A new near-infrared ratiometric fluorescent probe based on quinoline-fused rhodamine dye for sensitive detection of cysteine and homocysteine in mitochondria

Abstract

A novel quinoline-fused Rhodamine dye is designed and synthesized to achieve near-infrared fluorescent emission by expanding the π-conjugated system. Ratiometric fluorescent probe (RhQ) is further constructed by introducing the 3,5-ditrifluormethylthiophenol moiety into dye through a thioester bond to take advantage of spirocyclization open-ring states of Rhodamine platform. The probe exhibits remarkable dual-channel fluorescence response toward Cys/Hcy in aqueous solutions between near-infrared and visible emission, arising from the formation of closed spirolactam configuration disrupting molecular π-conjugation system. RhQ is highly selective and sensitive to Cys/Hcy with detection limits of 0.12 μM and 0.25 μM for Cys and Hcy, respectively. Moreover, imaging in cellular experiment indicates that probe displays excellent mitochondrial targeting ability, lower cytotoxicity and ratiometric responses with two well-defined emissions to ensure exactly comparison and quantitative analysis of Cys/Hcy changes in the cell.