Porphyrin-Based Covalent Organic Framework Thin Films as Cathodic Materials for On-Off-On Photoelectrochemical Sensing of Lead Ions

Currently, cathodic photoelectrochemical (PEC) sensors, which could effectively reduce background interference, are urgently required for ultrasensitive environmental monitoring. Herein, porphyrin-based covalent organic framework (TAPP-COF) thin films were fabricated via a bottom-up growth approach on the liquid/liquid interface and applied as a photocathode material to on-off-on PEC sensing of Pb2+. Benefitting from the unique charge channels of COFs and the good photoelectric properties of porphyrin, the as-prepared TAPP-COF thin films presented an improved photocathodic current, with a strongly enhanced signal-on response with low background. Then, CdSe@SiO2 quantum dots (QDs), as a quenching agent, were introduced through a hybridization chain reaction (HCR) to obtain a signal off PEC response. Afterward, with the introduction of target Pb2+, CdSe@SiO2 QDs were detached from TAPP-COF thin films, and the PEC response transformed into a signal-on state. Benefiting from the multiple-quenching and steric hindrance effect of CdSe@SiO2 QDs and the photocathodic property of TAPP-COFs, accurate monitoring of Pb2+ in a wide detection range from 0.05 to 1000 nM with a lower detection limit of 0.012 nM was realized based on the proposed on-off-on PEC approach. Notably, the methodology provides an efficient platform for ultrasensitive determination of heavy metal ions, which would play a significant role in environmental monitoring and public safety fields.

Automated summary

Cathodic photoelectrochemical (PEC) sensors are urgently required for ultrasensitive environmental monitoring, and porphyrin-based covalent organic framework (TAPP-COF) thin films were fabricated and applied in this study. By utilizing CdSe@SiO2 quantum dots as a quenching agent and introducing target Pb2+, accurate monitoring with a wide detection range and low detection limit was achieved through an on-off-on PEC approach. This methodology provides an efficient platform for ultrasensitive determination of heavy metal ions, contributing significantly to environmental monitoring and public safety.