Abstract
This work presents a general method for producing edge-modified graphene using electrophilic aromatic substitution. Five types of edge-modified graphene were created from graphene/graphite nanoplatelets sourced commercially and produced by ultrasonic exfoliation of graphite in N-methyl-2-pyrrolidone. In contrast to published methods based on Friedel–Crafts acylation, this method does not introduce a carbonyl group that may retard electron transfer between the graphene sheet and its pendant groups. Graphene sulphonate (G–SO3−) was prepared by chlorosulphonation and then reduced to form graphene thiol (G–SH). The modifications tuned the graphene nanoparticles’ solubility: G–SO3− was readily dispersible in water, and G–SH was dispersible in toluene. The synthetic utility of the directly attached reactive moieties was demonstrated by creating a “glycographene” through radical addition of allyl mannoside to G–SH. Chemical modifications were confirmed by FT-IR and XPS. Based on XPS analysis of edge-modified GNPs, G–SO3− and G–SH had a S:C atomic ratio of 0.3:100. XPS showed that a significant amount of carbon sp2 character remained after functionalisation, indicating little modification to the conductive basal plane. The edge specificity of the modifications was visualised on edge-modified samples of graphene produced by chemical vapour deposition (CVD): scanning electron microscopy of gold nanoparticles attached to G–SH samples, epifluorescence microscopy of a glycographene bioconjugate with a fluorescently tagged lectin, and quenched stochastic optical reconstruction microscopy (qSTORM) of thiol-reactive fluorophores on CVD G–SH samples. Microelectrochemistry of unmodified CVD graphene and dye-modified CVD G–SH showed no statistically significant difference in interfacial electron transfer rate (k0). This platform synthesis technology can allow pristine graphene, rather than graphene oxide or its derivatives, to be used in applications that require the superior mechanical or electronic properties of pristine graphene, including theranostics and tissue engineering.Graphical Electrophilic aromatic substitution produces edge-specific modifications to CVD graphene and graphene nanoplatelets that are suitable for specific attachment of biomolecules
Highlights
Graphene, a ‘‘two-dimensional’’ material made of sp2hybridised carbon, is an attractive platform for nanomedicine, including drug delivery [1], theranostics [2], non-viral gene transfer [3], regenerative medicine [4, 5], sensors [6], and bioelectronics [7], because of its unique combination of properties including high carrier mobility [8], high yield strength [9, 10], and facile chemical modification [11]
Most existing covalent functionalisation of graphene family nanomaterials is based on grafting molecules through oxygen-containing functional groups of graphene oxide (GO), followed by chemical or thermal reduction to obtain reduced graphene oxide [15, 16]
Chemical modifications were confirmed by FT-IR and X-ray photoelectron spectra (XPS)
Summary
A ‘‘two-dimensional’’ material made of sp2hybridised carbon, is an attractive platform for nanomedicine, including drug delivery [1], theranostics [2], non-viral gene transfer [3], regenerative medicine [4, 5], sensors [6], and bioelectronics [7], because of its unique combination of properties including high carrier mobility [8], high yield strength [9, 10], and facile chemical modification [11]. Most existing covalent functionalisation of graphene family nanomaterials is based on grafting molecules through oxygen-containing functional groups of graphene oxide (GO), followed by chemical or thermal reduction to obtain reduced graphene oxide (rGO) [15, 16]. Graphene oxide (GO) is an oxidised, exfoliated form of graphite with a prevalence of oxygen-containing functional groups (carboxyl, hydroxyl and epoxide) on its exfoliated sheets. GO has become widely applied because it provides hydrophilic functional groups that allow it to form a stable dispersion in aqueous and polar solvents [17]. The oxidation process, generates defects on the GO sheets which disrupt p–p conjugation, leading to the loss of mechanical strength, as well as reduced electrical and thermal conductivity [18, 19]. GO-based materials are not well suited to applications that require on robust mechanical or electronic properties
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