Fluorophores “turned-on” by corrosion reactions can be detected at the single-molecule level

Corrosion is an interfacial process that has a profound impact on society. While the mechanism of iron corrosion has been known for centuries, we haven’t been able to visualize corrosion at the molecular scale due to the spatial and temporal limits of current microscopies and the long time scale of corrosion to develop larger microscale features. We demonstrate that fluorogenic molecules that “turn-on” upon redox reactions can sense the corrosion of iron at the single molecule scale. We first observe the cathodic reduction of non-fluorescent resazurin to fluorescent resorufin in the presence of iron in bulk solution. We show that the fluorescence signal is directly related to the amount of electrons that are available due to corrosion progression and can be used to quantify the catalyzed increase in the rate of corrosion by NaCl. By using modern fluorescence microscopy instrumentation we detect real-time, single-molecule “turn-on” of resazurin by corrosion, overcoming the previous limitations of microscopic fluorescence corrosion detection. Analysis of the total number of individual resorufin molecules shows heterogeneities during the progression of corrosion that are not observed in ensemble measurements.