A 1,8-naphthalimide-based fluorescent chemosensor for the sequential recognition of silver and sulfur ions and its application in bioimaging†

Abstract

Silver ions (Ag⁺) play roles in sterilization, anti-oxidation, electrolyte balance and metabolism promotion. Nevertheless, a high Ag⁺ content can cause significant harm to the human body. Similarly, sulfur is an essential trace element in organisms, which plays a huge role in normal physiological activities and is widely used in the treatment of diseases. However, abnormal sulfide levels in vivo can induce many diseases. Accordingly, it is particularly important to develop detection methods with high sensitivity and selectivity toward Ag⁺ and sulfide ions. Herein, a 1,8-naphthalimide-based fluorescent (NBV) chemosensor was prepared for the sequential recognition of Ag⁺ and S²⁻. In the presence of Ag⁺, the fluorescence of the NBV chemosensor was significantly quenched due to the formation of an NBV–Ag⁺ complex. After continued addition of S²⁻, the fluorescence of the system was restored and largely consistent with that of NBV. The recognition mechanism of NBV–Ag⁺ towards S²⁻ was attributed to the strong coordination between S²⁻ and Ag⁺, which led to the release of NBV from the NBV–Ag⁺ complex and restoration of the fluorescence of the NBV chemosensor. The detection limits of the NBV chemosensor towards Ag⁺ and S²⁻ were 18.2 nM and 13.3 nM, respectively. Additionally, the sequential recognition of NBV towards Ag⁺ and S²⁻ offered many advantages, including fast response speed, strong anti-interference ability, wide pH applicability and high biocompatibility. Most importantly, the NBV chemosensor was successfully used for the fluorescence imaging of Ag⁺ and S²⁻ in living cells and mice, showing significant promises.