Abstract
In this work, an amperometric biosensor has been designed for the fast detection of sulphite in aqueous solutions. A sulphite oxidation peak at is observed using cyclic voltammetry and exhibits a linear peak increase with sulphite concentration. A calibration curve (current versus sulphite concentration) was produced to characterise the biosensors. However, the complex wine solutions revealed no observable signal indicating that the polyphenols and/or proteins present in wine inhibited the electron transfer. With the use of polymer films, control of pH, gold nanoparticles and/or enzymes and proteins, it was hoped that the design may be improved increasing the stability and signal. However, work to date has not been successful in getting the sensor to work in wine or other beverages.
Summary
Sulphur dioxide is added to wine at nearly every stage of production and serves as both an anti-microbial agent and an antioxidant. Currently, sulphur dioxide measurement is time consuming and costly (particularly in terms of staff time or outsourcing) and cheaper, rapid methods have long been sought. The molecular form of sulphur dioxide is heavily influenced by the pH of the solution and it exists in various forms ranging from molecular SO2 at low pH to sulphite ion at high pH. As wine is kept at a pH of 3-4, sulphur dioxide is converted to mainly bisulphite ions with a small amount of molecular SO2.
Early work at Flinders demonstrated the successful detection of sulphite in standard solutions using an enzymatic electrochemical approach. This project built on that work to develop a robust, simple, reproducible construction protocol for the sensor and then test all analytical properties of the sensor both using standard solutions and representative wine samples. The successful development of the sensor could lead to a dramatic reduction in the effort required at wineries to measure SO2 concentrations.
The construction of the biosensor with surface attachment chemistry on gold was done successfully and proved to be very reproducible. In short a small molecule with an affinity for the substrate was first attached to the surface. These molecules provided attachment points for the active species in the sensor and these biologically active compounds were attached using standard coupling chemistry. The sensors were then tested for responses in standard aqueous solutions to determine important sensor parameters such as sensitivity, response times, reproducibility, lifetime and linearity of response.