Voltammetric sensor based on carbon nanotubes and cerium dioxide nanoparticles for Ponceau 4R

Synthetic azo dyes including red Ponceau 4R (E124) are widely applied in the food industry to provide a bright, attractive, and stable color to foodstuff. Nevertheless, negative health effects can appear with high dye consumption. Therefore, the Ponceau 4R content in foods is strictly controlled. Voltammetric sensors are a promising tool for solving this problem. A glassy carbon electrode with layer-by-layer coverage of multi-walled carbon nanotubes and cerium dioxide nanoparticle dispersion in cetylpyridinium bromide has been designed as a novel sensitive voltammetric sensor for Ponceau 4R. The modifier combination provides an 80 mV cathodic shift of the Ponceau 4R oxidation peak and 1.7-fold higher oxidation currents compared to the bare GCE due to the synergistic effect of nanomaterials. Moreover, the appearance of cathodic step on the Ponceau 4R voltammograms indicates an increase in the electron transfer rate that is clearly confirmed by the electrochemical impedance spectroscopy data (k_et = 1.15 × 10^–3 and 5.19 × 10^–5 cm s^–1 for the modified and bare GCE, respectively). Ponceau 4R electrooxidation is a quasi-reversible, pH-independent, and diffusion-driven process. Differential pulse mode (pulse amplitude of 75 mV and time of 25 ms) in Britton–Robinson buffer pH 2.0 has been applied for Ponceau 4R quantification. The sensor response at 0.76 V is linear in the range of 0.10–1.0 and 1.0–7.5 μM of Ponceau 4R with the detection limit of 23 nM, which is sufficient for practical application. Recovery of dye in model solutions (99-101%) confirms high accuracy of the sensor developed.