A ratiometric fluorescent sensor for tracking Cu(I) fluctuation in endoplasmic reticulum

A two-photon ratiometric fluorescent sensor for Cu+ in endoplasmic reticulum (ER), CNSB, was developed via coumarin/ASBD integration based on FRET mechanism. In solution, CNSB shows reversible, highly-specific ratiometric response to Cu+. Moreover, CNSB exhibits suitable K-d value, suggesting the possibility of detecting Cu+ in the living cells. The probe can enter the MCF-7 cells easily and specifically locates in the ER. The highly specific ratiometric response of CNSB toward Cu+ in MCF-7 cells provides the sensor the capacity to visualize both exogenous and endogenous Cu+ in the ER via fluorescence imaging. Next, CNSB was utilized to detect the fluctuation and distribution of Cu+ under ER stress in MCF-7 cells, which confirmed directly the relationship between Cu+ enhancement and ER stress. Meanwhile, the two-photon ability of coumarin facilitated the sensor to visualize Cu+ fluctuation via two-photon fluorescence imaging. In addition, the spatial distribution of Cu+ in the heart slice of the 14-day-old rat was demonstrated using CNSB. This study demonstrates the promising potential of CNSB in clarifying the Cu+-dependent signaling in the ER stress-related diseases.