Leucine-modified carbon paste electrode for multi dye electroanalysis: a high-performance approach

Indigo carmine (IC) has been used for over a century in textiles and medicine, but its potential environmental risks have made its detection increasingly important. To address this, we developed a poly(L-leucine) modified carbon paste electrode (P(LL)MCPE using a simple electro polymerization method. This modified electrode shows a strong oxidation signal at pH 7.0 and was characterized using the SEM technique to confirm successful surface modification. Its electrochemical behavior was evaluated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). We optimized parameters like the effect of pH, scan rate variation, accumulation parameters, and concentration variation of IC and selectivity detection for IC, Fast shalpon black (FB), tartrazine (TT), and methyl red (MR). The electrode gave linear responses between 0.2 and 2.6 μM (CV) and 0.2 to 2.4 μM (DPV), with excellent sensitivity down to a limit of detection (LOD) of 0.02 μM (CV) and 0.06 μM (DPV) and limit of quantification (LOQ) of 0.67 μM (CV) and 0.23 μM (DPV). The fabricated sensor was presenting good stability, reproducibility, repeatability, and selectivity, even when interfering substances were present. Finally, the sensor proved effective for IC detection in a real sample application in tap water, with good recovery.