Highly Selective and Sensitive Ratiometric Detection of Sn(2+) Ions Using NIR-Excited Rhodamine-B-Linked Upconversion Nanophosphors

[Image: see text] Detection of Sn(2+) ions in environmental and biological samples is essential owing to the toxicological risk posed by excess use tin worldwide. Herein, we have designed a nanoprobe involving upconversion nanophosphors linked with a rhodamine-based fluorophore, which is selectively sensitive to the presence of Sn(2+) ions. Upon excitation with near-infrared (NIR) light, the green emission of the nanophosphor is reabsorbed by the fluorophore with an efficiency that varies directly with the concentration of the Sn(2+) ions. We have explored this NIR-excited fluorescence resonance energy transfer (FRET) process for the quantitative and ratiometric detection of Sn(2+) ions in an aqueous phase. We have observed an excellent linear correlation between the ratiometric emission signal variation and the Sn(2+) ion concentration in the lower micromolar range. The detection limit of Sn(2+) ions observed using our FRET-based nanoprobe is about 10 times lower than that observed using other colorimetric or fluorescence-based techniques. Due to the minimal autofluorescence and great penetration depth of NIR light, this method is ideally suited for the selective and ultrasensitive detection of Sn(2+) ions in complex biological or environmental samples.