High Quality Content by WIKIPEDIA articles! The reduction-oxidation sensitive green fluorescent protein (roGFP) is a redox sensitive biosensor. Two cysteines were introduced into the beta barrel structure of the GFP, the oxidation state (reduced dithiol or the oxidized disulfide) of the engineered thiols determines the fluorescence properties of the sensor. Originally different roGFP versions were presented, for in vivo imaging of reducing compartments such as the cytosol roGFP2, with cysteines introduced at the amino acid positions 147 and 204, turned out to be the most suitable version. roGFP2 preferentially interacts with glutaredoxins and therefore reports the cellular glutathione redox potential. The specificity of roGFP2 for glutathione is further increased by linking it to the human glutaredoxin 1 (Grx1). By expressing the Grx1-roGFP fusion sensors in the organism of interest and/or targeting the protein to a cellular compartment allows to measure the glutathione redox potential in a specific cellular compartment at real-time and therefore provides major advantages compared to other invasive static methods e.g. HPLC.