Real-time and visual monitoring coating damage and metal corrosion based on the multiple chromatic transition of TMB triggered by highly active N-CDs/Fe3O4 peroxidase mimics and Fe3+

Self-reporting corrosion protection coatings offer effective means to detect potential failures in advance, allowing for timely maintenance and extending the lifespan of metal materials. However, there currently remains a challenge in developing techniques capable of concurrently monitoring coating damage and metal corrosion throughout a procedure. Herein, N-CDs/Fe 3 O 4 hybrid nanoparticles with high peroxidase-like activity were fabricated through a two-step hydrothermal process which exhibit superior affinity (K m =1.2 mM) towards H 2 O 2 than HRP and effectively turn-on the color of TMB . Combined with the excellent responsiveness towards 8-HQ and the strict linear dependent relationships towards Fe 3+ (ranging from 0.75 to 15.15 μM), a novel colorimetric assay is established to not only turn on the signals to report the appearance of damage, but additionally switch the colors of TMB system to reveal the possible crack propagation and metal corrosion underneath. Moreover, the pre-existing corrosion, characterized by higher Fe 3+ concentration, is successfully indicated according to the color intensity enhancement compared with pristine metal sheet. Notably, such a multifunctional colorimetric assay enables the real-time and visual monitoring coating damage and metal corrosion simply through a Python program integrated into smartphones, serving as a promising strategy for promptly alerting of potential structural failures.