Cysteine and viscosity double-locked responsive fluorescent probe for imaging in HeLa cells

Abstract

Cysteine (Cys) fluctuation is a vital factor for maintaining redox homeostasis, while cellular viscosity is pivotal in tumor microenvironments. In this article, we developed a cascade-detection red-fluorescent probe for cysteine (Cys) recognition and a viscosity-activatable probe, (E)-6-(2-(4-cyano-5-(dicyanomethylene)-2,2-dimethyl-2,5-dihydrofuran-3-yl)vinyl)naphthalen-2-yl acrylate (CDFN-ACY). CDFN-ACY is composed of a donor–π-acceptor (D–π–A) fluorophore and an acrylic ester response group specifically designed for Cys level detection. The 6-hydroxy-2-naphthaldehyde unit serves as the electron-donor component, while the 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile group functions as the electron-withdrawing moiety. Notably, upon reaction with Cys, CDFN-ACY released an intermediate compound, CDFN-OH, that can further respond to changes in viscosity. CDFN-ACY showed a red fluorescence emission response at 612 nm along with a large Stokes shift (272 nm) and exhibited excellent performance as it offered high sensitivity and rapid response for Cys detection. Moreover, the precursor fragment CDFN-OH demonstrated significant spectral response changes to viscosity variations. Notably, it displayed a remarkable fluorescence enhancement at 612 nm. Importantly, CDFN-ACY was successfully employed to visualize both Cys levels and viscosity within living cells. This study demonstrates that CDFN-ACY is capable for the visualization of variations in both Cys levels and viscosity through cascade responses.