## 1 Introduction
Graphene is the basis of many other carbon structures, such as 3D graphite which is formed through the stacking of graphene, the isolation of single-layer graphite in the form of 2D graphene, 1D nanotubes formed by rolling the graphene, and 0D fullerenes formed by wrapping the graphene sheets into spherical structures [4; 16; 17]. Graphene's structure offers unique mechanical, optical, thermal, and electronic properties that are very attractive for use in biomedical applications. Graphene has an extremely large surface area that is calculated at 2630 m\({}^{2}\) g\({}^{-1}\), a strong Young's modulus of 1100 GPa, and a high thermal conductivity of 5000 W m\({}^{-1}\) K\({}^{-1}\)[18]. Graphene is found in the form of graphene oxide (GO), reduced GO (rGO), graphene nanoribbons, nanoplatelets, quantum dots (QDs), aerogels, and foam. The structure of GO (Figure 1) can most commonly be described using the Lerf-Kilnowski model which describes GO as a planar sp\({}^{2}\) hybridised hexagonal lattice decorated with sp\({}^{3}\) alcohol or epoxide bonds, with carboxylic acid groups populating the edges [17]. GO prepared by the [PERSON]'s method retains many of the favourable characteristics of graphene, but the oxygenated functional groups make the material hydrophilic, thereby increasing its solubility and providing additional points of binding for molecules [17]. Through chemical, electrochemical, or thermal reduction, rGO can also be synthesised, which restores the electrical conductivity of GO [18]. In addition, graphene and graphene-based nanomaterials are extremely flexible in their ability for functionalisation and hybridisation, which is useful when tailoring nanomaterials for use in targeted tracking and/or treating diseased cells/tissues [18]. The high surface area, planar nature, and delocalised free \(\pi\)-electrons allow non-covalent modifications; the oxygen-containing groups that decorate the graphene surface are used for covalent modifications. Covalent modifications are most common for GO or rGO and involve agents, such as polyethylene glycol (PEG), folic acid (FA), or chitosan to increase the solubility and stability of the graphene derivative within physiological environments and solutions [19]. Non-covalent modifications utilise supramolecular interactions, such as \(\pi\)-\(\pi\) stacking and hydrophobic interactions between graphene and coating molecules in order to increase the amphiilicity of the nanomaterial, as well as the binding capacity, reactivity, biocompatibility, and sensing properties [19; 20; 21]. Non-covalent functionalisations include the use of polymers, biomolecules, drugs, and carbon nanoallotropes, which are important in reducing the cytotoxic effects of graphene nanomaterials [21]. Graphene and its derivatives have been extensively studied for their use in targeted and non-targeted drug delivery applications. Due to its exceptionally large surface area and aromatic structure, graphene has the potential for high drug loading capacity of various biomolecules and drugs, particularly aromatic drugs, through highly efficient \(\pi\)-\(\pi\) stacking. Previous research in this area has mostly focused on graphene's use in the delivery of chemotherapeutics. Drugs, such as DOX, camptothecin, paclitaxel, and cisplatin, have been tested [22]. Table 1 shows a non-exhaustive list but highlights the variety in previous studies that have incorporated therapeutics onto graphene-based drug delivery vehicles. Figure 1: Structure of pristine graphene, GO, rGO, and functionalised graphene. Sourced and adapted with permission from Ref. [17]. The ability to easily functionalise graphene and its derivatives offers versatility to the drugs that can be loaded, but also in terms of the targeting ligands that can be incorporated, increasing the specificity of targeted delivery [22]. [PERSON] et al. developed a GO functionalised with stabilising sulfonic acid groups and folic acid molecules that were covalently bound to the NGO surface.