Doping Method Determines Para- or Superparamagnetic Properties of Photostable and Surface-Modifiable Quantum Dots for Multimodal Bioimaging

Abstract

Semiconductor quantum dots (QDs) are widely used for optical applications and bioimaging. In comparison to organic dyes used for fluorescent labeling, QDs exhibit very high photostability and can be further surface modified. Equipping QDs with magnetic properties (mQDs) makes it possible to combine fluorescence and magnetic resonance imaging analyses. For this purpose, we have prepared water-dispersible and magnetic CdTe/ZnS mQDs, whereby ferrous ions are selectively incorporated in either their cores or their shells. This study aims at understanding the differences in optical, structural, and magnetic properties between these core- and shell-doped mQDs. Field-dependent isothermal magnetic susceptibility measurements show that shell-doped mQDs exhibit paramagnetic and their core-doped equivalents super­paramagnetic behavior near room temperature. Shell doping results in about 1.7 times higher photoluminescence quantum yields and 1.4 times higher doping efficiency than core doping. X-ray diffraction patterns reveal that core doping leads to defects in the lattice and hence to a severe decrease in crystallinity, whereas shell doping has no significant impact on the crystal structure and consequently fewer disadvantages regarding the mQD’s quantum yield. These selective doping approaches, particularly shell doping, allow for the tailored design of paramagnetic QDs having modifiable and biocompatible particle surfaces. The organic ligandsin this study N-acetyl-l-cysteinesufficiently prevent leakage of toxic metal ions, as shown by cytotoxicity assays with HepG2 cells. Confocal laser scanning microscopy shows that mQDs are internalized by these cells and accumulated near their nuclei. This study shows that biocompatible, fluorescent, and paramagnetic QDs are promising photostable labels for multimodal bioimaging.

A Review of Advanced Multifunctional Magnetic Nanostructures for Cancer Diagnosis and Therapy Integrated into an Artificial Intelligence Approach

“…When SQDs are combined with magnetic properties, they can be used for magnetic resonance imaging as well as fluorescence imaging toward the diagnosis of cancer. A water-dispersible and magnetic CdTe/ZnS mQD can be selectively incorporated with ferrous ions in either the core or shell [ 151 ]. In particular, shell doping allows for the customized design of paramagnetic SQDs with biocompatible and modifiable surfaces.…”

Self-assembling ferrimagnetic fluorescent micelles for bioimaging guided efficient magnetic hyperthermia therapy

“…In the past decades, several feasible synthetic methods for the preparation of magneto-fluorescent nanoparticles have been approved, such as self-assembly, co-encapsulation into organic or inorganic structures, physical attachment, chemical bonding-based conjugation, element doping, and heterostructure crystal growth. 2,6,22,23 Because major high-quality MNPs and QDs were synthesized by the high-temperature oilphase method, these nanoparticles must be transformed into water-soluble compounds for biological applications. 1,20 Compared with other synthetic methods, the self-assembly method based on amphiphilic polymers has revealed superiority and accessibility by easily achieved hydrophobic interactions between hydrophobic segments of polymers and hydrophobic MNPs/QDs.…”

Preparation and Biomedical Applications of Multicolor Carbon Dots: Recent Advances and Future Challenges

“…[ 38–40 ] Albeit with biological imaging agents in vitro and in vivo, heavy metals as the essential elements for the core materials of available high‐performance semiconductor quantum dots (QDs) exist substantial toxicity, carcinogenic effects, and environmental hazard, even at low levels. [ 41–45 ] Historically, boasting the natural virtues of fascinating optical properties (e.g., up/down‐conversion and excitation‐dependent fluorescence emission, high fluorescence quantum yields (QY), and long fluorescence lifetime), eco‐friendliness, high water‐dispersible peculiarity, easy surface‐functionality, low cost, highly abundant, and inexpensive raw materials, noninvasiveness, low cytotoxicity, and good biocompatibility afford CDs suitable as the elegant alternatives for toxic QDs containing heavy metals. [ 46–49 ] On the other hand, the CDs have excellent photostability against photobleaching and photoblinking as compared with the conventional organic dyes (typically fluorescein and rhodamine B).…”