Nickel and Zinc Ferrite Nanoparticles Tailored Screen Printed Electrodes for Non-Enzymatic Electrochemical Sensing

Abstract This work aims to develop a fast, cheap, and easy-to-use sensor for paracetamol detection. Non-enzymatic electrochemical sensing was selected because of the electrochemical activity of paracetamol and the easy and cheap way of sensing it using the commercially available Screen-printed carbon electrodes (SPCEs). In order to improve the sensing, five concentrations of zinc ferrite (ZnxFe1−xO4, x from 0.2 to 1) nanoparticles, five concentrations of nickel ferrite (NixFe1−xO4, x from 0.2 to 1) nanoparticles, and magnetite nanoparticles were synthesized using an auto-precipitation method followed by a hydrothermal synthesis. Nanoparticles act as catalytic agents, improving the electron transfer rate and, therefore, the sensitivity and the limit of detection (LOD). These new materials’ quality has been tested by means of SEM imaging, XRD, and Raman spectroscopy. The SEM imaging highlight that the synthesized nanoparticle formed agglomerates of micrometric size while the XRD and Raman were used to check the composition. Four 3:1 w/V dispersions of each ferrite were done using deionized (DI) water, ethanol, methanol, and a 10% V/V solution of isopropanol in DI water. C11L SPCEs with 0.12cm2 carbon working electrode, carbon counter electrode, and Ag/AgCl reference electrode were bought from Dropsens. The synthesized nanoparticles were deposited on top of several SPCEs using drop-casting, a simple technique based on putting a drop of the dispersed ferrite on top of the electrode and leaving it dry. Cyclic voltammetry (CV) was used to test bare and coated electrodes in 1 mM paracetamol solution in 0.1M PBS. The volume of the drop and the solvent of the dispersion were the first two variables optimized. After various optimizations step, methanol resulted as the best solvent and 2.5μL as the best drop volume. An increase of around 35% of the oxidation’s peak current with respect to the bare electrode was observed. Using the optimized conditions, a kinetic characterization was performed; in particular, electron transfer coefficient (α) and kinetic rate constant (k) were calculated using Laviron equations. Calibration curves were obtained for the bare and the best materials, using seven known concentrations from 0 mM to 3 mM paracetamol in 0.1 M PBS solution, plotting the oxidation’s peak currents with respect to the concentration. Three electrodes for each used material were measured for the calibration curve to have an inter-sensor error. Higher sensitivity was observed for all modified electrodes compared to the bare electrode. Quantitatively, the bare electrode has a sensitivity of 27 ± 1.3μA/mM with a limit of detection (LOD) of 6.9 ± 0.3μM . The performances of the coated electrodes are similar; the best material seems to be the zinc ferrite, with a sensitivity of 34.9 ± 0.7μA/mM and a LOD of 15.5 ± 0.3μM. So a final increase of around 29% in the sensitivity was achieved. Finally, chronoamperometry measurements were done to calculate the active area of the electrodes resulting in 0.7 ± 0.2 cm2 for the zinc ferrite electrode. This work can be further developed: by trying in-flow measurements, checking the selectivity using other analytes, and developing a custom portable potentiostat to make possible in-situ measurements.