Ni/Co Stacked Metal–Organic Framework-Based Nanoelectronic Device Integrated with Smartphone for Real-Time Nitrite Sensing

Metal–organic frameworks (MOFs) are 3D materials with advanced characteristics due to their porous nature and the presence of catalytic nodal metal centers. These materials can be of enormous importance as sensor matrix components for wide applications, such as environmental monitoring. In this work, we have attempted the stacking of two MOFs, a NiMOF, followed by CoMOF, which was further functionalized with gold nanoparticles to detect nitrite ions (NO2–) in real/environmental water samples. Nitrite is a naturally occurring plant nutrient present in the soil and is also used as a preservative in industries; however, it can generate carcinogenic precursors at higher concentrations. The catalytic sensing probe was developed to detect NO2– through its electrochemical oxidation to NO3– at a specific potential. The glassy carbon electrode/nickel MOF/cobalt MOF (GCE/NiMOF/CoMOF) surface was constructed through a facile and faster approach of electrodeposition. The final sensing probe was thoroughly characterized by various physical and electrochemical techniques. It displayed enhanced analytical performance in terms of its wide linear dynamic range between 0.01 to 1000 μM and a limit of detection of 4.2 nM. It exhibited a rapid average response time of about <1.5 s, making it an ultrasensitive sensing platform for NO2– in environmental water samples. A systematic integration with a smartphone application has also been proposed for on-site application of the sensor, where a single-fed input value determines the real-time NO2– concentration in test water samples.