The registration of aptamer–ligand (ochratoxin A) interactions based on ligand fluorescence changes

The fluorescent properties of ligands can change when they bind to specific receptors. Modulated by the transition of the ligand from the free to the bound state, fluorescence makes it possible both to detect this ligand and quantitatively register its binding. We characterized the interaction of ochratoxin A (OTA) with the specific G-quadruplex aptamer through excitation-emission matrix fluorescence spectroscopy. It was shown that the formation of the complex changes the OTA fluorescence spectrum both in the region of the main peak at λex/λem 380/430 nm and in the region of peak at λex/λem 265/425 nm. At pH 8.5 and OTA concentration of 30 nM, this peak is smaller in intensity than the main peak of fluorescence. The formation of the complex with the aptamer leads to an increase of the fluorescence at λex/λem 265/425 nm up to 6.5 times, which makes it up to 4.9 times more intense than fluorescence at 380/430 nm. Fluorescence of the G-quadruplex aptamer (donor) takes part in increasing of the OTA (acceptor) emission at λex/λem 265/425 nm due to the resonance energy transfer. The concentration regularities of the modulated fluorescence of OTA at λex/λem 265/425 nm have been studied. Their correspondence to the calculations of complexation conducted on the basis of the dissociation constant is shown.