A selective and sensitive monitoring of the OH radical using flavonoid-modified electrodes

Highlights: •Flavonoid or metal flavonoid-modified APTES-FTO electrodes for OH sensing. •(M-)Fls-APTES-FTO can serve as sensitive and selective electrochemical sensors. •Electrochemical monitoring of OH radical in physiological samples at pH 7.4. •Detection of OH concentration as low as 2–10 nM. •Quercetin-APTES-FTO proved as the most sensitive and promising electrode. -- Abstract: In the present work, three flavonoids (Fls) namely, quercetin (quer), morin (mor), and primuletin (prim) as well as their metal; (Cu(II) and Fe(III)) complexes (M-Fls) were deposited on APTES-FTO ((3-aminopropyl)triethoxysilane-fluorine doped tin oxide) electrodes. The formation of the (M-)Fls-APTES-FTO surface was verified and characterized through AT-FTIR. These surfaces were found to detect the OH radical at a concentration as low as 2 nM using cyclic and square wave voltammetry and the decrease in the anodic peak currents of (M-)Fls-APTES-FTO working electrodes could be taken as a measure of the OH radical concentration in the sample. Furthermore, a comparison of the decrease in the peak currents of (M-)Fls-APTES-FTO caused by OH to the decrease noted in the presence of 100-fold higher concentrations of other reactive oxygen species (ROS including superoxide anion, alkylperoxide anion, singlet oxygen, chlorine monoxide, and hydrogen peroxide), confirmed a high selectivity and rather insignificant interference by other ROS of no more than 4%. Thus, this method provides significant selectivity in the electrochemical detection of the OH radical. Among the (M-)Fls tested for hydroxyl radical detection, the most sensitive ones were Fe-quer, Cu-quer and Fe-mor deposited on APTES-FTO.