A Highly Selective Fluorescent Probe for Hg²⁺ Based on a 1,8-Naphthalimide Derivative

Hg²⁺ has a significant hazardous impact on the environment and ecosystem. There is a great demand for new methods with high selectivity and sensitivity to determine mercury in life systems and environments. In this paper, a novel turn-on Hg²⁺ fluorescent probe has been reported with a naphthalimide group. The Hg²⁺ fluorescent probe was designed by the inspiration of the well-known specific Hg²⁺-triggered thioacetal deprotection reaction. A 1,2-dithioalkyl group was chosen as the specific recognition site of Hg²⁺. The probe showed weak fluorescence without Hg²⁺, and the color of the solution was light yellow. In the presence of Hg²⁺, the probe reacted specifically with the mercury ion to produce an aldehyde and emitted strong fluorescence, and the color of the solution also turned light green, thus realizing the monitoring of the mercury ion. The Hg²⁺ fluorescent probe showed outstanding sensitivity and selectivity toward Hg²⁺. Furthermore, the Hg²⁺ fluorescent probe could work in a wide pH range. The linear relationship between the fluorescence intensity at 510 nm and the concentration of Hg²⁺ was obtained in a range of Hg²⁺ concentration from 2.5 × 10^-7 to 1.0 × 10^-5 M. The detection limit was found to be 4.0 × 10^-8 M for Hg²⁺. Furthermore, with little cell toxicity, the probe was successfully applied to the confocal image of Hg²⁺ in PC-12 cells.