Determination of theobromine in cocoa products and tea samples: A new sensitive and selective electrochemical sensor approach using Printex L6/Au and polyaniline

This study presents a novel, highly sensitive electrochemical sensor, PAni/Au/PL6C@Chi/SPPE, for detecting theobromine (TB) in complex food matrices. The sensor is based on a screen-printed polyethylene electrode modified with a nanocomposite of Printex L6 carbon (PL6C), gold nanoparticles (Au), polyaniline (PAni), and chitosan (Chi). Using a phosphate buffer solution at pH 8.0 as the optimal medium, the nanocomposite's surface morphology, wettability, and interfacial electrical properties were characterized by scanning electron microscopy (SEM), contact angle measurements, and electrochemical impedance spectroscopy (EIS), with key parameters optimized for maximum performance. Electrochemical analysis demonstrated that the modified sensor significantly enhanced the TB oxidation current compared to a bare electrode, indicating improved electron transfer kinetics. The optimized sensor exhibited excellent analytical performance, including a wide linear range (0.75–37.00 μmol L⁻¹), a low detection limit (0.076 μmol L⁻¹), high selectivity against common interferents, and excellent stability and reproducibility. The sensor's practical applicability was validated by quantifying TB in real samples like chocolate, cocoa powder, and tea, with results showing strong agreement with a comparative UV-Vis spectrophotometric method. This work offers a "fit-for-purpose", lab-made, and cost-effective platform suitable for routine food quality control.