Partnered Excited-State Intermolecular Proton Transfer Fluorescence (P-ESIPT) Signaling for Nitrate Sensing and High-Resolution Cell-Imaging.

Nitrite (NO) is a common pollutant and is widely present in the environment and in human bodies. The development of a rapid and accurate method for NO detection is always a very important task. Herein, we synthesized a partnered excited-state intermolecular proton transfer (ESIPT) fluorophore using the "multi-component one pot" method, and used this as a probe (ESIPT-F) for sensing NO. ESIPT-F exhibited bimodal emission in different solvents because of the solvent-mediated ESIPT reaction. The addition of NO caused an obvious change in colors and tautomeric fluorescence due to the graft of NO into the ESIPT-F molecules. From this basis, highly sensitive and selective analysis of NO was developed using tautomeric emission signaling, achieving sensitive detection of NO in the concentration range of 0~45 mM with a detection limit of 12.5 nM. More importantly, ESIPT-F showed the ability to anchor proteins and resulted in a recognition-driven "on-off" ESIPT process, enabling it to become a powerful tool for fluorescence imaging of proteins or protein-based subcellular organelles. MTT experimental results revealed that ESIPT-F is low cytotoxic and has good membrane permeability to cells. Thus, ESIPT-F was further employed to image the tunneling nanotube in vitro HEC-1A cells, displaying high-resolution performance.