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An injection molding process for the fabrication of disposable plastic microfluidic chips with a cycle time of 2 min has been designed, developed, and implemented. Of the sixteen commercially available grades of cyclo-olefin copolymer (COC) that were screened for autofluorescence and transparency to ultraviolet (UV) light, Topas 8007610 was identified as the most suitable for production. A robust solid metal mold insert defining the microfluidic channels was rapidly microfabricated using a process that significantly reduces the time required for electroplating. No wear of the insert was observed even after over 1000 cycles. The chips were bonded by thermal fusion using different bonding conditions. Each condition was tested and its suitability evaluated by burst pressure measurements. The COC microfluidic chips feature novel, integrated, reversible, standardized, ready-to-use interconnects that enable operation at pressures up to 15.6 MPa, the highest value reported to date. The suitability of these UV transparent, high pressure-resistant, disposable devices was demonstrated by in situ preparation of a high surface area porous polymer monolith within the channels.40981
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Introduction
Miniaturizing devices for biomedical analysis will lead to portable and self-contained point-of-care diagnostic tools.In addition to portability, efforts to scale-down chemical analysis with microfluidic devices are driven by the significant reduction in the volume of reagents and samples required for analysis as well as the acceleration of the process due to shorter distances the sample has to traverse. The microfluidic chips can be fabricated from a variety of materials including silicon, fused silica, glass, quartz, and plastics.1 The chemistry of these substrates is well understood and most also have the optical properties that are required for detection by laserinduced fluorescence (LIF). The first micro total analytical system (μTAS) to be introduced2 was made from inorganic materials because the micromachining processes developed for the fabrication of integrated circuits were readily adaptable. However, fabrication involved a multi-step process consisting of cleaning, mask deposition, lithography, and etching, which is both slow and expensive.3 Therefore, a transition from the conventional substrates to plastics4 would enable the cost-effective and high-volume production of disposable microfluidic devices. Today, the most common technologies for the preparation of microfluidic systems from plastics involve laser ablation,5 hot embossing,6 soft lithography,7 or injection molding.8 A wide variety of polymers such as polyimide, poly(methyl methacrylate), polycarbonate, poly(dimethylsiloxane), and polyolefins have already been used 9 with the choice of the specific material determined by its physical and chemical properties as well as the technology used for fabrication.
An obstacle that currently impedes broader use of microfluidics is the lack of standard interconnects for interfacing the macroscale environment with the microfluidic channels within the chip.10–12 The issue of convenience is especially important in high-throughput applications where the time constraints involved with the manipulation of several interconnects can be large enough to offset the economic advantages of migrating to a microfluidic platform.13 The failure of an inpidual interconnect can be detrimental to device operation and repair is often not an option. Although reports on the fabrication and use of microfluidic devices for analysis frequently omit their description, interconnects, are now receiving considerable attention and have been recently reviewed.13 Typically, capillaries, tubes, and pipette tips are glued to the fluid access holes. Unfortunately, this manual approach depends on the skill of the operator and is not always reproducible.10,14 Moreover, the use of glue may lead to chemical contamination.15 Therefore, multistep interconnect fabrication techniques that bar the glue from contacting working fluids10,16–19 as well as glue-free methods20,21 have been developed.