A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modified carbon nanotube electrode

Abstract

In this report, a novel type of cupric oxide (CuO) nanoparticles-modified multi-walled carbon nanotubes (MWCNTs) array electrode for sensitive nonenzymatic glucose detection has been fabricated. The morphology of the nanocomposite was characterized by transmission electron microscopy and X-ray diffraction. The electrochemical performance of the CuO/MWCNTs electrode for detection of glucose was investigated by cyclic voltammetry and chronoamperometry. The CuO/MWCNTs electrode showed much higher electrocatalytic activity and lower overvoltage than the bare MWCNTs electrode towards oxidation of glucose. At an applied potential of +0.40 V, the CuO/MWCNTs electrode presented a high sensitivity of 2596 μA mM⁻¹ cm⁻² to glucose. In addition, linear range was obtained over a concentration up to 1.2 mM with a detection limit of 0.2 μM (signal/noise = 3). The response time is about 1 s with addition of 0.10 mM glucose. More importantly, the CuO/MWCNTs electrode is also highly resistant against poisoning by chloride ion, and the interference from the oxidation of common interfering species such as ascorbic acid, dopamine, uric acid and carbohydrate compounds is effectively avoided. In addition, the CuO/MWCNTs electrode was also used to analyze glucose concentration in human serum samples. The CuO/MWCNTs electrode exhibits an enhanced electrocatalytic property, low working potential, high sensitivity, excellent selectivity, good stability, and fast amperometric sensing towards oxidation of glucose, thus is promising for the future development of nonenzymatic glucose sensors.

Introduction

Since reliable and fast determination of glucose is important in many areas such as biotechnology, clinical diagnostics and food industry, the development of electrochemical glucose sensor has attracted extensive attention (Wang, 2008, Wang, 2005, Rivas et al., 2007, Lin et al., 2004). Glucose oxidase (GOx) has been widely used to construct various amperometric biosensors for glucose detection, due to its high sensitivity and selectivity to glucose (Lim et al., 2005, Tang et al., 2004, Hocevar et al., 2004, Umar et al., 2009, Zhang et al., 2008). However, there are some disadvantages of the enzyme-modified electrodes, such as instability, high cost of enzymes, complicated immobilization procedure, critical operating situation, etc. Therefore, considerable attention has been paid to develop nonenzymatic electrodes to solve these problems. Noble metals (Li and Zhang, 2008, Park et al., 2003, Li et al., 2007), metal alloys (Wang et al., 2008, Sun et al., 2001), and metal nanoparticles (Rong et al., 2007, Kang et al., 2007, Cui et al., 2006, Jena and Raj, 2006) have been extensively investigated in the development of nonenzymatic glucose sensors. However, these electrodes have such drawbacks as low selectivity, high cost, or poisoning of chloride ion, which greatly limit their applications. Therefore, the development of a cheap, highly selective, fast and reliable nonenzymatic glucose sensor is still imperatively demanded (Wang et al., 2007, Chen et al., 2008, Jiang and Zhang, 2009).

Recently, carbon nanotubes (CNTs) have been rapidly becoming electrode material due to their high surface area, unique structures, excellent electrical conductivity, ultra-strong mechanical properties and high stability (Gooding, 2005, Agui et al., 2008). On the other hand, as a p-type semiconductor with a narrow band gap of 1.2 eV, CuO has been widely studied because of its numerous applications in catalysis, semiconductors, gas sensors, biosensors, and field transistors (Chen et al., 2003, Chowdhuri et al., 2004, Luque et al., 2005, Zeng et al., 2008, Zheng et al., 2000). Some efforts have been made on amperometric determination of glucose using nanostructured CuO. For instance, CuO nanowires on a Cu rod were used as electrode for detection of glucose with high sensitivity (Zhuang et al., 2008). However, the synthesis of CuO nanowires is tedious and time-consuming. In addition, exposing the active copper substrate to the environment will affect the performance of the sensor. In another work, CuO/Cu(OH)₂ nanoparticles deposited on graphite-like carbon films showed enhanced sensitivity and stability for glucose sensing (You et al., 2002). Most recently, the existence of CuO as impurity in carbon nanotubes was claimed to be responsible for electrocatalytic activity of glucose oxidation while using carbon nanotubes as electrode materials (Auley et al., 2008).

In the present work, vertically aligned multi-walled carbon nanotubes (MWCNTs) arrays on Ta foils were used as substrate for deposition of CuO nanoparticles by magnetron sputtering deposition. Well-aligned MWCNTs possess certain advantages because they can provide more landing sites and have space between each tube that would be favorable for dispersing nanoparticles compared to disordered CNTs powder. Modification of MWCNTs with CuO nanoparticles greatly improved the electrocatalytic properties of glucose oxidation and detection. Compared with the MWCNTs electrodes, the CuO/MWCNTs electrode presents high sensitivity, excellent selectivity, low potential, high stability, and fast amperometric response to the detection of glucose, which is promising for the development of nonenzymatic glucose sensors.