A Ratiometric and Switchable Fluorescent Sensor Based on Calix[4]arene-HBT With a Large Stokes Shift for the Real-Time Detecting of Zn2+ and Cu2+ in Living Cells

Though Zn2+ and Cu2+ have several critical roles in biological and environmental media, they may also induce a variety of detrimental effects. Hence, the monitoring of trace amounts of Zn2+ and Cu2+ in biological systems and ecological environment is of great significance due to their harmful impacts on living organisms. To serve this purpose, we designed and constructed a simple benzothiazole-calixarene (C-HBT)-based ratiometric and fluorometric probe with a large Stokes shift of 206 nm to recognize Zn2+ and Cu2+. The detection levels of C-HBT for Zn2+/Cu2+ were as low as 35.1 and 66.7 nM, respectively, and high binding constant values were obtained within an extremely short time (10.0 s). Furthermore, with the assistance of inexpensive, viable, and straightforward smartphone and cotton swab applications, C-HBT was successfully applied for the on-site and naked-eye recognition of Zn2+/Cu2+. Finally, the remarkable performance of C-HBT toward Zn2+/Cu2+ with negligible cytotoxicity was achieved in living cells.