Graphene field-effect transistors with tunable sensitivity for high performance Hg (Ⅱ) sensing

摘要

Graphene field-effect transistors (FETs) capped with ionophore were fabricated to demonstrate the highly sensitive and selective detection of Hg (Ⅱ) ions in solution. We systematically investigated the ion detection performances and sensing mechanism of this 2D material. Due to its ambipolar nature, graphene can work as either an n-type or a p-type sensor when a gate voltage is applied to switch its carrier characteristic, resulting in completely different sensing performances. The strong dependence of sensitivity on gate voltage was also investigated. Graphene FETs in optimal regimes were able to detect Hg~(2+) down to 0.1 ppb, one-fold lower than the World Health Organization tolerance level. Hg~(2+) ions can be effectively detected over a wide range of concentration (from 0.1 ppb to 1000 ppb) with graphene conductance change following the Langmuir isotherm for molecules adsorption on surface, and the time constant for ion adsorption extracted was only 3.5 s, approximately. The transfer characteristics of graphene FETs capped with mercury ionophore did not show obvious change by the existence of arsenite ions, demonstrating good selectivity. Our results illustrate the potential utility of ionophore integrated graphene FETs for monitoring heavy metal ions in solution.