Spectroscopic and Hydrodynamic Characterisation of DNA-Linked Gold Nanoparticle Dimers in Solution using Two-Photon Photoluminescence.

Two-photon photoluminescence (TPPL) emission spectra of DNA-gold nanoparticle (AuNP) monoconjugates and the corresponding DNA-linked AuNP dimers are obtained by photon time-of-flight spectroscopy. This technique is combined with two-photon photoluminescence fluctuation correlation spectroscopy (TPPL-FCS) to simultaneously monitor the optical and hydrodynamic behaviour of these nano-assemblies in solution, with single-particle sensitivity and microsecond temporal resolution. In this study, the AuNPs have an average core diameter of 12 nm, which renders their dark-field plasmonic light scattering too weak for single-particle imaging.

Photoluminescence spectra and quantum yields of gold nanosphere monomers and dimers in aqueous suspension.

The intrinsic one-photon excited photoluminescence (PL) of dimers and monomers of gold spheres suspended in water was studied by combining photon time-of-flight spectroscopy (PTOFS) and light scattering fluctuation correlation spectroscopy (LS-FCS). The samples are obtained by precisely controlling the dimerization of aqueous colloidal systems based on 50 and 80 nm gold nanospheres. The combination of PTOFS and LS-FCS enables the separate spectroscopic study of monomers and dimers even though they exist as a mixture in the samples.

Optical extinction and scattering cross sections of plasmonic nanoparticle dimers in aqueous suspension.

Absolute extinction and scattering cross sections for gold nanoparticle dimers were determined experimentally using a chemometric approach involving singular-value decomposition of the extinction and scattering spectra of slowly aggregating gold nanospheres in aqueous suspension. Quantitative spectroscopic data on plasmonic nanoparticle assemblies in liquid suspension are rare, in particular for particles larger than 40 nm, and in this work we demonstrate how such data can be obtained directly from the aggregating suspension. Our method can analyse, non invasively, the evolution of several sub-populations of nanoparticle assemblies.

The intrinsic luminescence of individual plasmonic nanostructures in aqueous suspension by photon time-of-flight spectroscopy.

We have studied the intrinsic one-photon excited luminescence of freely diffusing gold nanoparticles of different shapes in aqueous suspension. Gold nanospheres were used as a reference, since their luminescence has been investigated previously and their light absorption and scattering properties are described analytically by Mie theory. We then studied gold nanobipyramids and nanostars that have recently gained interest as building blocks for new plasmonic nanosensors.

Time-of-flight photon spectroscopy: a simple scheme to monitor simultaneously spectral and temporal fluctuations of emission on single nanoparticles.

Here we report on a novel scheme for spectral analysis that exploits the wavelength dependence of the time-of-flight of a photon in a dispersive medium. This versatile and cost-effective method, named time-of-flight photon spectroscopy (TOFPS), has the major advantage of being compatible with time-correlated single-photon counting experiments. Consequently, each photon acquired during an experiment is characterized by two parameters, its absolute time of arrival and its color, respectively.