A simple "turn-on" fluorescent probe capable of recognition cysteine with rapid response and high sensing in living cells and zebrafish

The first ER-targeting flavone-based fluorescent probe for Cys: Applications in real-time tracking in an epilepsy model and food analysis

Epilepsy is one of the most commonly-seen neurological disorders, and both endoplasmic reticulum stress (ERS) and oxidative stress (OS) have been demonstrated to be associated with epileptic seizures. As one of the three endogenous thiol-containing amino acids, cysteine (Cys) is recognized not only as an important biomarker of various biological processes but also widely used as a significant additive in the food industry. However, the exact role that Cys plays in ERS has not been well answered up to now. In this paper, we reported the first flavone-based fluorescent probe (namely BFC) with nice endoplasmic reticulum (ER)-targeting ability, which was capable of monitoring Cys in a fast response (3.0 min), large stokes shift (130 nm) and low detection limit (10.4 nM). The recognition mechanism of Cys could be attributed to the addition-cyclization reaction involving a Cys residue and an acrylate group, resulting in the release of the strong excited-state intramolecular proton transfer (ESIPT) emission molecule of benzoflavonol (BF). The low cytotoxicity and good biocompatibility of the probe BFC allowed for monitoring the fluctuation of endogenous Cys levels under both ERS and OS processes, as well as in zebrafish models of epilepsy. Quantitative determination of Cys with the probe BFC was also achieved in three different food samples. Additionally, a probe-immersed test strips integrated with a smartphone device was successfully constructed for on-site colorimetric detection of Cys. Undoubtedly, our work provided a valuable tool for tracking Cys levels in both an epilepsy model and real food samples.

A highly chromogenic selective Rhodamine-chloride-based fluorescence probe activated by cysteine and application in living cells and zebrafish

Cysteine (Cys), one of the biological thiols, which plays critical roles in biological system regulating the balance of redox homeostasis. In order to monitor the level of Cys in the living cells and organisms, a chromogenic fluorescence probe Rhocl-Cys based on Rhodamine chloride exhibiting the preferable performance of fluorescence turn-on response reacting with Cys was presented. Rhocl-Cys responded rapidly to Cys within 20 min, and had stable fluorescence intensity within pH 6.0-10.0, high selectivity towards Cys and the anti-inference capability with a low detection limit of 0.80 μM. In particular, Rhocl-Cys could qualitatively and quantitatively monitor the level of endogenous and exogenous Cys in living cells and successfully apply to zebrafish detecting Cys. Therefore, these results might further provide the basis exploring the role of Cys in biological system and facilitate as clinical diagnostic molecular tools.