Plasmon-enhanced optical nonlinearity in pyramidal silver nanocrystals.

This study investigates the coherent optical nonlinearity of two sets of anisotropic silver nanocrystals (NCs) showing plasmon peaks at 530 and 610 nm (hence named Ag-530 and Ag-610 NCs, respectively). The nonlinear optical (NLO) properties of Ag-530 and Ag-610 NCs are compared with spherical silver NCs exhibiting plasmon peak at 420 nm (hence called Ag-420 NCs). Resonant excitation induces significant one-photon absorption (1PA) saturation for all NCs, with Ag-610 NCs displaying exceptional transparency.

Nonlinear Absorption and Refraction of Highly Monodisperse and Luminescent ZnTe Quantum Dots and Their Self-Assembled Nanostructures: Implications for Optoelectronic Devices.

Zinc telluride (ZnTe) quantum dots (QDs) were synthesized by a unique supersaturation-controlled aqueous route. For a given pH, increasing the degree of initial supersaturation led to a decrease in the average diameter ( ) of the QDs and increased monodispersity. Three samples of ZnTe QDs having average sizes of 0.

Quercetin loaded folate targeted plasmonic silver nanoparticles for light activated chemo-photothermal therapy of DMBA induced breast cancer in Sprague Dawley rats.

Currently, the paucity of free drugs in conventional chemotherapy for breast-cancer curbs the desired therapeutic efficiency, often aggravating systemic toxicity. Quercetin (QRC) is a potential chemotherapeutic bio-flavonoid that is associated with poor hydrophilicity. In contrast to spherical silver nanoparticles (AgNPs), anisotropic AgNPs exhibit prominent plasmonic tunability in the near infrared (NIR) region allowing deep tissue penetration and endowing them with the ability to act as photothermal transducers as well.

Hollow Silver Nanostructures: The Role of Capping Agents in Tailoring the Shape, Structure, and Plasmonic Properties.

The shape- and structure-directing ability of capping agents, namely, acetic acid (AA) and folic acid (FA), has been analyzed in the synthesis of hollow plasmonic nanostructures via the nanoscale Kirkendall effect. FA was found to possess both shape-directing and structure-directing abilities when spherical solid Ag2O nanoparticles were transformed into hollow silver nanocubes (HAgNCs). In contrast, AA acted only as a structure-directing agent in the transformation from solid Ag2O nanospheres to hollow Ag nanospheres (HAgNSs).

Shape and size dependent nonlinear refraction and absorption in citrate-stabilized, near-IR plasmonic silver nanopyramids.

Using a combination of a mild stabilizer and a mild reductant, sodium citrate and hydrazine hydrate, anisotropic silver nanocrystals (NCs) were synthesized with tunable plasmon peaks at 550 nm, 700 nm, 800 nm, 900 nm and 1010 nm (the samples are named Ag-550, Ag-700, Ag-800, Ag-900 and Ag-1010, respectively). TEM investigations revealed that Ag-550 NCs were pentagonal nanoplates while the other four samples were nanopyramids with a pentagonal base with the edge length varying between 15 and 30 nm. The non-linear optical (NLO) properties of these NCs were studied by the Z-scan technique using the CW He-Ne laser (632.

Water-soluble, luminescent ZnTe quantum dots: supersaturation-controlled synthesis and self-assembly into nanoballs, nanonecklaces and nanowires.

A supersaturation-controlled aqueous synthesis route has been developed for ZnTe quantum dots (QDs) with high monodispersity, size tunability, stability, band-edge luminescence (full-width at half-maximum (FWHM) 10-12 nm) and negligibly small Stokes' shift (2-4 nm). The degree of supersaturation of the initial reaction mixture was varied by increasing the reagent concentration, but keeping the molar ratio Zn(2+) : thioglycolic acid : Te(2-) constant at 1 : 2.5 : 0.

Citrate-hydrazine hydrogen-bonding driven single-step synthesis of tunable near-IR plasmonic, anisotropic silver nanocrystals: implications for SERS spectroscopy of inorganic oxoanions.

A simplified, single-step aqueous synthesis route to tunable anisotropic silver nanocrystals (NCs) has been developed by tailoring the hydrogen-bonding interactions between a mild stabilizer, sodium citrate, and a mild reductant, hydrazine hydrate. The structure directing ability of the H-bonding interaction was harnessed by keeping a stoichiometric excess of hydrazine under ambient conditions (pH 7, 25 °C). Decreasing the synthesis temperature to 5 °C imparts rigidity to the citrate-hydrazine H-bonding network, and the plasmon peak moves from 500 to 550 nm (using 40 mM hydrazine).

