Easy and Fast Detection of Hypochlorite by a Bithiophene-Based Fluorescent Turn-on Sensor and its Applications to Test Strips, Real Water Samples, and Smartphone-Assisted Platform

We report a bithiophene-based fluorescence probe BDT (2,2’-(((1 E, 1’E)-[2,2’-bithiophene]-5,5’-diylbis(methaneylylidene))bis(azaneylylidene))bis(4-(tert-butyl)phenol)) for recognizing ClO⁻. BDT selectively responded to ClO⁻, leading to a blue fluorescence enhancement in a mixture of DMF/HEPES buffer (9:1, v/v). Importantly, BDT showed an ultrafast response (within 1 s) to ClO⁻ among the fluorescent turn-on chemosensors based on bithiophene. BDT recognized ClO⁻ through cleavage reaction with a low detection limit of 2.16 µM, and it had the ability to sense ClO⁻ across a pH range of 3–11. The recognition mechanism for ClO⁻ was investigated by ¹H nuclear magnetic resonance (NMR) titration, electrospray ionization mass spectrometry (ESI-MS), and density functional theory (DFT) calculations. In addition, BDT could be used to detect ClO⁻ using test strips as a convenient tool, allowing real-time monitoring rapidly. Practically, BDT exhibited reliable recoveries for quantifying ClO⁻ using a smartphone application with a spike-and-recovery method in real water samples such as drinking, tap, mineral, and river water.