Adjustable Synthesis of Ni-Based Metal–Organic Framework Membranes and Their Field-Effect Transistor Sensors for Mercury Detection

Due to high toxicity of mercury ions (Hg2+), many efforts have been devoted to realize the detection of Hg2+ with low concentration, in which to establish the relationship among the structure, electricity property, and detection activity of sensing materials is of prime importance. In this work, a field-effect transistor (FET) sensor based on a conductive Ni3(HITP)2 membrane was employed to realize Hg2+ detection. Such a Ni3(HITP)2 membrane was synthesized in situ by a one-step hydrothermal method, and the influence of the volume ratio of ammonia to water on its structure and Hg2+ detection performance was systematically investigated. It is found that with increasing the volume ratio of ammonia to water, the Ni3(HITP)2 membrane composed of flake-shaped structure becomes denser, its thickness increases from 24.1 to 114.7 nm, and the mobility of the Ni3(HITP)2 FETs increases nearly 2 orders of magnitudes. For Hg2+ detection, the Ni3(HITP)2 membrane is modified with a glutaraldehyde (GA) cross-linking agent and DNA probes. The optimized Ni3(HITP)2-GA-DNA FET-based sensor can detect Hg2+ with high specificity in a concentration range of 10 pM–100 nM. The excellent detection performance is attributed to the close contact between the Ni3(HITP)2 membrane and Si/SiO2 substrate, large surface area of the membrane, and specific bonding of Hg2+ with DNA probes modified on the membrane surface. This work will have a great significance for the application of metal–organic frameworks in electronic devices and ion detection.