Elsevier

Sensors and Actuators B: Chemical

Volume 220, 1 December 2015, Pages 1186-1195
Sensors and Actuators B: Chemical

Graphene nanodots encaged 3-D gold substrate as enzyme loading platform for the fabrication of high performance biosensors

https://doi.org/10.1016/j.snb.2015.06.044Get rights and content

Abstract

Herein, a uniform three-dimensional (3-D) graphene nanodots-encaged porous gold electrode was prepared via ion beam sputtering deposition (IBSD) and mild corrosion chemistry for efficient enzyme electrode fabrication. Enzymes, like glucose oxidase and catalase, were modified with pyrene functionalities and then loaded into the graphene nanodots encaged porous gold electrode via non-covalent π–π stacking interaction between pyrene and graphene. The fabricated enzyme electrodes showed profound reusability and repeatability, high sensitivity, inherent selectivity and enhanced detection range. As for glucose analysis a broad linear range from 0.05 to 100 mM was obtained and the linear range for hydrogen peroxide was 0.005 to 4 mM. Detection limits of 30 μM for glucose and 1 μM for hydrogen peroxide were achieved (S/N = 3), respectively. These electrodes can be applied to analyze the clinical samples with reliable results. The formation mechanism and 3-D structure of the porous electrode were investigated using high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). Most importantly, various other ideal biosensors can be fabricated using the same porous electrode and the same enzyme modification methodology.

Introduction

Due to their high sensitivity, inherent selectivity and easier instrumentation, enzyme electrodes have been used in many fields such as enzymatic biofuel cells [1], medical and food analysis [2], environment pollution monitoring [3] and clinical detection [4]. The support materials for enzymes immobilisation are very versatile, including conductive and non-conductive polymers, different types of gels, and various nanomaterial composites [5], [6], [7], [8]. However, the application and development of high-efficiency enzyme electrodes are still limited by the lacking of simple and stable enzyme immobilization platform [9] and the slow charge transport between the enzyme redox center and the electrode [10]. Electrocatalytic porous substrate incorporated with highly conductive material is usually an effective idea to solve the problems [11], [12].

As a true 2-dimensional carbon material with unique physicochemical properties (high surface area, good biocompatibility, strong mechanical strength, excellent thermal conductivity and fast electron transportation) [13], [14], graphene based materials have attracted a great deal of interest in the development of new chemical and biological sensors such as graphene-based gold composite modified electrode [14], glucose oxidase–graphene–chitosan nanocomposite film [15], platinum nanoparticle ensemble-on-graphene hybrid nanosheet modified electrode [16], graphene/Au nanoparticles/chitosan nanocomposites film [17], graphene–copper sulfide nanocomposite modified electrode [18] and etc. [19], which all show super performances. In order to improve the load of biomolecules to enhance the detection range and sensitivity, many porous materials such as porous silicon [20], mesoporous MnO2 [21], porous sol–gel films [22], porous graphene–metal nanoparticle composites [23] and porous gold [24], [25] have been widely employed to fabricate electrochemical biosensors. Undoubtedly, owing to their large surface-to-volume ratio, high catalytic sensitivity and prominent electrical and thermal conductivity porous gold will have a more promising prospect in the construction of sensors [12].

In earlier work, we have successfully constructed a graphene nanodots-encaged porous gold electrode which was fabricated by simultaneously sputtering two kinds of targets (Au target and a composite target of Al and graphite) onto glass substrates by an Ar ion beam, followed with mild corrosion using dilute hydrochloric acid to afford the graphene nanodots encaged 3-D gold substrate and was used for the detection of heavy metal ions [26]. In this paper, similar technique was used to fabricate the electrode but Al was substituted for ZnO target in order to gain a better porous structure. Take advantage of porous gold structure and embedded graphene, the as-prepared electrode was used as a platform to fabricate various enzyme electrodes and excellent results were obtained. Enzymes, like GOx and catalase (CAT), were modified with pyrene functionalities and then loaded into the graphene nanodots encaged porous gold electrode via non-covalent π–π stacking interaction between pyrene and graphene. In this paper we mainly focused on the fabrication of GOx and CAT enzyme electrodes for the analysis of glucose and hydrogen peroxide. Most importantly, various other high-performance enzyme electrodes can also be fabricated using the same porous electrode and the same enzyme modification methodology.

