Disposable sensor based on enzyme-free Ni nanowire array electrode to detect glutamate Mamun Jamal, Maksudul Hasan, Alan Mathewson, Kafil M. Razeeb n Tyndall National Institute, Microsystems Centre, University College Cork, Lee Maltings, Dyke Parade, Cork, Ireland article info Available online 21 July 2012 Keywords: Ni nanowire Pt nanoparticle L-glutamic acid Enzyme free sensor Amperometry abstract Enzyme free electrochemical sensor platform based on a vertically aligned nickel nanowire array (NiNAE) and Pt coated nickel nanowire array (Pt/NiNAE) have been developed to detect glutamate. Morphological characterisation of Ni electrodes was carried out using scanning and transmission electron microscopy combined with energy dispersive X-ray (SEM–EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Cyclic voltammetry (CV) and amperometry were used to evaluate the catalytic activity of the NiNAE and the Pt/NiNAE for glutamate. It has been found that both NiNAE and Pt/NiNAE electrodes showed remarkably enhanced electrocatalytic activity towards glutamate compared to planar Ni electrodes, and showed higher catalytic activity when compared to other metallic nanostructure electrodes such as gold nanowire array electrodes (AuNAE) and Pt coated gold nanowire array electrode (Pt/AuNAE). The sensitivity of NiNAE and Pt/NiNAE has been found to be 65 and 96 mA mM 1 cm 2 , respectively, which is approximately 6 to 9 times higher than the state of the art glutamate sensor. Under optimal detection conditions, the as prepared sensors exhibited linear behaviour for glutamate detection in the concentration up to 8 mM for both NiNAE and Pt/NiNAE with a limit of detection of 68 and 83 mM, respectively. Experimental results show that the vertically aligned ordered nickel nanowire array electrode (NiNAE) has significant promise for fabricating cost effective, enzyme-less, sensitive, stable and selective sensor platform. & 2012 Elsevier B.V. All rights reserved. 1. Introduction L-glutamate (anion of glutamic acid) is one of the 20 standard amino acids used by all organisms. It plays an important role in food processing, clinical applications and is also well known as a flavour enhancer, commonly found in various foods. The excessive intake of this flavour enhancer can cause allergic effects such as headache and stomach pain (Chang et al., 2007; Jamal et al., 2010; Mizutani et al., 1998). L-glutamate is also an excitatory neurotransmitter in the central nervous system of vertebrates, and is a potent neuro- excitatory amino acid associated with certain behaviour patterns such as aggressive behaviour, visual task learning, morphine-induced muscular rigidity and retrograde amnesia (Compagnone et al., 1992; Corren and Saxon, 2000; Francis, 2003; Gordon, 2010; Volterra and Meldolesi, 2005). Furthermore, L-glutamate has importance in the diagnosis and treatment of myocardial and hepatic disease (Dufour et al., 2000). The measurement of liver enzymes alanine aminotrans- ferase (ALT) and aspartate aminotransferase (AST) in physiological fluids provide valuable information in the diagnosis of liver disease and both are widely used as a biomarker. Both ALT and AST measurements are based on glutamate detection (Chang et al., 2007; Jamal et al., 2009). An amperometric sensor based on glutamate oxidase (GlutOx) has becoming more popular over the last 10 years due to its sensitivity, cost effectiveness and portability compared to the laboratory based detection methods such as chromatography (Swanepoel et al., 1996), fluorescence (Chapman and Zhou, 1999), spectrophotometry (Valero and Garcia-Carmona, 1998) and capillary electrophoresis (Tucci et al., 1998). GlutOx is a flavoenzyme that catalyzes oxidative deamination of glutamate in the presence of oxygen (O 2 ) and generates hydrogen peroxide (H 2 O 2 ). Quantitation of glutamate is achieved by electrochemical oxidation of H 2 O 2 . Two generations of sensors were developed, which are distinguished by their electron transfer mechanisms. The first generation sensor is the most commonly used method, and measures either depletion of O 2 (Wu et al., 2005) or the generation of H 2 O 2 (Hascup et al., 2008; O’Neill et al., 2004). The second generation sensor uses a redox- mediator to transfer electrons from the electrochemical reaction to a transducer. In comparing the two generations of glutamate sensors by Qin et al. (2008), it is reported that the second generation sensors have relatively low reproducibility and low glutamate sensitivity. Also in 2010, our group described a glutamate sensor (Jamal et al., 2010) based on the first generation principle, which has been found to be much superior compare to the sensor developed by Jamal et al. (2009) which was based on second generation principle. Recently Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics 0956-5663/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bios.2012.07.024 n Corresponding author. Tel.: þ353 21 490 4078; fax: þ353 21 427 0271. E-mail address: kafil.mahmood@tyndall.ie (K.M. Razeeb). Biosensors and Bioelectronics 40 (2013) 213–218