A novel colorimetric “on–off–on” fluorescent probe based on tris(salicylaldehyde) for the sequential recognition of Cu2+/Hcy and its application in bioimaging

Abstract

This study introduces a novel salicylaldehyde hydrazine-based small-molecule sensor DBD, which can sequentially recognize Cu²⁺ and Hcy in a DMSO/PBS (1/1, v/v, pH = 7.4) solution. Upon addition of Cu²⁺ ions, the emission intensity at 515 nm was rapidly quenched by 98.1%, with a detection limit of 7.47 nM, demonstrating its high sensitivity, selectivity, and robust anti-interference capability. The coordination ratio between DBD and Cu²⁺ was determined to be 1 : 1, with a high complexation constant of 1.62 × 10⁴ M⁻¹ as evidenced by the Job plot, MS, ¹H NMR, and DFT calculations. The DBD–Cu²⁺ complex was capable of further recognizing Hcy in the same system, exhibiting an “on–off–on” fluorescence response with a recovery efficiency approximately from 91% to 56% over seven cycles and a detection limit of 55.6 nM. Colorimetric experiments using inexpensive paper strips confirmed that the probe DBD can sequentially detect Cu²⁺ and Hcy. Additionally, the applicability of DBD in the detection of Cu²⁺ in actual different water samples was validated with satisfactory precision. Motivated by its favorable performance at physiological pH, the probe DBD was utilized for bio-imaging of Cu²⁺ and Hcy in A549 living cells and zebrafish larvae. These results indicate that DBD is a promising candidate for detecting Cu²⁺ and Hcy in biological systems.