Insights into the Ochratoxin A/Aptamer Interactions on a Functionalized Silicon Surface by FTIR and UV–Vis Studies
Résumé
The association of a mycotoxin ochratoxin A (OTA) with a high-affinity DNA aptamer (anti-OTA) immobilized on a functionalized surface has been investigated at the molecular level. Anti-OTA aptamers are coupled by aminolysis in several steps on an acid-terminated alkyl monolayer grafted on a silicon substrate and Fourier-transform infrared (FTIR) spectroscopy in attenuated-total-reflection (ATR) geometry is used to assess the immobilization of anti-OTA (in its unfolded single-strand form) and determine its areal density (ca. 1.4 /nm 2). IR spectra further demonstrate that the OTA/anti-OTA association is efficient, selective and that several association/dissociation cycles may be conducted on the same surface. The areal density of OTA measured after association on the surface (IR spectroscopy) and after dissociation from the surface (UV-Vis spectroscopy) falls in the range 0.16-0.3 /nm 2 which is close to the areal density of a closed-packed monolayer of anti-OTA aptamers folded to form their G-quadruplex structure. The interactions between OTA and its aptamer at the surface are discussed with the help of DFT calculationsto identify the complex IR vibrational modes of OTA in solutionand UV-Vis spectroscopyto determine the protonation state of the adsorbing species (i.e., OTA dissolved in the buffer solution)- .
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