Dye‐linked Upconverting Nanophosphor‐based Ratiometric Chemosensor for NIR‐excited and FRET‐mediated Ultrasensitive Detection of Sulfide Ions

Abstract

In this article, a NIR-excited ratiometric method for selective and ultrasensitive detection of sulfide (S 2À ) ions in an aqueous environment is presented, which is reliant on fluorescence resonance energy transfer (FRET). The chemosensor-design is based on an upconverting nanophosphor (UCNP)-linked coloured complex between a rhodamine-B derivative and stannous ions (RBD-Sn 2 + ). Under the excitation of NIR light, the green emission of UCNP (at 542 nm) is reabsorbed by the linked RBD-Sn 2 + complex via FRET, which in turn emits in the orange (at 582 nm). S 2À ions specifically interact with the linked RBD-Sn 2 + complex and quantitatively bleach its colour, leading to reduction in FRET and consequent recovery of the green emission of UCNP. We investigated the quantitative and ratiometric detection of S 2À ions in aqueous phase using this NIR-excited FRET-based approach. The concentration of S 2À ions is quantitatively connected to the ratiometric emission signal under NIR excitation. We have found that the detection limit for S 2À ions using our FRET-based nanoprobe is around ten times lower than that of colorimetric or fluorescence-based approaches. Owing to the use of NIR-light as excitation source, our proposed sensor can demonstrate background-free sensing of S 2À in complex environmental and biological samples.