Mitochondria-Targeted Colorimetric and Ratiometric Fluorescent Probe for Hg²⁺ with Large Stokes Shift

In this study, probe 1, a novel mitochondria-targeted fluorescent probe for the colorimetric and ratiometric detection of Hg²⁺, was developed. Upon addition of Hg²⁺ to the solution of 1, distinct spectral changes were observed. The absorption spectra underwent a blue shift from 510 nm to 450 nm (Δλ = 60 nm), and the solution color changed from red to pale yellow under daylight. Concurrently, a significant blue shift occurred from 645 nm to 540 nm (Δλ = 105 nm) in the fluorescence spectra. There were remarkable variations in the fluorescence intensity ratio of F_{540 nm}/F_{645 nm} with the R/R₀ value reaching up to 824-fold, and the fluorescence color changed from red to green under a 365 nm UV lamp. Probe 1 featured a large Stokes shift of 135 nm, high sensitivity with an LOD of 25.5 nm, and excellent selectivity for Hg²⁺ even in the presence of other analytes. Furthermore, 1 was successfully applied for the ratiometric imaging of intracellular Hg²⁺ and was confirmed to localize specifically within mitochondria.