Synthesis of a dual-emissive pyrene-based fluorescent probe for imaging intracellular viscosity

Abstract

A pyrene-based fluorescent molecular probe (Py2-5EG) was synthesized for optical detection of viscosity vari-ation. Py2-5EG was synthesized by the reaction of two hydroxyl groups at the two ends of pentaethylene glycol with pyrene via a two-step reaction. Unlike typical pyrene compounds, the monomer fluorescence of Py2-5EG was not observed even in a dilute solution. Instead, the monomer fluorescence gradually increased with the increase in solvent viscosity. Blue fluorescent emission was observed from the monomer in a more viscous medium, and greenish blue emission from excimer was dominant in a less viscous medium in which dynamic excimer formation was involved. The observed fluorescence change of Py2-5EG was ratiometric and depended on the solution viscosity. A microscopic change in cellular viscosity was clearly observed inside and outside the mitochondria of living cells via different fluorescence colors of blue and green. The viscosity inside and outside mitochondria was determined using the fluorescence colors. Py2-5EG featured noticeable fluorescence emission shift in response to viscosity, and this phenomenon can be applied as a fluorescent probe, estimating the viscosity of various solutions as well as inside living cells.