Glucose Biosensors Based on Vertically-Aligned Multi-walled Carbon Nanotubes

Vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) were grown using plasma enhanced chemical vapor deposition (PECVD) technique. These VA-MWCNTs were then dip coated by Poly methyl methacrylate (PMMA) followed by annealing. Samples were then polished to expose the tips of CNTs. Biological molecules Glucose Oxidase (GOx) were then immobilized on the exposed tips of these nanoelectrode ensembles. Here we present further characterization of these devices, with results on the detection limits and measurement stability. We found that these sensors can be reused for longer than six months when kept in proper storage conditions. INTRODUCTION In the efforts to develop better and smaller blood glucose sensors, carbon nanotubes (CNTs) have been used as the electrode materials for these sensors. CNTs possess excellent chemical and physical stabilities to be used in biosensors as reported in literature [1-3]. While preparing CNT based glucose biosensors, the most common and extensively used enzyme, Glucose Oxidase (GOx), is amalgamated with CNTs [4-9]. GOx enzyme was first discovered by Müller [10] in 1928 as the catalyst to for the oxidation of glucose to gluconic acid in the presence of dissolved oxygen [11]. Since CNTs possess fast electrocatalytic speed and electron transfer rate, it is a common assumption that CNTs can capture the electrons from the deeply embedded redox centres in GOx and act as transducers in CNT based glucose biosensors [12]. Wang et al. used CNT composites as the electrode materials for glucose sensors. Simultaneously they filled the mixture of CNTs and GOx in a polyamide tube and the potted the other end with the nafion coating and recorded the current response of the sensor [13]. Since then various techniques such as cross-linking [14], physical adsorption [15], etc. has been used to improve the immobilization of GOx onto surface of different electrodes including CNTs. All these techniques are complicated and involved non-compatible reagents which produces biosensors that do not exhibit good stability and longer life time. Since inception, the issues which has been discussed so far pertains to improving stability, attaining high sensitivity and low limit of detection and response time of CNT based biosensors. However, reports on durability, and reusability of GOxCNT based biosensors are sparse. In most of the cases the dispersion of CNTs affects the immobilization of enzyme and limits its performance [16]. It is evident that as grown CNTs have closed shell and it does not allow high degree of functionality. Keeping this in mind Lin et al. employed opened end CNTs and fabricated glucose biosensors based on CNT nanoelectrode nanoensembles (CNNEs) [1]. But again, very less has been discussed about the durability of the biosensors and stability of the enzyme. Overcoming Mater. Res. Soc. Symp. Proc. Vol. 1204 © 2010 Materials Research Society 1204-K13-05