Implementation of a simple functionalisation of graphene (Gii-Sens) in the determination of a suitable linker for use in biocatalytic devices

• Novel graphene foams are shown to be ideal electrodes for glucose biosensors. • XPS and Raman characterise electrodes and their modification with pyrene-NHS. • GDH successfully immobilised on pyrene-NHS functionalised graphene foam. • Linear response to increasing glucose concentration over suitable range. • Glucose sensitivity of 22.7 μA/mM/cm ^2 shows promise of this metal-free sensor. We adapted a single-step method to functionalise three-dimensional graphene foam (Gii-Sens) electrodes with a 1-pyrenebutyric acid N-hydroxysuccinimide ester (Pyr-NHS). The physical and chemical properties of these functionalised electrodes were subsequently probed via Raman spectroscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Combined with data acquired from cyclic voltammetry and electrical impedance spectroscopy, we confirmed the presence of Pyr-NHS on the surface of the graphene foam in sufficient quantity for it to serve as a suitable linker for the immobilisation of the enzyme glucose dehydrogenase (GDH) on the electrode. Evidence of this immobilisation was provided through electrochemical characterisation, before demonstrating an active enzyme response from GDH via the mediated oxidation of glucose at the electrode surface. A proportional relationship between the concentration of glucose and the peak anodic current from the redox mediator p-aminophenol led to the determination of a high sensitivity of 22.7 µA/mM/cm 2 and a limit of detection of 5.25 µM. Such a result confirms the viability of these functionalised graphene foam electrodes as a metal-free high-performing anode within miniaturised, glucose-based biocatalytic devices, including enzymatic biofuel cells and biosensors.