Fig. 5

Monitoring redox kinetics. a Schematic showing the redox reaction of Cu²⁺ ions (spin ½) to cuprous ions (spin zero) via ascorbic acid at a ratio of 1:1. b Dynamic quantum probe relaxation microscopy using a two point T ₁ measurement scheme to detect redox reactions of spin active molecules. The first time point, τ _ref, is used to normalise the fluorescence signal over the entire FOV (50 × 50 µm) with the second time point τ _sp set to the T ₁ time of the NV probes. By monitoring the normalised intensity over time, changes in the T ₁ rate will manifest as a change in the fluorescence intensity as shown schematically in the inset of b. c Two-point T ₁ measurement showing the control experiment (red squares) consisting of a dilution of the Cu²⁺ from 100 mM to 50 mM with water and the reduction of Cu²⁺ using ascorbic acid (blue circles). The Cu⁺ is found to disproportionate/re-oxidise over a period of 1 h. The fluorescence intensity was determined from the FOV at measurement intervals of 3 s