Cellular and Intravital Imaging of NAD(P)H by a Red-Emitting Quinolinium-Based Fluorescent Probe that Features a Shift of Its Product from Mitochondria to the Nucleus.

NAD(P)H is a vital hydrogen donor and electron carrier involved in numerous biological processes. The development of small-molecule tools for intravital imaging of NAD(P)H is significant for further exploring their pathophysiological roles. Herein, we rationally designed a fluorescent probe NADH-R by a simple graft of pyridiniumylbutenenitrile on a 1-methylquinolinium moiety in the 3-position. Benefited from the reduction of quinolinium by NAD(P)H, this probe releases the free push-pull fluorophore NADH-RH, allowing a turn-on red-emitting fluorescence response together with an ultralow detection limit of 12 nM. Under the assistance of the probe, we first monitored exogenous and endogenous generation of NAD(P)H in living cells, subsequently observed dynamic changes of NAD(P)H levels in living cells under different metabolic perturbations, and finally visualized the declined NAD(P)H levels in live mouse brain in a stroke model. Unexpectedly, the time-dependent colocalization experiment revealed that the probe reacts with mitochondrial NAD(P)H, followed by a shift of its reduced product NADH-RH from mitochondria to the nucleus, highlighting that NADH-RH is a novel nucleus-directed dye scaffold, which would facilitate the development of nucleus-targeting fluorescent probes and drugs.