Reversibly monitoring oxidation and reduction events in living biological systems: Recent development of redox-responsive reversible NIR biosensors and their applications in in vitro/in vivo fluorescence imaging.

Reactive oxygen species (ROS) and changes in their redox cycles have great therapeutic potential for treating serious redox-related human diseases such as acute and chronic inflammation, diabetes, cancer and neurodegenerative disorders. This article presents a survey of the recently (2011-2016) developed NIR small-molecule biosensors for reversibly monitoring oxidation and reduction events in living cells and small animals through in vitro/in vivo fluorescence imaging. Emission and absorption profile, design strategy and fluorescence sensing mechanism, ROS selectivity and sensitivity, reversibility, ability of subcellular location and cytotoxicity are discussed for the NIR small-molecule biosensors capable of quantitatively, continuously and reversibly detecting transient ROS burst and redox changes at cellular level.