Our effort has been made to develop the As(III) switch - on fluorescence biosensor based on MoS2 nanosheets. The simple sensing platform is developed for As(III) detection on an FAM-labeled Ars-3 ssDNA as a signal reporter and MoS2 nanosheets as the quencher. The prepared MoS2 nanosheets were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy ((FT-IR)). In presence of As(III) in solution, FAM-labeled Ars-3 ssDNA will coordinate with As(III) through phosphate and amine groups due to its high affinity to As(III), further induces the conformational change in the ssDNA and leading to formed G-quadruplex structure. As a result, the FAM-labeled G-quadruplex/As(III) complex enhances the fluorescence intensity via increasing concentration. The detection limit as low as 18 nM is achieved. The present biosensor is rapid and it also exhibits high sensitivity and selectivity to other metal ions, which reveals the excellent recovery of As(III) ions in monitoring the real environmental water samples. (C) 2017 Elsevier B.V. All rights reserved.