Progress in spectroscopic probes with cleavable active bonds

Spectroscopic probes may be defined as the molecules that can react with analytes (targets) accompanying the changes of their spectroscopic (chromogenic, fluorescent, or chemiluminescent) properties; based on such changes the targets can thus be determined. Spectroscopic probes have been extensively investigated and used widely in many fields because of their powerful ability to improve analytical sensitivity and to offer greater temporal and spatial sampling capability. In this review, special interest is devoted to a new type of spectroscopic probe that is constructed with a cleavable active bond as a linker. This type of spectroscopic probe, developed greatly in the past few years, has opened a novel alternate route to the specific determination of analytes with high hydrolytic reactivity, e.g., from metal ions to enzyme activity, and enabled many biological processes to be monitored in situ and in real-time. Theoretically, various photophysical processes, such as photoinduced electron transfer, photoinduced proton transfer, and fluorescence resonance energy transfer, can be used to design spectroscopic probes with cleavable active bonds for selective detection of analytes. Herein we review the progress and application of this type of spectroscopic probe, including spectroscopic response mechanism and the probes with active bonds cleavable by enzyme, metal ion and reactive oxygen species.