Analysis of Enhancement of Analytes Adsorption Due to Flow Stirring by Electro-thermal Force in a biosensor

• Main Authors: Chih-Kai Yang, 楊智凱
• Other Authors: Jeng-Shian Chang
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/93930385434402902892

碩士 === 臺灣大學 === 應用力學研究所 === 95 === Specific binding reaction of an analyte-ligand protein pair is a natural characteristic which is applied to design biosensors, such as micro-cantilever beam based biosensor, the Surface Plasmon Resonance (SPR) sensor, and the Quartz Crystal Microbalance (QCM) sensor. By applying a non-uniform AC electric field to the flow micro-channel of the biosensor, the electro-thermal force can be generated, a pair of stirring vortices can be formed to stir the flow field and the diffusion boundary layer on the reaction surface, and hence increase the transport of the analytes to the reaction surface to enhance the association or dissociation of analyte-ligand complex. This work simulates the binding reaction kinetics of two common-used proteins, CRP and IgG, in a reaction chamber (micro-channel) of a biosensor. For a diffusion-limited protein, whose Damköhler number is greater than unity, the diffusion boundary layer on the reaction surface would hinder the binding reaction from association and dissociation. Several crucial factors which influence the binding reaction curves in the simulation are discussed, including concentration of analyte, position of reaction surface, channel height, and width of reaction surface. A higher channel causes the diffusive transport of the analyte to take longer time to reach the reaction surface, which in term decreases the reaction rate of the protein pairs. The width of the reaction surface plays an important role in the formation of the boundary layer. The wider reaction surface takes more time to allow diffusion to overcome the wider diffusion boundary layer, resulting in a slower binding rate and a longer time to reach saturation. The blocking effect of the flow field by the existence of the reaction surface at the different position of the micro-channel could cause different degrees of enhancement to the association and the dissociation. It is found that by changing the position of the reaction surface the largest enhancement is found at the position near the negative electrode. For the configuration of the micro-channel we studied, the initial slope of the curve of the analyte-ligand complex versus time can be raised up to 5.166 for CRP and 1.934 for IgG in association, and 3.744 for CRP and 1.277 for IgG in dissociation, respectively, under the applied AC field 15 Vrms peak-to-peak and operating frequency 100 kHz. An improved design with neck region near the reaction surface is demonstrated. The reaction surface is fixed to locate at the middle of the bottom side. With the existence of the stirring flow field, the association rate of the 30 μm-neck is 2.733 times to that of the original channel (no neck). The results of 3-D simulation demonstrate the lateral diffusion effect. Furthermore, the design of the U-shape reaction surface enhances the reaction velocity due to its hollow region. The presented data of simulation are useful in designing the biosensors.