Carbon nanotube microwave-assisted thermal bonding of plastic micro biochip

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Carbon nanotube microwave-assisted thermal bonding of plastic micro biochip

 

Author: Wong, Lai-pik Jolie
Title: Carbon nanotube microwave-assisted thermal bonding of plastic micro biochip
Degree: M.Phil.
Year: 2011
Subject: Biochips.
Microfluidic devices.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Industrial and Systems Engineering
Pages: xvi, 129 p. : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2507191
URI: http://theses.lib.polyu.edu.hk/handle/200/6469
Abstract: Microfluidic device has been an emerging field in the past decades. The mounting demand of biochips in the health care area has shifted the manufacturing markets from silicon and glass to polymer. In order to fabricate a plastic biochip, bonding is a critical issue to be addressed to provide a reliable performance. Various bonding methods have been developed such as thermal bonding using low pressure strategy, holed pressure equalizing plates, and hybrid assembly; adhesive bonding using PDMS; solvent bonding using DMSO and methanol; and microwave bonding using a gold thin film. Although there are plenty of methods for plastic chip bonding, thermal bonding is still the preferential method to be used because it can provide a contamination-free homogenous assembly of the final products. Thermal bonding requires heating up of two polymeric substrates to their glass transition state (Tg) and the substrates are sealed under the ultimate contact by applied pressure. However, it always results in an immense energy loss and a microstructural deformation on the bonded biochip, due to the heating of bulky bonding machine and the prolonged waiting time for heat sink during bonding respectively.
In this work, a new thermal bonding method assisted by microwave irradiation with the advantages of material homogeneity, leakage-free and negligible deformation has been developed. Given the promising microwave absorption properties, gold nanoparticles (GNPs) and carbon nanotubes (CNTs) have been used as the microwave absorbers to examine the feasibility on sealing plastic biochips in this study. It was found that CNTs were capable to release tremendous amount of heat energy to seal plastic biochip in an extremely short exposure time of microwave irradiation. The key microstructures on the plastic biochip were the microchannels with dimensions of 50 μm in depth and 100 μm in width. Unlike the previously developed method that CNTs were casted at the bonding interface, they were spray-coated on the non-bonding side of a planar substrate. With this, the bonding interface was homogeneous. The parameters including CNT thickness and exposure time of the proposed bonding method were further optimized to seal the plastic biochips. The microstructures were completely sealed and their integrity was found to be well-maintained through the cross-sectional images observed under microscope. Leakage test was conducted and an injected dye successfully passed through the sealed microchannels without leakage. The bonded biochip was able to withstand a pressure of 2 MPa as found in the tensile test. The bonding method developed in this study possesses the criteria in material homogeneity on bonded assembly, leakage-free on sealing and negligible deformation on prime structures. This bonding method is able to be conducted with short processing time and high bonding efficiency, and to be potentially developed as a high throughput process. CNT-microwave-assisted thermal bonding featuring with these criteria has been developed as a promising alternative for bonding plastic biochips in industrial scale production.

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