Design strategies and progress on xanthene-based fluorescent probe for metal ions

Metal ions play critical roles in numerous fundamental life processes. Hence, there is a great need to effectively monitor and image metal ions. Fluorescent probes are one of the most effective methods for measuring metal ions. In general, according to the different recognition mechanisms of fluorescent probes, they can be divided into two categories: reversible probes and irreversible probes. Among the various fluorophores, rhodamine and fluorescein, as the typical representatives of xanthene, have been paid much attention in biological imaging due to their high absorption coefficient, high fluorescence quantum yield, and water solubility. This review highlights the recent advances on chelation-based xanthene fluorescent probes that have been used for detecting metal ions. The focus has been on the design strategies to improve the selectivity and sensitivity of fluorescent probes by introducing different recognition moieties. Meanwhile, their recognition mechanism and applications are particularly highlighted.