Laser Engraved Graphene Flexible Electrodes for Melatonin Biosensing

Sensitive and accurate biosensors are in high demand in the field of bioelectronics. This project focuses on melatonin, an important electroactive hormone that regulates physiological processes in the brain, such as circadian rhythm, and has been used for treatment of neurological disorders. Melatonin sensors provide insight into the physiology and therapeutic effects of melatonin, though few solutions exist for real-time monitoring with adequate selectivity. The solution, with respect to this project, involves laser engraved graphene (LEG) electrodes on polyimide substrate, developed for the electrochemical sensing of melatonin. This sensor could function as either an implant or a wearable sensor, requiring the flexibility of the polyimide in order to better integrate with the wearer. The LEG has the unique property of being drawn on the polyimide, producing high electrochemical surface area (ESA) electrodes, ideal for increasing electrode capacitance. Using these electrodes, cyclic voltammetry (CV) is performed to detect melatonin at the oxidation potential of 0.7 V vs Ag/AgCl. To increase the sensitivity of the sensor, the laser power and electrode geometrical surface area (GSA) were varied according to the electrode with the highest sensitivity to melatonin. In this case, this is 25% of maximum CO2 laser power with a 2 mm GSA diameter. To achieve increased selectivity, the LEG electrode is functionalized with artificial receptors, in this case, a molecular imprinted polymer (MIP), that is ‘imprinted’ with the melatonin molecule. MIPs can be compared against non-imprinted polymers (NIPs) to determine whether imprinting has been achieved, shown by an increased sensitivity to the melatonin peak in CV characterizations. This project utilizes the monomer pyrrole in the electrodeposition of polypyrrole MIP on the LEG electrode. The application of the MIP increased the capacitance of the electrode, indicating successful electrodeposition. Further study is required to make conclusions on the change in target selectivity of this electrode.