A Novel Schiff Base Probe Based on Fluorescein for Fluorometric and Colorimetric Dual-Mode Rapid Detection of Cu2+

Copper is an important environmental pollutant that poses a significant threat to human health and environmental safety. Therefore, the development of methods for detecting Cu2+ is of great significance. A novel fluorometric/colorimetric dual-mode sensor for detecting Cu2+ was synthesized by Schiff base reaction using fluorescein hydrazide and 8-hydroxyjulonidine-9-carboxaldehyde as raw materials. Cu2+ could form a complex with the probe in a stoichiometric ratio of 1:1. Within 1 min, the fluorescence of the probe rapidly quenched at 540 nm, and the absorbance reached a stable state at 452 nm. The color of the solution changed from light yellow to yellow, achieving real-time and visual detection of Cu2+. This probe exhibited exceptional selectivity for Cu2+. Within the range of 0–12 μM, the fluorescence intensity of the probe demonstrated a strong linear correlation with the concentration of Cu2+ (R2 = 0.994), with a detection limit of 0.22 µM. In the ultraviolet colorimetric method, when the Cu2+ concentration reached 14 μM, the absorbance stabilized (R2 = 0.996), and the detection limit for Cu2+ was determined to be 0.38 µM. Furthermore, this probe enabled reversible detection of Cu2+, and its performance in real water sample analysis and cellular bioimaging was proven to be highly satisfactory.