**5. Conclusions**

**Potential application Interaction GO–CS or r GO–CS** *via covalent* **Reference** Water treatment (U(vi) removal) Amidation [101] Water treatment (antifouling) Amidation [100] Water treatment (removal Cr(IV)) Amidation [97] Water treatment (desalting) Nucleophilic addition (Ring opening) [87] Water treatment (Fuschine removal) Amidation [99] DNA biosensor Amidation [88] Drug delivery Amidation [89] Drug delivery Amidation [90] Lipase immobilization Amidation [92] Osteoblasts growth Amidation [91] Growth of cells C3H10T1/2 Amidation [93] Drug delivery (Fluorescein sodium) Amidation [94] Nanocatalyst Amidation [103] Nanocatalyst Amidation [102] Nanocomposite (GO–CS –HAP, bioactivity) Amidation [96] Nanocomposite Amidation [84] Nanocomposite Amidation [121] Nanocomposite Amidation/Esterification [21] Nanocomposite Nucleophilic addition (Ring opening) [86] Nanocomposite Esterification [85]

Potential application Interaction GO–CS or r GO–CS

Sensor of *Pseudomonas aeruginosa and Staphylococcus aureus*

28630 Recent Advances in Graphene Research

*via non‐covalent*

Hydrogen bond/electrostatic attractions [116]

Hemolytic activity Electrostatic adsorption [104] Multifunctional paper Electrostatic interaction [105] Glucose and urea detection Electrostatic interaction [106] Removal contaminants Electrostatic interaction [107] Nanocomposite (PVA) Hydrogen bond/electrostatic interaction [119] Supramolecular hydrogel Hydrogen bond/electrostatic interaction [113] L929 cells and MG‐63 cells growth Hydrogen bond/electrostatic interaction [118] Bulirubin adsorbent hydrogel Hydrogen bond/electrostatic interaction [114] Electrochemical electrode Hydrogen bond/electrostatic interaction [115] *E. Coli* growth Hydrogen bond/electrostatic interaction [117] During the last years, many efforts have been done in order to exploit the outstanding properties of graphenic materials in fields such as catalysis, nanocomposites, cell batteries, and so on. As a result of its versatility, the chemically route to produce graphene oxide and reduced graphene oxide offers a possible solution for requirements about scalability, cost‐effective, and easy way to obtain suited amounts of graphene for its applicability. Both GO and rGO can take some advantages over pristine graphene because of the rich chemistry of their functional groups present on the surface. These groups can be used as points to anchor specific molecules according the necessities, which granted the shown multifunctionality. Specifically, in rGO, the restoration of sp2 domains through the reduction reaction offers a conductive material which can be applied in fields where the conductivity is overriding. Additionally, emerging routes to achieve non‐covalent and covalent functionalization of graphenic materials have been reported. In this chapter, we outline recent progress in covalent and non‐covalent functionalization of graphenic materials with biopolymers such as keratin and chitosan. Both are aimed on the development of a multifunctional platform capable of being used in different fields.

Functionalization of graphene‐based materials with biomolecules offers an additional advant‐ age to orient these materials for biological applications, increasing, for example, their com‐ patibility. Biofunctionalization with small or medium size biopolymer chains, as in the case of some proteins or polysaccharides, enables the formation of hybrid or conjugated systems through a series of several interaction or reaction points. This, as a result of the presence of different chemical functionalities, as in the case of keratin, or a repeated functional group, as in the case of chitosan, in each polymeric unit. This aspect allows to fully cover the nanocarbon surface with along with a strong biomolecule immobilization.

To the best of our knowledge, as we have discussed in this chapter, there are just a couple of works related to the functionalization of graphenic materials through a redox reaction system. This approach has been commonly used to achieve high degree of attachments in natural and synthetic polymeric materials. A redox reaction brings the benefit to yield a random covalent functionalization practically using all the available chemical groups in both materials, at relatively low reaction temperature. Therefore, the resulting surface will possess few func‐ tional groups, if any at all. In the case of the non‐covalent functionalization of reduced graphene oxide, the opposite behavior will take place. The functional groups of the biomole‐ cule will be exposed on the conjugated system surface. This proves its utility if an additional functionalization, specific group reactions, or a further adsorption process is desired.

We want to awake the interest of the reader in the study of these approaches and to compare their advantages in disadvantages for other systems.
