Bismuth oxynitrates nanostructures for electrochemical sensors modification: Paracetamol, Dopamine and Uric Acid sensing

Nowadays, the use of sensors has achieved great importance in various fields. Agriculture, pollution detection, and food safety are just some of the fields that have demanded the use of increasingly precise and accurate sensors. Of all of them, the medical field has paid great attention to the use of sensors in diagnosing and treating diseases. The use of drugs for surgical or therapeutic purposes involves careful attention to the doses administered to the patient. Overdosing a specific drug can lead to organ transplantation and/or malfunctioning of apparatuses and systems. An example is the use of paracetamol as a pain-relieving and antipyretic agent, the improper use of which can lead to liver and kidney failure. The onset of disease is often associated with changes in particular chemicals in the body, as is the case with dopamine levels in the brain that can be an alarm bell for Parkinson's disease or uric acid levels associated with gout. This is why the importance of accurate and stable detection of quantities of chemical species arises. Electrochemical sensors have great potential by acting as sensitive and inexpensive devices. The world of nanomaterials represents a great possibility for achieving this goal. In recent years, various nanostructures have been used to improve the performance of electrochemical sensors. In the list of materials, bismuth has an excellent reputation due to the high stability of its nanostructures and its biocompatibility. In this project, several bismuth nitrates were synthesised and used to modify electrodes (DropSens 100) for the detection of paracetamol dopamine and uric acid in a neutral solution. Particular attention was given to the synthesis process in which different amounts of PEG were used. The latter takes on the role of a surfactant in the production of the materials, which can lead to greater stability of the dispersed phases and particular morphological characteristics of the final product. Once the materials were synthesised, they were analysed using analysis techniques such as Raman and IR spectroscopy and the use of SEM. The modified sensors were compared to the bare sensor using the cyclic voltammetry technique. The interaction between electrodes and analyte was studied for different scan rates to derive kinetic constant rate and transfer coefficients. The latter two, derived using Laviron's theory, were used to compare the electrochemical properties of the sensors. From the analyses, it was obtained that the use of high concentrations of PEG (2 to 4 times the amount of bismuth salts) in the synthesis process is linked to an increase in the constant rate. For the paracetamol detection, it was obtained a value of 5.72 ± 0.67 {ms}^{-1} and for the dopamine detection a value of 42.82 ± 0.48 {ms}^{-1}. The performances of the various sensors were also evaluated by changing the analyte concentrations to reconstruct the calibration curves. Bismuth nanostructures made it possible to realise more sensitive sensors by increasing the sensitivity. The electrode modified with bismuth oxynitrates produced with 4 times the amount of PEG with respect to the bismuth salts weight presented a sensitivity of 42.82 ± 0.48 \mu A/mM for the paracetamol detection, 16.67 ± 1.31 \mu A/mM\ r the dopamine detection and 9.59 ± 0.41 \mu A/mM. The electrochemical analyses carried out in this work were aimed at highlighting the electrocatalytic properties of bismuth and the role that a surfactant such as PEG plays in the synthesis of materials.