Carbon Dots/α-Fe2O3-Fe3O4 nanocomposite: Efficient synthesis and application as a novel electrochemical aptasensor for the ultrasensitive determination of aflatoxin B1
Introduction
Acting as a group of food fungal mycotoxins, aflatoxins (AFs) are secondary metabolites of Aspergillus flavus and Aspergillus parasiticus (He, Sun, Pu, & Huang, 2020). The AFs mainly comprise of aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin M1 (AFM1), aflatoxin G1 (AFG1), and aflatoxin G2 (AFG2), et al. Among them, the AFB1 is the most poisonous, which is deemed as a group I carcinogen by the International Agency for Research on Cancer (Rushing & Selim, 2019). As known, AFB1 is commonly present in some agricultural products such as rice, corn, peanuts, wheat, and so on. Accordingly, the maximum contamination level of AFB1 in foodstuffs has been stipulated by many countries. The tolerable limit of AFB1 is set as 20 ng/mL in China and the United States, 2 μg/kg in the European Union, and 5 μg/kg in Korea, respectively (Rushing and Selim, 2019, Tan et al., 2019). Thus, the valid determination of AFB1 is highly desired. Till now, many analytical methods have been applied to measure AFB1, including enzyme-linked immunosorbent assay (ELISA) (Zhan, Hu, Li, Huang, & Xiong, 2020), high-performance liquid chromatography (HPLC) (Geng, Wang, Gao, Ning, & Guan, 2018), surfaces enhanced Raman scattering (Li et al., 2020), fluorescence method (Tan et al., 2019), and so on. Nevertheless, the above methods display several disadvantages including process-complicated, time-consuming, labor-intensive, instruments-expensive, or poor sensitivity. Therefore, the design of a fast, sensitive, and economic method for the detection of AFB1 has become a research hotspot. Recently, the electrochemical sensor has attracted significant attention due to its high sensitivity, easily operation, and speediness (Beheshti-Marnani et al., 2019, Cui et al., 2020, Goud et al., 2017, Krittayavathananon and Sawangphruk, 2017, Li et al., 2020, Qian et al., 2014, Xiong et al., 2020, Xu et al., 2018, Zhang et al., 2019). It is well known that electrode-modified materials have a certain relationship with the performance of electrochemical sensors. At present, many electrode-modified materials have been applied to construct electrochemical sensors for measuring AFB1, such as Thionine-reduced graphene oxide/Au nanoparticle (THI-rGO-Au) (Li et al., 2020), electrochemical rGO/poly(5-formylindole)/Au nanoparticle (ErGO/P5FIn/Au) (Zhang et al., 2019), graphene oxide/hexamethylenediamine (GO/HMDA) (Goud et al., 2017), reduced graphene oxide (rGO) (Beheshti-Marnani et al., 2019, Krittayavathananon and Sawangphruk, 2017), GO/poly(4-vinyl pyridine) (GO/P4VP) (Cui et al., 2020), DNA tetrahedron-structured probe/HRP/polyaniline (DTP/HRP/PANI) (Xiong et al., 2020), and so on. Most of the above materials have made a lot of contributions to measure AFB1, however, the above materials were either unstable or uneconomical to synthesize.
As a member of “zero-dimensional” carbon nanomaterials, carbon dots (CDs) have excellent luminescence performance, good stability, easy preparation, non-toxicity, and so on. They have been widely applied in biosensors, cell imaging, photocatalysis, and other fields (Li et al., 2021, Lin et al., 2021, Xu and Liu, 2021). Compared with other electrode-modified materials, CDs have the advantages of better biocompatibility, low cytotoxicity, and extraordinary electrical conductivity. Therefore, CDs have been regarded as good electrode-modified material in electrochemical biosensors. For example, we prepared Pd-Au@CDs nanocomposite for the preparation of the novel electrochemical DNA biosensor (Huang, Lin, Zhu, & Tong, 2017). Divya et al. used CDs-AgNPs to construct an electrochemical DNA biosensor with high sensitivity (Divya et al., 2019). Aftab et al. constructed an electrochemical detector of anti-HIV drug rilpivirine based on CDs co-catalyzed with MWCNTs and Ag nanoparticles (Aftab, Kurbanoglu, Ozcelikay, Bakirhan, Shah, & Ozkan, 2019).
