A highly parallel, polymerase chain reaction (PCR) multireactor platform is in high demand to satisfy the high throughput requirements for exploiting the accumulated genetic information from the Human Genome Project. By incorporating continuous flow PCR (CFPCR) devices in a polymer 96-well titer plate format, DNA amplification can be performed with steady-state temperature control and faster reaction speed at lower cost. Prior to the realization of a PCR multi-reactor platform, consisting of a sample delivery chip, a PCR multireactor chip, and a thermal cycler, optimization of the geometry for CFPCR devices in a titer plate-based PCR multi-reactor chip based on manufacturing feasibility is necessary. A prototype PCR multi-reactor chip was designed in a 96-well titer plate format with twelve different CFPCR configurations. High quality metallic, large area mold inserts (LAMIs) were fabricated using an SU-8 based UV-LIGA technique by overplating nickel in SU-8 electroplating templates. Micro molding of polycarbonate (PC) was done using hot embossing, resulting in good replication fidelity over the large surface area. Thermal fusion bonding of the molded PC chips using a custom-made bonding jig yielded acceptable sealing results. The manufacturability investigation throughout the design and the process sequence suggested that the microchannel walls require a minimum width of at least 20 μm and an aspect ratio of 2 for structural rigidity. An optimal CFPCR device for use in a PCR multi-reactor chip can be selected with a series of amplification experiments with the development of a thermal cycler.
Highly parallelized biochemical analysis is a significant step toward achieving high throughput processing of patient samples for diagnosis and treatment monitoring. The standard microtiter plate is used to carry out multiple reactions for high throughput screening. By incorporating polymer microfluidic devices at each well in the microtiter plate format, the capability of the format could be significantly enhanced for high throughput processing of large numbers of biochemical samples in a cost-effective manner. Low cost replication of the microtiter plates is done using micro molding techniques, so microfabrication technology for making large area mold inserts (LAMIs) containing microfluidic devices at each well of a microtiter plate format is needed. A large area mold insert (LAMI) in the footprint of the standard microtiter plate was fabricated using an SU-8 based UV-LIGA technique. Excellent lithography results, with vertical sidewalls, were obtained by utilizing flycutting to minimize SU-8 film thickness variation and a UV filter for attenuating high absorbance UV wavelengths. Overplating of nickel in the SU-8 polymeric molds was used to make high quality metallic mold inserts with vertical sidewalls. Micro molding of polycarbonate (PC) was done using hot embossing, resulting in good replication fidelity over the large surface area. Thermal fusion bonding of the molded PC chips yielded good sealing results and the developed polymer microfluidic platforms showed good fluidic uniformity.
Metallic large area mold inserts (LAMIs) are essential for the replication of polymer microfluidic devices. Successful molding of micro- or nanoscale features over large areas is dependent on improving the dimensional control of the mold inserts, particularly those fabricated by electrodeposition using the LIGA or UV-LIGA processes. A systematic approach to controlling the internal stress of the nickel deposits, which was essential for predicting the final flatness of the LAMIs prior to electroplating, was carried out. The internal stress of the nickel deposits from a nickel sulfamate solution was estimated using a bent strip stress measurement method after maintaining electroplating chemicals and conditions and reducing contamination. Over-electroplating of the nickel LAMIs was performed on SU-8 electroplating molds on 150 mm diameter Si wafers. Detailed characterization of the nickel LAMIs to determine the relationship between the overall flatness of the LAMIs and the internal stress identified a suitable process window in terms of the current densities (10–20 mA/cm2) and the internal stress (−8.3 ∼ −3.0 MPa) for the high quality nickel LAMIs with an overall flatness of 100 μm.
A polymer-based, multiplex single molecule detection module (SMD) was developed with a fluidic substrate and a cover plate. The fluidic substrate was fabricated using a single-step, double-sided hot embossing in poly(methyl methacrylate) (PMMA) with sampling zone microchannels on the bottom side and microlenses on the top. Shallow sampling zone microchannels (5 μm deep and 100 μm wide) were made to improve sampling efficiency and microlenses were adopted to collect the fluorescent radiation from the sampling zone microchannels. A cyclic olefin copolymer (COC) embedded waveguide in PMMA along with an integrated coupling prism was fabricated using polydimethylsiloxane (PDMS) stencils and melted COC (40% w/v in toluene) on the cover plate. The COC waveguide with a COC integrated coupling prism will be used for evanescent excitation of fluorescent samples in the sampling zone microchannels. The fluidic substrate was bonded with the cover plate using thermal fusion bonding based on a pressure-assisted boiling point control system. This approach allowed for sealing of shallow microchannels without observable sagging of the cover plate, which was confirmed by leakage testing with fluorescent dyes. The completed SMD module will be tested for characterization of the optical performances such as signal-to-noise ratio and sampling efficiency and it will provide the capability for rapid screening of stroke at low cost.
A multi-scale fluidic motherboard, which can be used in a universal molecular processing system (uMPS) integrated with task-specific processing modules, was designed and fabricated in thermoplastics. The motherboard consists of a coverplate and a substrate. The coverplate included fluidic interconnects and thermal grooves on the top side, and the corresponding interconnects on the bottom side. The substrate was comprised of cell lysis microchannels, micromixers, and flow-connecting microchannels on the top side, and reservoirs for sample inputs and waste output, thermal grooves, and valve seats for flow control on the bottom side. The coverplates and substrates were fabricated with double-sided hot embossing of polycarbonate (PC) using four micromilled brass molds, two for the coverplate and another two for the substrate. Evaluation of the relative front-to-backside alignment for the double-sided hot embossing yielded an accuracy of 25 μm ± 14 μm (average ± standard deviation) for the coverplates and 30 μm ± 20 μm for the substrates. Thermal fusion bonding (TFB) of the coverplate and substrate was done using a spring plunger bonding setup with a range of temperatures and pressures. The motherboard bonded at 154 °C and 12.0 psi for 2 hours in a convection oven produced complete bonding with a little deformation of the valve seats. The complete motherboard will be integrated with the task-specific processing modules in the uMPS for investigating circulating markers from whole blood for precision molecular diagnosis of disease at low cost and with high fidelity.
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