This work reports a sensitive sensor for the electrochemical determination of trace mercury (Hg2+) by employing ultrathin graphitic carbon nitride (utg-C3N4) nanosheet as enhanced sensing platform. The utg-C3N4 nanosheets were obtained by exfoliating the bulk g-C3N4, which was synthesized via a thermal polycondensation process. The as-prepared samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM), which confirmed graphite-like structure with thickness of about 8 nm. The g-C3N4 nanosheets can be easily attached on the surface of glassy carbon (GC) electrode free of any film-forming agent. It was found that Utg-C3N4 modified GC electrode showed enhanced electrochemical response to Hg2+ in comparison with bulk g-C3N4, which could be ascribed to the strong affinity between utg-C3N4 and Hg2+ through its -NH and -NH2 groups. This allows detection of Hg2+ in aqueous solutions with high sensitivity and selectivity. Under the optimized experimental conditions, the anodic stripping voltammetric (ASV) currents are linearly responsible to Hg2+ concentrations in the range of 0.1-15 mu g/L with a detection limit of 0.023 mu g/L (S/N = 3). The sensitivity of the as-constructed sensor is about 6.8 mu A (mu g/L)(-1)cm(-2). In addition, the proposed sensor was applied in determining Hg2+ in practical samples and the results are comparable to those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) method. (C) 2015 Elsevier Ltd. All rights reserved.