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 (F520 nm/F694 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.