A mitochondria-targeted ratiometric fluorescent nanoprobe for imaging of peroxynitrite in living cells

Peroxynitrite (ONOO^-) is a series of basic biological oxidants involved in physiological and pathological processes. The detection of ONOO^- in biological systems has been challenging due to its extremely short half-life and low steady-state concentration. In this work, a ratiometric fluorescent nanoprobe for ONOO^- was constructed by coupling covalently of graphene quantum dots (GQDs) with cyanine 5.5 (Cy5.5). This nanoprobe (GQD-Cy5.5) could selectively accumulate in mitochondrial, appears two strong fluorescence emission peaks at 520 and 694 nm. In the presence of ONOO^-, the intensity of fluorescence emission peak at 520 nm increased and the intensity of fluorescence emission peak at 694 nm decreased. The ratio (F_{520 nm}/F_{694 nm}) of fluorescence intensity at two emission peaks had a good linear relationship with the concentration of ONOO^- in the range of 0-6.0 μM, and the detection limit was 0.03 μM. The excellent properties of the nanoprobe enable its applications in the ratiometric fluorescence imaging of endogenous ONOO^- in cell mitochondria.