Electrochemical determination of quercetin on sol-gel electrode modified with nanodiamond

Antioxidants are substances that may protect cells from the damage caused by unstable molecules such as free radicals. Flavonoids are phenolic substances widely found in fruits and vegetables. The previous studies showed that the ingestion of flavonoids reduces the risk of cardiovascular diseases, metabolic disorders, and certain types of cancer. These effects are due to the physiological activity of flavonoids in the reduction of oxidative stress, inhibiting low-density lipoproteins oxidation and platelet aggregation, and acting as vasodilators in blood vessels. Quercetin (QU), a plant pigment is a potent antioxidant flavonoid and more specifically a flavonol, found mostly in onions, grapes, berries, cherries, broccoli, and citrus fruits. 1 The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. 2 Nanodiamonds or diamond nanoparticles with a size below 1 micrometer. They can be produced by impact events such as an explosion or meteoritic impacts. Because of their inexpensive, large-scale synthesis, potential for surface functionalization, and high biocompatibility, nanodiamonds are widely investigated as a potential material in biological and electronic applications and quantum engineering. There are three main aspects in the structure of diamond nanoparticles to be considered: the overall shape, the core, and the surface. Through multiple diffraction experiments, it has been determined that the overall shape of diamond nanoparticles is either spherical or elliptical. At the core of diamond nanoparticles lies a diamond cage, which is composed mainly of carbons. 3 Herein, we report the fabrication of ND modified electrode for the sensitive and selective detection of QU. The unique properties of ND modified electrode translate to enhanced electrocatalytic activity and lower overpotential towards the detection of QU. The effect of scan rate and pH on the redox electrochemical QU at ND modified electrode as studied and discussed. By using differential pulse voltammetry as sensitive method the calibration curve was plotted in the concentration range of 0.1 µM to 75 µm. The detection limit was calculated as 0.04 µm based on signal to noise ratio of 3. Lastly, the present method was applied to determine QU in vegetable samples t and satisfactory results were obtained with good accuracy.