Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg²

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg²⁺ are better than to other metal ions (Ag⁺, Al³⁺, Ba²⁺, Cd²⁺, Co³⁺, Cu²⁺, Cr³⁺, Fe³⁺, Ga²⁺, K⁺, Mg²⁺, Na⁺, Ni²⁺, Pb²⁺, and Zn²⁺). According to the standard curve diagram, the detection limits of CH -R6G and CN-R6G were determined to be 1.34 × 10^-8 and 1.56 × 10^-8 M, respectively. Reaction of the probes with Hg²⁺ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH -R6G and CN-R6G have been successfully used for imaging Hg²⁺ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg²⁺ in vivo.