A specific fluorescent probe for fast detection and cellular imaging of cysteine based on a water-soluble conjugated polymer combined with copper(II)

Publication date: 1 June 2019

Source: Talanta, Volume 198

Author(s): Lihua Liu, Qiang Zhang, Jing Wang, Linlin Zhao, Lixia Liu, Yan Lu

Abstract

In pure water system, the specific and rapid detection of cysteine (Cys) is very important and challenging. Herein, a new optical probe was developed for the purpose based on the complex of cupric ion (Cu²⁺) with a water-soluble conjugated polymer, poly[3-(3-N,N-diacetateaminopropoxy)-4-methyl thiophene disodium salts] (PTCO₂). The fluorescence of PTCO₂ in 100% aqueous solution can almost completely extinguished by Cu²⁺ ions due to its intrinsic paramagnetic properties. Among various amino acids, only Cys causes immediately the efficient recovery of the Cu²⁺-quenched fluorescence of PTCO₂ with ~31-folds fluorescence enhancement because of the stronger affinity of Cys to Cu²⁺ leading to the formation of Cu²⁺-Cys complex through Cu-S bond and separation of Cu²⁺ from weak-fluorescent PTCO₂-Cu(II) ensemble and thereby restoring the free PTCO₂ fluorescence. In tris-HCl buffer solution (2 mM, pH 7.4), the intensity of the restored fluorescence is linear with the concentration of Cys, ranging from 0 to 120 μM and the estimated detection limit of Cys is 3.3 × 10⁻⁷ M with the correlation coefficient R = 0.9981. In addition, the PTCO₂-Cu(II) ensemble probe exhibits low cytotoxicity and good membrane penetration, and its application in living cell imaging of Cys has also been explored.

Graphical abstract

Specific and fast detection of cysteine (Cys) in pure water was achieved based on a new fluorescent probe PTCO₂-Cu(II) through replacement strategy. The probe also shows good pH-stability, membrane penetration and biocompatibility, and can be applied to cell imaging of Cys.

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