Schematic of the ultra-sensitive MOF-based iodine gas sensor.
Schematic of the ultra-sensitive MOF-based iodine gas sensor.

Nuclear power currently provides around 10% of global energy demand but could offer a low-carbon alternative to fossil fuels. However, societal concerns about safety, particularly in the event of accidents or fuel reprocessing, remain. Hazardous radionuclides are typically emitted in the form of gases, principally iodine and its isotopes, which affect human metabolism and can cause cancer. However, existing iodine sensors have low sensitivity, poor selectivity, limited reusability, and only work at higher temperatures. Now researchers from the University of Oxford have designed a new iodine gas sensor based on a metal-organic framework (MOF) [Babal et al., Materials Today (2022),].

“We have developed an extremely sensitive iodine sensor, which is one of the urgent needs for detection of ultra-trace gas-phase radioactive iodine in the event of a nuclear breach,” explains Jin-Chong Tan, who led the work.

The prototype iodine sensors are based on MOFs, which are compounds of metal ions or clusters linked by organic ligands to form usually porous one-, two-, or three-dimensional structures. These materials are ideal for sensing because of their high surface area, tunable pore size, versatile structure and combination of structural, thermal and chemical robustness. MOFs can be tailor-made to have specific interaction sites to target gas molecules selectively.

“We rationally designed a MOF material that exhibits record-breaking performance with an almost billion-fold enhancement in the electrical response thanks to its optimized hydrophobicity,” says Tan.

The sensor devices comprise a MOF thin film deposited onto a platform of interdigitated comb-like electrodes. Tuning the level of hydrophobicity in the MOF facilitates easy migration of iodine molecules through the channels, while interaction sites temporarily anchor the target molecules for ultra-trace sensing with a very fast response time. The best results were achieved with an inkjet-printed 3-layer MOF based on Zn(II) ions (ZIF-70).

“The inkjet-printed sensor chips have reversibly selective and ultra-trace ppb-level iodine sensing capabilities in the gas phase, both at the lower (Hz) and higher frequencies (MHz), which is important for engineering integration into commercial electronics,” points out Tan.

The researchers’ approach has not only led to the first industrially viable prototype MOF-based iodine sensor but also offers a general design route to using MOFs for real-time detection of hazardous and toxic chemicals at trace levels. The team are now focused on manufacturing bespoke long-lasting sensors aimed at different analytes.