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

Ratiometric chemosensor (UCNP@PAA-RBD-Sn²⁺) for FRET based S²⁻ ions sensing following NIR light irradiation. This sensor and technique provides high selectivity and ultra-sensitivity towards the S²⁻ ions, with a limit of detection (LOD) of 0.03 μM, which is far lower than WHO allowed contamination limit and previously reported probes for the same.

Abstract

In this article, a NIR-excited ratiometric method for selective and ultrasensitive detection of sulfide (S²⁻) 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-Sn²⁺). Under the excitation of NIR light, the green emission of UCNP (at 542 nm) is reabsorbed by the linked RBD-Sn²⁺ complex via FRET, which in turn emits in the orange (at 582 nm). S²⁻ ions specifically interact with the linked RBD-Sn²⁺ 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 S²⁻ ions in aqueous phase using this NIR-excited FRET-based approach. The concentration of S²⁻ ions is quantitatively connected to the ratiometric emission signal under NIR excitation. We have found that the detection limit for S²⁻ 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 S²⁻ in complex environmental and biological samples.

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