We show that plasmonic nanoresonators composed of two gold nanoparticles change not only the intensity but also the spectral shape of the emission of fluorescent molecules. The plasmonic resonance frequency can be tuned by varying the distance between the nanoparticles, which allows us to selectively favor transitions of a fluorescent molecule to a specific vibrational ground state. Experimental data from correlated scattering and fluorescence microscopy agree well with calculations in the framework of generalized Mie theory. Our results show that the widely used description of a dye molecule near a metal surface as a mere two-level system is inadequate.
Semiconductor and metal nanocrystals (NCs) and their assemblies have attracted significant interest from many branches of science and technology. Hybrid assemblies built of semiconductor and noble metal NCs are expected not only to combine the properties of the constituent building blocks but also to generate new, collective phenomena based on interparticle interactions at the nanoscale, 1 particularly the coupling of excitons in semiconductor NCs with plasmon resonances in their metal counterparts. Understanding of interaction mechanisms between optically active species like semiconductor NCs and neighboring metal nanoparticles can help establish conditions either for quenching of the fluorescence of semiconductor NCs through the creation of an additional nonradiative decay channel via resonant energy transfer to metal NCs 2 or for metal-enhanced fluorescence of chromophores 3 similar to the SERS mechanism. 4 Regular superstructures of nanoparticles with well-defined geometrical parameters offer the unique possibility to control coupling between excitons and plasmons in threedimensional metamaterials. 5 Studies of collective optical properties of hybrid materials comprising semiconductor and metal NCs are ideally conducted on samples with a high degree of ordering, where not only the size of the NCs but also the mutual arrangement of the NC building blocks and the spacing between them are controlled on a large scale. Glassy solids 6 or layer-by-layered assembled structures 7 of differently sized semiconductor NCs do not provide long-range order achievable in self-assembled NC superlattices. 8,9 In particular, binary nanoparticle superlattices (BNSLs) of monodisperse semiconductor and noble metal NCs 9 are appealing objects for studying the collective optical excitations. In this letter, we report for the first time on the preparation and the fluorescence spectroscopy study of long-range ordered BNSLs, self-assembled from CdSe NCs emitting in the visible spectral range and gold NCs with a nanoparticle plasmon resonance in the visible spectral range.Monodisperse 8.7 nm CdSe NCs and 5.5 nm Au NCs were synthesized following the procedures reported in refs 10 and 11, respectively. For structural analysis, BNSLs of CdSe and Au were self-assembled (see ref 9 for details) from the toluene solutions on ultrathin carbon films supported by a copper grid (type A, Ted Pella, Inc.). TEM studies revealed that four different structural types of BNSLs (Figure 1a-d) could be obtained by varying relative concentrations of CdSe and Au NCs. A BNSL isostructural with the AuCu intermetallic compound has been formed using a particle number ratio of CdSe:Au of 1:0.7 (Figure 1 a,e). A BNSL isostructural with AlB 2 was obtained from a solution containing an excess of Au NCs (∼1:5 CdSe/Au particle ratio) (Figure 1b,f). The same particle ratio led to the formation of CaCu 5 -type ( Figure 1c,g) and cub-AB 13 -type (Figure 1d,h) superlattices when small amounts of dodecanethiol and trioctylphosphine oxide have been added to the colloidal so...
Unbiased gold nanoparticles are negatively charged in aqueous solution but not hydrated. Optical spectroscopy of voltage-clamped single gold nanoparticles reveals evidence that anion adsorption starts at positive potentials above the point of zero charge, causing severe but reversible plasmon damping in combination with a spectral red shift exceeding the linear double layer charging effect. Plasmon damping by adsorbate is relevant for the use of nanoparticles in catalysis, in biodiagnostics, and in surface enhanced Raman scattering.
We show how to change optically the distance between two protein-linked gold nanoparticles by Raman-induced motion of the linker protein. Rayleigh scattering spectroscopy of the coupled-particle plasmon allows us to compare the inter-nanoparticle distance of individual protein-linked gold nanoparticle dimers before and after surface-enhanced Raman scattering (SERS). We find that low-intensity (50 microW/microm2) laser light in resonance with the nanoparticle-dimer plasmon provokes a change of the inter-nanoparticle distance on the order of 0.5 nm whenever SERS from the proteins connecting the nanoparticles can be observed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.