Employing heavy metal-free colloidal quantum dots in solution-processed white light-emitting diodes.

We report in this communication the design and fabrication of solution-processed white light-emitting diodes (LEDs) containing a bilayer of heavy metal-free colloidal quantum dots (QDs) and polymer in the device active region. White electroluminescence was obtained in the LEDs by mixing the red emission of ZnCuInS/ZnS core/shell QDs and the blue-green emission of poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine). A high color rendering index of 92 was achieved as compared to a 5310 K blackbody reference by virtue of broadband emission of the QDs. The Commission Internationale de l'Eclairage chromaticity coordinates of the white LED output exhibit a distinctive bias dependence. Finally, aging of the white LEDs was studied, revealing the difference between the photochemical stabilities of the QDs and polymer molecules and the consequent effect on the color evolution of the LEDs.

Lasing from colloidal InP/ZnS quantum dots.

High-quality InP/ZnS core-shell nanocrystal quantum dots (NQDs) were synthesized as a heavy-metal-free alternative to the gain media of cadmium-based colloidal nanoparticles. Upon UV excitation, amplified spontaneous emission (ASE) and optical gain were observed, for the first time, in close-packed InP/ZnS core-shell NQDs. The ASE wavelength can be selected by tailoring the nanocrystal size over a broad range of the spectrum. Moreover, the optical gain profile of InP/ZnS NQDs was matched to the second order feedback of holographic polymer-dispersed liquid crystal gratings, leading to the very first demonstration of an optically-pumped, nanocrystal laser based on InP/ZnS core-shell NQDs.

Aptamer-based detection of epithelial tumor marker mucin 1 with quantum dot-based fluorescence readout.

Mucin 1 (MUC1) is a glycoprotein expressed on most epithelial cell surfaces, which has been confirmed as a useful biomarker for the diagnosis of early cancers. In this paper, we report an aptamer-based, quantitative detection protocol for MUC1 using a 3-component DNA hybridization system with quantum dot (QD)-labeling: in the absence of MUC1 peptides, strong fluorescence is observed upon mixing the three specially designed DNA strands (quencher, QD-labeled reporter, and the MUC1 aptamer stem); in the presence of MUC1 peptides, a successive decrease in fluorescence intensity is detected since the MUC1 peptide binds to the aptamer strand in such a way to allow the quencher and fluorescence reporter to be brought into close proximity (which leads to the occurrence of fluorescence resonance energy transfer, FRET, between the quencher and QD). The detection limit for MUC1 with this novel approach is in the nanomolar (nM) level, and a linear response can be established for the approximate range found in blood serum. This study also provided further insight into the aptamer/analyte binding site/mode for MUC1, which augments the possibility of improving this detection methodology for the early diagnosis of different types of epithelial cancers of large populations.

Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications.

We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs) overcoated with Cd(0.5)Zn(0.5)S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd(0.5)Zn(0.5)S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3).

Study on Growth Kinetics of CdSe Nanocrystals with a New Model.

A model which involves both bulk diffusion process and surface reaction process has been developed for describing the growth behaviour of nanoparticles. When the model is employed, hypothesising that either of the processes alone dominates the overall growth process is unnecessary. Conversely, the relative magnitude of contributions from both processes could be obtained from the model. Using this model in our system, the growth process of CdSe QDs demonstrated two different growth stages. During the first stage, the growth of CdSe QDs was dominated by bulk diffusion, whereas, neither the bulk diffusion process nor the surface reaction process could be neglected during the later stage. At last, we successfully modelled the Ostwald ripening of CdSe QDs with LSW theories.