Hollow metal-organic frameworks micro-/nanoreactors via in-situ cascade engineering: boosting neurotransmitter sensitive recognition

Porous materials show promise as electroanalytical sensors for disease diagnosis, especially neurotransmitter detection, but are hindered by poor mass transfer and limited active site accessibility. To overcome these, we developed an in-situ cascade engineering method to fabricate a hollow ZIF-polypyrrole hybrid (HZIF(Zn)@PPy), achieving outstanding sensing performance. Fe(acac)₃ is immobilized on ZIF(Zn) via molecular dimension effects, initiating pyrrole polymerization to form a PPy coating. Hydrogen ions released during this process permeate ZIF pores, etching unstable frameworks to create ~ 70 nm hollow cavities through a self-sustaining cascade mechanism. Expanding this approach, we synthesized heterobimetallic HZIF(ZnM)@PPy composites (M = Fe, Cr, Al, Mn, Cu, Ca, Mg, Co, and Ni) and extended it to alternative MOF precursors (ZIF-67, ZIF-90, MIL-88B, and UiO-66), deepening our understanding of hollow structure evolution. Using dopamine as a model analyte, the HZIF(ZnNi)@PPy sensor exhibited superior performance with a wide linear range (0.01–900 µmol/L) and an ultra-low detection limit (0.003 µmol/L, S/ N = 3). This study pioneers a rational design strategy for hollow electrochemical sensors, offering valuable insights for advancing disease diagnostics and therapeutic monitoring.