A ratiometric fluorescent probe with strong intramolecular charge transfer (ICT) character has been designed for the detection of alkaline phosphatase (ALP). In the presence of ALP, probe 1 showed a dramatic bathochromic shift from 550 to 650 nm in the fluorescence spectrum and an obvious ratiometric signal with an isoemissive point was observed. The spectral change was attributed to the hydrolysis and cleavage of a phosphate group from the probe that changed the ability of the intramolecular charge transfer. The fluorescence intensity ratio displayed a linear relationship against the concentration of ALP in the concentration range from 50 to 200 U L−1. Other biological species, including lysozyme, trypsin, pepsin, acetyl cholinesterase, carboxylesterase, and bovine serum albumin, did not induce distinct spectral changes of the probe, indicating its selective sensing ability to ALP. Furthermore, probe 1 was also successfully applied to image endogenous ALP activity in living cells.

We have developed a new ruthenium complex, Ru(bpy)2[4-(2,2′-bipyridin-4-yloxy)phenol]Cl2 (RuL), as a fluorescent sensor to detect peroxynitrite (ONOO−). The results showed that the addition of ONOO− to the aqueous solution of RuL would result in distinct fluorescence quenching at 600 nm. RuL exhibits a good selectivity for ONOO− over other reactive oxygen species (ROS) and reactive nitrite species (RNS), and the reaction time is less than 1.5 s. The sensing mechanism is proposed as the oxidative O-dealkylation reaction.Graphical abstractWe have developed a new ruthenium complex, Ru(bpy)2[4-(2,2′-bipyridin-4-yloxy)phenol]Cl2 (RuL), as a fluorescent sensor to detect peroxynitrite (ONOO−). The results showed that the addition of ONOO− to the aqueous solution of RuL would result in distinct fluorescence quenching at 600 nm. RuL exhibits a good selectivity for ONOO− over other reactive oxygen species (ROS) and nitrite species (RNS), and the reaction time is less than 1.5 s. The sensing mechanism is proposed as the oxidative O-dealkylation reaction.Highlights► We have presented a new fluorescent sensor (RuL) for the detection of peroxynitrite. ► The sensing mechanism is proposed as the oxidative O-dealkylation reaction. ► RuL could recognize peroxynitrite specifically among other ROS/RNS. ► The reaction time of RuL and peroxynitrite is less than 1.5 s.

A new rhodamine-derived Schiff base (RS) was synthesized and its sensing property to metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ ions to the aqueous solution of RS gave a visual color change as well as significantly fluorescent enhancement, while other ions including Pb2+, Cd2+, Cr3+, Zn2+, Cu2+, Fe2+, Co3+, Ni2+, Ca2+, Mg2+, K+ and Na+ ions did not induce any distinct color/spectral changes, which constituted a Hg2+-selective fluorescent OFF–ON chemosensor. The Hg2+-induced ring-opening of spirolactam of rhodamine in RS resulted in the dual chromo- and fluorogenic observation.