Electrochemical sensors functionalized with Bi5O7NO3/Bi2O3 heterostructures for non-enzymatic paracetamol sensing: theoretical model and characterization

Given the risks associated with liver transplant operations and the protagonist role of paracetamol overdose in cases of hepatotoxicity, there's a growing need for a fast, cheap and easy to use method for its detection. Compared to traditional methods like HPLC, spectrophotometry, colourimetry and chemiluminescence, electrochemical sensors have the potential of reaching less fortunate hospitals that cannot afford expensive equipment and serve as a quick point-of-care screening method for suspected cases of paracetamol toxicity. Moreover in the field of therapeutic drug monitoring a lot of effort has been put in developing electrochemical sensors to better control the depth of anesthesia, where paracetamol is usually a component. Enzymatic biosensors have the disadvantage of being generally unstable and sensitive to pH and temperature variations. Non-enzymatic electrochemical sensors overcome some of these limitations showing very good sensitivities and limit of detection, though at the cost of limited specificity. In this work a computational study was initially performed, based on a semi-empirical method (PM3). The interaction of a molecule of Paracetamol with a cluster of Bi5O7NO3 is evaluated and then through the use of Marcus theory the rate constant for electron transfer is obtained. Such an investigation allowed to set a theoretical framework for the study of defect design. In particular, through a solid state method different heterostructures of Bi2O3/Bi5O7NO3 were produced with the objective of exploring their role as potential electrocatalysts. Their performance was evaluated by cyclic voltammetry on commercial screen printed electrodes by Dropsens, where the working electrode was functionalized with an aqueous dispersion of the produced catalysts. Through the use of Laviron equation a kinetic study was performed and the rate constants of electron transfer calculated. A good agreement was found between the values of rate constant obtained though experimental and computational means. Furthermore, the electrocatalytic activity of the heterostructures was identified as superior to that of single phase subnitrate. This was both observed both in the kinetic study and in the calibration curves. From a morphological study done with the Scanning Electron Microcope (SEM), it was also remarked that the partial oxidation of the bismuth subnitrate induces a change in shape, from particular to lamellar. Based on the electrochemical tests performed, and the knowledge acquired in the theoretical work, the best performing material is selected for the fabrication of a paper-based biosensor.