Porphyrin-Based Porous Organic Frameworks as a Biomimetic Catalyst for Highly Efficient Colorimetric Immunoassay

Herein, we synthesized a cost-effective iron porphyrin (FePor)-based covalent organic polymer (COP), FePor-TFPA-COP, through an easy aromatic substitution reaction between pyrrole and tris(4-formylphenyl)amine (TFPA). The triangular pyramid-shaped, N-centric structure of TFPA facilitated the formation of FePor-TFPA-COP with three-dimensional porous structure, larger surface area, and abundant surface catalytically active sites. FePor-TFPA-COP exhibited strong intrinsic peroxidase activity toward a classical peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), in the presence of H₂O₂. Compared with horseradish peroxidase (HRP), FePor-TFPA-COP exhibited several advantages such as easy storage, high sensitivity, and prominently chemical and catalytic stability under the harsh conditions, which guaranteed the accuracy and reliability of measurements. Utilizing the excellent catalytic activity, a FePor-TFPA-COP-based colorimetric immunoassay was first established for α-fetoprotein (AFP) detection and showed high sensitivity, stability, and acceptable reproducibility. The linear response range for AFP was 5 pg/mL to 100 ng/mL and the detection limitation was 1 pg/mL. The routine provided a brilliant biomimetic catalyst to develop the nonenzyme immunoassay. More importantly, the high chemical and catalytic stability and sensitivity facilitated future practical applications under various conditions.