Microstructural and optical properties of CdSe/CdS/ZnS core-shell-shell quantum dots

Continuous Flow Synthesis of Cd1-x Znx S and CdS/ZnS Core/Shell Semiconductor Nanoparticles by MicroJet Reactor Technology

From aqueous precursor solutions of metal salts and sodium sulfide using MicroJet Reactor (MJR) technology Cd_1-x Zn_x S and CdS/ZnS core/shell semiconductor nanoparticles were synthesized. The MJR approach represents an automated, continuous, flexible and scalable route for nanoparticle synthesis, providing a tight control over process parameters and thus simple size, shape and composition control. Since particle sizes below the excitonic Bohr radius were obtained by MJR, the nanoparticulate materials exhibit quantum confinement effects. By varying the precursor ratio the band gap of Cd_1-x Zn_x S Quantum Dots (QDs) could be targeted from 3.1 to 3.6 eV. CdS/ZnS core/shell QDs were prepared by enclosing CdS particles from MJR with ZnS produced by thermal decomposition of a Zn-MPA complex. Adjustment of the shell thickness increased the photoluminescence intensity by 43 %. Synthesis of ternary sulfides in the form of core/shell particles broadens the spectrum of materials accessible by MJR and demonstrates the extraordinary flexibility of the technology.

Quantum Dots: Synthesis, Antibody Conjugation, and HER2-Receptor Targeting for Breast Cancer Therapy

Breast cancer is becoming one of the main lethal carcinomas in the recent era, and its occurrence rate is increasing day by day. There are different breast cancer biomarkers, and their overexpression takes place in the metastasis of cancer cells. The most prevalent breast cancer biomarker is the human epidermal growth factor receptor2 (HER2). As this biomarker is overexpressed in malignant breast tissues, it has become the main focus in targeted therapies to fight breast cancer. There is a cascade of mechanisms involved in metastasis and cell proliferation in cancer cells. Nanotechnology has become extremely advanced in targeting and imaging cancerous cells. Quantum dots (QDs) are semiconductor NPs, and they are used for bioimaging, biolabeling, and biosensing. They are synthesized by different approaches such as top-down, bottom-up, and synthetic methods. Fully human monoclonal antibodies synthesized using transgenic mice having human immunoglobulin are used to target malignant cells. For the HER2 receptor, herceptin® (trastuzumab) is the most specific antibody (Ab), and it is conjugated with QDs by using different types of coupling mechanisms. This quantum dot monoclonal antibody (QD-mAb) conjugate is localized by injecting it into the blood vessel. After the injection, it goes through a series of steps to reach the intracellular space, and bioimaging of specifically the HER2 receptor occurs, where apoptosis of the cancer cells takes place either by the liberation of Ab or the free radicals.

Tuning of nonlinear absorption in highly luminescent CdSe based quantum dots with core-shell and core/multi-shell architectures

We present our effort on an efficient way of tuning the nonlinear absorption mechanisms in ultra-small CdSe based quantum dots by implementing core-shell and core/multi-shell architectures. Depending on the size, architecture and composition of the QDs, these materials exhibited resonant and near-resonant nonlinear optical absorption properties such as saturable (SA) and reverse saturable (RSA) absorption for 5 ns pulses of 532 nm. These QDs exhibited a non-monotonic dependence of the effective two-photon absorption coefficient (β) under nanosecond excitation with a maximum value for a thinner shell. We obtained a nonlinear absorption enhancement of an order of magnitude by adopting the core-shell architecture compared to their individual counterparts. Interestingly, CdSe QDs exhibit SA and/or RSA depending on their size and show a switching over from SA to RSA as the input intensity increases. We explained the enhanced nonlinear absorption in core-shell QDs compared to their individual counterparts in view of enhanced local fields associated with the core-shell structure. Thus, the present nanostructured materials are excellent candidates as saturable absorbers and optical limiters.

Formation, element-migration and broadband luminescence in quantum dot-doped glass fibers

All solid-state PbS quantum dot (QD)-doped glass precursor fibers avoiding crystallization during fiber-drawing process are successfully fabricated by melt-in-tube technique. By subsequent heat treatment schedule, controllable crystallization of PbS QDs can be obtained in the glass precursor fibers, contributing to broad near-infrared emissions from PbS QD-doped glass fibers. Nevertheless, we find that element-migration and volatilization of sulfur simultaneously happen during the whole fiber-drawing process, because of the huge difference between the melting temperature of core glass and the fiber-drawing temperature. Element-migration pathways along the fiber length were revealed. Such PbS QD-doped glass fiber with broadband emissions will be a potential application as gain medium of broadband fiber amplifiers and fiber lasers.

Colloidal nanophotonics: the emerging technology platform

Dating back to decades or even centuries ago, colloidal nanophotonics during the last ten years rapidly extends towards light emitting devices, lasers, sensors and photonic circuitry to manifest itself as an emerging technology platform rather than an entirely academic research field.