Graphitic carbon nitride-based materials for biomedical applications

Graphitic carbon nitride (g-C3N4)-based materials are emerging fluorescent polymeric materials mainly consisting of C and N atoms (the basic structural units can be seen in Scheme 14.1), which have gained huge attention in various fields because of their attractive features including facile synthesis and functionalization, high physicochemical stability, stabilized electron field emission, wide-band optical transparence, controllable band gap and band position, and low toxicity (Y. Dong et al., 2016; G. G. Liao, Gong, Zhang, et al., 2019; Liao et al., 2020, Liao, Li, Li and Fang, 2021; Safaei et al., 2018). In particular, their excellent biocompatibility and stability, unique fluorescent feature, and low cost and toxicity enable g-C3N4-based materials to become attractive candidates for biomedical applications (A.-J. Wang et al., 2016; Xiong et al., 2017), e.g., diagnosis and therapy, biosensing, and antibacterial applications, which showed superior properties to other biomaterials with conventional nanostructures, e.g., nanoparticles, tubes, wires, cages, etc. In addition, biosafety and toxicity evaluations have also been conducted, including cytotoxicities, biodistribution, excretion, and hemo/histocompatibility, and the g-C3N4-based materials have demonstrated good biocompatibility, water solubility, and biometabolizability, which guarantee that they meet the requirements of practical clinical applications (L. Feng et al., 2016a; X. Zhang et al., 2013). These evidence illustrate that the emerging g-C3N4-based materials show great potential in biomedical applications. It must be noted, however, that their practical application is still restricted because of their intrinsic shortcomings, e.g., relatively large particles size and low electrical conductivity (Chan et al., 2016; C. Ye et al., 2015). Therefore, the development of modified g-C3N4 with good water solubility and biodegradability, small size, thin nanosheets thickness, and enhanced light absorption is crucial to achieve target-specific biomedical applications. Many attempts including the synthesis of new g-C3N4-based hybrids with multifunction and high performance have been widely reported. In this chapter, we systematically summarize synthetic strategies of g-C3N4-based materials and outline their recent advances in various biomedical applications such as diagnostic imaging, therapeutic application, biosensors, and antibacterial application. In addition, biosafety and toxicity evaluations of g-C3N4-based materials are also discussed in depth. Finally, the state-of-the-art progress, challenges, and perspectives of g-C3N4-based materials in biomedical applications are highlighted and discussed in detail. It is believed that the emerging g-C3N4-based materials are very promising for biomedical applications.