Detection of hazardous mercury ion using [5]helicene-based fluorescence probe with "TurnON" sensing response for practical applications

Highlights: • [5]Helicene-based probe can detect Hg²⁺with "Turn–ON" fluorescence response. • The DL for Hg²⁺ was 1.2 ppb and lower than MCL of Hg²⁺ by WHO and U.S. EPA. • The probe can detect Hg²⁺ in sea water, vegetable tissue and brain tumor cell. • The probe can apply into paper test strips for qualitative detection of Hg²⁺. • The probe recognized Hg²⁺ via the simple chemical reaction of desulfurization. A new fluorescence probe based on [5]helicene derivative (MT) was designed and synthesized. The chemical structure of the probe was fully characterized by NMR, mass spectrometry and X-ray crystallography. MT which is the combination of thioamide[5]helicene with Schiff base-thiophene moiety, exhibited a high selectivity to detect Hg²⁺ through irreversible desulfurization reaction with "TurnON" fluorescence response and large Stokes shift of 110 nm in aqueous methanol solution. The detection limit of MT was 1.2 ppb (6.0 × 10⁻³ µM), which is lower than the limit of Hg²⁺ level in drinking water, as specified by WHO (6.0 ppb) and U.S. EPA (2.0 ppb). The Hg²⁺ detection range of the probe was 0.07–1.6 µM with good linearity. Under UV irradiation, MT possessed the capability to detect Hg²⁺ in diverse context of real samples, including drinking and sea waters, vegetable tissue and brain tumor cell. In addition, MT could be used as a paper test strip for monitoring and screening of Hg²⁺ contamination in environment.