Bimetallic nanoparticles decorated hollow nanoporous carbon framework as nanozyme biosensor for highly sensitive electrochemical sensing of uric acid
Introduction
Uric acid (UA; 2,6,8-trihydroxypurine), as the ultimate metabolite of purine nucleotides, is released by the kidneys into human fluids (Jain et al., 2019). The regular window of UA in healthy human serum is generally 120–460 μM (Liu et al., 2017a). The excess value of UA is used as a momentous biomarker for many clinical diseases, such as uarthritis, nephrosis, and cardiovascular diseases (Shahamirifard et al., 2018). Recent research suggests that the below normal UA level is an important indicator of neuropapillitis, neurodegenerative diseases, sclerosis, and aplastic anemia (Lu et al., 2019; Nigam and Bush, 2019; Long et al., 2016), thus letting determination of the low UA concentrations in human fluids become a crucial challenge. Electrochemical biosensors have many characteristics, such as high accuracy, easy operation, miniaturized devices, which are regarded as the desired devices for UA monitoring (Sha et al., 2019). Nevertheless, the current electrochemical biosensors are insufficient for determination of UA at a low level. Hence, building an ultrasensitive electrochemical biosensor for UA monitoring is highly imperative.
Nanozymes, the nanomaterials with enzyme-mimetic activity, hold tremendous promise for a variety of applications, such as electrochemical sensors, catalysis, and energy conversion (Huang et al., 2019; Cai et al., 2019; Xu et al., 2018). As the substitutions to biological enzymes, nanozymes have inherent superiorities, such as high activity, strong stability (Wang et al., 2018a). Although the great breakthroughs by taking advantage of some nanozymes have been made in the fabrication of highly efficient electrochemical biosensors (Cai et al., 2019; Xu et al., 2018; Li et al., 2019; Tian et al., 2018), constructing more innovative nanozymes is highly desired. Currently, one of the prevalent problems in designing nanozymes is that the substrate can directly and casually diffuse into active sites, which leads to weak selectivity (Wu et al., 2019).
Nanozyme electrochemical biosensors need to have a highly conductive architecture with discriminative features (Maduraiveeran et al., 2018). Hence, a facile assembly of active sites and suitable architectures is a great challenge to be tackled. Metal-organic frameworks (MOFs) present ordered cavity, high metal ion contents, adjustable chemical properties, and are becoming the prospective precursors to construct porous metal-carbon hybrids (Hu et al., 2015).
For enzymatic electrochemical biosensors, the direct electron transfer (DET) between active sites of enzymes and electrode is mainly explored by adjusting the favorable enzyme orientation on electrically conductive vehicles (Lee et al., 2019; Nguyen et al., 2019). However, enzymatic electrochemical biosensors still have major limitations, such as high cost, poor stability. In this study, we explore the use of ultrafine gold/cobalt (Au/Co) nanoparticles (NPs) decorated hollow nanoporous carbon framework (Au/Co@HNCF) as a nanozyme to fabricate UA electrochemical biosensor. The Au/Co@HNCF is constructed by pyrolysis of the Au (III)-etching zeolitic imidazolate framework-67 (ZIF-67). Considering that recent studies reveal a low UA concentration is interrelated with more variety of diseases, it is vital to build a highly selective UA electrochemical biosensor that has a lower detection limit.
Section snippets
Reagents
Cobalt (II) nitrate hexahydrate, 2-methylimidazole (2-MeIm), uric acid (UA), L-serine (Ser), L-asparagine (Asp), ascorbic acid (AA), urea, glycine (Gly), L-histidine (His), glucose (Glu), dopamine (DA), N-methylpyrrolidinone (NMP), and polyvinylidene fluoride (PVDF) were purchased from J&K Chemical Reagent Company (Beijing, China). HAuCl4 solution (23.5–23.8 wt% Au) was obtained from Aladdin (Shanghai, China).
Synthesis of Au (III)-etching ZIF-67
The synthesis routes of ZIF-67 are presented in the supplementary materials.
Synthesis routes
The two-step synthesis routes for Au/Co@HNCF are presented in Fig. S1. In the first step, the Au (III) ions act as more powerful electron acceptors, thereby producing stronger coordination interactions with 2-MeIm. The etching processes proceed on the surfaces of ZIF-67 tendentiously. Thus, the core-shell architectures are acquired. In the second step, the Au (III)-etching ZIF-67 precursor is pyrolyzed into Au/Co@HNCF. The organic ligand (2-MeIm) acts as the reducing agent and carbon source
Conclusions
In summary, the unique Au/Co@HNCF as a nanozyme has been effectively constructed by pyrolysis of the Au (III)-etching ZIF-67. Benefiting from highly active Au/Co NPs, abundant catalytic sites, and hierarchically ordered porous carbon of Au/Co@HNCF, the fabricated nanozyme electrochemical biosensor for UA determination displays ultrahigh sensitivity and prominent selectivity. Moreover, the Au/Co@HNCF biosensor exhibits a very low detection limit (0.023 μM), which thus could be employed to delve
CRediT authorship contribution statement
Kaidong Wang: Methodology, Conceptualization, Software, Visualization, Validation, Writing - original draft, Writing - review & editing. Can Wu: Methodology, Formal analysis, Writing - review & editing. Feng Wang: Formal analysis, Writing - review & editing. Minghao Liao: Investigation, Formal analysis. Guoqiang Jiang: Supervision, Formal analysis, Writing - review & editing, Funding acquisition, Project administration.
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.
Acknowledgements
This work was supported by the National Natural Science Foundation of China [grant numbers 21576148, 21520102008]. The authors are grateful for the supports from Dr. Qiang Shu in the Department of Rheumatology at Qi Lu Hospital of Shangdong University in China.
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