A naked-eye and ratiometric near-infrared probe for palladium via modulation of a π-conjugated system of cyanines.

A ratiometric and colorimetric cyanine-based palladium sensor with an excellent selectivity and sensitivity has been designed. Notably, the modulation of π-conjugated electrons in cyanine dyes can result in a ratiometric fluorescence change with a large Stokes shift (270 nm), especially for realizing palladium detection in aqueous samples using indicator paper and in living cells by ratiometric mode. The limit of detection is as low as 0.3 ppb.