Sensitivity of activatable reactive oxygen species probes by fluorescence spectroelectrochemistry.

We have developed a new analytical method of evaluating activatable fluorescent probes for ROS detection using integrated fluorescence spectroelectrochemistry. The Tafel formalism was applied to describe the process of the probes' oxidation under electrochemical conditions and identify a novel parameter defined as the threshold oxidation potential. This potential can serve as an approximation to the equilibrium potential and can be utilized for determining the sensitivity of a probe to oxidation. Based upon the measured values of threshold potentials, the order of sensitivity towards oxidation among several commonly used probes was determined to be the following (from highest to lowest): 2,7-dihydrodichlorofluorescein > dihydroethidium > dihydrorhodamine 123 > dihydrorhodamine 6G. The presented approach opens up a new direction in synthesizing and screening novel ROS probes with a well-defined sensitivity for in vitro and in vivo applications.