A newly nitrobenzoxadiazole (NBD)-fused reversible fluorescence probe for pH monitoring and application in bioimaging

pH plays an essential role in virtually all biological processes, which thus needs to be tightly regulated. Especially small changes in pH value in biological systems will affect the normal metabolic functions of animals and plants. Therefore, it is very important to accurately track changes in pH in biological systems. Herein, we rationally fabricated a new molecular pH probe (NBD-pbz) based on conjugation of the 2-Piperazin-1-yl-1,3-benzothiazole (pbz) and 7-nitro-1,2,3-benzoxadiazole (NBD) building blocks. The following test on NBD-pbz revealed that it can offer a sensitive and selective tracking of pH changes from 3.2 to 7.6 with pK(a) 5.51, and not only in eukaryotic cells (especially the imaging of ocular tumor cell OCM-1) and zebrafish but also in mung bean sprouts via fluorometric turn on response and an intramolecular charge transfer (ICT) based working mechanism strategy. Therefore, this NBD-pbz probe not only replenishes the current repertory of molecular pH probes but also extends the application of pH probes to monitor pH variation in the plant kingdom, which will undoubtedly arouse greater research interest in the field.