Novel Sensors Using Flexible Electrode Materials

Flexible wearable sensors are emerging devices which can aid in tracking and monitoring medical treatments and conditions. One of the potential applications of flexible sensors is monitoring therapeutic ranges of drugs to ensure that safety and efficacy of the treatment are maintained. However, the effective dosage of various drugs is close to the toxic dosage which results in the requirement to frequently monitor drug concentration during case administration. Paracetamol is a widely used mild analgesic to treat fever and relieve mild to moderate pain and is considered safe when blood levels of the drug are in the range of 66 – 132 μM (10 ‒ 20 μg mL-1). In addition, Clozapine is a highly effective anti-psychotic medication that is approved for treatment-resistant schizophrenia. Psychiatrists estimate that clozapine drug levels associated with blood serum need to be lower than 1.84 μM (600 ng mL-1) to allow effective treatment and prevent severe side effects including toxicity, seizure, and myocarditis. To improve sensitivity of drug sensors, various materials have been used for the surface modification of electrodes.Polypyrrole (PPy) fibre electrodes were fabricated by electropolymerisation onto carbon fibres using cyclic voltammetry (CV). The use of PPy/sodium dodecyl sulfate (PPy.SDS) coated carbon fibre via differential pulse voltammetry (DPV) allowed sensing of paracetamol with the detection limit (3σ S/N) of 33.8 µM. A linear response range was observed at 50 – 500 µM which covers the safe therapeutic range. For a paracetamol concentration of 100 µM, the DPV anodic peak current (at 0.5 V vs. Ag/AgCl) was unaffected by the addition of interferents: 100 µM dopamine and 100 µM ascorbic acid.Reduced graphene oxide (rGO) coated carbon fibre electrode and PPy-rGO coated carbon fibre electrode were fabricated by electrochemical deposition (CV and potentiostatic technique) onto carbon fibres. Two distinguished oxidation peaks at 0.49 V and 0.25 V (vs. Ag/AgCl) were observed at the rGO fibre electrode during the simultaneous detection of paracetamol and dopamine, respectively, by CV. The detection limit (3σ S/N) of the rGO carbon fibre electrode for DPV determination of paracetamol was at 21.1 µM and 9.0 µM for dopamine. In comparison, the simultaneous determination of paracetamol and dopamine by CV at the PPy-rGO fibre electrode gave oxidation peaks of paracetamol and dopamine at 0.55 V and 0.25 V (vs. Ag/AgCl), respectively. The detection limit (3σ S/N) for paracetamol was notably improved to 3.7 µM and 6.0 µM for dopamine at the PPy-rGO carbon fibre electrode during DPV.The optimisation of the nanoscale conductive eutectic gallium indium (EGaIn)-rGO and Galinstan-rGO coated carbon fibres for drug sensing applications were electrodeposited onto the carbon fibres via CV. The simultaneous determination of dopamine and paracetamol is possible at the liquid metal-rGO flexible fibre electrodes via CV by showing two oxidation peaks with the peak-to-peak separation (ΔEp) of 0.32 and 0.55 V (vs. Ag/AgCl) for the EGaIn-rGO and Galinstan-rGO fibre electrodes, respectively. In addition, clozapine detection was also carried out to investigate the sensing ability of the various flexible electrode (PPy, rGO, PPy-rGO, EGaIn-rGO and Galinstan-rGO coated carbon fibres). The rGO, EGaIn-rGO and Galinstan-rGO fibre electrode showed the successful and repeatable detection of clozapine with the limit of detection of 5.8, 10.9 and 6.3 µM (S/N = 3), respectively.While many publications deal with the surface modification of bulk electrodes, there are few examples of fibre-based electrode modification that could be used for wearable applications. This thesis developed the modified fibre-based electrodes using electrochemical techniques to improve the electrochemical sensing properties of conducting fibre electrodes and to determine their ability to sense paracetamol and antipsychotic drug clozapine monitoring