In this research, graphitic carbon nitride (g-C3N4) is synthesized through the direct pyrolysis of the melamine, and the pristine g-C3N4 is further treated by sufficient protonation and ultrasonication. The resultant g-C3N4 nanosheets, with two-dimensional thin nature, exhibit enhanced ionic conductivity and large specific surface area. Density function theory (DFT) calculations of the electrical properties of the protonated g-C3N4 nanosheets demonstrate that the higher level of protonation enables g-C3N4 to have better conductivity. In addition, the protonated g-C3N4 nanosheets also show excellent electro-catalytic activity and have been employed as electrochemical sensing platforms for the non-enzymatic electrochemical sensing hydrogen peroxide (H2O2) and the selective determination of paracetamol (PCM). The results demonstrate that the protonated g-C3N4 nanosheets, as sensor materials, achieve superior electrochemical sensing performance. The exfoliated g-C3N4 nanosheets have great potential for application in further sensor development and biomedical analysis. (c) 2016 Elsevier Ltd. All rights reserved.