Unveiling the effect of Bi in ZnFe<inf>2</inf>O<inf>4</inf> nanoparticles in electrochemical sensors

This work investigates the effect of the inclusion of Bi3+ ions in ZnFe2O4 nanoparticles on electron transfer at the electrochemical interface. ZnBixFe2-xO4 (x = 0, 0.5, 1, 2) nanomaterials are synthesized and the impact of Bi3+ ions on the chemical features of ZnFe2O4 nanoparticles is studied by using different materials’ characterization techniques. The effect of the change in the chemical composition of ZnFe2O4 nanoparticles on the electrochemical sensing performance is extensively studied and correlated with the electrochemical sensitivity and kinetic rate constant. Screen-printed electrodes functionalized with ZnBixFe2-xO4 nanomaterials have an excellent enhancement of electrochemical sensing performance towards paracetamol, as a test molecule, compared to the carbon electrodes. The highest sensitivity (37.8 ± 0.2 μA/mM) and the best kinetic rate constant (13.1 ± 2.8 ms−1) are achieved by the ZnFe2O4 sensor, while the ZnBi2O4 sensor achieved a sensitivity of (23.5 ± 0.6) μA/mM with a kinetic rate constant of (0.45 ± 0.16) ms−1. The ZnFe2O4 sensor is found to have a direct electron transfer, whereas the other sensors participate in a surface state-mediated electron transfer at the electrochemical interface. This research shows a clear path to the potential applications of spinel oxide-based electrochemical sensors for specific drugs or molecules detection.