Tapasi Sen

Surface energy transfer from rhodamine 6G to gold nanoparticles: A spectroscopic ruler

Here, the authors report the energy transfer from rhodamine 6G dyes to gold nanoparticles. There is a pronounced effect on the photoluminescence and a shortening of the lifetime of the dye when interacting with the Au nanoparticles. The calculated distance (d) between the donor and acceptor varies from 86.06to102.47A with changing the concentrations of Au and dye. Analysis suggests that the energy transfer from dye to the Au nanoparticles is a surface energy transfer process and follows a 1∕d4 distance dependence.

Photophysical properties of Au-CdTe hybrid nanostructures of varying sizes and shapes.

We design well-defined metal-semiconductor nanostructures using thiol-functionalized CdTe quantum dots (QDs)/quantum rods (QRs) with bovine serum albumin (BSA) protein-conjugated Au nanoparticles (NPs)/nanorods (NRs) in aqueous solution. The main focus of this article is to address the impacts of size and shape on the photophysical properties, including radiative and nonradiative decay processes and energy transfers, of Au-CdTe hybrid nanostructures. The red shifting of the plasmonic band and the strong photoluminescence (PL) quenching reveal a strong interaction between plasmons and excitons in these Au-CdTe hybrid nanostructures. The PL quenching of CdTe QDs varies from 40 to 86 % by changing the size and shape of the Au NPs. The radiative as well as the nonradiative decay rates of the CdTe QDs/QRs are found to be affected in the presence of both Au NPs and NRs. A significant change in the nonradiative decay rate from 4.72×10(6) to 3.92×10(10) s(-1) is obtained for Au NR-conjugated CdTe QDs. It is seen that the sizes and shapes of the Au NPs have a pronounced effect on the distance-dependent energy transfer. Such metal-semiconductor hybrid nanostructures should have great potentials for nonlinear optical properties, photovoltaic devices, and chemical sensors.

DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering

We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 × 1010 and 8 × 109, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing.

Angular modulation of single-molecule fluorescence by gold nanoparticles on DNA origami templates

Abstract We study the angular fluorescence intensity modulation of a single dye positioned near a spherical gold nanoparticle, induced by rotation of linearly polarized excitation light. Accurate positioning and alignment of nanoparticle and fluorophore with respect to each other and the incoming electric field is achieved by a three-dimensional, self-assembled DNA origami. An intensity map is obtained for a fixed distance and two different nanoparticle diameters, revealing polarization-dependent enhancement and quenching of fluorescence intensity in good agreement to numerical simulations.

Shell thickness matters! Energy transfer and rectification study of Au/ZnO core/shell nanoparticles.

In the present study we report the influence of shell thickness on fluorescence resonance energy transfer between Au/ZnO core-shell nanoparticles and Rhodamine 6G dye by steady-state and time-resolved spectroscopy and rectification behaviours. Au/ZnO core-shell nanoparticles with different shell thickness were synthesized in aqueous solution by chemically depositing zinc oxide on gold nanoparticles surface. A pronounced effect on the photoluminescence (PL) intensity and shortening of the decay time of the dye in presence of Au/ZnO core-shell nanoparticles is observed. The calculated energy transfer efficiencies from dye to Au/ZnO are 62.5%, 79.2%, 53.6% and 46.7% for 1.5nm, 3nm, 5nm and 8nm thickness of shell, respectively. Using FRET process, the calculated distances (r) are 117.8, 113.2Å 129.9Å and 136.7Å for 1.5nm, 3nm, 5nm and 8nm thick Au/ZnO core-shell nanoparticles, respectively. The distances (d) between the donor and acceptor are 71.0, 57.8, 76.2 and 81.6Å for 1.5nm, 3nm, 5nm and 8nm thick core-shell Au/ZnO nanoparticles, respectively, using the efficiency of surface energy transfer (SET). The current-voltage (I-V) curve of hybrid Au/ZnO clearly exhibits a rectifying nature and represents the n-type Schottky diode characteristics with a typical turn-on voltage of between 0.6 and 1.3V. It was found that the rectifying ratio increases from 20 to 90 with decreasing the thickness of the shell from 5nm to 3nm and with shell thickness of 8nm, electrical transport through the core-shell is similar to what is observed with pure ZnO samples nanoparticles. The results indicated that the Au/ZnO core-shell nanoparticles with an average shell thickness of 3nm exhibited the maximum energy transfer efficiencies (79.2%) and rectification (rectifying ratio 90).

STEADY STATE AND TIME RESOLVED SPECTROSCOPIC STUDY OF CONFINED DYE INSIDE γ-CD IN PRESENCE OF Au NANOPARTICLES

The photophysical properties of the confined dye inside the γ-CD in presence of Au nanoparticles have been studied by steady state and time resolved spectroscopy. It is found that the photoluminescence quenching of C480 dye increases from 26% to 49% due to confinement of dye inside γ-CD. The designing of such new optical based materials having coumarin 480 dye inside the γ-CD in presence of Au nanoparticles may have potential applications for light harvesting system.

SURFACE ENERGY TRANSFER BETWEEN NANOSTRUCTURED GOLD AND DYE MOLECULES

Here, we report the surface energy transfer from Rhodamine 6G dye to assembled gold nanoparticles. There is a pronounced effect on the PL and a shortening of the lifetime of the dye, and the calculated distances (d) between the donor and acceptor are 85.5 A, 91.3 A, and 109.5 A for 50, 75, and 125 μM MNA capped Au NPs, respectively. Analysis suggests that the energy transfer from dye to the assembled Au nanoparticles is dominant by surface energy transfer and it follows 1/d4 distance dependence.