Heavy metal ions are not subject to biodegradation and could cause the environmental pollution of natural resources and water. Many of the heavy metals are highly toxic and dangerous to human health, even at a minimum amount. This work considered an optical method for detecting heavy metal ions using colloidal luminescent semiconductor quantum dots (QDs). Over the past decade, QDs have been used in the development of sensitive fluorescence sensors for ions of heavy metal. In this work, we combined the fluorescent properties of AgInS₂/ZnS ternary QDs and the magnetism of superparamagnetic Fe₃O₄ nanoparticles embedded in a matrix of porous calcium carbonate microspheres for the detection of toxic ions of heavy metal: Co²⁺, Ni²⁺, and Pb²⁺. We demonstrate a relationship between the level of quenching of the photoluminescence of sensors under exposure to the heavy metal ions and the concentration of these ions, allowing their detection in aqueous solutions at concentrations of Co²⁺, Ni²⁺, and Pb²⁺ as low as ≈0.01 ppm, ≈0.1 ppm, and ≈0.01 ppm, respectively. It also has importance for application of the ability to concentrate and extract the sensor with analytes from the solution using a magnetic field.

Carbon dots can be used for the fabrication of colloidal multi-purpose complexes for sensing and bio-visualization due to their easy and scalable synthesis, control of their spectral responses over a wide spectral range, and possibility of surface functionalization to meet the application task. Here, we developed a chemical protocol of colloidal complex formation via covalent bonding between carbon dots and plasmonic metal nanoparticles in order to influence and improve their fluorescence. We demonstrate how interactions between carbon dots and metal nanoparticles in the formed complexes, and thus their optical responses, depend on the type of bonds between particles, the architecture of the complexes, and the degree of overlapping of absorption and emission of carbon dots with the plasmon resonance of metals. For the most optimized architecture, emission enhancement reaching up to 5.4- and 4.9-fold for complexes with silver and gold nanoparticles has been achieved, respectively. Our study expands the toolkit of functional materials based on carbon dots for applications in photonics and biomedicine to photonics.

In this paper, we studied the properties of a multifunctional system, in which the luminescent and magnetic properties are combined. The calcium carbonate microspheres are used as porous matrices for complexes combining luminescence properties of AgInS2/ZnS quantum dots and magnetic properties of Fe3O4 nanoparticles. The study investigates the effect of magnetic nanoparticles concentration on optical properties of quantum dots in CaCO3-Fe3O4@AgInS2/ZnS complexes. It is shown that applying calcium carbonate microspheres as a matrix permits to reduce quenching of the quantum dots luminescence. Keywords: hybrid system; ternary quantum dots; magnetic nanoparticles; iron oxide; calcium carbonate microspheres.

In this paper, we studied the properties of a multifunctional system, in which the luminescent and magnetic properties are combined. The calcium carbonate microspheres are used as porous matrices for complexes combining luminescence properties of AgInS₂/ZnS quantum dots and magnetic properties of Fe₃O₄ nanoparticles. The study investigates the effect of magnetic nanoparticles concentration on optical properties of quantum dots in CaCO₃-Fe₃O₄@AgInS₂/ZnS complexes. It is shown that applying calcium carbonate microspheres as a matrix permits to reduce quenching of the quantum dots luminescence. Keywords: hybrid system; ternary quantum dots, magnetic nanoparticles, iron oxide; calcium carbonate microspheres.