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

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.