Design and Analysis of a Cantilever Biosensor Based on a Boron Nitride Nanotube M.S. Islam, A.Z. Kouzani School of Engineering Deakin University Geelong, Victoria 3217, Australia msi, kouzani@deakin.edu.au W.P. Michalski Australian Animal Health Laboratory CSIRO Livestock Industries Geelong, Victoria 3220, Australia wojtek.michalski@csiro.au Abstract—In this paper, we introduce a single-walled boron nitride nanotube (SWBNNT)-based cantilever biosensor, and investigate its bending deformation. The BNNT-based cantilever is modelled by accounting that the surface of the cantilever beam is coated with the antibody molecule. We have considered two main approaches for the mechanical deformation of the BNNT beam. The first one is differential surface stress produced by the binding of biomolecules onto its surface, and the second one is the charge released from the biomolecular interaction. In addition, other parameters including length of beam, variation of beam’s location and chiralities of the BNNT have been taken into consideration to design the cantilever biosensor. The computed results are in good agreement with the well known electrostatic equations that govern the deformation of the cantilever. Keywords-cantilever; biosensor; affinity; electrostatics I. INTRODUCTION Nano Electro Mechanical Systems (NEMS) technology is creating a significant deal of interest in medical and environmental diagnostics due to its potential performance and cost advantages at nanoscale. The diagnostics devices that are developed in NEMS allow detection of very small concentrations of target molecules, and provide better sensitivity than conventional biosensors. Among the enabling nanostructures, Boron Nitride Nanotubes (BNNTs) are a promising candidate for diagnostics applications because of their unique electronic structure and properties [1, 2]. Unlike widely used Carbon Nanotubes (CNTs), the properties of BNNTs are independent of their diameter and layers [3] . In addition, the BN structure in BNNTs is much more thermally and chemically stable than a graphitic carbon structure in CNTs. Such properties together with their excellent mechanical properties and thermal conductivity make BNNTs a potential candidate for biosensing applications. Only a very few works on BNNT based biosensor [4, 5] have been reported in the literature. Cantilever-based biosensing is an emerging method that has attracted a lot of interests. The cantilever can measure minute deformations resulting either from the surface stress, charge release, heat flow, differential expansion, mechanical, electric or magnetic forces [6]. Surface stress offers a means to deflections facilitating the measurement of physical or biochemical interactions. This is because the differential adsorption or binding applies expanding intramolecular forces on the coated surface causing the cantilever to bend down. In fact, in response to any chemical, physical or environmental factors, it produces an equivalent mechanical motion in the nanometer scale. However, depending on the mechanical properties of the device, the sensing (capacitance, piezoresistance or resonance frequency) principle varies. Also, based on the parameters used for measuring the change, it can be either cantilever bending (deflection mode) or shifts in resonant frequency (resonance mode). A cantilever can be used for many other applications including gas sensor, pH sensing, DNA hybridization, liquid sensing and protein detection. Knowles et al. [7] developed a microcantilever system for the protein accumulation where the surface stress generated by the interaction between the protein and the coated beam was used to detect the protein. Whereas, Li et al. [8] designed a cantilever array with receptor molecules to simultaneously detect cancer and cardiac markers. As compared to the widely used CNT biosensor, BNNT provides better performance in terms of deflection and chemical stability [9]. The sensitivity of the cantilever biosensor is greatly influenced by its proper surface functionalization, and the selectivity is accomplished by immobilizing specific receptors on the top surface. Unlike other cantilever biosensors, where aluminum thin films, polysilicon and SU8 are used as the beam for the cantilever [10], in this work, a single walled BNNT is used as the beam which offers the greater flexibility for the surface functionalization and of course the flexible mechanical properties. It is rather simple and much more reliable to functionalize the BNNT’s surface through passive adsorption and covalent immobilization of the plasma. The surface of the BNNT beam is coated with a conductive polymer film and specific antibodies are physically immobilized on the top of BNNT beam where antigens are specifically adsorbed on the antibodies. And, a molecular layer is used to protect the sensor against any unspecific adsorption. The use of the a conductive polymer posses the following benefits: (i) turning away the adhesion issue with polymer/metal, (ii) controlling the stiffness of the cantilever especially for lower Young’s modulus of the conducting polymer compared to Au, and (iii) X.J. Dai ITRI Deakin University Geelong, Victoria 3217, Australia jane.dai@deakin.edu.au 978-1-4244-6888-1/10/$26.00 ©2010 IEEE TENCON 2010 1951