## 4 Synthesis of Graphene and Its Derivatives
The copper-oxide graphene composite was synthesized by electrochemical exfoliation and used for the fabrication of a functionalized non-enzymatic glucose biosensor. Mono-layered graphene flakes were synthesized by this method, in which graphite electrode acts as the anode and platinum electrode acts as the cathode. The electrochemical biosensor fabricated using the CuO-rGO composite exhibited potential advances such as high selective response towards glucose in the presence of other interrupting species, high sensitivity of 2182 \(\upmu\)A mM\({}^{-1}\) cm\({}^{-1}\), and better linear response up to 22 mM [117]. [PERSON] et al. [118] introduced very desirable glucose detection results using modified electrode-based copper nanoparticles that decorated reduced graphene oxide ERGO/CuNPs using the modified Hummer's method for GO preparation, followed by an electrochemical reduction for rGO preparation. However, the electrodeposition method was highly desired to deposit the copper nanoparticles for electrode modification. Unzipping/opening of the CNTs process for graphene fabrication can be attributed under the top-down approach. It can be achieved by a solution-based oxidative treatment with an oxidizing agent such as hypermanganate as well as through the way of plasma etching of multi-walled CNTs (MWCNTs) with PMMA films to produce graphene nanoribbons [101; 119; 120; 41]. In this method, the utilization of the produced graphene from MWCNTs is restricted in the electrochemical applications due to the presence of intercalated metallic impurities that alter the electrochemical properties of graphene as well as toxicity [119]. Graphene can be epitaxially grown on electrically insulating surfaces such as silicon wafers through withdrawal of Si atoms from silicon carbide (SiC) and consequent graphitization of the carbon atoms, depending on the high-annealing temperature and the ultrahigh vacuum. The produced graphene sheet exhibits a variable charge carrier mobility depending on the substrate face on which the graphene sheets are grown. The carrier mobility ranges of the graphene sheet on Si-terminated face and C-terminated face are 500-2000 and 10,000-30,000 cm\({}^{2}\) V\({}^{-1}\) S\({}^{-1}\), respectively [120]. The Georgia Tech team developed a confinement-controlled sublimation (CCS) process which involves the enclosure of graphite with the SiC growth crystals, thus, segregating the evaporated silicon and enhancing the equilibrium process. This (CCS) method leads to the production of nano-patterned graphene structures with high mobility on both surfaces of the SiC substrate [121]. The epitaxial graphene (EG) is mainly applicable for laboratory studies and slot applications, such as high-frequency transistors due to the dependence on the high temperature, limitation of EG size with the size of wafers in the technique, as well as the high cost of silicon carbide wafers [120]. In general, both strategies, unzipping CNTs and epitaxial growth on SiC, require the involvement of high temperature and vacuum conditions, expensive gases, highly defined microfabrication devices, thus, hampering the utilization in a large industrial scale [121]. Chemical vapor deposition (CVD) has been sighted as the most up-and-coming approach to growing large-scale graphene films with a high quality. The graphene sheets are assembled by the thermal decomposition of hydrocarbons, such as methane, and the self-organization of the composed carbon atoms on transition metal substrates, mostly Cu and Ni, followed by segregation of the graphite layer on a metal substrate through CVD [122; 123; 124; 125]. Among the various transition metals used, the copper substrate is ideal to produce a single layer of graphene sheets with high electrical properties due to its controlled catalytic activity and low solubility of the formed carbons; however, the crystalline nickel substrate is still used in this method but it is challenging to provide monolayer films with adequate electrochemical properties [99; 101].