Simple replication methods for producing nanoslits in thermoplastics and the transport dynamics of double-stranded DNA through these slits.

Mixed-scale nano- and microfluidic networks were fabricated in thermoplastics using simple and robust methods that did not require the use of sophisticated equipment to produce the nanostructures. High-precision micromilling (HPMM) and photolithography were used to generate mixed-scale molding tools that were subsequently used for producing fluidic networks into thermoplastics such as poly(methyl methacrylate), PMMA, cyclic olefin copolymer, COC, and polycarbonate, PC. Nanoslit arrays were imprinted into the polymer using a nanoimprinting tool, which was composed of an optical mask with patterns that were 2-7 µm in width and a depth defined by the Cr layer (100 nm), which was deposited onto glass. The device also contained a microchannel network that was hot embossed into the polymer substrate using a metal molding tool prepared via HPMM. The mixed-scale device could also be used as a master to produce a polymer stamp, which was made from polydimethylsiloxane, PDMS, and used to generate the mixed-scale fluidic network in a single step. Thermal fusion bonding of the cover plate to the substrate at a temperature below their respective T(g) was accomplished by oxygen plasma treatment of both the substrate and cover plate, which significantly reduced thermally induced structural deformation during assembly: ∼6% for PMMA and ∼9% for COC nanoslits. The electrokinetic transport properties of double-stranded DNA (dsDNA) through the polymeric nanoslits (PMMA and COC) were carried out. In these polymer devices, the dsDNA demonstrated a field-dependent electrophoretic mobility with intermittent transport dynamics. DNA mobilities were found to be 8.2 ± 0.7 × 10(-4) cm(2) V(-1) s(-1) and 7.6 ± 0.6 × 10(-4) cm(2) V(-1) s(-1) for PMMA and COC, respectively, at a field strength of 25 V cm(-1). The extension factors for λ-DNA were 0.46 in PMMA and 0.53 in COC for the nanoslits (2-6% standard deviation).

Fabrication of a cyclic olefin copolymer planar waveguide embedded in a multi-channel poly(methyl methacrylate) fluidic chip for evanescence excitation.

The fabrication and characterization of a novel cyclic olefin copolymer (COC) waveguide embedded in a poly(methyl methacrylate), PMMA, fluidic chip configured in a multi-channel format with an integrated monolithic prism for evanescent fluorescence excitation are reported. The fabrication approach allowed the embedded waveguide to be situated orthogonal to a series of fluidic channels within the PMMA wafer to sample fluorescent solutions in these channels using the evanescence properties of the waveguide. Construction of the device was achieved using several fabrication techniques including high precision micromilling, hot embossing and stenciling of a polymer melt to form the waveguide and coupling prism. A waveguide channel was fabricated in the fluidic chip's cover plate, also made from PMMA, and was loaded with a COC solution using a pre-cast poly(dimethylsiloxane), PDMS, stencil containing a prism-shaped recess. The PMMA substrate contained multiple channels (100 microm wide x 30 microm deep with a pitch of 100 microm) that were situated orthogonal to the waveguide to allow penetration of the evanescent field into the sampling solution. The optical properties of the waveguide in terms of its transmission properties and penetration depth of the evanescent field in the adjacent solution were evaluated. Finally, the device was used for laser-induced fluorescence evanescent excitation of a dye solution hydrodynamically flowing through multiple microfluidic channels in the chip and processed using a microscope equipped with a charge-coupled device (CCD) for parallel readout. The device and optical system were able to image 11 channels simultaneously with a limit-of-detection of 7.1 x 10(-20) mol at a signal-to-noise ratio of 2. The waveguide was simple to manufacture and could be scaled to illuminate much higher channel numbers making it appropriate for high-throughput measurements using evanescent excitation.

Microfluidic package design for magnetoresistive biosensors.

In order for Magnetoresistive Biosensor technology to become a mainstream product for clinical and consumer use, several outstanding technical issues must be solved. This paper will focus on one of those issues, which is the need to adapt standard semiconductor packaging processes to fall within some biosensor fabrication process constraints. A set of materials and interconnection methods that meet these biosensor requirements are presented. The resulting architecture is compatible with laboratory assembly, but can be scaled up to small and medium manufacturing quantities by using larger 2-dimensional areas per production batch.

Polymer microfluidic chips with integrated waveguides for reading microarrays.

A microfluidic chip with an integrated planar waveguide was fabricated in poly(methyl methacrylate), PMMA, using a single-step, double-sided hot-embossing approach. The waveguide was embedded in air on three sides, the solution being interrogated on the fourth. DNA probes were covalently attached to the waveguide surface by plasma activating the PMMA and the use of carbodiimide coupling chemistry. Successful hybridization events were read using evanescent excitation monitored by an imaging microscope, which offered high spatial resolution (2 microm) and a large field-of-view (20 mm diameter field-of-view), providing imaging of the entire array without scanning. The application of the microfluidic/waveguide assembly was demonstrated by detecting low abundant point mutations; insertion C mutations in BRCA1 genes associated with breast cancer were analyzed using a universal array coupled to an allele-specific ligation assay. DNA probes consisting of amine-terminated oligonucleotides were printed inside the microfluidic channel using a noncontact microspotter. Mutant and wild-type genomic DNAs of BRCA1 were PCR (polymerase chain reaction) amplified, with the amplicons subjected to ligation detection reactions (LDRs). LDR solutions were allowed to flow over the microarray positioned on the polymer waveguide with successful ligation events discerned through fluorescence signatures present at certain locations of the array. The microfluidic/waveguide assembly could detect polymorphisms present at <1% of the total DNA content.