Genetically encoded fluorescent sensors for measuring transition and heavy metals in biological systems

•Genetically encoded fluorescent sensors are powerful tools for measurement of cellular labile transition metals.•Design strategies of genetically encoded transition metal sensors are overviewed.•Recent development of genetically encoded sensors for zinc, copper and heavy metals is discussed.•Future perspectives of genetically encoded fluorescent sensors for transition metals are outlined. Great progress has been made in expanding the repertoire of genetically encoded fluorescent sensors for monitoring intracellular transition metals (TMs). This powerful toolkit permits dynamic and non-invasive detection of TMs with high spatial-temporal resolution, which enables us to better understand the roles of TM homeostasis in both physiological and pathological settings. Here we summarize the recent development of genetically encoded fluorescent sensors for intracellular detection of TMs such as zinc and copper, as well as heavy metals including lead, cadmium, mercury, and arsenic.