Facile tuning of plasmon bands in hollow silver nanoshells using mild reductant and mild stabilizer.

Hollow silver nanoshells with tunable plasmon bands have been synthesized using Ag2O nanoparticles at an optimized temperature of 20 °C. The plasmon peak has been tuned in a wide range from 460 nm to 605 nm employing a combination of mild reductant and a mild stabilizer, hydrazine hydrate and sodium citrate, respectively. In contrast, the combination of strong reductant and strong stabilizer, NaBH4 and hydrophilic thiols, resulted in limited plasmon tunability (455-510 nm).

Synthesis, characterization, and self-organization of dendrimer-encapsulated HgTe quantum dots.

Mercury telluride (HgTe) quantum dots (QDs) were synthesized in methanol at 5 degrees C using generation 5 (G5) and 7 (G7) polyamidoamine (PAMAM) dendrimers, which function both as nucleation sites and as nanoparticle stabilizers. Transmission electron microscopy (TEM) data indicate these particles were slightly oblate, with an average aspect ratio of 1.3 +/- 0.

Surface charge tunability and size dependent luminescence anisotropy of aqueous synthesized ZnS/Dendrimer nanocomposites.

Highly water-soluble, biocompatible, fluorescent, ZnS/Dendrimer nanocomposites have been synthesized, for the first time, with amino-, carboxyl- or hydroxyl-terminated Polyamidoamine dendrimer. Average size of ZnS nanoparticles within the dendrimer matrix was found to be in the range of 2.2-3.

Mechanistic aspects of quantum dot based probing of Cu (II) ions: role of dendrimer in sensor efficiency.

Selective quenching of luminescence of quantum dots (QDs) by Cu2+ ions vis-à-vis other physiologically relevant cations has been reexamined. In view of the contradiction regarding the mechanism, we have attempted to show why Cu2+ ions quench QD-luminescence by taking CdS and CdTe QDs with varying surface groups. A detailed study of the solvent effect and also size dependence on the observed luminescence has been carried out.

Volatile interface of biological oxidant and luminescent CdTe quantum dots: implications in nanodiagnostics.

In order to explore the feasibility of using quantum dots (QDs) as nanodiagnostic tools in cells under oxidative stress, the interaction of cysteine-functionalized CdTe QDs with peroxynitrite (PN), a powerful biological oxidant, was spectroscopically investigated. The photoluminescence (PL) of CdTe QDs was quenched to the extent of 85% at 86 microM concentration of peroxynitrite. In contrast, the loss of PL intensity was merely 7% for CdS QDs under identical conditions.

Conformation and activity dependent interaction of glucose oxidase with CdTe quantum dots: towards developing a nanoparticle based enzymatic assay.

Nanomolar concentrations of cysteine-capped CdTe quantum dots (QDs) quenched the fluorescence of tryptophan moieties in glucose oxidase (GOX), while the fluorescence of the other fluorophore in the enzyme, FAD (Flavin Adenine Dinucleotide), was not affected by the QDs. The quenching followed a linear Stern-Volmer equation and its static nature was confirmed by time-resolved photoluminescence (PL) spectroscopy. The binding of substrate to the GOX resulted in a decrease of the Stern-Volmer quenching constant, which is attributable to a change in tertiary structure of GOX as revealed by circular dichroism (CD) spectroscopy.

Size tunablity of CdTe crystallites in dendrimer nanocomposites and temperature dependent focusing of size distribution.

CdTe/Dendrimer nanocomposites have been synthesized for the first time in aqueous and nonaqueous media using PAMAM dendrimer (Generation 5.0). The average size of the as-prepared nanocomposites, as determined from dynamic light scattering (DLS) measurements, was found to be typically 182 nm and 23 nm in water and methanol, respectively under identical conditions of temperature (5 degrees C) and reagent ratio (Cd2+:Te2-, 1:0.

Size tunable synthesis of cysteine-capped CdS nanoparticles by gamma-irradiation.

Highly water soluble and biocompatible L-cysteine-capped CdS nanoparticles having narrow size distribution were synthesized for the first time by gamma-irradiation technique without using any additional stabilizer. FTIR study shows that CdS nanoparticles are capped through mercapto-group of cysteine amino acid while its free amino and carboxylate groups make it amenable to bio-conjugation. Size and luminescence of the nanoparticles can be well controlled by varying the parameters like radiation dose, pH and concentration of cysteine.

Size dependent interaction of biofunctionalized CdS nanoparticles with tyrosine at different pH.

Enhancement of fluorescence of CdS nanoparticles by tyrosine at pH 10 in contrast to Stern-Volmer quenching at pH 7 was observed and both the effects were found to depend on the size of the nanoparticles.