Quantitative Fluorescence Ratio Imaging of Intralysosomal Chloride Ions with Single Excitation/Dual Maximum Emission

Graphical All aglow! A new fluorescence ratio imaging probe, 6-methoxyquinolinium–dansyl (MQ-DS), with single excitation/dual maximum emission, responds precisely and instantaneously to changes of Cl − concentrations in lysosomes (see picture). It is utilized successfully to quantitatively visualize fluctuations of Cl − in live cells and in vivo. Fluorescence ratio imaging is currently being used to quantitatively detect biologically active molecules in biosystems; however, two excitations of most existing fluorescent ratiometric probes account for cumbersome operating conditions for imaging. Thus, a fluorescent ratiometric probe, 6-methoxyquinolinium–dansyl (MQ-DS), for Cl − with single excitation/dual maximum emission has been developed. MQ-DS can preferably localize into lysosomes and display excellent photostability. Upon excitation at a single wavelength, it responds precisely and instantaneously to changes in Cl − concentrations, and it can be conveniently utilized to implement real-time fluorescence ratio imaging to quantitatively track alterations in Cl − levels inside cells treated under various pH conditions, and also in zebrafish with acute wounds. The successful application of the new probe in bioimaging may greatly facilitate a complete understanding of the physiological functions of Cl − .