Citation: Zhang, J.; Jing, Y.; Zhang, P.;
Xu, B. Fluorescent Oxygen-Doped
g-C
3
N
4
Quantum Dots for Selective
Detection Fe
3+
Ions in Cell Imaging.
Nanomaterials 2022, 12, 1826. https://
doi.org/10.3390/nano12111826
Academic Editors: Deepak Kukkar
and Ki-Hyun Kim
Received: 25 April 2022
Accepted: 24 May 2022
Published: 26 May 2022
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Article
Fluorescent Oxygen-Doped g-C
3
N
4
Quantum Dots for Selective
Detection Fe
3+
Ions in Cell Imaging
Jiahui Zhang
1,†
, Yan Jing
2,†
, Peng Zhang
1,
* and Benhua Xu
2
1
Qinghai Provincial Key Laboratory of New Light Alloys, Qinghai Provincial Engineering Research Center of
High-Performance Light Metal Alloys and Forming, Qinghai University, Xining 810016, China;
z276475670@126.com
2
Chemical Engineering College, Qinghai University, Xining 810016, China; jingyan@163.com (Y.J.);
xubenhua@qhu.edu.cn (B.X.)
* Correspondence: zhangpeng@qhu.edu.cn or zhangp_13@163.com
† These authors contributed equally to this work.
Abstract:
Herein, oxygen-doped g-C
3
N
4
quantum dots (OCNQDs) were fabricated through sintering
and ultrasonic-assisted liquid-phase exfoliation methods. The obtained OCNQDs with uniform
size show high crystalline quality, and the average diameter is 6.7
±
0.5 nm. Furthermore, the
OCNQDs display excellent fluorescence properties, good water solubility, and excellent photo
stability. The OCNQDs as fluorescence probe show high sensitivity and selectivity to Fe
3+
ions.
Furthermore, the fluorescent OCNQDs are applied for live cell imaging and Fe
3+
ions detecting
in living cells with low cytotoxicity, good biocompatibility, and high permeability. Overall, the
fluorescent OCNQDs fabricated in this work can be promising candidates for a range of chemical
sensors and bioimaging applications.
Keywords: oxygen-doped g-C
3
N
4
quantum dots; fluorescence; metal ion detection; bioimaging
1. Introduction
Fe
3+
is one of the most fundamental trace metal cations in the human body, which
exhibits many critical physiological functions such as electron transfer, metabolic reactions,
and neuroregulation [
1
,
2
]. However, abnormal levels of Fe
3+
in the body can destroy
the physiological functions of organisms, which can cause several of diseases involving
anemia, insomnia, and some iron metabolism disorder diseases [
3
,
4
]. Therefore, developing
economical and accurate methods to detect Fe
3+
in various liquid samples, as well as in
living cells is necessary. To date, due to the disadvantages such as complexity, time-
consuming, valuableness, and tedious preparation, the traditional analytical approaches
are limited to detect metal ions economically and effectively in aqueous solution and living
cells [
5
–
8
]. Therefore, the fluorescent probe has caught widespread attention as a simple,
low-cost, and nontoxic sensing platform [
9
–
12
]. Among them, metal-free quantum dot-
based fluorescent nanoprobes are appropriate for biosensing and bioimaging due to the
merits of low toxicity and no secondary contamination during applications.
g-C
3
N
4
quantum dots (gCNQDs) are the typical representative of metal-free quantum
dots and have demonstrated advantages of fascinating optical properties, good biosafety,
good water solubility, and easy functionalization, which enable gCNQDs unprecedented
opportunities as fluorescent probe for metal ions detecting and bioimaging [
13
–
15
]. To
date, the gCNQDs obtained by sonicating 2D g-C
3
N
4
(gCN) nanosheets and 1D gCN
nanowires have been developed to detect Cu
2+
and Fe
3+
[
16
,
17
]. In order to further expand
the fluorescence performance of gCN, the amount of functionalization strategies involving
doping and surface functionalization have been exploited. For example, gCN can be
modified with organic ligands, micromolecules, organic dyes [
18
–
20
], and carboxyl [
21
].
gCN can be doped with nonmetal and metal elements [
22
]. Hence, gCNQDs could be
Nanomaterials 2022, 12, 1826. https://doi.org/10.3390/nano12111826 https://www.mdpi.com/journal/nanomaterials
