Hierarchically structured nanoporous organic polymers as a rapid electrochemical platform for monitoring trace heavy metal ions

Rapid electrochemical monitoring and detection of toxic heavy metal ions using chemically modified carbon paste electrodes (CPEs) is of great importance, but the development of chemically stable and porous CPE substrates with unique sensing properties remains challenging. Here, we synthesized nine low-cost nanoporous organic polymer (NOP) matrices under mild CPE conditions and developed highly sensitive graphite powder (GP)@NOP composite electrodes for sensing of trace heavy metal ions. These NOP substrates have great potential for electrochemical sensing due to their large surface area, layered porosity and excellent stability. The electrochemical properties, dominated by the pore structures of the NOPs, are simply turned by regulating the nature of the building blocks and crosslinkers. The micropores facilitate highly sensitive and selective detection and the mesopores benefit mass transfer. Using GP@NOP complex electrodes, the concentrations of the analyte show linear relationship with the oxidation current peak values over a concentration range of 0.0010–0.012 μg L⁻¹ with high correlation coefficients up to 0.996. Super-high sensitivity with a low detection limit (0.0003 μg L⁻¹) and excellent reproducibility (relative standard deviation ≤ 7.4 %) is demonstrated, superior to the pristine GP electrode and most known electrodes. This study expands a novel application for NOPs and an alternative straightforward approach for the rapid and reliable detection of heavy metal ions.