Development of a graphene-based electrochemical immuno-biosensor for the sepsis biomarker procalcitonin

Sepsis is a global health issue that is the primary source of death by infection. It is often deadly and being able to deliver an appropriate diagnosis as early as possible is crucial to ensuring a positive outcome of the patient. The currently lack of an adequate clinical diagnostic tool (speed, accuracy and so on) thus imposes a human and financial burden. Current research on providing the market with a quantitative and rapid (less than 40 minutes) point-of-care device focuses on the simultaneous detection of a range of biomarkers of sepsis whose concentration profiles in serum change over time in ways that have been clearly established in terms of indicating the severity of the condition. Among these, procalcitonin has been judged the most likely individual biomarker to indicate a sepsis condition of bacterial origin. The work of this thesis focuses on the development of a graphene- based sensor for procalcitonin, and a proof-of-concept was established for the electrochemical detection of procalcitonin in aqueous solution on a graphene platform. Electrochemical methods were chosen for their fast response, sensitivity, selectivity and low-cost, while graphene was chosen for its conductivity and transparency, which allows future combination of optical means of detection with electrochemistry. The difficulty of producing graphene electrodes with sufficient reproducibility for sensor development has been addressed, with partial success. Also, it has been shown that highly oriented pyrolytic graphite (HOPG) can be used as a model for biosensing on graphene. In terms of combining electrochemical and optical read outs, it was shown that graphene can support localised surface plasmon resonance (of gold nanostructures) and preliminary results suggest that this method could also be used for the detection of procalcitonin. Finally, another material that attracts particular attention in electrochemical biosensing is boron doped diamond (BDD) and this thesis also describes photo-electrochemistry at a BDD electrode as a possible future biosensing platform.