The development of effective molecular probes to detect and image the levels of oxidative stress in cells remains a challenge. Herein we report the design, synthesis and preliminary biological evaluation of a novel optical probe to monitor oxidation of thiol groups in cysteine-based phosphatases (CBPs). Following orthogonal protecting approaches we synthesised a new vanadyl complex designed to bind to CBPs. This complex is functionalised with a well-known dimedone derivative (to covalently trap sulfenic acids, SOHs) and a coumarin-based fluorophore for optical visualization. We show that this new probe efficiently binds to a range of phosphatases in vitro with nanomolar affinity. Moreover, preliminary flow cytometry and microscopy studies in live HCT116 cells show that this probe can successfully image cellular levels of sulfenic acids - one of the species resulting from protein oxidative damage.