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

Detection of Sn 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 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 ions. We have explored this NIR-excited fluorescence resonance energy transfer (FRET) process for the quantitative and ratiometric detection of Sn ions in an aqueous phase. We have observed an excellent linear correlation between the ratiometric emission signal variation and the Sn ion concentration in the lower micromolar range. The detection limit of Sn 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 ions in complex biological or environmental samples.