Elsevier

Sensors and Actuators B: Chemical

Volume 284, 1 April 2019, Pages 354-361
Sensors and Actuators B: Chemical

ZnO/porous carbon composite from a mixed-ligand MOF for ultrasensitive electrochemical immunosensing of C-reactive protein

https://doi.org/10.1016/j.snb.2018.12.150Get rights and content

Highlights

  • A novel lable-free CRP immunosensor based on the ZnO/MPC composite was fabricated.

  • ZnO/MPC obtained by pyrolysis of mixed-ligand MOF was highly efficient as supports for CRP immunosensor.

  • The developed immunosensor was simple, highly sensitive and specificity.

  • The immunosensor was used to detect CRP in human serum sample.

Abstract

Carbon-based nano-composite materials obtained via simple thermolysis of metal-organic framework (MOF) have competitive virtues in accordance of layered porosity, controllable morphologies, and easily functionalizing with other metal/metallic oxides or hetero atoms. These make them directly as high activity catalysts or supports for various electrochemical sensor. Herein, we developed a novel ZnO/porous carbon matrix (ZnO/MPC)-based electrochemical immunosensing through thermolysis of a mixed-ligand MOF (Zn-BDC-TED) for real sample analysis of C-reactive protein. The ZnO/MPC and ionic liquid (IL) composite membrane modified electrode displayed prominent conductivity and biocompatibility for ultrasensitive detection of C-reactive protein (CRP). Subsequently, the step-by-step assembly process of the CRP immunosensor was monitored by electrochemical measurements including cyclic voltammogram (CV) and electrochemical impedance spectra (EIS). After the parameter optimization, the differential pulse voltammetry (DPV) response decreased linearly with the logarithm of CRP levels in an extensive range of 0.01–1000 ng·mL−1, and the detection limit was as low as 5.0 pg·mL−1. Meanwhile, the lable-free immunosensor also showed excellent selectivity, reproducibility and stability. We believe that ZnO/MPC composite and many carbon-based nano-composite materials obtained via simple thermolysis of MOF will be a prospective platform for sensitive detecting other biomarkers.

Introduction

C-reactive protein (CRP, ˜120 kDa) is a cytokine-induced “acute-phase” protein. Additionally, high level of CRP in serum would be related to many diseases risk, such as inflammatory and cardiovascular diseases [1,2]. In clinical diagnosis, it is often served as an early indicator of inflammation and infection [3]. Hence, it’s indispensable to exploit a precise and reliable method for monitoring CRP in pharmaceutical research and clinical diagnosis. Multifarious techniques for testing CRP have been exploited during the past few years, including surface plasmon resonance [4], fluorescence [5], piezoelectric [6], and electrochemical techniques [[7], [8], [9]]. Among these techniques, electrochemical immunoassay has received much attention in virtue of its flexibility, easy miniaturization, high sensitivity, low-cost and user-friendliness [10]. Yagati et al. [11] used reduced graphene oxide-nanoparticle (rGO-AuNP) hybrid to construct a label-free CRP immunosensor, and the limit of detection was 0.06 ng·mL−1 ranged from 1 to 1000 ng·mL−1. In addition, Wang et al. [1] designed an electrochemical aptasensor based on RNA aptamer for CRP detection employing functionalized silica microballoon as immunity assay probe, which is possessed of high sensitivity. Nevertheless, most aptamers-based electrochemical biosensors usually suffered from sophisticated steps and time-consuming. Though it is easy to operate for label-free CRP immunosensors, the sensitivity, detection limit, selectivity and stability for specific recognition of traditional antibody-antigen still need to be improved.

For the sake of constructing an excellent label-free immunosensor, it is significant that the activity of biomolecules immobilized onto the electrode surface should be maintained without affected [12]. Therefore, the design and preparation of the ideal electrode modified materials that can immobilize antibodies effectively and sufficiently for electrochemical immunosensors became the key to this work. The advanced sensing properties of nanostructures ZnO like nontoxicity, high surface-to-bulk ratio, excellent biocompatibility, chemical stability and electrochemical activities have triggered a vast interest among the investigators to develop the applications especially in electrochemical sensors [13,14]. Apart from these, ZnO can be electrostatically bonded to low isoelectric point enzymes or proteins and served as a potential biosensor electrode because of it’s high isoelectric point of about 9.5 [14,15]. Recently, ZnO has been used as immobilizing matrix to fabricate various biosensors such as glucose, cholesterol and various antigen [[16], [17], [18]]. Nevertheless, the semiconducting properties of ZnO restrict its further advancement in the field of electrochemical immunosensor due to its constrained charge transfer feature. Fortunately, this weakness can be overcome by making hybrid composite. Noble metals (Au, Ag, Pt, Pd) and various carbon materials were usually used to improve sensitivities in sensing fields.

There is no doubt that carbon materials became a good choice due to its competitive price. Porous carbon nanomaterials have attracted considerable attention among all extant carbon materials for constructing electrochemical biosensors because of their special features such as good conductivity, large accessible surface area, tunable pore structure, chemical stability and wide electrochemical stability window [19], which can make up for the disadvantages of ZnO. What especially attractive is that carbon-based nano-composite materials obtained through simple thermolysis of metal-organic framework (MOF) have competitive virtues in accordance of layered porosity, controllable morphologies, and easily functionalizing with other metal/metallic oxides or hetero atoms, making them directly as high activity catalysts or supports for various electrochemical sensor. Until now, a large number of carbon-based nanomaterials from MOF have been synthesized, but these materials for electrochemical immunosensor have not received sufficient attention [20,21].

Based on the above, using simple thermolysis of a mixed-ligand MOF (Zn-BDC-TED) method, we prepared hybrid composite ZnO/porous carbon matrix (ZnO/MPC) whose two or more elements strengthen the individual of each material as a result of their cooperative effects and distinct chemical and physical natures for various applications [22]. Moreover, a novel lable-free CRP electrochemical immunosensor was constructed using ZnO/MPC/IL composite film as an efficient immobilization matrix. The process and performance of this CRP immunosensor were studied by a variety of electrochemical technologies. The large surface area and excellent electrical conductivity of ZnO/MPC make it a prominent carrier to capture more anti-CRP.

Section snippets

Experimental section

The chemicals, apparatus, and electrochemical measurements are described in the Supplementary Material.

Characterization of ZnO/MPC

The SEM images were obtained to characterize the morphologies of Zn-BDC-TED and its derivative ZnO/MPC composite. As shown in Fig. 1A and its magnification diagram Fig. 1A', Zn-BDC-TED presents a cube-like block structure, and was surrounded by a large number of nanosheets with different scale and thickness. After the calcination of Zn-BDC-TED, the surface morphology was changed (Fig. 1B) due to the formation of ZnO/MPC, which was composed of smaller irregular particles. Furthermore, its higher

Conclusions

In a word, we recommended a novel lable-free electrochemical immune sensor based on the ZnO/MPC composite prepared by pyrolysis of mixed-ligand MOF, obtaining an improved performance. Furthermore, the immunosensor realized the ultrasensitive detection of CRP with an extensive range (0.01–1000 ng·mL−1) and the detection limit was low to 5.0 pg·mL−1. The excellent performance of the immunosensor may be ascribed to the superior conductivity, a biocompatible microenvironment for the biomolecules

Acknowledgments

The authors appreciate the support from the National Natural Science Foundation of China (No. 21575111), Natural Science Foundation of Shaanxi Province (2017JM2038).

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