A highly selective and sensitive salamo-salen-salamo hybrid fluorometic chemosensor for identification of Zn2+ and the continuous recognition of phosphate anions

The dynamic chemical diversity of elements, ions and molecules that form the basis of life offers both a challenge and an opportunity for study. Small-molecule fluorescent probes can make use of selective, bioorthogonal chemistries to report on specific analytes in cells and in more complex biological specimens. These probes offer powerful reagents to interrogate the physiology and pathology of reactive chemical species in their native environments with minimal perturbation to living systems. This Review presents a survey of tools and tactics for using such probes to detect biologically important chemical analytes. We highlight design criteria for effective chemical tools for use in biological applications as well as gaps for future exploration.

The cyanine platforms including cyanine, hemicyanine, and squaraine are good candidates for developing chemosensors because of their excellent photophysical properties, outstanding biocompatibility, and low toxicity to living systems. A huge amount of research work involving chemosensors based on the cyanine platforms has emerged in recent years. This review focuses on the development from 2000 to 2015, in which cyanine, hemicyanine, and squaraine sensors will be separately summarized. In each section, a systematization according to the type of detection mechanism is established. The basic principles about the design of the chemosensors and their applications as bioimaging agents are clearly discussed. In addition, we emphasize the advances that have been made in improving the detection performance through incorporation of the chemosensors into nanoparticles.

A novel coumarin-based fluorogenic probe bearing the 2-picolyl unit (1) was developed as a fluorescent chemosensor with high selectivity and suitable affinity in biological systems toward Cu(2+) over other cations tested. The fluorescence on-off mechanism was studied by femtosecond time-resolved fluorescence (TRF) upconversion technique and ab initio calculations. The receptor can be applied to the monitoring of Cu(2+) ion in aqueous solution with a pH span 4-10. To confirm the suitability of 1 for biological applications, we also employed it for the fluorescence detection of the changes of intracellular Cu(2+) in cultured cells. The results indicate that 1 should be useful for the fluorescence microscopic imaging and the study on the biological functions of Cu(2+).