Electrochimica Acta 96 (2013) 164–172 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al h om epa ge: www.elsevier.com/locate/electacta A highly sensitive nonenzymatic glucose sensor based on multi-walled carbon nanotubes decorated with nickel and copper nanoparticles Kuo-Chiang Lin, Yu-Ching Lin, Shen-Ming Chen ∗ Electroanalysis and Bioelectrochemistry Lab, Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, No. 1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan a r t i c l e i n f o Article history: Received 27 November 2012 Received in revised form 20 February 2013 Accepted 20 February 2013 Available online 28 February 2013 Keywords: Glucose sensor Copper Nickel Nanoparticles Carbon nanotubes a b s t r a c t Novel nickel and copper nanoparticles decorated multi-walled carbon nanotubes (Ni/Cu/MWCNT) have been successfully fabricated for sensitive nonenzymatic glucose detection by the sequential electro- deposition of nickel and copper nanoparticles (NPs) on an MWCNT-modified electrode. X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses reveal that the Ni and Cu NPs were successfully deposited on the MWCNTs in this hybrid composite. The electrode shows good activity towards glucose oxidation with low over-potential and a current response that is 2.5–20 times greater than that obtained using Ni/GCE, Cu/GCE, Ni/Cu/GCE, Ni/MWCNT/GCE, and Cu/MWCNT/GCE. The optimised conditions based on current response are a Ni:Cu ratio of 1:1 and pH 13. Amperometry (E app. = +0.575 V) indicates a short response time of 1 s; two specific linear ranges of 2.5 × 10 -8 –8 × 10 -4 M and 2 × 10 -3 –8 × 10 -3 M, with high sensitivities of 2633 A mM -1 cm -2 and 2437 A mM -1 cm -2 , respectively; and a low detection limit of 2.5 × 10 -8 M (S/N = 3). This electrode can effectively analyse glucose concentration in human serum samples, avoiding interference, and is a promising nonenzymatic glucose sensor due to its low overpotential, high sensitivity, good selectivity, good stability, fast response, and low cost. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction For diabetic patients, regular measurements of blood glucose levels are required to determine whether the treatments are working effectively [1]. Enzyme-modified electrodes have some disadvantages, such as instability, the high cost of enzymes, compli- cated immobilisation procedures, and critical operating conditions. Therefore, considerable attention had been paid to developing nonenzymatic electrodes to overcome these problems. As a result, there is an ever-growing demand to create electrochemical glu- cose sensors with high sensitivity, high reliability, short response times, good recyclability, and low cost, especially nonenzymatic amperometric biosensors [2], which are currently the most popular. The direct electrocatalytic oxidation of glucose at a nonenzy- matic electrode would have advantages over enzymatic electrodes. Recently, efforts to develop a practical nonenzymatic glucose sensor have been centred on achieving a breakthrough in electro- catalysis. In this context, different substrates, such as platinum [3], gold [4], copper [5], alloys (containing Pt, Pb, Au, Pd, Ir, and Ru) [6–9], and metal oxidates (IrO 2 , MnO 2 , and CuO) [10–12], have been studied. The most important finding in this area to date is that the ∗ Corresponding author. Tel.: +886 2 27017147; fax: +886 2 27025238. E-mail address: smchen78@ms15.hinet.net (S.-M. Chen). highly active surface area of the electrode material plays a key role in the electrooxidation of glucose. During recent years, nanomaterials, such as carbon nanotubes (CNTs) and transition metallic nanoparticles (NPs), have been widely applied in sensors and biosensors. CNTs are an attractive material for electroanalysis due to their high surface/volume ratio and chemical stability [13–16]. Transition metallic NPs, including gold (Au), platinum (Pt), palladium (Pd), copper (Cu), nickel (Ni), and silver (Ag), can be used to increase electrochemical activities. Sensors and biosensors modified with metallic NPs have demon- strated good performances due to their increased surface area and enhanced mass transport and catalysis as well as good bio- compatibility, with control over the microenvironment, relative to macroelectrodes [16–18]. Therefore, their use has been an impor- tant strategy in the construction of glucose nonenzymatic sensors with nanomaterials, such as nanoporous Pt electrodes [19,20] and electrodes modified with CNTs [21,22], Ni NPs [23], Au NPs [24,25], Cu NPs [26,27], and CNTs with Cu NPs [28,29]. High sensitivity and fast amperometric detection of glucose had been reported using the methods mentioned above due to an increase in the electrocat- alytic active area and the promotion of electron transfer in glucose oxidation reactions. However, pure metal NPs (such as Ni NPs and pure Cu NPs) are difficult to prepare and have poor stability for electroanalysis due to their ready oxidisation in air and solution [18]. The reported meth- ods for the synthesis of colloidal Cu NPs, such as the use of reverse 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.02.098