Genetic research chip governs flow of fluids, not electrons

Princeton, NJ —Orchid BioSciences develops commercial applications for genetic diversity technologies, products, and services—primarily in the pharmaceutical and medical industries. The company's research focuses principally on single nucleotide polymorphisms (SNPs), which they describe as "the most common form of genetic diversity." Orchid analyzes SNPs to facilitate drug development and improve the effectiveness of existing drugs. Additional applications of Orchid's research lie in forensics, paternity, and tissue transplant testing, as well as improved crop development and livestock breeding programs.

Orchid BioSciences designed this five-layer microfluidics chip to synthesize and analyze genetic material in 384 individual reaction sites. But first they had to find a material that could seal those sites simultaneously.

Now that human genome sequencing has been decoded, many new opportunities exist for SNP analysis, and Orchid has developed new analysis techniques and technologies to be applied to SNPs, including a microfluidics chip designed to enable bench level reactions with less reagent than originally required. The prototype chip, says Gary Schnerr, executive director of engineering for Orchid, "is a multi-layered silicon and glass device that creates a 384-well 3D structure in one quarter the space of a standard micro-titer plate."

Orchid developed the chip to increase the density of test sites while meeting the challenges of fabricating silicon and glass. "Although the materials used in the new chip seem similar to computer chips, the microfluidics device differs from a semiconductor because fluid flow differs from electron flow," Schnerr says. "With fluids, you have to care about bends, orifices, and surface topography. You endeavor to minimize flow resistance, potential fluid traps, and moving parts so we have zero dead-volume, no moving-part capillary valves to control fluid flow."

Schnerr likens the design of the chip to 16 parallel lines in a row on one layer, and 24 columns crossing those lines on another layer. "At each junction point we have a reaction site—384 in all—in a multilevel structure. The chip has five distinct layers, and measures 1/10th of an inch in thickness."

To seal each reaction site from the outside environment and adjacent sites, Orchid went to Greene, Tweed and Co. (Kulpsville, PA), a manufacturer of specialty seals and other products. Schnerr says, "We had a chip with many points where fluid can flow down through layers to the reactor plate. Each point is structured with two orifices to deliver fluid, a fluid head, gasket and reactor site. To isolate each individual reactor site, insert its reagents, and remove the product after the reaction, we needed a robust seal that was also reusable."

Each junction point on the Orchid BioSciences microfluidics chip has two orifices to deliver fluid, a fluid head, a gasket, and a reactor site. To isolate each reactor site for insertion of reagents, and removal of the reaction product, Green, Tweed & Co. developed custom formulations for seal materials that combined compressibility and chemical resistance.

The seal presented a design challenge. Not only did each of the 384 sites need to be sealed simultaneously, but the seals had to provide the finish, flatness, and cleanliness of the glass top of the chip. Schnerr says, "The chip has very smooth surfaces, which is a positive factor. On the other hand, it has very little sealing surface. Then, in addition to the lack of space, a major consideration was material compatibility. The seal had to be made of materials that don't react with the reagents, or the results would be compromised."

With help from Orchid, designers at Greene, Tweed & Co. developed custom formulations for seal materials. "Because the seal goes on fragile material that can't take much pressure, we needed a particular combination of material softness or compressibility and chemical resistance," Schnerr says. The companies collaborated to develop a non-reactive material formulation that could be manufactured in quantity.

Barry Chadwick, medical product manager for Greene, Tweed & Co., adds, "the maximum seal thickness was 0.010 inches. We used proprietary precision manufacturing techniques to ensure final tolerances were achieved."

For more information about seals from Greene, Tweed & Co.: Enter 541