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Oct 15, 2009 (Vol. 29, No. 18)

Use of Microarrays Increasing Rapidly

Academia Paves the Way with More Portable, Reproducible, and User-Friendly Tools

  • Nano Fountain Pen Technology

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    The tapered end of a nanopipette used in nano fountain pen technology. (Ben-Gurion University)

    The team has, in parallel, published several papers describing a nano fountain pen (NFP) technology for depositing nanoscale spots with atomic-force sensing accuracy. In addition to generating the bioarray spots, the device can also be used in the fabrication of polymer lenses that focus the fluorescence signal generated by each spot to help improve signal detection.

    The ability to generate spots at the nanometer scale has already been demonstrated using dip-pen lithography (DPN), a technique that uses an atomic-force microscope probe dipped in an “ink” of biological molecules to deliver a spot on a solid support.

    In contrast, the nano fountain pen technology developed by Dr. Gheber’s team uses cantilevered nanopipettes as the atomic-force microscope sensors. The heat-drawn nanopipettes have a sharp-end aperture of about 100 nm. When the capillaries are filled with the molecular ink, the liquid flows to the end of the pipette but does not flow out until the tip is contacted onto a surface.

    According to Dr. Gheber, published work has already shown that the technology can be used to print a line of protein G with a width of about 500 nm and thickness of 40 nm, GFP dots of about 280 nm and thickness of 4 nm, and functional enzymes, without the requirement for specific treatment of the substrate.

    The nano fountain pen technology has been exploited in the University’s development of polymer microlenses that help focus and enhance fluorescence signals generated by miniaturized spots. The microlens monomers are deposited onto the reverse of a glass microarray surface, over the area of each biological spot. UV-assisted polymerization generates spherical polymer microlenses of about four to nine microns in diameter, which focus the signal generated by each spot. The optical properties of the microlenses can also be controlled by varying the deposition time of the monomer solution.

    “Our nano fountain pen and microlens platforms represent new technologies we hope will help overcome some of the technical hurdles of chip miniaturization,” Dr. Gheber noted. “Such technological capabilities must be combined with mathematical models to help accurately define optimum spot and probe parameters, together with surface chemistry. Combine these capabilities with new methods for constructing and imaging each chip in a single instrument, and the potential for using microarrays in clinical and diagnostic fields becomes evident.”

  • Spot Characteristics

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    Microarrays of cells created using the parylene peel-off technology can be useful for testing drug efficacies and cancer studies.

    Researchers at Cornell University’s department of applied and engineering physics have addressed the issue of microarray spot uniformity, shape, and resolution, by exploiting the principle of a childhood drawing aid—the stencil.

    “Our parylene peel-array technology centers on a simple concept of a polymer stencil placed on top of the surface of the array,” explained Christine Tan, the technology’s developer. “The stencil acts as a physical constraint for spotted biomolecules, so you can deposit your molecules by whatever method you choose over the top, and then peel off the parylene layer to leave highly uniform spots. The technology can be used to generate any size, shape, or density of spot pattern.

    “Some of our most recent work has even demonstrated the feasibility of generating nanometer-sized array features with nanoscale resolution comparable to existing printing technologies like dip-pen lithography. This could potentially allow the future production of nanoarrays using existing arrayjet printers or spotters, which are currently only capable of printing spots with diameters in the 10–100s of microns range.”

    The flexibility of the system is inherent in its simplicity, Tan said. “The peel-arrays can be used either as stand-alone technology, to generate large uniform arrays of any biomolecule or even cells, or as a complement to any existing microarray-spotting method. The stencils act to cleanup print-spot morphology and can facilitate the printing of multiple species on a surface.

    “When combined with standard DNA-printing instrumentation, for example, we have shown the reproducibility of DNA microarrays is significantly improved. By reducing the traditional DNA-drying artefacts of donut-shaped spots, we can make the standard deviations of DNA microarray experiments much smaller.”

    Importantly, the peel-array technology can be used in wet or dry environments and has demonstrated major benefits in applications such as patterning lipid bilayers and proteins, where hydration is required to maintain bilayer and protein integrity, Tan added.

    Additional studies with patterning fibronectin have confirmed that by using the parylene peel-arrays the protein retains its 3-D conformity and functionality for cell binding. “The parylene stencils allow users to pattern molecules and keep them hydrated. We have also used the stencils to generate uniform, large-area arrays of single tumor cells to investigate the role of cell-cell interaction in cancer, and to pattern lipid bilayers embedded with antigen for studying immune cell activation.”

    Tan is looking for investors to start a business. “This is a useful technology with many potential applications in drug screening, cancer studies, biosensors, and basic science research,” she said. “We hope to make this simple and adaptable product available to everyone who uses microarrays.”

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