A colorimetric and ratiometric fluorescent sensor for sequentially detecting Cu and arginine based on a coumarin-rhodamine B derivative and its application for bioimaging.

In this work, a colorimetric and ratiometric fluorescent sensor based on a coumarin-rhodamine B hybrid for the sequential recognition of Cu and arginine (Arg) the FRET mechanism was designed and synthesized. With the addition of Cu, the solution displayed a colorimetric change from pale yellow to pink which is discernible by the naked eye. Additionally, the fluorescence intensities of the sensor exhibited ratiometric changes for the detection of Cu at 490 and 615 nm under a single excitation wavelength of 350 nm, which corresponded to the emissions of coumarin and rhodamine B moieties, respectively. The fluorescence color change could be visualized from blue to pink. The limits of detection were determined to be as low as 0.50 and 0.47 μM for UV-vis and fluorescence measurements, respectively. More importantly, the sensor not only can recognize Cu and form a sensor-Cu complex but can also sequentially detect Arg with the resulting complex. The detection limits for Arg were as low as 0.60 μM (UV-vis measurement) and 0.33 μM (fluorescence measurement), respectively. A fluorescence imaging experiment in living cells demonstrated that the fabricated sensor could be utilized in ratiometric fluorescence imaging towards intracellular Cu, which is promising for the detection of low-level Cu and Arg with potentially practical significance.