Optimizing heterostructure of nanocomposites holds great potential for making full use of their ability. Herein, gold nanoparticles (AuNPs) were in situ synthesized over the surface of graphitic carbon nitride (g-C3N4) via one-step pyrolyzation route using a single source precursor. The precursor of melamine chloroauric (C3H6N6H+center dot AuCl4-) was obtained through chemical precipitation reaction between melamine and chloroauric acid. The morphological analysis confirmed the compact contact between Au nanoparticles and g-C3N4. Then, the Au-g-C3N4 nanocomposites were employed to fabricate electrochemical sensor by modifying glassy carbon electrode (GCE). Electrochemical experiments showed that the Au-g-C3N4 exhibited enhanced electrocatalytic activity towards tetracycline oxidation as compared with either pure g-C3N4 or Au nanoparticles. Based on cyclic voltammetry (CV) method, the sensor was applied in the detection of tetracycline with a low detection limit of 0.03 mu M (S/N = 3) and the linear range of concentration were 0.1-20 mu M and 20-200 mu M, respectively. Moreover, such an electrochemical sensor demonstrated high stability and good selectivity. Finally, the electrochemical sensor was applied to drug assays and exhibited sufficient precision and accuracy. Therefore, this work paves a new way of preparing gC(3)N(4)-based heterostructures and provides an efficient method for the detection of tetracycline in clinical analysis and quality control. (C) 2018 Elsevier Inc. All rights reserved.