Picosecond Lifetimes with High Quantum Yields from Single-Photon-Emitting Colloidal Nanostructures at Room Temperature.

Minimizing the luminescence lifetime while maintaining a high emission quantum yield is paramount in optimizing the excitation cross-section, radiative decay rate, and brightness of quantum solid-state light sources, particularly at room temperature, where nonradiative processes can dominate. We demonstrate here that DNA-templated 60 and 80 nm diameter gold nanoparticle dimers, featuring one fluorescent molecule, provide single-photon emission with lifetimes that can fall below 10 ps and typical quantum yields in a 45-70% range. Since these colloidal nanostructures are obtained as a purified aqueous suspension, fluorescence spectroscopy can be performed on both fixed and freely diffusing nanostructures to quantitatively estimate the distributions of decay rate and fluorescence intensity enhancements. These data are in excellent agreement with theoretical calculations and demonstrate that millions of bright fluorescent nanostructures, with radiative lifetimes below 100 ps, can be produced in parallel.

Widefield spectral monitoring of nanometer distance changes in DNA-templated plasmon rulers.

The nanometer-scale sensitivity of electromagnetic plasmon coupling allows the translation of minute morphological changes in nanostructures into macroscopic optical signals. We demonstrate here a widefield spectral analysis of 40 nm diameter gold nanoparticle (AuNP) dimers, linked by a short DNA double strand, using a low-cost color CCD camera and allowing a quantitative estimation of interparticle distances in a 3-20 nm range. This analysis can be extended to lower spacings and a parallel monitoring of dimer orientations by performing a simple polarization analysis. Our measurement approach is calibrated against confocal scattering spectroscopy using AuNP dimers that are distorted from a stretched geometry at low ionic strength to touching particles at high salt concentrations. We then apply it to identify dimers featuring two different conformations of the same DNA template and discuss the parallel colorimetric sensing of short sequence-specific DNA single strands using dynamic plasmon rulers.

Nanoscale optical properties of metal nanoparticles probed by Second Harmonic Generation microscopy.

We report spatial and vectorial imaging of local fields' confinement properties in metal nanoparticles with branched shapes, using Second Harmonic Generation (SHG) microscopy. Taking advantage of the coherent nature of this nonlinear process, the technique provides a direct evidence of the coupling between the excitation polarization and both localization and polarization specificities of local fields at the sub-diffraction scale. These combined features, which are governed by the nanoparticles' symmetry, are not accessible using other contrasts such as linear optical techniques or two-photon luminescence.