Cysteine optical sensing with an up-conversion host and two chemosensors derived from rhodamine: Construction,...

This paper focused on two rhodamine chemosensors for cysteine optical sensing. To minimize their photobleaching caused by excitation light, up-conversion NaYF₄:Yb³⁺/Er³⁺ nanocrystals were prepared and used as excitation host. Photophysical measurement on this host and the two chemosensors suggested that chemosensor absorption matched well with host emission. An efficient energy transfer between them was discussed and confirmed by their spectral analysis and emission lifetime comparison. Job's plot suggested that our chemosensors followed a simple recognition mechanism towards cysteine with binding stoichiometry of 1:1. Both chemosensors showed emission "off-on" effect triggered by cysteine and good photostability. Linear working curves with maximum sensitivity of 2.61 were obtained. S substituent was positive to improve selectivity.