Modification of microcantilevers using layer-by-layer nanoassembly film for glucose measurement

Here, we report a new approach of glucose measurement by using a multilayer modified microcantilever. Glucose oxidase (GOx)/ polyethyleneimine (PEI) multilayer modified microcantilever underwent bending when it was exposed to glucose solutions. The magnitudes of bending were proportional to the concentrations of glucose. This technique provides a new platform for enzyme functionalized cantilever biosensors. 2004 Elsevier B.V. All rights reserved. Monitoring blood sugar levels is a critical component of diabetes care. Extensive research is still underway to develop new methods and technologies for improved glucose monitoring. Advances in the field of micro/ nano-electro-mechanical systems (MEMS and NEMS) now offer unique opportunities in the design of small and ultrasensitive analytical methods. One of the most promising MEMS is microcantilevers, which have been proven to be an outstanding platform for chemical and biological sensors [1–7]. Integrated circuits of microcantilever-based chips have been developed for processing the data and transmit it as radio signals to a remote receiver [7]. The unique characteristic of microcantilevers is their ability to undergo bending due to molecular adsorption or binding-induced change in surface tension. This is achieved by confining the adsorption to one side of the cantilever. The cantilever can be made of any materials that can deflect when force or surface stress is applied on the cantilever surfaces, the deflection amplitude depends on the thickness, the length, and the materials of the cantilevers. 0009-2614/$ see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.08.019 * Corresponding author. Fax: +1 318 257 5104/5125. E-mail address: [email protected] (H.-F. Ji). Many electroenzymatic glucose measurement methods are based on the catalytic activity of glucose oxidase (GOx) [8,9]. The foundation of these devices is the oxidation of glucose, which produces gluconic acid, as shown in the following equation. b-D-glucoseþO2 þH2O ! Glucose Oxidase D-gluconic acidþH2O2 ð1Þ The reaction results in a decrease in pH, which has been monitored as an indirect measurement of glucose concentration. The detection scheme based on the monitoring of GOx-catalyzed oxidation products of glucose is suitable for continuous monitoring of glucose. Our initial efforts in the development of GOx modified microcantilever glucose sensors focused on conventional surface conjugation chemistry [10]. For instance, aminopropylthiol was used to form a monolayer on the gold surface of a microcantilever, then the microcantilever was treated with 1-[3-(dimethylamino)propyl]3ethylcarbodiimide hydrochloride to conjugate GOx on the cantilever surface. However, similar to the a work reported recently, [11] only slight microcantilever response (<7 nm deflection for a 200 lm-long silicon microcantilever) was observed upon exposure of these microcantiTime, s