Study on a Biosensor and a Micromixer Utilizing Electrothermal Effect
Date Issued
2015
Date
2015
Author(s)
Huang, Yao-Hung
Abstract
In this work, a conventional commercial quartz crystal microbalance (QCM) with a reaction chamber modified by integrating into our designed multi-microelectrodes to produce electrothermal vortex flow is used to perform a series of frequency shift measurements due to the adding mass coming from the specific binding of the analytes in the fluid flow and the immobilized ligands on the QCM sensing surface. In a diffusion-limited sensing process, it often takes a long time to complete a detection due to the slow motion of analytes. Electrothermal vortex flow can efficiently drive the analyte movement in the fluid toward the sensing surface and accelerate the detection with the additional advantages of small amount analytes, acceptable local temperature rise, and negligible pressure loss of the fluid flow. In the experiments, the analytes carried in the PBS buffer solution is firstly guided to flow through the micro-channel to displace the solution in the flow cell completely. In the beginning, the binding of analyte and ligand proceeds due to pure diffusion of analytes to the binding surface of the QCM sensor. After about 10-15 min, the binding rate is observed to a near quasi-static state. At this moment, to avoid the mutual interference of electric fields produced by QCM electrodes and electrothermal microelectrodes, we first cease the QCM frequency sensing by removing the applied alternating voltage and then add the driving voltage to the multi-microelectrodes to activate the electrothermal vortex flow for about 5 min. Then we shut down ETE and start QCM sensing again. As control groups, blank experiments without applying electrothermal effect (ETE) are also done for the purpose of comparisons. Amine latex beads as analytes (diameter, 20nm and 1μm) were used in the experiments. Cysteamines as ligands are pre-self-assembled on the gold-coated QCM surface. In the case of 20-nm amine latex beads in ETE phase, the resonant frequency variations at concentrations of 1013 and 1014 spheres/mL were 24.6 ± 4.9 and 53.2 ± 10.6 Hz, respectively. In the control group without ETE, the respective variations were 2.7 ± 0.5 Hz and 18.1± 3.6 Hz, respectively. In the case of 1-μm amine latex beads with ETE, the resonant frequency variations at concentrations of 108 and 109 spheres/mL were 15.6± 2.3 and 33.1± 8.3 Hz, respectively, while those in the control group without ETE were 2.2 ± 1.2 Hz and 13.1±2.6 Hz, respectively. In addition, the images of the binding surfaces with or without applying ETE are taken through the scanning electron microscopy (SEM). Comparing the images, it clearly indicates that ETE does raise the specific binding of the analytes and ligands and efficiently improve the performance the QCM sensor. In addition, biochemical applications often require rapid mixing of different fluid samples. At the microscale level, the fluid flow is usually highly ordered laminar flow and the lack of turbulence makes the diffusion be the primary mechanism for mixing. The electrothermal effect can be generated to induce disturbance to the flow field and hence promote the mixing efficiency for the micromixer. In ETE phase, the mixing indexes within 2000μm mixing length at flow rate of 20, 50 and 100 μl/hr were 93.6%, 88.4% and 80.7 %, respectively. In the control group without ETE, the mixing indexes were 57.3%, 23.5% and 21.7 %, respectively.
Subjects
electrothermal effect
quartz crystal microbalance
micromixer
binding efficiency
Type
thesis
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