![](https://csdnimg.cn/release/download_crawler_static/89108877/bg1.jpg)
Bioorganic Chemistry 126 (2022) 105902
Available online 24 May 2022
0045-2068/© 2022 Elsevier Inc. All rights reserved.
Highly selective uorescent probe based on AIE for identifying cysteine/
homocysteine
Wei Wang
a
, Zihao Peng
a
, Min Ji
b
, Junqing Chen
a
,
*
, Peng Wang
c
,
*
a
School of Chemistry and Chemical Engineering, Southeast University, Nanjing, Jiangsu 211189, PR China
b
School of Biological Science & Medical Engineering, Southeast University, Nanjing, Jiangsu 210096, PR China
c
School of Engineering, China Pharmaceutical University, Nanjing 210009, PR China
ARTICLE INFO
Keywords:
Fluorescent probe
Cysteine
Homocysteine
AIE
Fluorescence imaging
ABSTRACT
Cysteine (Cys) and homocysteine (Hcy) are involved in maintaining homeostasis in the body and are relevant to
various diseases. While the level of Cys and Hcy is much lower than GSH in the living system, which leads to a
major challenge to selectively identify Cys/Hcy in the presence of large amounts of GSH. In this paper, an AIE
uorescent probe SQM-NBD was obtained by connecting NBD to the hydroxyl group of the uorophore SQM-OH
for selective detection of Cys/Hcy. Probe SQM-NBD had no uorescence itself. But, under the disturbance of
GSH, the uorescence signal of probe SQM-NBD could be turned on by Cys/Hcy. The study of the response
mechanism showed that probe SQM-NBD could release both SQM-OH and Cys/Hcy-NBD after reacting with Cys/
Hcy. While Cys/Hcy continued to quench the uorescence of SQM-OH through the combination of Michael
addition and the ion rich environment, resulting in only the uorescence signal of Cys/Hcy-NBD being observed.
SQM-NBD appeared superior sensitivity to Cys/Hcy, with LOD of 54 nM and 72 nM, respectively. Signicantly,
probe SQM-NBD realized the application of uorescence imaging of Cys/Hcy in HeLa cells, indicating that probe
SQM-NBD has the potential for Cys/Hcy identication under physiological and pathological conditions.
1. Introduction
Biothiols such as cysteine (Cys), homocysteine (Hcy), and gluta-
thione (GSH) play important roles in maintaining the Redox and phys-
iological balance in the living system [1]. Among them, Cys is an
important antioxidant that can protect cells from oxidative damage. It
can coordinate with a variety of heavy metals to relieve heavy metal
poisoning [2–4]. Moreover, the loss of Cys can lead to many diseases
including slow growth, hair decoloration, muscle and fat loss, and skin
damage in children [5–7]. Hcy is involved in the DNA synthesis and
methylation in organisms and is also closely related to cardiovascular
diseases. Even slight uctuations in the Hcy level may contribute to the
development of cardiovascular diseases [8–10]. Due to the distinctive
physiological properties of Cys/Hcy, it is imperative to explore tech-
niques for Cys/Hcy detection. However, since the molecular structure
and properties of Cys/Hcy bear a strong resemblance to GSH, and the
content of Cys/Hcy is much lower than that of GSH, the detection of
Cys/Hcy is highly susceptible to the disturbance of GSH [11–13].
Therefore, the development of methods that can selectively detect Cys/
Hcy under GSH disturbance is a great challenge.
In recent years, organic small-molecule uorescent probes have been
widely used in the detection of Cys/Hcy with convenience and effec-
tiveness. Detection mechanisms include Michael addition [14], sulfon-
amide and sulfonate cleavage [15], disulde exchange [16], conjugated
addition cyclization [17], aldehydes cyclization [18], mercaptan
halogen nucleophilic substitution [19], and metal complex replacement
coordination [20]. However, the applications of most developed uo-
rescence probes in the aqueous environment are limited due to the
aggregation-induced quenching (ACQ) effect [21–23]. In contrast, the
AIE effect, rst reported by the Tang group, could effectively overcome
this shortcoming. Unlike ACQ uorophore, AIE uorophore shows
strong uorescence when molecules gather together [24–25]. In addi-
tion, AIE uorophore is characterized by low background noise, high
signal-to-noise ratio (SNR), high brightness, and good photostability,
which is conducive to uorescence imaging of Cys/Hcy in living cells
[26–29].
In this paper, probe SQM-NBD was produced using
ethylenethiophenol-modied quinoline-malononitrile SQM-OH as uo-
rophore and 7-nitro-2,1,3-benzoxadiazole (NBD) as recognition section.
The recognition group NBD has been widely used for the selective
* Corresponding authors.
E-mail addresses: jqchen@seu.edu.cn (J. Chen), wangpeng@cpu.edu.cn (P. Wang).
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
https://doi.org/10.1016/j.bioorg.2022.105902
Received 26 April 2022; Received in revised form 16 May 2022; Accepted 20 May 2022