Elsevier

Talanta

Volume 116, 15 November 2013, Pages 1054-1059
Talanta

One-step fabrication of bio-functionalized nanoporous gold/poly(3,4-ethylenedioxythiophene) hybrid electrodes for amperometric glucose sensing

https://doi.org/10.1016/j.talanta.2013.08.014Get rights and content

Highlights

  • Biofunctionalized NPG/PEDOT/GOx hybrid films are firstly synthesized by one-step electropolymerization.

  • The optimized NPG/PEDOT/GOx biosensor prepared by only two cycles exhibits wide linear range (0.1–15 mM) and high sensitivity (7.3 μA mM−1 cm−2).

  • The proposed NPG/CP hybrid film is expected to extend to other redox enzymes.

  • The ultrathin NPG/CP hybrid film (~100 nm) allows miniature biosensors fabricated in a facile way.

Abstract

We report a simple, one-step synthesis of hybrid film by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) on nanoporous gold (NPG) for applications in amperometric glucose biosensors. The enzyme, glucose oxidase (GOx), is entrapped into poly(3,4-ethylenedioxythiophene) (PEDOT) matrix, simultaneously. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) studies show the NPG preserve its original bicontinuous nanoporous structure and the PEDOT film grows uniformly with a thickness of ~10 nm. The modified electrodes have been investigated by cyclic voltammetry (CV) and single potential step chronoamperometry (SPSC). The influence of PEDOT film's thickness has been explored to optimize sensor behaviors. Mediated by p-benzoquinone (BQ), the calibration curves have been obtained by applying relatively low constant potential of 200 mV (vs. SCE). The NPG/PEDOT/GOx (2CVs) biosensor exhibits high sensitivity of 7.3 μA mM−1 cm−2 and a wide linear range of 0.1–15 mM, making it suitable for reliable analytic applications.

Introduction

Development of amperometric glucose biosensors is currently one of the most active areas of interests concerning research. The determination of glucose in the blood plays a crucial role in aspects for food safety and health, especially for diabetes [1]. To fabricate novel biosensors, many immobilization strategies have been adopted such as covalent binding, cross-linking, adsorption and entrapment [2]. Conducting polymers (CPs), which are high conductive, superiorly stable, easily synthesized and suitable for electrochemical reactions, have been used for enzyme immobilization [3]. The entrapment of enzyme molecules within CP film by polymerizing the monomers in the presence of enzyme is a fast and attractive approach to construct biosensors. In addition, the thickness of sensing film can be easily controlled by changing the number of cycles or deposition time during electropolymerization [4].

Among the promising family of CPs, poly(3,4-ethylenedioxythiophene) (PEDOT) can serve as electrochemically stable, homogeneous and versatile films [5]. Additionally, 3,4-ethylenedioxythiophene (EDOT), is commercially available and can be facilely electropolymerized at relatively low applied potentials even in aqueous solutions [6], [7]. Since Fabiano and his coworkers firstly found the GOx entrapment in PEDOT on the surface of Pt disks [8], there are continuing interests for development of new materials to improve sensor behaviors dependent on biocompatibility for enzyme and enhancement of electron transfer. In recent years, graphene/PEDOT [9] and PEDOT/Au nanoparticles [10] have been developed for biosensor applications due to their unique properties. However, graphene would have a big risk for in-vivo detection taking its nano-toxicity into account [11], and Au nanoparticles need the substrate for support [12], which have shown limitation in practical applications like online medical monitoring.

Dealloyed nanoporous gold (NPG) is a new and developing material, which possesses self-organized and three-dimensional nanoporous structure in a self-supporting bulk form [13]. NPG has attracted tremendous attentions as widely used multifunctional materials in electroanalysis [14], [15], energy storage [16], [17], biofuel cells [18], and catalysis [19], [20]. In addition, the ultrathin hybrid films of NPG and CPs, such as NPG/polypyrole [21] and NPG/polyaniline [22], have been achieved as high-performance electrochemical supercapacitors due to their promising electron transfer capability, “soft” mechanical property and high stability. Meanwhile, NPG is biocompatible for enzyme immobilization [23]. It is thereby expected that NPG/CPs composites will show synergistic effects in the electrochemical performance, considering their superiorities, specific nanostructure, good interaction, ultrathin and flexible membrane. In this study, we firstly report a one-step fabricated NPG/PEDOT/GOx hybrid electrodes that would shine the way to explore novel biosensors in future.

Section snippets

Reagents and apparatus

GOx from Aspergillus niger (EC 1.1.3.4, type II, ≥15,000 units/g) was purchased from Sigma-Aldrich company (Saint Louis, USA). Sodium dihydrogen phosphate (AR grade), disodium hydrogen phosphate (AR grade), lithium perchlorate (99.9% metals basis), BQ, and β-d-glucose (GC, ≥99.5%) were supplied by Aladdin (China). EDOT, polyethylene glycol 20000 (PEG20000), sulfuric acid and nitric acid were ordered from Shanghai Sinopharm Chemical Co., Ltd. (Shanghai, China). All chemicals were used as

Electropolymerization

The solubility of EDOT in water is small (with a limit of ~14 mM at 20 °C) [24]. PEG is introduced to help EDOT to disperse well in aqueous solutions. The enhanced solubility of EDOT is the result of the formation of a pseudo–complex [25]. The electropolymerization process is shown in Fig. 1. Compared with the absence of enzyme (Fig. 1C), the lower peak current is observed in the presence of GOx (Fig. 1B), which is due to the incorporation of GOx with the PEDOT matrix. Since GOx from Aspergillus

Conclusions

In the present work, NPG/PEDOT/GOx hybrid films have been synthesized by one-step electropolymerization. Under the relatively low constant potential of 200 mV (vs. SCE) and mediated by BQ, the biosensors are selectively response to glucose. We have demonstrated the truly support-free NPG is suitable for enzyme immobilization, due to its high surface-to-volume ratio, electrocatalytic activity and biocompatibility. Additionally, the performance of glucose determination depends on the thickness of

Acknowledgments

This work was sponsored by the National 973 (2012CB932800) Program Project of China. We also thank the support from the Shandong University (No. 31370056431211 and no. 31370070614018). We appreciate the kind support and meaningful discussion with Prof. Yi Ding and his group members.

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