Section snippets

Materials

Catalase (CAT) (3500 U mg−1) was purchased from Aladdin. 1-Pyrenebutyric acid (PBA), N-hydroxysuccinimide (NHS), 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide hydrochloride (EDC), glucose oxidase (GOx) (50 U mg−1) and horseradish peroxidase (HRP) (RZ-3, 250 U mg−1) were purchased from Sigma-Aldrich. N,N-Dimethylformamide (DMF, AR) was purchased from Tianjin Guangfu Co. Ltd. Hydrogen peroxide (30%, AR), hydrochloric acid (37%, AR), hydroxgmonoferrocene (HMF), potassium phosphate dibasic (AR) and

Fabrication of graphene nanodots-encaged porous gold enzyme electrodes

The implications of this work for analytical science are four fold. First, with extremely high electronic mobility graphene is used for an effective electron transfer relay to promote the charge communication between the underlying electrode and the enzyme. Second, fabrication of graphene based enzyme electrodes by non-covalent π–π stacking interaction would not destroy the graphene's super-conjugated structure, thus graphene's superb electrical conductivity will not be compromised. Thirdly,

Conclusions

In summary, we have successfully fabricated a uniform 3-D graphene nanodots-encaged porous gold electrode via IBSD method. The electrodes were fabricated using Au target, ZnO target and graphite target, which were simultaneously sputtered onto glass substrates by an Ar ion beam, followed with hydrochloric acid treatment. GOx and CAT have been successfully modified with pyrene functionalities and loaded into the 3-D porous gold electrode via non-covalent π–π stacking interaction for detection of

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51173087 and 21305133), Natural Science Foundation of Shandong (ZR2011EMM001), Taishan Scholars Program for financial support, and Jilin Province Science and Technology Development Plan Project (No. 201201006).

Jianmei Wang received the bachelor's degree in microelectronics from Qingdao University, China, in 2014. Now, she is going to be a postgraduate student of Qingdao University. Her current research interests focus on the nanomaterials and electrochemistry.

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Jianmei Wang received the bachelor's degree in microelectronics from Qingdao University, China, in 2014. Now, she is going to be a postgraduate student of Qingdao University. Her current research interests focus on the nanomaterials and electrochemistry.

Huihui Zhu received the bachelor's degree in microelectronics from Qingdao University, China, in 2014. Now, she is going to be a postgraduate student of Qingdao University. Her current research interests focus on the nanomaterials and electrochemistry.

Yuanhong Xu received her Ph.D degree from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Now, she is a professor in Qingdao University. Her research interests focus on synthesis of nanomaterials and the application in electrochemistry and electrochemiluminesence.

Wenrong Yang received his Ph.D degree in chemistry in 2002 from the University of New South Wales. He currently is Deakin University, working on biological and biomedical applications of CNTs and graphene. He also is exploring single-molecule conductivity by scanning probe microscopy.

Ao Liu received the bachelor's degree in applied physics from Qingdao University, China, in 2014. Now, he is going to be a postgraduate student of Qingdao University. His current research interests focus on thin-film transistor.

Fukai Shan received his Ph.D degree from Fudan University in 2000. Now, he is a professor in Qingdao University. His research interests focus on semiconductor materials and thin-film transistor.

Mengmei Cao received the bachelor's degree in material science from Qingdao University, China, in 2012. Now, she is a postgraduate student of Qingdao University. Her current research interests focus on the modification of graphene and electrochemistry.

Jingquan Liu received his bachelor's degree from Shandong University in 1989. His master's and Ph.D degrees were obtained from the University of New South Wales (UNSW) in 1999 and 2004, respectively. His research interests focus on the synthesis of various bio- and nano-hybrids of versatile polymeric architectures.

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