doi:10.1016/j.bios.2004.05.009
Copyright © 2004 Elsevier B.V. All rights reserved.
Selective glucose detection based on the concept of electrochemical depletion of electroactive species in diffusion layer
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Kang Wang, Jing-Juan Xu, Da-Cheng Sun, Hui Wei and Xing-Hua Xia
, 
The State Key Laboratory of Coordination Chemistry, Department of Chemistry, Institute of Analytical Science, Nanjing University, Nanjing 210093, China
Received 24 February 2004;
Revised 22 May 2004;
accepted 31 May 2004.
Available online 2 July 2004.
Abstract
A glucose detection approach based on the concept of electrochemical depletion of electroactive species in diffusion layer was established, using scanning electrochemical microscopy (SECM). By controlling the glucose oxidase (GOD) modified electrode (substrate electrode) at a proper potential of electrochemical oxidation of interfering electroactive species, i.e., ascorbic acid (AA), an interference-free microcircumstance was formed in the diffusion layer of the substrate electrode. Consequently, we could successfully sense hydrogen peroxide generated from an enzymatic reaction by locating a Pt ultramicroelectrode (UME) (tip electrode, 5 μm in radius) into the diffusion layer of the substrate electrode. Properties of this interference-removing approach based on electrochemical depletion were systematically investigated. Results showed that the interference-removing efficiency was significantly determined by the tip-substrate distance and substrate potential. When the tip-substrate distance was 11 μm (2.2 times of the tip electrode radius) and the substrate potential was 0.5 V, nearly 90% of AA (0.5 mM) could be depleted within 30 s without consumption of H2O2. Under these conditions, 0.1 mM AA showed no influence on the detection of 0.5 mM glucose. The linear range of glucose detection is 0.01–1 mM with a detection limit (DL) of 0.005 mM (correlation coefficient is 0.9948). This research will open a new way for developing selective micro-biosensors.
Author Keywords: Biosensor; Glucose detection; Diffusion layer; Electrochemical depletion; SECM; Selectivity
Fig. 1. Scheme and principle of the glucose detection and interference-removing approach in the diffusion layer of GOD-modified GCE.
Fig. 2. SEM image of the poly-PPD–GOD membrane.
Fig. 3. Normalized current–distance curves recorded with a Pt UME (rT = 5 μm) in a solution of 1 mM K4Fe(CN)6 (solid curve) or in a solution of 1 mM K4Fe(CN)6 + 50 mM glucose (dotted curve). Open circles denote the theoretically calculated current-distance behavior for an insulating substrate.
Fig. 4. Dependence of the Pt tip currents (rT = 5 μm, ET = 700 mV) on the tip-substrate distance in PBS containing 0.1 mM glucose.
Fig. 5. Response currents of the tip electrode taken at the polarization time of 5 s as a function of glucose concentration. Inset denotes the current responses of the tip electrode (rT = 5 μm) at 0.7 V for different glucose concentrations as a function of time. The tip-substrate separation distance was 11 μm.
Fig. 6. Voltammograms of a GCE and a Pt UME (rT = 5 μm) in PBS (doted curves) and PBS containing 0.1 mM AA (solid curves) or 0.1 mM H2O2 (dashed curves) at a scan rate of 50 mV/s.
Fig. 7. Dependence of the normalized currents of a Pt tip electrode (rT = 5 μm) at 0.5 V (curves ‘a’ and ‘d’) and 0.7 V (curves ‘b’ and ‘c’) on the substrate potential. The tip-substrate distance is kept at 2.2 rT (11 μm) and the tip currents were taken at the polarization time of 30 s. The tip current of iT,0 was measured with the substrate electrode at open-circuit potential. ‘a’: 0.5 mM AA, ET = 0.5 V; ‘b’: 0.5 mM AA, ET = 0.7 V; ‘c’: 0.5 mM glucose, ET = 0.7 V; ‘d’: 0.5 mM glucose, ET = 0.5 V.
Fig. 8. Dependence of the normalized response current in 0.5 mM AA on the normalized tip-substrate distance. Tip currents were measured with (iT,S) or without (iT,0) applying 0.5 V on the substrate electrode (ET = 0.5 V).
Fig. 9. Amperometric dynamic response of a Pt tip electrode (rT = 5 μm, ET = 0.5 V) with and without applying an oxidation potential to the substrate electrode. Tip-substrate distance was kept at 11 μm. ‘a’: 0.1 mM AA + 0.5 mM glucose, substrate electrode at open circuit potential; ‘b’: 0.1 mM AA + 0.5 mM glucose, Esub = 0.5 V; ‘c’: 0.5 mM glucose, Esub = 0.5 V; ‘d’: PBS supporting electrolyte (pH 7.4), Esub = 0.5 V.
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