Elena S. Speranskaya

Hydrophilic, Bright CuInS2 Quantum Dots as Cd-Free Fluorescent Labels in Quantitative Immunoassay

We report on the synthesis of core-shell CuInS2/ZnS quantum dots (QDs) in organic solution, their encapsulation with a PEG-containing amphiphilic polymer, and the application of the resulting water-soluble QDs as fluorescent label in quantitative immunoassay. By optimizing the methods for core synthesis and shell growth, CuInS2/ZnS QDs were obtained with a quantum yield of 50% on average after hydrophilization. After conjugation with an aflatoxin B1-protein derivative, the obtained QDs were used as fluorescent labels in microplate immunoassay for the quantitative determination of the mycotoxin aflatoxin B1. QDs-based immunoassay showed higher sensitivity compared to enzyme-based immunoassay.

Quantum Dot Loaded Liposomes As Fluorescent Labels for Immunoassay

Liposomes loaded with water-soluble and water-insoluble quantum dots (QD) were for the first time applied as labels in different heterogeneous immunoassays for the determination of food contaminants, using mycotoxin zearalenone (ZEN) as a model. A great deal of work was devoted to the optimal choice of phospholipids for the liposomes preparation and to the factors which are important for the stability and size of obtained liposomes. Thin-film hydration and reverse-phase evaporation techniques were evaluated in terms of stability of the obtained liposomes and their efficiency for QD loading. Conjugation of liposomes with proteins and the influence of cross-linkers to the nonspecific interaction of the obtained liposomes with the surface of microtiter plates and cartridges were investigated and 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide ester was found as the optimal cross-linker. The limits of detection (LOD) for ZEN of fluorescence-labeled immunosorbent assays were 0.6 μg kg(-1), 0.08 μg kg(-1), and 0.02 μg kg(-1), using QD, liposomes loaded with water-soluble QD, and water-insoluble QD, respectively. Similarly, the developed qualitative on-site tests using the different QD labels and taking into account the EU maximum residues level for ZEN in unprocessed cereals showed cutoff levels of 100, 50, and 20 μg kg(-1).

Synthesis of hydrophilic CuInS2/ZnS quantum dots with different polymeric shells and study of their cytotoxicity and hemocompatibility

In this work, there is a detailed description of the whole process of biocompatible CIS/ZnS QDs production. Special attention was paid to the stability of QDs against photooxidation. It was shown that Cu/In ratio greatly affected not only nanocrystals PLQYs but photostability as well. CIS/ZnS QDs with Cu/In = 1:4 ratio showed high photostability under UV illumination both in toluene and aqueous solutions. Meanwhile, photoluminescence of CIS/ZnS QDs with Cu/In = 1:1 ratio was completely quenched after several hours under UV illumination, though their initial QY was as high as 40% with peak maximum at 740 nm. QDs were transferred to water by polymer encapsulation and were subsequently modified with polyethers Jeffamines, cheap analogues of PEG-derivatives. Three types of hydrophilic QDs differing in size, PEG content, and surface charge were obtained for further investigation and comparison of their cytotoxicity and hemocompatibility. It was shown that both leucocytes size distribution and coagulation activation change after introduction of polyethers into QDs polymeric shell, while red blood cells and platelets size distribution as well as hemolysis rate did not show any different results among different QDs and the polymer itself. All three types of QDs showed only slight cytotoxicity. Confocal microscopy proves penetration of hydrophilic CIS/ZnS QDs inside cells, so the low QDs cytotoxocity cannot be explained by low cellular uptake of the QDs and indicated low QDs toxicity in general.

Fluorescent Quantum Dots: Synthesis, Modification, and Application in Immunoassays

Fluorescent semiconductor nanocrystals (called quantum dots (QDs)) possess unique optic properties which make them promising material in various applications. In particular, QDs demonstrate narrow florescence peaks with a location depending on the size of the nanocrystal, a wide absorption spectra, and high photostability. The current review is devoted to the synthesis and modification of semiconductor QDs used as fluorescent probes in bioanalysis. Such QDs should exhibit bright fluorescence, form stable aqueous colloid solutions at various pH, and have functional groups available for covalent binding with biomolecules. Major steps of QD preparation that meet these requirements are presented: synthesis of cores in organic solvent, methods of coating cores with shells of higher band-gap semiconductors, and ways of QD hydrophilization. Particular attention has been given to the preparation and modification of QDs using stable and available reagents. Advantages of QDs over organic dyes and recent advances in the application of QDs as fluorescent probes in immunochemical assays have been also considered.

Preparation of water soluble zinc-blende CdSe/ZnS quantum dots

Zinc-blende CdSe cores were used to produce CdSe/ZnS core-shell quantum dots with green emission (λem = 520 nm). The shell growth was realized at low temperature using stable reagents as ZnS precursors. The optimal conditions for shell growth were determined. It was shown that the reaction time and concentration of ZnS precursors in initial solution strongly affects the optical properties of the resulted coreshell quantum dots. The CdSe/ZnS quantum dots were transferred to aqueous solution by ligand exchange with mercaptopropionic acid, and denaturated bovine serum albumin was added to improve chemical stability of CdSe/ZnS solution. As a result, highly luminescent water-soluble CdSe/ZnS quantum dots (quantum yield 36%) which can be used as biolabels in immunoassay were obtained.

Luminescence monitoring of particle delivery into rat skin in vivo

Delivery of upconversion microparticles [Y2O3:Yb, Er] and quantum dots (CuInS2/ZnS coated with PEG-based amphiphilic polymer) into rat skin using the fractional laser microablation has been studied in vivo. Luminescence spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis were used for visualization of nanoparticles in microchannels. Results have shown that the upconversion microparticles are detected more efficiently in comparison with the quantum dots. The fluorescence intensity of the inserted upconversion microparticles is higher, when the Omnipaque™ was applied as a skin optical clearing agent. The fluorescent images of upconversion nanoparticle distribution indicate the advantage of particle delivery into skin by ultrasound.

The influence of synthetic conditions on optical properties of cadmium selenide quantum dots

In this work we consider the technique used to prepare CdSe quantum dots (QDs) both in a high-boiling solvent (octadecene) and in an aqueous solution. It has been shown that, if octadecene is used as a medium for synthesis, the increase in synthetic temperature and reaction time leads to a substantial decrease in the QDs trap luminescence intensity. In addition, an increase in the synthesis temperature reduces the scatter of particles in sizes. In addition to the hydrofobic QDs, CdSe QDs have also been synthesized in an aqueous solution using mercaptopropionic acid as a stabilizer. Using these QDs as an example, the possibility of increasing the stability of QDs covered by mercaptopropionic acid in the presence of sodium sulfite has been shown for the first time. The role of sodium sulfite consists of the chemical binding of dissolved oxygen.