A pyrene-based fluorescent sensor (PHP) was synthesized for Cu(II) detection. It had high selectivity towards Cu2+ ions via photoinduced electron transfer (PET) based fluorescence enhancement. In the presence of Cu2+, PHP provided significant blue emission, while Ag+, Al3+, Ca2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, and Zn2+ metal ions produced only minor changes in the fluorescence spectra. The association constant (Ka) for Cu2+ binding to PHP had a value of 1.0 × 104 M-1. The maximum emission change induced by Cu2+ binding to the chemosensor PHP was observed over the pH range 5.0-10.0. Confocal fluorescence microscopy imaging using RAW264.7 cells showed that PHP can be used as an effective fluorescent probe for detecting Cu2+ in living cells.