Synthesis, characterization and modification of functionalized pyrimidine stabilized gold nanoparticles on ITO electrode for the determination of tannic acid.

This paper describes the synthesis of 4-amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles (AHMP-AuNPs) in aqueous medium and their immobilization on indium tin oxide (ITO) electrode modified with (3-mercaptopropyl)trimethoxysilane (MPTS) sol-gel for the determination of tannic acid (TA). The high resolution transmission electron microscopy (HR-TEM) images show that the particles are spherical in shape with a diameter of ~6 nm. The heterogeneous electron transfer rate constant (k(et)) of [Fe(CN)₆]³⁻/⁴⁻ at ITO/MPTS/AHMP-AuNPs electrode was found to be 1.14×10⁻⁷ m/s. This value was much higher than the values obtained at ITO/MPTS (4.94×10⁻⁹ m/s) and bare ITO (8.79×10⁻⁸ m/s) electrodes, indicating that the electron transfer reaction was faster at AuNPs modified electrode. Further, the ITO/MPTS/AHMP-AuNPs electrode shows excellent electrocatalytic activity toward TA oxidation when compared to bare ITO electrode. This was understood from the obtained higher heterogeneous rate constant (k(s)) value at AuNPs modified electrode (7.35×10⁻⁵ m/s) than at bare ITO electrode (5.45×10⁻⁶ m/s). Using the amperometry method, detection of 20 nmol/L TA was achieved. The practical application of the present method was demonstrated by determining the concentration of TA in commercial beer samples.