ABSTRACT
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.
Subject(s)
Gold/chemistry , Nanostructures/chemistry , Nanostructures/radiation effects , Surface Plasmon Resonance/methods , Water/chemistry , Adsorption/radiation effects , Electromagnetic Fields , Gold/radiation effects , Materials Testing , Solutions , Surface Properties/radiation effectsABSTRACT
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.
Subject(s)
Carbocyanines/chemistry , Fluorescent Dyes/chemistry , Gold/chemistry , Metal Nanoparticles/chemistry , Spectrometry, Fluorescence/methods , Surface Plasmon Resonance/methods , Antibodies/chemistry , Digoxigenin/chemistry , Digoxigenin/immunology , Serum Albumin, Bovine/chemistryABSTRACT
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.
