A Facile Method for the Non-Covalent Amine Functionalization of Carbon-Based Surfaces for Use in Biosensor Development

Abstract

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene’s exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

Application of Molecular Vapour Deposited Al2O3 for Graphene-Based Biosensor Passivation and Improvements in Graphene Device Homogeneity

“…This is suggested by the large sp 2 carbon peak at 284 eV, which represents the C=C component in graphene [ 80 ], whilst the additional peaks representative of sp 3 carbon, C-O, and C=O at 284.79, 285.48, and 286.12 eV, respectively, are minimal, with the calculated area of sp 2 carbon representing 94.44% of the total area of the spectra [ 30 , 81 ]. However, after processing the graphene into graphene devices, the presence of C-C sp 3 , C-O, and C=O peaks increase, with the formation of additional C-N [ 27 , 82 ], C-O-C, and O-C=O bonds at 285.42, 286.73, and 290.35 eV [ 30 , 81 ], respectively. The peak area of sp 2 carbon also greatly decreases, only amounting to 57.16% of the total area of the carbon spectra.…”

“…The electropolymerisation of DAN creates a polymer film across the graphene surface, which introduces -NH 2 functional groups on the graphene surface, allowing for antibodies to bind to the amine groups for sensing purposes. It has been reported that pDAN is very robust, capable of remaining on the graphene surfaces after multiple subsequent washes due to strong Van der walls forces [ 27 ]. The electrochemical polymerisation process of polymerising DAN through CV [ 30 , 85 ] uses dilute H 2 SO 4 as the electrolyte for covalently binding the monomers.…”

“…These include π-π stacking of molecules with functional groups which assist biosensor coupling, hydrogen bond interactions or direct covalent attachment to the graphene [24][25][26]. Non-covalent methods of graphene functionalisation do not alter the graphene crystalline structure, allowing for the graphene to maintain its high electron mobility [27]. Covalent methods of chemical functionalisation convert the sp 2 carbon-carbon bonds in the graphene to sp 3 bonds and can be achieved using various functionalisation methods, such as diazotization [28,29].…”

Graphene Bioelectronic Nose for the Detection of Odorants with Human Olfactory Receptor 2AG1

“…Graphene, a 2D nanomaterial composed of a single layer of sp 2 hybridised carbons, possesses superior electrical properties such as high carrier mobility and electron transfer rates at room temperature [30], which present opportunities for applications in a diverse range of fields such as medical, solar cells, energy storage, transparent electrodes, transistors and nanocomposites [31]. In particular, graphene-based sensing devices have features such as label-free detection, high sensitivity and selectivity, biocompatibility and ease of functionalization [32][33][34]. The ability to fabricate graphene devices using standard lithographic processes presents significant advantages over CNT-based sensors in terms of reliability of device platforms and potential multiplexing capability for any bioelectronic nose.…”

Assessing Surface Coverage of Aminophenyl Bonding Sites on Diazotised Glassy Carbon Electrodes for Optimised Electrochemical Biosensor Performance

“…Additionally, our recent work already demonstrated that improving and optimising the amine surface coverage onto the support system (carbon, graphene, etc) would improve the sensor performance by improving the antibody immobilisation via carbodiimide reaction [ 17 , 40 , 41 , 42 ]. In addition, the utilisation of carboxylic acid groups of antibodies for binding also prevents the potential loss of biological activity of the antibody fragment.…”