Valentina V. Goftman

Synthesis, modification, bioconjugation of silica coated fluorescent quantum dots and their application for mycotoxin detection.

To create bright and stable fluorescent biolabels for immunoassay detection of mycotoxin deoxynivalenol in food and feed, CdSe/CdS/ZnS core-shell quantum dots (QDs) were encapsulated in silica nanoparticles through a water-in-oil reverse microemulsion process. The optical properties and stability of the obtained silica coated QDs (QD@SiO2), modified with amino, carboxyl and epoxy groups and stabilized with polyethylene glycol fragments, were characterized in order to assess their bioapplicability. The developed co-condensation techniques allowed maintaining 80% of the initial fluorescent properties and yielded stable fluorescent labels that could be easily activated and bioconjugated. Further, the modified QD@SiO2 were efficiently conjugated with antibodies and applied as a novel label in a microtiter plate based immunoassay and a quantitative column-based rapid immunotest for deoxynivalenol detection with IC50 of 473 and 20 ng/ml, respectively.

A fluorescent immunochromatographic strip test using Quantum Dots for fumonisins detection.

A fluorescent immunochromatographic strip test (ICST) based on the use of Quantum Dots (QD) was developed and applied to detect fumonisins in maize samples. A limit of detection for fumonisin B1 of 2.8 µg L(-1) was achieved, with an analytical working range of 3-350 µg L(-1), corresponding to 30-3500 µg kg(-1) in maize flour samples, according with the extraction procedure. The time required to perform the analysis was 22 min, including sample preparation. Recovery values in the range from 91.4% to 105.4% with coefficients of variation not exceeding 5% were obtained for fortified and naturally contaminated maize flour samples. To evaluate the possible improvements due to the use of QD for ICST technology, we performed a direct comparison of the proposed QD-ICST to a gold nanoparticles- and a chemiluminescent-ICST previously developed for fumonisins detection, in which the same immunoreagents were employed.

Rapid immunochemical tests for qualitative and quantitative determination of T-2 and HT-2 toxins

Rapid immunotests were developed for qualitative and quantitative detection of T-2 and HT-2 toxins in cereal samples. Specific antibodies were immobilized either onto polyethylene filters or sepharose gel inside the transparent column. The tests combined the basic functions of purification, concentration and immunodetection of the target analytes through the enzymatic reaction of horseradish peroxidase (HRP). To make the test suitable for detection of both T-2 and HT-2 toxins, anti-T-2 toxin antibody was combined with HT-2 toxin–HRP conjugate. Matrix interference was eliminated by appropriate dilution of sample extracts with polyethylenglycol solution followed by filtration through a solid sorbent in a separate clean-up column. For the qualitative assay (visual detection) the cut-off level was 2 ng mL−1 of T-2 and HT-2 toxins, while the quantitative assay enabled the detection of 0.55 ng g−1 T-2 toxin and 1.7 ng g−1 HT-2 toxin in spiked wheat samples. Analysis of naturally contaminated wheat samples resulted in a good agreement between the developed immunotest and confirmatory LC-MS/MS. The proposed immunotest is fast, easy-to-use and suitable for rapid screening of T-2 and HT-2 toxins in wheat.

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.

Synthesis of cadmium-free quantum dots based on CuInS2 nanocrystals

We report an efficient synthesis Cd-free CuInS2/ZnS (CIS/ZnS) quantum dots (QDs) using low toxic precursors and investigation of their optical properties. The nanocrystals have been obtained via reaction between the acetate salts of the corresponding metals and elemental sulfur in the presence of dodecanethiol in octadecene media at 220°C. Influence of various experimental variables, including temperature, time, ratio of Cu and In precursors were investigated. Thus, it was shown that the photoluminescence (PL) emission wavelength can be tuned by conveniently changing the stoichiometric ratio of the components. The plain CIS nanocrystals did show PL emission but with quite low PL quantum yield (QY). In order to increase the QY of QD luminescence by compensation of the surface defects of QDs cores, the process of covering with ZnS shells was done. During shelling process, increasing of QY and blue shift of emission maximum were detected.

Multicolored silica coated CdSe core/shell quantum dots

Silanization is a convenient route to provide water-solubility to the quantum dots (QDs) with different structure. Green, orange and red emitting CdSe-based QDs were synthesized by varying of number and material of wider-band gap shells and fluorescent properties of QDs were characterized before and after silanization. It was shown that structure of the QD influences on the quantum yield of the silanized QDs: the better CdSe core is protected with wider-band gap semiconductor shells, the more fluorescence properties remain after silica coated QD possess. Hence silica coated QDs have a great perspectives for the multiplex analysis.

Thermosensitivity of nanothermometer: CdSe/ZnS vs. CuInS2/ZnS

Manuscript is devoted to the comparison of CdSe/ZnS and CuInS2/ZnS quantum dots thermosensitivity in the view of their applications as nanothermometers. It was found the luminescence spectrum of CuInS2/ZnS quantum dots consists of two components, which are described by Gauss type functions and connected with different types of defects into nanoparticles. The heat treatments provide different effects such as spectral shifts, FWHM and amplitude for these too components. CdSe/ZnS nanoparticles spectra shifted to the red region; the average speed of spectrum shift is 0.065 nm per degree.

Freeze-dried polymer-coated quantum dots for perspective biomedical application

Freeze-drying as known as lyophilization has been considered as a possible technique to improve the long-term stability of colloidal luminescent quantum dots (QDs) for perspective biomedical application. The paper describes synthesis of biocompatible CdSe-based core/shell QDs and discusses their optical and physical properties before and after freezedrying. Importantly, the dried nanoparticles can be stored for a long time under usual conditions and then can easily be redisperse in water at a desired concentration without such hard manipulations as sonication or heating. In this work two PEG-amine derivatives were applied for QDs pegylation: monoamine Jeffamine M1000 and diamine JeffamineED-2003. The use of different Jeffamines allows us to obtain QDs with different length of PEG chains and different ζ-potential. The influence of polymer composition on optical properties of the nanocrystals and on their stability after freeze-drying was studied.