Determination of caffeine @ gold nanoparticles modified gold (Au) electrode: a preliminary study

Caffeine is a natural alkaloid exerting many physiological effects, such as stimulation of the central nervous system, diuresis and gastric acid secretion. It is widely distributed in plant products and beverages and its quantification is mainly of pharmaceutical and alimentary concern. In this paper, we describe an electrochemical study based on the modification of a gold electrode (Au) surface by deposition of functionalized gold nanoparticles by Cyclic Voltammetry (CV). The oxidation system is characterized by an anodic peak in the positive-going step and by the absence of any cathodic peak on the reverse scan, indicating that the oxidation is irreversible. At the modified electrode, the voltammetric peak height increases vs. that @ the bare one, depending on the nanoparticles functionalization. The best performances were observed @ Au electrode modified with colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix. In order to optimize the influence of different electrolytes on the sensor response, different electrolytic solutions (nitric acid, sulfuric acid, phosphoric acid and hydrochloric acid) were used. The electrochemical behavior of caffeine was also studied in aprotic medium with the aim to clear up the different mechanisms the oxidative process occurs through in aqueous and in aprotic medium.