A DISPOSABLE ULTRASENSITIVE SCREEN-PRINTED-CARBON ELECTRODE BASED ON CONDUCTIVE POLYMERS FOR THEOBROMINE DETECTION

In this work, a screen-printed carbon electrode (SPCE) modified with Vulcan (V) carbon black on Chitosan (Chi), V@Chi, was developed, followed by electropolymerization of pyrrole (PPy), addition of gold (Au) particles and electropolymerization of cysteine ​​(p-L-Cys). The resulting electrode was named L-Cys/PPy/Au/V@Chi/SPCE and applied for theobromine (TB) detection^[1]. The stability, reproducibility and sensitivity of the SPCE were evaluated through cycle voltammetry (CV) using 1.0 mmol L^-1 Fe(CN)₆^3−/4− in 0.1 mol L^-1 KCl. The SPCE was constructed with a conductive layer composed of 70% graphite ink and showed a significant increase in the electroactive area. The FEG-SEM images by revealed a greater complexity of the surface compared to the unmodified electrode. The analytical curve was established with concentrations ranging from 0.01 to 5.0 μmol L^-1 at pH 8.0 (E vs. graphite= 1.25 V), resulting in a limit of detection of 0.00235 μmol L^-1. During the interference studies, the platform demonstrated high selectivity for TB over eight interferents compounds. In addition, the L-Cys/PPy/Au/V@Chi/SPCE presented TB recovery percentages ranging from 100.87% to 106.25%, when applied in tap water, green tea, and black tea samples. Thus, the electrochemical platform proved to be a reproducible, selective, and low-cost sensor for the TB detection in different complex matrices. The modifications performed on the SPCE increased the sensitivity of the electrode, making it viable for applications in real samples.