for the radiative and nonradiative decay rates and with finite-difference time-domain (FDTD) calculations of the scattering line width. We find the data and calculations in good agreement for an appropriate choice of the bulk optical constants of silver and find that the dipole-limit approximations capture the observed size and energydependence of the plasmon line widths.

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl 2 . A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms. The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy. With their hollow and open structures, the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering. KEYWORDSGold nanostructures, galvanic replacement, hollow nanostructures, localized surface plasmon resonance, surface-enhanced Raman scattering Hollow nanostructures of noble metals (e.g., Au, Pt, and Pd) have gained attention in recent years for a variety of applications including catalysis [1], optical sensing [2], drug delivery [3], biomedical imaging [4 6], and photothermal therapy [7 10] due to their tunable optical properties and large surface areas. Among various synthetic approaches, the galvanic replacement reaction represents the most versatile route to bimetallic hollow nanostructures [1, 11 16]. Bimetallic hollow nanostructures have been synthesized by reacting Ag nanostructures (or templates) with a salt precursor containing a less reactive metal such as Au, Pt or Pd. In particular, the replacement reaction between Ag nanocubes and AuCl 4 (Eq. (1)) has been extensively explored as a robust method for generating hollow nanostructures in the form of nanoboxes and nanocages [17]. 3Ag(s)+AuCl 4 (aq) 3AgCl(s)+Au(s)+Cl (aq) (1) T h e w a l l t h i c k n e s s a n d p o r o s i t y o f t h e s e nanostructures are determined by the amount of AuCl 4 added to the reaction system. In practice, such control can be easily achieved by titrating Ag nanocubes with different volumes of an aqueous AuCl 4 solution.Recently, several methods have been utilized to further control the porosity and wall thickness of these nanostructures. For example, when the corners of the Ag nanocubes were truncated before undergoing the 442 Nano Res (2008) [19]. This procedure reduced the wall thickness and caused pores to form on the side faces. At a certain point of the reaction, the pores on each side face were able to coalesce into a single large hole, which led to the formation of a cubic nanoframe, a structure not previously achieved with AuCl 4 alone. However, if this specific point was passed during the synthesis, the Au nanoframe broke into small pieces because the ridges became too thin and fragile. The Au nanoframes formed via this route were so sensitive to the reaction conditions that the reported yield never exceeded 5% 10%. In contrast, when AuCl 2 was employed as a precursor to Au instead of AuCl 4 , nanoboxes with thicker walls could be generated due to the difference in stoichiometry: in the reaction with AuCl 2 (Eq....

Coupled plasmonic/chromophore systems are of interest in applications ranging from fluorescent biosensors to solar photovoltaics and photoelectrochemical cells because near-field coupling to metal nanostructures can dramatically alter the optical performance of nearby materials. We show that CdSe quantum dots (QDs) near single silver nanoprisms can exhibit photoluminescence lifetimes and quantum yields that depend on the excitation wavelength, in apparent violation of the Kasha-Vavilov rule. We attribute the variation in QD lifetime with excitation wavelength to the wavelength-dependent coupling of higher-order plasmon modes to different spatial subpopulations of nearby QDs. At the QD emission wavelength, these subpopulations are coupled to far-field radiation with varying efficiency by the nanoprism dipolar resonance. These results offer an easily accessible new route to design metachromophores with tailored optical properties.