Natalia A. Burmistrova

Immunochemical methods for the determination of mycotoxins

The state-of-the-art immunochemical methods for the determination of mycotoxins are considered. Both instrumental (enzyme-linked immunosorbent assay, polarization fluoroimmunoassay, and sensor devices) and noninstrumental methods are presented. The principles of particular methods are considered, and the examples of the use of these methods for the determination of mycotoxins from various groups in food products and animal feeds are given; the main lines of development are discussed.

Simultaneous determination of several mycotoxins by rapid immunofiltration assay

A method is developed for the simultaneous rapid determination of three mycotoxins, zearalenone (ZEN), ochratoxin A (OTA), and fumonisin B1 (Fum) by membrane immunofiltration analysis using a marker enzyme of alkaline phosphatase (AP) and two mycotoxins, deoxynivalenol (DON) and total T-2 toxin (T2) and HT-2 toxin (HT2) with horseradish peroxidase (HRP). The analysis is based on a competitive interaction between the antigene, free and bound to the enzyme, and antibodies immobilized on a membrane. The procedures of membrane fabrication and the conditions of mycotoxin to determination in model mixtures and extracts from wheat, corn, and silage are optimized. The influence of sample preparation on the results of analysis is studied. It is shown that the additives of polymers favor the reduction of the matrix effect in the analysis of complex matrixes using conjugated HRP. The methods developed allow the determination of mycotoxins at a level of the maximal permissible concentrations legislated by EU directives. The corresponding values (μg/kg) are 50, 2.5, and 500 in wheat; 100, 2.5, and 500 in corn; and 125, 25, and 1250 in silage for the simultaneous quantification of ZEN, OTA, and Fum (AP marker). For the determination of DON and total T2/HT2 with HRP, 1250 (1000) and 100 (500) in wheat and corn(silage). The procedures were validated by the analysis of spiked and naturally contaminated samples. The analysis of 10 samples takes 25 min.

The optical properties of quantum dots integrated in a hollow core photon crystal fiber

The use of photonic crystal fibers as a basis elements for biosensor construction is a perspective trend. The advantages of this approach are the use of micro and nano volumes of samples and a significant strengthening of the analytical signal while increasing the optical path length. Quantum dots are the most promising fluorescent markers for use in the photonic crystal fibers based analysis. The advantages of quantum dots, in this case, are associated with stability, wide range of excitation and extremely narrow range of high luminescence intensity. In this work we have investigated the behavior and optical properties of CdSe core-shell nanocrystals (quantum dots) after they including into hollow central defect of hollow core chirped photonic crystal fibers with internal surface modified by polyaniline films.

Quantum dots luminescence in the photonic cristal fibers modified with polymer layers

The luminescence of the quantum dots of different colors glow in the samples of photonic crystal fibers modified with self-organizing layers of polyaniline was studied.

Trends in biosensor development: Multifunctional platforms and enhanced labels

Hot-points in biosensors development, such as an application of new bifunctional platforms with an example of photonic crystal fibers and multiplexing of labels with an example of multiloaded with quantum dots nanostructures are discussed.

Luminescence of europium (III) complexes for visualization

With the purpose to develop bright non-toxic luminescent label for theranostic application we have studied complexation of lanthanide dipicolinates (2,6-pyridinedicarboxylates) by sodium alginate and effect of thermal exposure of synthesized micro-capsules on their luminescent properties. Synthesized micro-capsules are stable in acidic medium but dissolve at pH ~ 4 due to transformation of cationic europium dipicolinate complex to anionic. Luminescence studies have shown that emission spectra of europium(III)-alginate complexes (both chloride and dipicolinate) contain two intensive bands characteristic to Eu3+ ion (5D0 → 7F1 (590 nm) and 5D0 → 7F1 (612 nm)). We have also found that at 160ºC europium(III)- alginate micro-capsules decompose to black, soot-like substance, therefore, their thermal treatment must be performed in closed environment (i.e., sealed ampoules).

Modification of inner surface of photonic crystal fibers with self-assembled polyaniline films

Photonic crystal fibers (PCFs) with a hollow core are one of the most promising solid support of fiber-optic sensors. The main advantages of PCF as sensor elements in clinical analysis are minimization of optical interactions from the sample and the ability to analyze small volume of samples. At the same time, low sorption capacity of glass which is the basic material for the fabrication of the PCF, limits their use in the development of biosensors. Modification of the inner surface of the PCF can be the solution of the problem. In this work the synthesis of self-assembled films of polyaniline (PANI) on the inner surface of the PCFs was carried out. The modified PCFs were studied by spectroscopy and electron microscopy. It was found that the covering of the inner surface of the PCFs with PANI leads to a shift of the local maximums of the transmission spectrum PCFs up to 25 nm. These makes possible to design the method of varying of photonic bandgaps location.

Intramolecular photoinduced electron transfer of fluorescent probes based on 1,8-naphthalimide and aniline derivatives

The effect of conformation and electronic structure of fluorescent probes based on 1,8-naphthalimide and aniline derivatives (4-methoxyaniline and N,N-dimethyl-p-phenylenediamine) on the intramolecular photoinduced electron transfer (PET) was investigated by density functional theory calculations (B3LYP/6-31G (d, p)). We established restricted rotation around spacer bonds of the model compounds and their protonated and oxidized forms do not block the convergence of the nitrogen atoms involved in the electron transfer at a distance of ~3Å, which is adequately for PET. Computed values of protonation free energy for the gas-phase (ΔG298 r) show that the investigated fluorescent probes are predominantly protonated on the nitrogen atoms of the donor moiety. Electron population and localization of the frontier orbitals (LUMO, HOMO, HOMO-1) on the donor and acceptor moieties are transformed under protonation and one-electron oxidation of fluorescent probes. The results show that appearance or disappearance of the PET can be predicted by the energy difference between the frontier orbitals and the nature of their location of donor and acceptor moieties, which is in agreement with the PET theory and observed experimental data.