Excited-state intramolecular hydrogen-bonding-assisted restricted rotation: A mechanism for monitoring intracellular viscosity and distinguishing malignant, differentiating, and apoptotic cancer cells

Abstract

We have successfully developed a sensor (IP1) that utilizes a confocal-based live-cell imaging technique for distinguishing malignant, differentiating, and under-apoptosis cancer cells. The intracellular viscosity (IVis) is minimum in the cancer cell, intermediate in differentiating cells, and maximum in the apoptotic cells. Therefore, we have developed a molecular rotor (IP1) that can sense the changes in intracellular viscosity. IP1 works on the viscosity-assisted restricted-rotation mechanism and is facilitated by the excited-state intramolecular hydrogen-bonding phenomenon (ESIHB). The use of ESIHB has fine-tuned the viscosity-sensing properties of IP1, which in turn has greatly helped in our quest of distinguishing the malignant, differentiating, and apoptotic cancer cells by the IP1 probe. It was very effective in monitoring apoptosis by increased fluorescence intensity by the confocal live-cell imaging technique. The noncytotoxic behavior, even at 10 μg/mL concentration, is a charming feature of the developed probe. To the best of our knowledge, this is the first report for the ESIHB-based fluorescence probe that can distinguish malignant, differentiating, and apoptotic cancer cells by the use of live-cell imaging techniques.