Iron-porphyrin-based covalent-organic frameworks for electrochemical sensing H₂O₂ and pH

Here, a novel iron-porphyrin-based covalent organic framework (COF_{p-Fepor NH2-BTA}) was synthesized and applied for electrochemical sensing H₂O₂ and pH which involved in many biological processes. The COF_{p-Fepor NH2-BTA} was obtained by post-modification of porphyrin-based COF (COF_{p-por NH2-BTA}) which was firstly synthesized by aldehyde-ammonia condensation reaction between 1,3,5-benzenetricarboxaldehyde and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H- porphine. The COF_{p-por NH2-BTA} was proved to be regular and uniform spherical particles with diameter about 1 μm, as well as possessed good crystalline structure and abundant micropores of about 1.4 nm. The resulted COF_{p-Fepor NH2-BTA} after post-modification with Fe²⁺ maintained the original shape and crystalline structure of COF_{p-por NH2-BTA}, while the micropores decreased to be about 0.89 nm. Electrochemical results indicated that the synthesized COF_{p-Fepor NH2-BTA} had good electrochemical redox and proton activity owing to iron-porphyrin, enabling to simultaneously be used as mimic peroxidase to catalyze the reduction of hydrogen peroxide (H₂O₂) and evaluate pH using current and potential as signal, respectively. The prepared sensor showed good performance for H₂O₂ detection from 6.85 nM to 7 μM with the detection limit of 2.06 nM (S/N = 3), and pH test from 3.0 to 9.0. This work demonstrated that the iron-porphyrin-based COF could be used as a mimic peroxidase to apply in biological fields.