Hierarchically porous ZIF‐67‐based Au with enhanced electromagnetic, chemical, and mass‐transfer properties for flexible gas–liquid SERS sensing

Abstract Metal–organic framework materials exhibit considerable potential as molecularly selective surface‐enhanced Raman spectroscopy (SERS) substrates because of their microporous structures, which enrich small molecules while excluding larger ones. In this study, we develop a template‐assisted chemical‐etching strategy to prepare layered tuneable SERS substrates based on hierarchical porous zeolitic imidazolate framework‐67 (HP‐ZIF‐67) with a rhombic dodecahedral structure. The synergistic SERS enhancement mechanisms of HP‐ZIF‐67, which combine electromagnetic (EM) and chemical (CM) effects, were systematically studied through numerical simulations and experiments. Calculations revealed that under 633‐nm laser excitation, the contributions of the EM and CM effects to the total SERS enhancement factor of HP‐ZIF‐67 were 60% and 40%, respectively. The hierarchical porous structure enhanced the fluid‐flow flux over the microporous ZIF‐67 because the increased pore radius reduced the viscous resistance and facilitated rapid molecular transport through the interconnected macro‐meso‐channels. Precise modulation of the CM and EM effects, combined with enhanced mass transfer, facilitated the development of HP‐ZIF‐67 and HP‐ZIF‐67@Au as efficient SERS sensors. An investigation of the relationship between pore‐size distribution and EM effects revealed the pivotal role of light confinement by whispering‐gallery‐mode microcavities in enhancing the SERS performance. The optimised HP‐ZIF‐67@Au composites functioned as flexible and highly sensitive in situ SERS sensors for gases and liquids, including volatile organic‐compound gas and liquid‐pesticide residues. This study introduces a novel design concept and provides a robust theoretical foundation for the future development of exhaled‐breath point‐of‐care diagnostic devices and sweat‐based wearable biomedical sensors.