An optical sensing composite for cysteine detection using up-conversion nanoparticles and a rhodamine-derived chemosensor: Construction, characterization, photophysical feature and sensing performance

• Up-conversion nanocrystals were prepared and modified with α-cyclodextrin.
• These nanocrystals were used to excite a chemosensor for cysteine detection.
• A sensing system was constructed with these nanocrystals and this chemosensor.
• Emission “turn-on” effect was observed for cysteine with good selectivity.

In this paper, we reported an optical sensing composite for cysteine detection. A chemosensor derived from rhodamine 6G was synthesized and characterized. To minimize its photobleaching, up-conversion nanocrystals β-NaYF4:Yb3 +/Er3 + were prepared and modified with α-cyclodextrin, serving as excitation host. Under 980 nm laser excitation, emission of these up-conversion nanocrystals overlapped well with the absorption of our chemosensor. Energy transfer between them was analyzed and confirmed by emission decay analysis. Job's analysis suggested that the complexation equilibrium between our chemosensor and cysteine was a simple one with binding stoichiometry of 1:1. A sensing system was constructed with up-conversion nanocrystals (modified with α-cyclodextrin) and this chemosensor. Emission “turn-on” effect was observed only for cysteine but immune to other competing amino acids and thiols, showing a good selectivity.

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