Portable cyanide monitoring using a benzothiazolium-based ratiometric fluorescent probe coupled with smartphone imaging, test strips, and living cell imaging

Real-time monitoring of highly toxic cyanide (CN^-) using low-cost and visually detectable fluorescent probes is essential for minimizing its environmental and biological hazards. Herein, a novel benzothiazolium-based donor-π-acceptor (D-π-A) fluorescent probe (MBT) was developed for the sensitive and selective detection of CN^-. MBT exhibited high sensitivity, rapid response (∼2.0 min), excellent selectivity, a low detection limit (0.162 μM), broad pH applicability, and strong anti-interference capability. Owing to these favorable sensing characteristics, MBT was successfully applied to the quantitative determination of CN^- in real water samples. Furthermore, the probe was readily integrated into TLC-based test strips, enabling rapid visual detection of CN^- through a distinct fluorescence color transition from red to cyan under 365 nm UV irradiation. In addition, MBT was successfully employed for fluorescence imaging of intracellular CN^- in HeLa cells, demonstrating good biocompatibility and bioimaging capability. The combination of excellent analytical performance, portable visual detection, and cellular imaging highlights the potential of MBT as a practical sensing platform for environmental monitoring and biological applications.