Modification of anionic cyanine dyes and application in cysteine detection

Anionic cyanine is an organic fluorescent dye with excellent optical properties. Compared to cationic cyanine, anionic cyanine has been less studied and applied due to the lack of modification sites. However, when the cyclohexene ring in the anionic cyanine skeleton is replaced by a tetrahydropyridine ring, the modification site will be added, forming a novel cyanine dye AHC-N-R with NIR emission. Photophysical properties show that this anionic cyanine retains the excellent optical properties of conventional cyanine and is expected to adjust the fluorescence emission by changing the substituent groups. Acrylates were introduced in this dye to synthesize the cysteine fluorescent probe AHC-NBn-AE. The amino and sulfhydryl groups in cysteine condense with acrylate to form 1,4-thiazepane analogs and release fluorophores AHC-NBn-OH, restoring fluorescence at 650 nm. The fluorescence recovery of the probe was linearly related to the concentration of cysteine for 0.3–50.0 μmol/L. The detection limit was 0.1 μmol/L (S/N = 3, n = 9). There was almost no interference with DL-homocysteine, glutathione and several common amino acids to cysteine. The cysteine content of the L-cysteine capsule was successfully tested. The recovery rate was 94.4 %–101.5 %.