Polyvinylpyrrolidone (PVP) (Film-forming agent) was dissolved in EtGly to obtain a 0.2 g mL solution (PVP/EtGly). Sodium iodide (0.4g/mL) was added and dissolved. The solution was added to the CNFA and gently stirred for 24 h to obtain homogeneous inks. The samples are labeled according to: CNFA1content(/CNFA2content), e.g., Ade380 and Glu300 as CNFAs synthesized from adenine and glucose by pre-carbonization at 380 °C and 300 °C, respectively.