Continuous MOF Membrane-Based Sensors via Functionalization of Interdigitated Electrodes

Abstract

Three M-MOF-74 (M = Co, Mg, Ni) metal-organic framework (MOF) thin film membranes have been synthesized through a sensor functionalization method for the direct electrical detection of NO2. The two-step surface functionalization procedure on the glass/Pt interdigitated electrodes resulted in a terminal carboxylate group, with both steps confirmed through infrared spectroscopic analysis. This surface functionalization allowed the MOF materials to grow largely in a uniform manner over the surface of the electrode forming a thin film membrane over the Pt sensing electrodes. The growth of each membrane was confirmed through scanning electron microscopy (SEM) and X-ray diffraction analysis. The Ni and Mg MOFs grew as a continuous but non-defect free membrane with overlapping polycrystallites across the glass surface, whereas the Co-MOF-74 grew discontinuously. To demonstrate the use of these MOF membranes as an NO2 gas sensor, Ni-MOF-74 was chosen as it was consistently fabricated as the best thin and homogenous membrane, as confirmed by SEM. The membrane was exposed to 5 ppm NO2 and the impedance magnitude was observed to decrease 123× in 4 h, with a larger change in impedance and a faster response than the bulk material. Importantly, the use of these membranes as a sensor for NO2 does not require them to be defect-free, but solely continuous and overlapping growth.

A photoprogrammable electronic nose with switchable selectivity for VOCs using MOF films

“…We like to stress that these MOF lms can be prepared as pinhole-free membranes, 42 thus they are also suited for other sensing techniques where crack-free sensor coatings are required or are at least very benecial, like in transducer techniques based on impedance spectroscopy. 69 Such photoswitchable MOF-lms, where the guest affinity and guest-host interaction can be congured, can also be used with different transducer techniques, in particular in sensor setups where MOFs have proven to show very good sensor performance. For instance, in sensors based on electrochemical impedance spectroscopy in combination with substrates with deposited electrodes, 70 on eld-effect-transistors, 71,72 on surfaceacoustic-wave sensor 73 and also optical sensors.…”

“…based on impedance measurement or surface-acoustic wave sensors. 69,76,77 QCMbased sensor arrays can be rather small, so that they can be used as portable e-noses.…”

“…We like to stress that these MOF films can be prepared as pinhole-free membranes, 42 thus they are also suited for other sensing techniques where crack-free sensor coatings are required or are at least very beneficial, like in transducer techniques based on impedance spectroscopy. 69 …”

Advanced Functional Membranes for Sensor Technologies

“…The main function of inorganic membranes has been as a support structure, by increasing the sensor surface area, to carry out a capillary action, or as mediators of fluid transport by capillary action. As mentioned in Table 1, glass membranes also are good examples of inorganic membranes that have been reported [38][39][40] for biosensor applications. In this table, more examples of inorganic membranes are given; nevertheless, the reports of organic membranes in sensing applications are much more numerous.…”

“…Aluminum or aluminum oxide [22][23][24][25] Gold [26][27][28] Silver [29][30][31] Titanium oxide [32][33][34] Silicon nitride [35][36][37] Glass membranes [38][39][40] Organic Cellulose nitrate, nitrocellulose, cellulose acetate…”