Lyudmila Turyanska

Temperature dependence of the photoluminescence emission from thiol-capped PbS quantum dots

The authors report the temperature dependence of the near-infrared photoluminescence (PL) emission from thiol-capped PbS quantum dots. The high thermal stability of the PL allows the authors to study the thermal broadening of the dot emission over an extended temperature range (4–300K). The authors show that the linewidth of the dot PL emission is strongly enhanced at temperatures above 150K. This behavior is attributed to dephasing of the quantum electronic states by carrier interaction with longitudinal optical phonons. The authors’ data also indicate that the strength of the carrier-phonon coupling is larger in smaller dots.

Molecular beam epitaxy of GaBiAs on (311)B GaAs substrates

We report the growth by molecular beam epitaxy of GaBixAs1−x epilayers on (311)B GaAs substrates. We use high-resolution x-ray diffraction (HRXRD), transmission electron microscopy, and Z-contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the (311)B epilayers than in (001) epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy.

The Biocompatibility of Apoferritin‐Encapsulated PbS Quantum Dots

The biocompatibility of a nanocomposite based on a Pbs quantum dots (QD) entrapped in the hollow core of an apoferritin protein cage is examined. This offers a water-soluble hybrid construct with stable and tunable fluorescence emission at wavelengths larger than 1000nm. Native polyacrylamide gel-electrophoresis studies show that the PbS QDs do not alter the external surface of apoferritin or its migratory behavior. Apoferritin is obtained from ferritin molecules by reductive dissolution of its iron oxide core. MTT assays were performed on normal and cancer cell lines and recorded the cell viability after treatment with AFt-PbS at different concentrations and up to 72-hour. Cells were cultured under optimum conditions in RPMI nutrient medium supplemented with 10 fetal bovine serum, and subcultivated twice weekly to maintain logarithmic growth. Cells were seeded into 96-well microtiter plates at a density of 5 A� 103 per well and allowed 24-hour to adhere before AFt, PbS QDs and AFt-PbS composites were introduced with final concentrations of QDs.

Tailoring the physical properties of thiol-capped PbS quantum dots by thermal annealing.

We show that the thermal annealing of thiol-capped PbS colloidal quantum dots provides a means of narrowing the nanoparticle size distribution, increasing the size of the quantum dots and facilitating their coalescence preferentially along the 100 crystallographic axes. We exploit these phenomena to tune the photoluminescence emission of an ensemble of dots and to narrow the optical linewidth to values that compare with those reported at room temperature for single PbS quantum dots. We probe the influence of annealing on the electronic properties of the quantum dots by temperature dependent studies of the photoluminescence and magneto-photoluminescence.

Fabrication of polypyrrole nano-arrays in lysozyme single crystals

A template-directed method for the synthesis and organization of partially oxidized polypyrrole (PPy) nanoscale arrays within the solvent channels of glutaraldehyde-cross-linked lysozyme single crystals is presented. Macroscopic single crystals of the periodically arranged protein-polymer superstructure are electrically conductive, insoluble in water and organic solvents, and display increased levels of mechanical plasticity compared with native cross-linked lysozyme crystals.

Apoferritin-encapsulated PbS quantum dots significantly inhibit growth of colorectal carcinoma cells

Colorectal carcinoma (CRC) is the 3rd most common cancer worldwide, thus development of novel therapeutic strategies is imperative. Herein potent, selective dose-dependent antitumor activity of horse spleen apoferritin encapsulated PbS quantum dots (AFt-PbS) against two human-derived colorectal carcinoma cell lines is reported (GI50∼ 70 μg mL-1). Following in vitro exposure to AFt-PbS, CRC cells fail to recover proliferative capacity, and undergo apoptosis triggered by the generation of reactive oxygen species (ROS). In stark contrast, the AFt-PbS nanocomposites do not affect the growth and cell cycle of non-tumor human microvessel endothelial HMEC-1 cells (GI50 > 500 μg mL-1). In vivo, AFt-PbS QDs are well tolerated by mice. Neither adverse health nor behavioral indicators were observed throughout the 15 day study. The photoluminescence of AFt-PbS combined with selective antitumor activity offer potential development of AFt-PbS for simultaneous non-invasive imaging and treatment of malignant tissue.

The differential effect of apoferritin-PbS nanocomposites on cell cycle progression in normal and cancerous cells

We report the effects induced by near-infrared apoferritin-PbS (AFt-PbS) nanocomposites on cell cycle progression in non-tumorigenic and cancerous human cells. By using flow cytometry and Annexin V assay, we show that the cell cycle of non-tumorigenic cells is not altered by exposure to AFt-PbS nanoparticles at concentrations up to 1 mg mL−1. In contrast, exposure of human-derived breast cancer cell lines to AFt-PbS at concentrations > 0.2 mg mL−1 triggers apoptotic cell death. The selective death of cancerous cells and the near-infrared fluorescence properties of AFt-PbS could be exploited in both nanomedicine and in vivo imaging studies.

An apoferritin-based drug delivery system for the tyrosine kinase inhibitor Gefitinib

Anticancer drug Gefitinib encapsulated within human heavy chain apoferritin by diffusion allows pH-controlled sustained release of cargo. The combination of increased cellular uptake, and potent and enhanced antitumor activity against the HER2 overexpressing SKBR3 cell line compared to Gefitinib alone, makes it a promising carrier for delivery of drugs to tumor sites.

Electron spin coherence near room temperature in magnetic quantum dots

We report on an example of confined magnetic ions with long spin coherence near room temperature. This was achieved by confining single Mn2+ spins in colloidal semiconductor quantum dots (QDs) and by dispersing the QDs in a proton-spin free matrix. The controlled suppression of Mn–Mn interactions and minimization of Mn–nuclear spin dipolar interactions result in unprecedentedly long phase memory (TM ~ 8 μs) and spin–lattice relaxation (T1 ~ 10 ms) time constants for Mn2+ ions at T = 4.5 K, and in electron spin coherence observable near room temperature (TM ~ 1 μs).

High magnetic field quantum transport in Au nanoparticle–cellulose films

We report the magneto-transport properties of cellulose films comprising interconnected networks of gold nanoparticles (Au NPs). Cellulose is a biopolymer that can be made electrically conducting by cellulose regeneration in Au NP dispersions. The mechanism of electronic conduction in the Au-cellulose films changes from variable range hopping to metallic-like conduction with decreasing resistivity. Our experiments in high magnetic fields (up to 45 T) reveal negative magnetoresistance in the highly resistive films. This is attributed to the spin polarization of the Au NPs and the magnetic field induced suppression of electron spin flips during spin-polarized tunneling in the NP network.