A. O. Orlova

Intrinsic Chirality of CdSe/ZnS Quantum Dots and Quantum Rods.

A new class of chiral nanoparticles is of great interest not only for nanotechnology, but also for many other fields of scientific endeavor. Normally the chirality in semiconductor nanocrystals is induced by the initial presence of chiral ligands/stabilizer molecules. Here we report intrinsic chirality of ZnS coated CdSe quantum dots (QDs) and quantum rods (QRs) stabilized by achiral ligands. As-prepared ensembles of these nanocrystals have been found to be a racemic mixture of d- and l-nanocrystals which also includes a portion of nonchiral nanocrystals and so in total the solution does not show a circular dichroism (CD) signal. We have developed a new enantioselective phase transfer technique to separate chiral nanocrystals using an appropriate chiral ligand and obtain optically active ensembles of CdSe/ZnS QDs and QRs. After enantioselective phase transfer, the nanocrystals isolated in organic phase, still capped with achiral ligands, now display circular dichroism (CD). We propose that the intrinsic chirality of CdSe/ZnS nanocrystals is caused by the presence of naturally occurring chiral defects.

Electrically controlled polarized photoluminescence of CdSe/ZnS nanorods embedded in a liquid crystal template

A novel homogeneous composite material, consisting of luminescent CdSe/ZnS quantum nanorods, embedded in the nematic liquid crystal 5CB, has been prepared. Liquid crystal cells and free-standing stretched polymer films incorporating this composite material were characterized using polarized micro-photoluminescence and electro-optical measurements under an applied electric field. A liquid crystal induced, macroscopic orientation of the nanorods in a thin layer of the material has been demonstrated. A conventional liquid crystal cell, filled with this composite, exhibits 40% modulation of the nanorods photoluminescence intensity when subjected to an external electric field. These results indicate that quantum nanorods may have practical applications in photonic devices.

Energy transfer in complexes of water-soluble quantum dots and chlorin e6 molecules in different environments

Summary The photoexcitation energy transfer is found and investigated in complexes of CdSe/ZnS cationic quantum dots and chlorin e6 molecules formed by covalent bonding and electrostatic interaction in aqueous solution and in porous track membranes. The quantum dots and chlorin e6 molecules form stable complexes that exhibit Förster resonance energy transfer (FRET) from quantum dots to chlorin e6 regardless of complex formation conditions. Competitive channels of photoexcitation energy dissipation in the complexes, which hamper the FRET process, were found and discussed.

Formation of QD-porphyrin molecule complexes in aqueous solutions

The spectral and luminescent manifestations of the electrostatic formation of quantum dot (QD)-porphyrin complexes are studied. The QD luminescence in these complexes is found to be efficiently quenched. The luminescence of molecules complexed with QDs is also partially quenched. The luminescence excitation spectra of porphyrin molecules associated with QDs exhibit a contribution of the QD absorption spectrum, which indicates that energy is transferred from QDs to porphyrin. The efficiency of the nonradiative resonant energy transfer from a QD to a porphyrin molecule is estimated. The observed experimental data agree well with a proposed model of formation of complexes of the QD-organic molecule type.

Spectral-luminescence study of the formation of QD-sulfophthalocyanine molecule complexes in an aqueous solution

The spectral-luminescence manifestations of the formation of quantum dot (QD)-phthalocyanine complexes as a result of electrostatic interaction have been investigated. Effective QD luminescence quenching has been found in complexes of this type. The luminescence of the molecules associated in complexes with QDs is also partially quenched. A mathematical model of the formation of QD-organic molecule complexes is proposed.

Enantioselective cellular uptake of chiral semiconductor nanocrystals

The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

Dissociative CdSe/ZnS Quantum Dot-Molecule Complex for Luminescent Sensing of Metal Ions in Aqueous Solutions

The optical properties of dissociative luminescent sensors based on a complex consisting of highly luminescent hydrophobic core/shell CdSe/ZnS quantum dots (QDs) and 1-(2-pyridilazo)-2-naphtol (PAN) molecules in organic solutions and a polymer film are reported. It is demonstrated, using Ni2+ and Co2+ ions as an illustrative example, that the QD/PAN sensor may have applications in the quantitative luminescent sensing of metal ions in aqueous solutions.

Anisotropy of optical transitions in ordered ensemble of CdSe quantum rods

We report on the observation of spectral dependence of absorption anisotropy in a CdSe quantum rod (QR) ensemble, which is aligned in a polymer film with a nanocrystal concentration of 2×10(-5) M. The experimental data on the polarization direction and anisotropy factor were obtained for the lowest excitonic transition and the second group of transitions in the QR. The nonzero constant value of anisotropy was investigated for the high-energy transitions, and is evidence of the one-dimensional confinement in the QR.

Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

A complex for the fluorescence analysis of macro- and microsamples in the near-infrared

This paper describes the design features and technical parameters of a complex for characterizing the fluorescence parameters of macro- and microsamples in the near-IR region. Along with the standard 90°setup for exciting and recording the fluorescence, a microfluorimetric technique is used. Two types of InGaAs photodiodes are compared, and the features of the measurements are discussed, using as an example the recording of the IR fluorescence spectra of PbS quantum dots.