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21. Polycations as Aptamer-Binding Modulators for Sensitive Fluorescence Anisotropy Assay of Aflatoxin B1.

Author

Samokhvalov, Alexey V., Mironova, Alena A., Eremin, Sergei A., Zherdev, Anatoly V., and Dzantiev, Boris B.

Subjects
FLUORESCENCE anisotropy, APTAMERS, AFLATOXINS, POLYETHYLENE glycol, FOOD contamination, POISONS
Abstract

Fluorescence induced by the excitation of a fluorophore with plane-polarized light has a different polarization depending on the size of the fluorophore-containing reagent and the rate of its rotation. Based on this effect, many analytical systems have been implemented in which an analyte contained in a sample and labeled with a fluorophore (usually fluorescein) competes to bind to antibodies. Replacing antibodies in such assays with aptamers, low-cost and stable oligonucleotide receptors, is complicated because binding a fluorophore to them causes a less significant change in the polarization of emissions. This work proposes and characterizes the compounds of the reaction medium that improve analyte binding and reduce the mobility of the aptamer–fluorophore complex, providing a higher analytical signal and a lower detection limit. This study was conducted on aflatoxin B1 (AFB1), a ubiquitous toxicant contaminating foods of plant origins. Eight aptamers specific to AFB1 with the same binding site and different regions stabilizing their structures were compared for affinity, based on which the aptamer with 38 nucleotides in length was selected. The polymers that interact reversibly with oligonucleotides, such as poly-L-lysine and polyethylene glycol, were tested. It was found that they provide the desired reduction in the depolarization of emitted light as well as high concentrations of magnesium cations. In the selected optimal medium, AFB1 detection reached a limit of 1 ng/mL, which was 12 times lower than in the tris buffer commonly used for anti-AFB1 aptamers. The assay time was 30 min. This method is suitable for controlling almond samples according to the maximum permissible levels of their contamination by AFB1. The proposed approach could be applied to improve other aptamer-based analytical systems. [ABSTRACT FROM AUTHOR]

Published
2024
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50. Ability of Antibodies Immobilized on Gold Nanoparticles to Bind Small Antigen Fluorescein.

Author

Sotnikov, Dmitriy V., Byzova, Nadezhda A., Zherdev, Anatoly V., and Dzantiev, Boris B.

Subjects
GOLD nanoparticles, FLUORESCEIN, ANTIGENS, NANOPARTICLE size, BINDING sites, IMMUNOGLOBULINS, SURFACE plasmon resonance, RAMAN scattering
Abstract

The analytical applications of antibodies are often associated with their immobilization on different carriers, which is accompanied by a loss of antigen-binding activity for a sufficient proportion of the bound antibodies. In contrast to data on plain carriers, minimal data are available on the properties of antibodies on the surfaces of nanoparticles. Protein antigens have been predominantly investigated, for which space restrictions do not allow them to occupy all active sites of immobilized antibodies. This study considered a low-molecular-weight compound, fluorescein, as an antigen. Spherical gold nanoparticles with five different sizes, two differently charged forms of fluorescein, and three different levels of surface coverage by immobilized antibodies were tested. For gold nanoparticles with diameters from 14 to 35.5 nm with monolayers of immobilized antibodies, the percentage of molecules capable of binding carboxyfluorescein varied from 6% to 17%. The binding of aminofluorescein was more efficient; for gold nanoparticles with an average diameter of 21 nm, the percentage of active binding sites for the immobilized antibodies reached 27% compared with 13% for the carboxyfluorescein case. A fourfold reduction in the coverage of the nanoparticles' surface compared with that of the monolayer did not lead to reliable changes in the percentage of active binding sites. The obtained data demonstrate that an antigen's binding to immobilized antibodies is limited even for small antigens and depends on the size of the nanoparticles and the electrostatic repulsion near their surface. [ABSTRACT FROM AUTHOR]

Published
2023
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