Carbon dots doped lanthanide coordination polymers as dual-function fluorescent probe for ratio sensing Fe2+/3+ and ascorbic acid

•A new dual-function fluorescent probe was designed for simultaneous ratio-metric detection of Fe2+ and Fe3+.•The fluorescent owing to two probes could switch on effectively upon excitation at a single wavelength.•The composite probe could also be applied in ratio-metric detection of AA in the presence of Fe3+.•The fluorescent probe could allow for multi-analyte ratio-metric assay in one system. A novel kind of carbon dots (CDs) doped lanthanide coordination polymers (LnCPs) was designed for fluorescence ratio-metric measurements of Fe2+ and Fe3+. Herein, blue-light emitting CDs, as the Fe3+-sensitive probe, were incorporated into the Fe2+-sensitive LnCPs through the self-adaptive ability. The obtained composite probe can be efficiently excited at a single wavelength and shows good separate emission peaks. Upon exposure to Fe2+ or Fe3+, the fluorescence of corresponding sensitive probe was quenched, while that of another probe maintained constant serving as an inert reference, allowing for the intensity-based ratio-metric assay for Fe2+ and Fe3+, respectively. Furthermore, by virtue of the reduction capability of ascorbic acid (AA), which can reduce Fe3+ to Fe2+, this composite probe enabled ratio-metric determination of AA as well. The rational design strategy for multi-analyte assay, and the facile preparation and operation make it possible for simultaneous monitoring two or more relevant analytes in one system.