Electrochemical method has been recognized as a promising technique for the determination of ultratrace heavy metal due to its portability, high sensitivity, good selectivity and low cost. In order to achieve a more sensitive electroanalysis, a variety of nanomaterials have been modified and applied to the surface of working electrode.

　　Ultrathin materials with atomic thickness have drawn attention from scientists due to their promising practical applications. The atomic thickness and extremely huge percentage of specific facet ultrathin nanosheets materials exposed can lead to some new properties, which is totally different from their corresponding bulk counterparts. Researchers indeed prove that ultrathin nanosheets materials can greatly enhance electrochemical activities. Much more attention has been attracted to the applications of catalysts, Li-ion battery, electrocatalysts, etc. ,but the research on the electrochemical sensing of heavy metal ions is seldom.

　　In the previous study, it has been found that an electrode modified with exfoliated ZrP ultrathin sheets can be utilized for Pb(II) detection with good selectivity and sensitivity (Anal. Chem. 2013, 85, 3984−3990). The studies further confirm atomically thin sheets can improve reactivity and expose active functional groups efficiently. Based on the work, an important progress on improving the electrochemical response of As(III) on ultrathin nanomaterials has been made by research group of Prof. HUANG Xingjiu and Prof. LIU Jinhuai from Institute of Intelligent Machines (IIM). The corresponding results have been accepted by Electrochimica Acta (Electrochimica Acta, 2016, 191, 142-148).

　　Ultrathin SnO₂ nanosheets with high reactive exposed surface modified electrode for electrochemical sensing of As(III) is proposed. Ultrathin SnO₂ nanosheets are synthesized via a simple hydrothermal process successfully with the thickness of about 0.52 nm. This oxide is used as electrode modifier, and the modified electrode exhibits good performance in stripping determination of As(III). The LOD actually measured is 5 µg L^-1 which is below the guideline value given by the World Health Organization (WHO). Compared with SnO₂ bulks, ultrathin SnO₂ nanosheets exhibit stronger adsorption capability and better detection performance toward As(III) maybe due to the atomic thickness and extremely huge percentage of (110) facet ultrathin nanosheets materials exposed. Finally, this system is successfully applied for the analysis of a real sample collected from Inner Mongolia, China. Most importantly, the study provides a potential use of ultrathin materials for improving the electrochemical performance of bare gold electrode in mild acid condition.

　　This work is supported by the National Key Scientific Program-Nanoscience and Nanotechnology (2011CB933700 and 2013CB934300), the National High Technology Research and Development Program of China (863 Program) (2013AA065602), and the National Natural Science Foundation of China (21475133, 21277146, and 61474122).