A novel lipid droplets/lysosomes-targeting colorimetric and ratiometric fluorescent probe for Cu²⁺ and its...

A novel multifunctional fluorescent probe LL2 was prepared via a one-step condensation reaction between 3-formyl-N-butylcarbazole and 2-Hydroxy-1-naphthylhydrazone. LL2 can work as a colorimetric probe for Cu²⁺, and can also selectively recognize Cu²⁺ via ratiometric fluorescence signal. After the addition of Cu²⁺, the probe LL2 responded rapidly within 5 s and reached stability within 30 s. In natural light, when Cu²⁺ were added to the solution, the color of probe LL2 changed from yellowish to colorless, while there was a discernible fluorescence changed from green to blue under a 365 nm UV lamp. The ratiometric fluorescence intensity (F₄₄₉/F₅₁₀) showed a good linear relationship (R² = 0.9902) with Cu²⁺ concentration in the concentration range of 0-5 μmol/L, and the minimum detection limit was 1.96 μM. Cell imaging experiments showed that LL2 could capture fluorescence signals in the green and blue channels of HepG2 cells through fluorescence confocal microscope, and successfully recognize exogenous Cu²⁺ in HepG2 cells. In addition, fluorescence co-localization experiments showed that LL2 could target both lipid droplets and lysosomes. Meanwhile, LL2 could be applied to filter paper strip assay and detection of Cu²⁺ in actual water samples. These results indicated that probe LL2 has a good capability for monitoring Cu²⁺ in environment and living cells.