Novel portable coumarin-derived fluorescent probe for highly rapid and selective Cu2+ detection: Versatile applications to environmental monitoring, plant, human serum, and in vivo bioimaging.

A highly rapid and sensitive novel coumarin-derived fluorescent chemosensor, PQTC, was developed and synthesized to selectively detect Cu2+. PQTC having intense yellowish-green fluorescence exhibited rapid response (less than 1 s) and high selectivity to Cu2+ via a fluorescence "turn-off". Limit of detection (LOD) for Cu2+ by PQTC was 0.39 μM, below the WHO guideline (31.5 μM). PQTC could effectively detect Cu2+ by fluorescence quenching in pH 6-10. The binding mechanism between PQTC and Cu2+ was proposed to form a tridentate complex by Job plot, 1H NMR titration, ESI-MS, and TD-DFT calculations. The practical utility of PQTC was evaluated in real environmental water (mineral, tap, sea, river water, and sewage). In addition, PQTC was effectively applied to a test strip and smartphone-based sensing platform for rapid, on-site quantitative monitoring of Cu2+. In particular, the test strip coated with PQTC could probe Cu2+ down to 20 μM, a very rare case among coumarin-based fluorescent probes. PQTC was also applied to detect Cu2+ in plant samples (Chinese cabbage and Enoki mushroom) as very rare examples. Notably, the biological applicability of PQTC was further extended to human serum analysis (LOD = 1.99 μM) and in vivo fluorescence imaging in Artemia and zebrafish, underscoring its broad applicability for both environmental and biological applications.