A new phenothiazine-based sensor for highly selective, ultrafast, ratiometric fluorescence and colorimetric sensing of Hg2+: Applications to bioimaging in living cells and test strips

[Display omitted] •Novel phenothiazine-based colorimetric and ratiometric fluorescent sensor PPM for Hg2+ is synthesized.•PPM shows high selectivity and low detection limit of 12.5 nM in a wide pH range.•The response time of PPM for Hg2+ is within 1 min and suitable for ultrafast detection of Hg2+.•PPM for Hg2+ shows good applicability for paper/TLC-based “naked-eye” colorimetric assay.•PPM was used for fluorescence imaging of Hg2+ in living cells. A new phenothiazine-based sensor PPM was successfully designed and synthesized, which shows highly selective, ultrafast, naked-eye colorimetric and turn-on ratiometric fluorescence sensing of Hg2+ on the basis of the ICT from phenothiazine to aldehyde. Upon addition of Hg2+, obvious blue fluorescence at 455 nm decreased while green fluorescence at 528 nm enhanced, which exhibits ratiometric fluorescent turn-on response along with a “naked-eye” color change from pale-blue to bright-green. The PPM for highly sensing of Hg2+ with a quite low detection limit (12.5 nM) and a wide pH application range. The sensing mechanism proved to be the Hg2+-triggered thioacetal deprotection reaction was confirmed. Importantly, PPM was successfully employed for highly selective detecting and imaging of Hg2+ in living cells, as well as on paper/TLC-based “naked-eye” colorimetric assay.