Signaling pathways in living cells which regulate cell cycle and activate defense mechanisms against environmental stresses are mainly controlled through cell redox potential status. The main cellular redox buffer is constituted by oxidized/reduced glutathione system (GSSG/2GSH). Physiological functions and pathological situations resulting from oxidative stress are driven by glutathione homeostasis and its dysfunction, respectively. Many methodologies devoted to the investigation of cellular redox potential relying on the determination of reduced and oxidized glutathione concentrations measured in various cellular compartments, tissues and organs have been reported. Most of them are till now based on separative and non-separative techniques and include extractive step from biological samples. They are time-consuming and tedious in order to preserve reduced to oxidized glutathione ratio, thus introducing bias in its evaluation. New trends are focused on in situ evaluation of redox state especially through the monitoring of glutathione pool. This review reports recent developments in fluorescence imaging of cellular redox state, especially those involving nanotechnologies.