[5]Helicene-rhodamine 6 G hybrid-based sensor for ultrasensitive Hg2+ detection and its biological applications

•New FRET sensor based on [5]helicene and modified rhodamine was prepared.•Sensor shows high sensitivity to Hg2+ with a low D.L. of 0.3 ppb which is lower than the limits of US.EPA and WHO.•Sensor binds to Hg2+, indicated by fluorescence enhancement and colorimetric change.•Sensor shows the intense fluorescence and very large pseudo-Stokes shift of 187 nm.•Sensor can be utilized in real samples, i.e. food, commercial products and biological cells. A novel chromogenic and fluorometric sensor based on [5]helicene-like-dye-bearing rhodamine 6 G thiohydrazide, i.e. NF09, was successfully designed and synthesized for the detection of Hg2+. NF09 exhibited ultrasensitive and highly selective recognition of Hg2+ on the basis of the fluorescence resonance energy transfer process from the [5]helicene-like donor to the rhodamine 6 G acceptor. The photophysical properties of the sensor illustrated the very large pseudo-Stokes shift of 187 nm. NF09 exhibited the effective determination of the trace levels of Hg2+, with a low detection limit of 0.3 ppb (1.5 nM), which was below the maximum Hg2+ concentration in drinking water specified by the United States Environmental Protection Agency. On the basis of the chromogenic change properties, NF09 can detect Hg2+ by naked-eye detection in real samples, such as skin-lightening cream, mussel, tuna fillet and salmon fillet. In addition, this sensor exhibited the efficient detection of Hg2+ in human cells and plant root tissues by fluorescence imaging. The successive detection and effective response of the sensor ensure that it can be utilized for the real-time monitoring and control of Hg2+ contamination outbreak.