Elsevier

Talanta

Volume 147, 15 January 2016, Pages 315-321
Talanta

Biosensing of glucose in flow injection analysis system based on glucose oxidase-quantum dot modified pencil graphite electrode

https://doi.org/10.1016/j.talanta.2015.09.050Get rights and content

Highlights

  • ZnS–CdS quantum dots was electrochemically deposited onto pencil graphite electrode.

  • We report biosensing of glucose in flow injection analysis.

  • Simple, economical and fast biosensor was constructed for glucose detection.

Abstract

A novel amperometric glucose biosensor was proposed in flow injection analysis (FIA) system using glucose oxidase (GOD) and Quantum dot (ZnS–CdS) modified Pencil Graphite Electrode (PGE). After ZnS–CdS film was electrochemically deposited onto PGE surface, GOD was immobilized on the surface of ZnS–CdS/PGE through crosslinking with chitosan (CT). A pair of well-defined reversible redox peak of GOD was observed at GOD/CT/ZnS–CdS/PGE based on enzyme electrode by direct electron transfer between the protein and electrode. Further, obtained GOD/CT/ZnS–CdS/PGE offers a disposable, low cost, selective and sensitive electrochemical biosensing of glucose in FIA system based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen. Under optimum conditions (flow rate, 1.3 mL min−1; transmission tubing length, 10 cm; injection volume, 100 μL; and constant applied potential, −500 mV vs. Ag/AgCl), the proposed method displayed a linear response to glucose in the range of 0.01–1.0 mM with detection limit of 3.0 µM. The results obtained from this study would provide the basis for further development of the biosensing using PGE based FIA systems.

Introduction

Nanomaterials have received great attention due to their unique chemical, physical and electronic properties that provide their broad applications in many areas such as catalysis, electrochemical and photoelectrochemical sensing and biosensing, electronics and photonics [1], [2], [3]. The unique properties of these materials have also been effectively exploited in the immobilization of biomolecules, the catalysis of electrochemical reactions, the enhancement of electron transfer between electrode and substrate, labeling of biomolecules and acting as a reactant [1], [2]. Facilitation of the direct electron transfer between the redox center of the enzyme and the electrode is one of the most important features of nanomaterials therefore mainly used in the construction of the third generation biosensors. Many kinds of nanomaterials such as metal nanoparticles, carbon nanotubes, graphene, metal oxide nanoparticles, semiconductor nanoparticles and hybrid nanoparticles have been widely used in direct electrochemistry of proteins, catalytic activity of many biomolecules and also construction of electrochemical sensors and biosensors [1], [2]. Among them, recently, semiconductor quantum dots (QDs) such as CdS, CdTe, CdSe, ZnS etc. have received considerable interest in the fields of electrochemical and especially photoelectrochemical biosensors due to their interesting optical and electronic properties [2], [3]. One of the important applications of QDs is the construction of glucose oxidase (GOD) based electrochemical and especially photoelectrochemical glucose biosensors [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. The QDs enhance the electron transfer reactivity of GOD due to direct electron transfer capability [3], [4], [5], [6], [7], [8], [9]. However, hybrid or core–shell QDs such as CdS–ZnS, CdSe–CdS or hybrid nanomaterial such as carbon nanotube-QDs, graphene-QDs etc. have been preferred instead of using only QDs or nanomaterials in the electrochemical studies [10], [11], [12], [13], [14]. The core–shell QDs or hybrid nanomaterials exhibit better charge separation than a single QD or nanomaterial based systems. The core–shell QDs and hybrid materials are ideal candidates for sensing and biosensing applications due to higher quantum yield, increased photostability in photoelectrochemical reactions, extremely large surface-to-atom ratio and good sensitivity to surface ligands [8], [15], [16]. Therefore, CdS–ZnS modified pencil graphite electrode (PGE) was preferred in this study.

The selection of the electrode material is very important in the construction of the electrochemical biosensor since the type of the electrode generally determines the selectivity, sensitivity, stability and the cost of the biosensor. When compared with the other carbon based electrodes, PGEs have the same advantages such as the high electrochemical reactivity, commercial availability, good mechanical rigidity, disposability, lower cost and the ease of modification [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27]. In addition, it was reported that the pencil lead electrodes offer a renewable surface which is simpler and faster than polishing procedures, in common with the solid electrodes, provide useful and reproducible results for the individual surfaces [17]. Thus PGEs have been extensively used in various electroanalytical studies [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27].

A useful approach for the construction of electrochemical sensors and biosensors is using of Flow Injection Analysis (FIA) in electrochemical techniques [28], [29]. FIA has some advantages for routine analytical determinations, such as low sample consumption, short analysis time based on a transient signal measurement in a flow-through detector, and using online method for difficult operations of separation and chemical conversion of analyses into detectable species. The GOD immobilization onto various modified electrodes have been proposed in FIA in order to enhance the accuracy, reproducibility, stability and response rates in the analysis [30], [31], [32], [33], [34], [35]. However, according to our search of the literature, electrochemical biosensing of glucose using FIA system depending on GOD immobilized onto quantum dot modified PGE has not been reported. This study shows a combination of QDs, PGE and FIA for biosensing of glucose which offers some advantages such as (i) a disposable, practical, easy-to-use and low cost biosensing due to the useful properties of PGE, (ii) fast and economic analysis (FIA exhibits fast analysis and lower cost because of lower consumption of reactant) and (iii) Efficient immobilization of GOD, good selectivity and sensitivity due to the unique functions of QDs.

Section snippets

Materials and apparatus

Glucose oxidase (GOD, from Aspergillus niger, E.C. 1.1.3.4) was purchased from Sigma. All other chemicals such as CdCl2, ZnCl2, Na2S2O3, glucose, chitosan, Na2EDTA, mercapto acetic acid (MAA), KCl, H3PO4, NaH2PO4, Na2HPO4, CH3OOH, etc. were commercially available as analytical reagent. All the solutions were prepared with ultrapure water from Elga Option Q7B water purification system (18.2  cm)

All electrochemical experiments were carried out using an Autolab PGSTAT 128N Potentiostat/Galvanostat

Characterization of GOD/CT/ZnS–CdS/PGE

Electrochemical impedance spectroscopy (EIS) is a useful technique providing detailed information on the impedance changes of the electrode surface which give useful information about the modification of the electrode surfaces. In a typical impedance spectrum, there are two parts: a semicircle portion and a linear portion. The semicircle part at higher frequencies and the linear part at lower frequencies correspond to the electron transfer-limited and diffusion-limited processes, respectively.

Conclusion

In this study, the development of a simple and highly sensitive electrochemical glucose biosensor based on a new modified electrode, which could be easily prepared by electrochemical precipitation of ZnS–CdS onto the surface of PGE, was described for the first time. In addition, PGE was used in FIA system using a newly constructed home-made photoelectrochemical flow cell for the electrochemical biosensing of glucose for the first time. As a result, a novel, fast and facile sensor was reported

Acknowledgment

We thank The Scientific and Technological Research Council of Turkey (TÜBİTAK) for financial support (Project number: 112T375).

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