Selective visualization of nitric oxide in living cells and tissue slices using a mitochondria-targetable fluorescent probe

Nitric oxide (NO) is an important messaging molecule which plays a vital role in many biological systems. Because the endogenous NO is synthesized mainly in the mitochondria of mammalian cells, the detection of NO in mitochondria is of great importance for studying the biological functions of NO. Here, a novel fluorescence turn-on probe (MTNO) for monitoring the mitochondrial NO is designed and synthesized. The fluorescence intensity of MTNO exhibits a ∼430-fold enhancement in response to NO with a detection limit as low as 14 nM. MTNO also shows good mitochondrial localization, pH insensitivity and high selectivity to NO. With the aid of MTNO, the imaging of exogenous and endogenous NO in living cells and tissue slices is achieved through two-photon microscopy.