Implementation of a simple functionalisation of graphene (Gii-Sens) in the determination of a suitable linker for use in biocatalytic devices
Highlights
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Gii-Sens has shown to be ideal electrodes for glucose biosensors.
- Glucose sensitivity of 22.7 μA/mM/cm^2 shows promise for metal-free sensors.
- The observable biocatalytic response from the electrodes, prepared through simple drop-casting methods onto commercially available 3D graphene foams, represents a promising first step to the development of metal-free biocatalytic devices based on this setup
Abstract
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/cm2 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.
Introduction
Devices that function via biocatalytic reactions, such as biosensors and biofuel cells [26, 27, 28], often rely on the unparalleled selectivity and specificity of enzymes to catalyse reactions involving biological compounds (i.e. glucose) implementation represent two bioelectrochemical systems that would benefit from the implementation of graphene electrodes.
Biosensor devices are important and powerful tools for the selective detection of chemical and biological materials and have been implemented across a broad range of numerous industrial practices, from environmental monitoring [29, 30] to significant medical applications, particularly for the determination of blood glucose levels [31, 32, 33, 34], which is vital for the management of the metabolic disorder diabetes mellitus [35].
Huge interest has also been directed towards enzymatic biofuel cells in recent years as they can generate electrical energy from renewable biological materials, which are implemented both as catalysts and fuels. Such a device is ideally suited for power generation in implantable or wearable microelectronic devices with various biomedical applications, including pacemakers and insulin pumps [36, 37, 38, 39, 40].
For such devices, graphene represents a superior choice of electrode, owing to its excellent electrical conductivity and high charge carrier mobility [3, 40] as well as its high surface area [42, 43, 44]. This large surface area leads to improved enzyme loading, which consequently enhances the enzyme activity per unit mass/volume, while the electron mobility in graphene enables facile electronic transfer between the electrode and the loaded enzyme [45, 46, 47, 48]. Graphene also exhibits low electrical noise levels from thermal effects, making graphene-enabled sensors highly sensitive [49,50]