Highly sensitive detection of mercury(II) ions with few-layer molybdenum disulfide

Two-dimensional (2D) layered transition metal dichalcogenide (TMD) materials (e.g., MoS₂) have attracted considerable interest due to their atomically thin geometry and semiconducting electronic properties. With ultrahigh surface to volume ratio, the electronic properties of these atomically thin semiconductors can be readily modulated by their environment. Here we report an investigation of the effects of mercury(II) (Hg²⁺) ions on the electrical transport properties of few-layer molybdenum disulfide (MoS₂). The interaction between Hg²⁺ions and few-layer MoS₂ was studied by field-effect transistor measurements and photoluminescence. Due to a high binding affinity between Hg²⁺ ions and the sulfur sites on the surface of MoS₂ layers, Hg²⁺ ions can strongly bind to MoS₂. We show that the binding of Hg²⁺ can produce a p-type doping effect to reduce the electron concentration in n-type few-layer MoS₂. It can thus effectively modulate the electron transport and photoluminescence properties in few-layer MoS₂. By monitoring the conductance change of few-layer MoS₂ in varying concentration Hg²⁺ solutions, we further show that few-layer MoS₂ transistors can function as highly sensitive sensors for rapid electrical detection of Hg²⁺ ion with a detection limit of 30 pM.