Toluidine blue-assisted synthesis of functionalized M (M = Cu, Co, Zn)-metal-organic frameworks for electrochemical immunoassay of proteins

• One-step TB-assisted synthesis strategy for fabricating functionalized MOFs. • The TB@Cu-MOFs, TB@Co-MOFs and TB@Zn-MOFs were synthesized. • A sensitive electrochemical immunoassay to detect IgG, MB and FMDV was developed. Toluidine blue (TB) as an electrochemically active molecule usually loads on metal organic frameworks (MOFs) surface to improve its electrochemical performance. In this paper, a simple synthesis strategy for one-step fabricating toluidine blue (TB)-functionalized metal organic frameworks (TB@MOFs) via the self-assembly approach was reported. This reaction of trimesic acid (H 3 BTC) as an organic ligand, TB as an electrochemical probe and a base for the deprotonation of H 3 BTC, and Zn 2+ , Cu 2+ or Co 2+ as the metal ion source leads to a rapid synthesis of three different MOFs, which all show exceptional electrochemical activity due to abundant TB molecules encapsulated in the MOFs. Varied instruments were used to characterize the TB@MOFs to verify the successful synthesis. Based on these three TB@MOFs sensing platforms, the sensitive label-free electrochemical immunosensors for the detection of pig immunoglobulin G (IgG), mycobacterium bovis (MB) and foot and mouth disease virus (FMDV) were developed with wide linear ranges and low detection limits. Furthermore, these immunosensors present good sensitivity, selectivity and stability in actual samples.