Synthesis of selenium-based BOPHY sensor for imaging of Cu(II) in living HeLa cells

•Organoselenium-based BOPHY probe for the selective and sensitive detection of Cu(II).•Probe showed fluorescence turn-on response in less than 1 s upon reaction with Cu(II).•The probe detected Cu(II) in nanomolar range (10.8 nM).•Utility of the probe for detection of Cu(II) was confirmed in HeLa cells.