We have studied the enhancement of luminescence of (CdSe)ZnS core−shell quantum dots on gold colloids as a function of semiconductor nanocrystal−metal nanoparticle distance. Using a layer-by-layer polyelectrolyte deposition technique to insert well-defined spacer layers between gold colloids and quantum dots, a distance-dependent enhancement and quenching of quantum dot photoluminescence has been observed. The maximum enhancement by a factor of 5 is achieved for a 9-layer spacer (≈11 nm). The efficient quantum dot excitation within the locally enhanced electromagnetic field produced by the gold nanoparticles is evidenced by the observation of the surface plasmon resonance in the photoluminescence excitation spectrum of (CdSe)ZnS nanocrystals.

Highly ordered quasi-nanowires from fluorescent semiconductor CdSe/ZnS spherical (quantum dots) or rod-like (quantum rods) nanoparticles were produced using DNA as a template. Positively charged nanoparticles were fixed along the negatively charged DNA backbone by electrostatic interaction. After incubation of the solution of DNA and nanoparticles at different stoichiometric ratios the complexes were applied to the hydrophobic surface and stretched using the molecular combing technique. Here, we demonstrate that fluorescent patterns with desirable morphology and properties can be formed by varying the nanoparticle charge and shape and their stoichiometry in the complex with DNA.

Pronounced 10(4)-fold enhancement of Raman scattering has been obtained for ZnO nanocrystals on substrates coated with 50 nm Ag nanoparticles under nonresonant excitation with a commercial red-emitting laser. This makes feasible beyond 10(-18) mole detection of ZnO nanocrystals with a commercial setup using a 0.1 mW continuous wave laser and can be purposefully used in analytical applications where conjugated nanocrystals serve as Raman markers. For Au-coated surfaces the enhancement is much lower and the heating effects in the course of Raman experiments are pronounced.

A layer-by-layer deposited polyelectrolyte spacer is used to attach CdSe nanocrystals (NCs), dye molecules and fluorescein-labelled bovine serum albumin (BSA-FITC) to flat glass and rough silver island surfaces in order to study the effect of spacer thickness on homogeneity and surface concentration of fluorophore coverage. Three different methods of fluorophore deposition atop the polyelectrolyte spacer are examined using steady-state spectroscopy, fluorescent microscopy and statistical analysis. The best homogeneous covering with nanocrystals at a controllable concentration was found for deposition from a solution of NCs which are electrostatically bound to polyelectrolyte macromolecules. This fluorophore deposition method allows one to avoid artefacts and to evaluate the fluorescence enhancement factor of BSA-FITC adsorbed on silver island films.

Plasmon-exciton coupling is of great importance to many optical devices and applications. One of the coupling manifestations is plasmon-enhanced fluorescence. Although this effect is demonstrated in numerous experimental and theoretical works, there are different particle shapes for which this effect is not fully investigated. In this work electrostatic complexes of gold nanorods and CdSe/CdZnS quantum dots were studied. Double-resonant gold nanorods have an advantage of the simultaneous enhancement of the absorption and emission when the plasmon bands match the excitation and fluorescence wavelengths of an emitter. A relationship between the concentration of quantum dots in the complexes and the enhancement factor was established. It was demonstrated that the enhancement factor is inversely proportional to the concentration of quantum dots. The maximal fluorescence enhancement by 10.8 times was observed in the complex with the smallest relative concentration of 2.5 quantum dots per rod and approximately 5 nm distance between them. Moreover, the influence of quantum dot location on the gold nanorod surface plays an important role. Theoretical study and experimental data indicate that only the position near the nanorod ends provides the enhancement. At the same time, the localization of quantum dots on the sides of the nanorods leads to the fluorescence quenching.