MOF-Derived Porous Hollow Co3O4@ZnO Cages for High-Performance MEMS Trimethylamine Sensors

Trimethylamine (TMA) sensors based on metal oxide semiconductors (MOS) have drawn great attention for real-time seafood quality evaluation. However, poor selectivity and baseline drift limit the practical applications of MOS TMA sensors. Engineering core@shell heterojunction structures with accumulation and depletion layers formed at the interface is regarded as an appealing way for enhanced gas sensing performances. Herein, we design porous hollow Co3O4@ZnO cages via a facile ZIF-67@ZIF-8-derived approach for TMA sensors. These sensors demonstrate great TMA resistive sensing performance (linear response at moderate TMA concentrations (<33 ppm)), and a high sensitivity of ∼41 is observed when exposed to 33 ppm TMA, with a response/recovery time of only 3/2 s. This superior performance benefits from the Co3O4@ZnO porous hollow structure with maximum heterojunctions and high surface area. Furthermore, great capacitive TMA sensing with linear sensitivity over the full testing concentration range (0.33–66 ppm) and better baseline stability were investigated. A possible capacitive sensing mechanism of TMA polarization was proposed. For practical usage, a portable sensing prototype based on the Co3O4@ZnO sensor was fabricated, and its satisfactory sensing behavior further confirms the potential for real-time TMA detection.