Magnetic-luminescent composites based on semiconductor quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs) can serve as a platform combining visualization and therapy. Here, we report the construction of QD-SPION nanocomposites based on synthesized SPIONs and alloyed QDs (CdxZn1−xSeyS1−y)/ZnS solubilized with L-cysteine molecules. The study of the spectral-luminescence characteristics, the kinetics of luminescence decay show the composite’s stability in a solution. After incubation with HeLa cells, QDs, SPIONs, and their composites form clusters on the cell surface and associate with endosomes inside the cells. Component-wise analysis of the photoluminescence decay of cell-associated QDs/SPIONs provides information about their localization and aggregate status.

Magneto-luminescent nanosystems can be widely applied in biomedicine, namely for disease theranostics, early tumor imaging, and as drug delivery and hyperthermia agents. The creation of such systems using superparamagnetic iron oxide nanoparticles (SPIONs) and semiconductor quantum dots (QDs) approach is popular, since SPIONs are characterized by excellent magnetic properties and zero coercive force, and QDs have advantages over the majority of organic phosphors. In this work, the alloyed (CdxZn1-xSeyS1-y)/ZnS quantum dots are used to reduce the probability of Förster Resonance Energy Transfer or electron transfer, that quench QD photoluminescence, due to a thick gradient semiconductor shell. Moreover, Magnetic Circular Dichroism (MCD) spectroscopy has been successfully applied as a method for monitoring both magnetic properties and colloidal stability of magnetic nanoparticles in a solution, which is crucial for their biomedical applications. The simplicity of SPION/QDs nanostructure formation due to the sequential addition of a SPION solution to a QD solution is a major advantage of this approach. It was demonstrated that these SPION/QDs nanostructures are stable, can be efficiently absorbed by the HeLa cells, and do not show high cytotoxicity at low concentrations (up to 25 nM).

The luminescent and magneto-optical properties of nanocomposites consisting of a superparamagnetic Fe3O4 core coated with a luminescent semiconductor CdSe layer, which, in turn, is surrounded by a passivating ZnS shell, are considered.

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