Photoelectrochemical sensing of tannic acid based on the use of TiO₂ sensitized with 5-methylphenazinium methosulfate and carboxy-functionalized CdTe quantum dots

The article describes a method for determination of tannic acid in extracts of medicinal plants. Tannic acid (TA) is an antioxidant and has anticancer and antimicrobial properties. Titanium dioxide nanoparticles (TiO₂) were co-sensitized with 5-methylphenazinium methosulfate (PMS) and carboxy-functionalized cadmium telluride quantum dots (CdTe QDs), and immobilized on a fluorine-doped tin oxide electrode. The surface morphology and electrochemical properties of the modified electrode were investigated by scanning electron microscopy and amperometry, respectively. A composite consisting of TiO₂, PMS and CdTe QDs in a nafion film has a response to TA under LED light higher than that observed for each separate component. Under optimized experimental conditions and at an applied voltage of +0.4 V vs Ag/AgCl, the photoelectrochemical sensor has a linear response in the 0.2 to 200 μmol L⁻¹ TA concentration range and a detection limit of 60 nmol L⁻¹. The sensor was successfully applied to the determination of TA in spiked extracts from three medicinal plants, with recovery values between 98.3 and 103.9 %. .