A nano-Ni based ultrasensitive nonenzymatic electrochemical sensor for glucose: Enhancing sensitivity through a nanowire array strategy

Abstract

Highly ordered Ni nanowire arrays (NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode shows very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0 × 10⁻⁷ to 7.0 × 10⁻³ M, a high sensitivity of 1043 μA mM⁻¹ cm⁻², and a low detection limit of 1 × 10⁻⁷ M. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.

Introduction

It was demonstrated by modern pathology and medicine investigation that, in diabetes patients, the risk for renal, retinal and neural complications is directly related to the magnitude of chronic elevations of blood glucose (Turner et al., 1999). Therefore, the development of fast and reliable methods for glucose determination is of considerable importance. Conventional spectrophotometric methods are limited in detection of glucose due to the lack of chromophoric or fluorophoric ligands for glucose. Electrochemical biosensors have received increasing attention due to their remarkable features such as high sensitivity, simple instrumentation, low production cost and promising response speed. Glucose oxidase (GOx) (Liu et al., 2007, Salimi et al., 2007, Kaushik et al., 2008, Liu et al., 2008) as enzymatic catalyst has been widely used for such kind of biosensor fabrication. However, the activity of GOx can be easily affected by temperature, pH, humidity, and toxic chemicals (Wilson and Turner, 1992). Another limitation is the severe interferences from other oxidable species in blood samples such as ascorbic and uric acids, since the electrode must be poised at +0.7 V (versus Ag/AgCl) or higher for the electrochemical detection of hydrogen peroxide generated as a co-product by enzyme-catalyzed oxidation of glucose (Hrapovic and Luong, 2003). Nonenzymatic glucose sensor seems to be an attractively alternative technique free from above-mentioned drawbacks.

The majority of reported nonenzymatic electrochemical glucose sensors are direct amperometric ones, which rely on the current response of glucose oxidation directly at the electrode surface. The electrocatalytic activity of the electrode material is, therefore, the key factor that affects both the sensitivity and selectivity of glucose detection for nonenzymatic glucose sensors (Safavi et al., 2009). Different metals such as platinum (Beden et al., 1996, Bae et al., 1991), gold (Hsiao et al., 1996), alloys (containing Pt, Pb, Au, Pd and Rh) (Sun et al., 2001) have been explored as electrode materials to develop enzyme-free sensors for glucose. However, these electrodes suffer from slow kinetics and surface fouling due to the absorption of intermediates and chloride ion (Ye et al., 2004). Recent years have seen a growing interest in development of nonenzymatic glucose sensors based on metallic nanoparticles, as such materials showed some unique features such as high surface area-to-volume ratios, rapid mass transport, improved electrocatalytic activity as well as biocompatibility with comparison to bulk electrode metallic materials (Lin et al., 2005, Mena et al., 2005, Welch and Compton, 2006). Several metallic nanoparticles such as Au (Tominaga et al., 2005, Tominaga et al., 2006), Cu (Casella et al., 1997, Xu et al., 2006), Pt (Rong et al., 2007), Pt/Pb (Cui et al., 2007) and Pt/Ir nanoparticles (Holt-Hindle et al., 2008) have been used to prepare nonenzymatic glucose sensors and exhibited good analytical performance for glucose detection.

The nickel electrode (Luo et al., 1991, Casella et al., 1991, Fermier and Colon, 1996) has been the most widely utilized electrode for determining glucose in alkaline media and the electrochemical property of metallic nickel electrode has been well investigated. It was suggested that the mechanism for its response involves Ni^2+/3+ couple on the oxidized Ni surface. Several Ni nanoparticles based enzyme-free biosensors for glucose have also been reported which showed great enhancement in the electro-oxidation of glucose compared to other metallic nanoparticles based electrodes. You et al. (2003) reported a nonenzymatic glucose electrode based on Ni nanoparticles dispersed in disordered graphite-like carbon (Ni–NDC), which showed at least 1 order of magnitude enhancement of the sensitivity to glucose compared to the bulk-Ni electrode. Cheng et al. (2008) reported the application of a nano-NiO modified carbon paste electrode to detect carbohydrates with high sensitivity and stability. Safavi et al. (2009) reported the fabrication of a novel nonenzymatic composite electrode based on the mixing powdered nanoscale nickel hydroxide with graphite powder and ionic liquid, which shows a highly sensitive, selective and extraordinary stable response towards glucose. Nanowires have attracted an increasing interest in the past five years, due to their promising applications in sensor development, nanoscale electronic and photonic devices fabrication. Compared to spherical nanoparticles, nanowires possess a number of unique optical, electrical and catalytic properties that endue them with new and important activities (Salem et al., 2004, Granot et al., 2005). And the high surface area-to-volume ratios of nanowires could increase the voltammetric signals for electroactive species that diffused from the bulk solution. Combining the advantageous features of the metallic Ni (You et al., 2005; Salimi and Roushani, 2005, Liu et al., 2009) and the three-dimensional nanostructured arrays (Bai et al., 2008) in electrocatalytic oxidation of glucose, we developed an enzyme-free glucose sensor based on the Ni nanowire arrays (NiNWAs), which was synthesized using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template. The proposed NiNWAs electrode allows highly sensitive, stable, and fast amperometric sensing of glucose. In addition, interference from the oxidation of common interfering species, such as ascorbic acid and uric acid, is effectively avoided.