# The Exploitation of Lysosomes in Cancer Therapy with Graphene-Based Nanomaterials
## 3 Graphene-Based Nanomaterials in Cancer Therapy  
GNMs are materials composed of graphene or graphene-like structures, including graphene oxide, reduced graphene oxide, graphene quantum dots, and different nanocarriers made from these materials. These materials are typically between one and several carbon atoms thick and have at least one lateral dimension \(<\) 100 nm. They exhibit unique physico-chemical properties and biological behaviors [19]. Graphene is a two-dimensional material composed of a planar monolayer of carbon atoms arranged in a honeycomb lattice (Figure 1). Its high-mechanical strength and stability result from the strong sp\({}^{2}\) sigma bonds that connect each atom to its three nearest neighbors. Graphene's valence band extends across the entire sheet, giving it unusually high electron and thermal conductivity. It is highly hydrophobic, and in a hydrophilic solvent, it forms large aggregates. Additionally, graphene has an extremely high surface area (\(\sim\)2600 m\({}^{2}\)/g). Synthesis of graphene is expensive, but synthesizing other GNMs on a large scale is easier and cheaper [20; 21]. Graphene oxide (GO) is a single-atom carbon layer with oxygen-containing hydrophilic functional groups, such as hydroxyl groups (-OH), epoxide groups (-O-), and carboxyl groups (-COOH) (Figure 1). These groups enable chemical modifications and high-water solubility, making it a hydrophilic alternative to graphene. GO can absorb near-infrared (NIR) radiation and convert it into heat, making it a potential candidate for PTT. Furthermore, GO exhibits excellent biocompatibility, high cellular uptake, and low toxicity [20; 22; 23; 24]. Reduced graphene oxide (rGO) is prepared by the reduction of GO, which eliminates the oxygen-containing compounds in GO and restores the sp\({}^{2}\) structure of graphene. The C/O ratio is much higher in rGO than in GO (Figure 1). Due to the loss of oxygen-containing groups, rGO exhibits hydrophobic behavior and lower dispersibility than GO. Owing to its ability to generate heat upon photoexcitation, rGO also has great potential for PTT and controlled heat-induced drug release [20; 24; 25]. Graphene quantum dots (GQDs) are zero-dimensional graphene nanoparticles composed of a single layer, or up to a few layers, of graphene sheets with lateral dimensions less than 100 nm (Figure 1). GQDs are chemically and physically stable, nontoxic, biocompatible, and soluble in water due to the functional groups at the edges. GQDs exhibit excellent photostability and tunable fluorescence. Therefore, they can be used for bioimaging and biosensing. The ability of GQDs to absorb radiation makes them valuable candidates for PTT and photodynamic therapy (PDT). PDT involves singlet oxygen (\({}^{1}\)O\({}_{2}\)) or other highly reactive oxygen species (ROS) produced by a light-irradiated photosensitizer to destroy abnormal cells [20; 21]. Various anticancer drugs can bind to the large surface area of GNMs through \(\pi\)-\(\pi\) stacking, as well as electrostatic and hydrophobic interactions (Figure 1). Graphene-based  
Figure 1: The structure of GNMs and graphene-based DDSs. DDSs improve drug solubility and bioavailability, protecting drugs from premature release and degradation in biological environments, thus prolonging their half-life. The functionalization of GNMs with specific antibodies or receptor ligands enhances drug concentration in the tumor tissue and stimulates its uptake in cancer cells. However, before potentially using GNM in therapy, one should be aware of its potential negative effects on human health. While clinical studies are still pending, some animal studies have shown that GNMs are safe for clinical use, while other investigations have shown that GNMs may cause acute inflammation and chronic injury to the liver, spleen, and kidney, and may suppress embryogenesis or have other adverse effects [26]. Obviously, the toxicity of GNMs depends on their type, size, charge, functionalization, impurities, concentration, and entering route [26].