A copper-bridged fluorescent sensor for sequential detection of Cu²⁺ and TKX-50: Synthesis, mechanism, and...

5,5'-bistetrazole-1,1'-diolate (TKX-50), known as a novel explosive, is characterized by its high energy and low sensibility. It is a preferred explosive for criminals to carry out illegal attacks, posing a significant security risk. Therefore, the development of an efficient and highly specific detection method for TKX-50 is of significant practical importance. Fluorescent chemical sensors have demonstrated tremendous potential in explosive detection due to their high sensitivity, rapid response, and visual detection capabilities.

A novel fluorescent chemical sensor N'-((E)-5-((E)-2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)-2-hydroxybenzylidene)-7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide (EXF) was designed and synthesized, and its structure was characterized by ¹H NMR, ¹³C NMR, and HRMS. The sensor can achieve continuous and specific detection of Cu²⁺ and TKX-50 through the 'on-off-on' fluorescence response. The EXF achieved a detection limit of 0.0968 μM for Cu²⁺. The complex [EXF-Cu²⁺] could specifically identify the novel explosive TKX-50 among a variety of explosives tested, with a detection limit of 0.0648 μM. In this study, the qualitative detection of Cu²⁺ and TKX-50 was carried out using test strips, and the quantitative determination of Cu²⁺ and TKX-50 in real water samples was successfully achieved based on the standard curve of a smartphone. Additionally, EXF can be used for the visualization of latent fingerprints (LFPs), demonstrating its potential application in the field of criminal investigations. The application of EXF for Cu²⁺ and TKX-50 imaging in living cells is also demonstrated.

The fluorescent sensor EXF establishes a connection between explosive detection and ion sensing by utilizing Cu²⁺ as a "bridge". This research not only provides innovative explosive detection technologies, but also offers valuable design principles for multifunctional fluorescent sensors. The test strips and smartphone platform have preliminarily achieved on-site rapid qualitative and quantitative detection. And the LFPs imaging and detection in living cells further expand the application field, which has significant practical application value.