Recently, magnetic nanoparticles have been widely used in biological fields such as magnetic resonance imaging, drug loading, and biosensors due to their advantages of easy recovery, low pollution, economy, environmental protection, and high electrocatalytic activity (Jiang et al., 2018, Kuang et al., 2020, Poo-arporn et al., 2019). They were also applied in electrochemical sensors, for example, Jiang et al. designed an enzyme-free homogeneous electrochemical DNA sensor based on Fe3O4@SiO2@β-cyclodextrin nanocomposite (Jiang et al., 2018). Poo-arporn et al. combined magnetic nanoparticles Fe3O4 with graphene to obtain magnetic nanoparticles with good electrochemical properties, which realized the determination of ractopamine in pork samples (Poo-arporn et al., 2019).
In this work, CDs were prepared by high-temperature carbonization with 5-sulfosalicylic acid and diethylene glycol as precursors. Then the as-prepared CDs were used as a surface modifier and reducing agent to synthesize the mixed crystalline magnetic of CDs/α-Fe2O3-Fe3O4 nanocomposite through the hydrothermal method (Scheme 1A). The CDs/α-Fe2O3-Fe3O4 nanocomposite has both excellent properties of CDs and α-Fe2O3-Fe3O4, which could be used as a good electrode-modified material to develop a novel electrochemical aptasensor. The surface of CDs is rich in hydroxyl and carboxyl functional groups, which facilitate the interaction with the amino groups of probe DNA (S1), providing a basic platform for the construction of a new type of aptasensor. In addition, The α-Fe2O3-Fe3O4 can not only improve the catalytic performance of the sensor but also have magnetism, which can realize the recovery of materials to avoid material waste and environmental pollution. Therefore, we prepared an electrochemical aptasensor based on S1/CDs/α-Fe2O3-Fe3O4 for the determination of AFB1 (Scheme 1B). The electrochemical aptasensor demonstrated ultrahigh sensitivity, excellent specificity, and an ultrawide linear range. Simultaneously, the electrochemical aptasensor was also used successfully to determine AFB1 in beer, rice, and peanuts indicating its broad application prospect.
Section snippets
Materials and reagents
1-ethyl-3-(3′-dimethylaminopropyl)carbodiimide (EDC), Tris-HCl, Ethylene Diamine Tetraacetic Acid (EDTA), 5-sulfosalicylic acid, diethylene glycol, and sodium acetate were obtained from Macklin Biochemical Co.; Ltd. AFB1, AFB2, AFM1, AFG1, AFG2, Methylene blue (MB), and N-hydroxysuccinimide (NHS) were obtained from sigma Sigma Aldrich. Probe DNA sequence (S1) (Goud et al., 2016): 5′-NH2-(CH2)6-TGG GGT TTT GGT GGC GGG TGG TGT ACG GGC GAG GG-3′ was purchased from Shenggong Bioengineering Co.; Ltd.
Characterization of CDs
As shown in Fig. S1A, TEM characterized the CDs’ morphology, the sizes of the synthesized CDs are relatively uniform with a diameter of 1–5 nm. Fig. S1B shows the CDs’ fluorescence spectra, the absorption spectrum of CDs has a strong and narrow peak at 350 nm and an emission peak at 460 nm. These fluorescent characteristics of CDs are consistent with previous reports (Luo et al., 2018).
Characterization of CDs/α-Fe2O3-Fe3O4
Figure 1A and 1B show the SEM and TEM images of CDs/α-Fe2O3-Fe3O4 nanocomposite, respectively. The CDs/α-Fe2O3
Conclusions
In this work, the CDs/α-Fe2O3-Fe3O4 nanocomposite was prepared by a simple, green hydrothermal method. CDs/α-Fe2O3-Fe3O4 nanocomposite was modified on the GCE to construct a new electrochemical aptasensor for the determination of AFB1 with ultrahigh sensitivity (0.5 pM), good stability, excellent specificity, and ultrawide linear range. What’s more, the electrochemical aptasensor was also applied successfully to determine AFB1 in Beer, Rice, and Peanuts, indicating the electrochemical
CRediT authorship contribution statement
Qitong Huang: Conceptualization, Data curation, Writing – original draft, Funding acquisition. Xiaofeng Lin: Data collection, Validation. Dejian Chen: Data collection. Qing-Xiao Tong: Conceptualization, Writing – review & editing, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by the National Natural Science Foundation of China (Nos. 82060599, 51973107, and 51673113), the Natural Science Foundation of Jiangxi Province (No. 20202BABL213018), the Science and Technology Project of Jiangxi Health Committee (No. 202131033), the Science and Technology Project of the Education Department of Jiangxi Province (No. GJJ190795), the Research Fund of Gannan Medical University (ZD201901, YQ202003), the Key Project of GDUPS (2019) and the Key Project of
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