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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

  • Laser-Printing Peptide Arrays

    Click Image To Enlarge +
    The inside of PEPperPRINT's peptide laser printer with drives for the printing gears

    PEPperPRINT has developed a laser-printing technology for combinatorial peptide synthesis, which it believes could bring the utility of peptide microarrays more in line with DNA microarrays in terms of array density, flexibility, and price. Spun out from the German Cancer Research Center in Heidelberg, PEPperPRINT just started commercializing its technology, offering high density peptide arrays on demand, along with iterative, high-throughput peptide-screening services for biomarker discovery and drug development.

    “PEPperPRINT was founded back in 2001 to develop technologies addressing issues that were holding back the attainment of affordable, flexible high-density peptide chip manufacture,” explained CEO Volker Stadler, Ph.D., who presented the technology at the Stockholm meeting.

    “At the time, we realized that existing processes that worked for the in situ synthesis of oligonucleotides such as lithographic methods weren’t as suitable for peptides. This is, at least in part, because while constructing DNA oligos requires only four monomers corresponding to the four bases, peptides are constructed from a pool of 20 amino acid monomers. Inkjet technologies are also far from ideal for printing amino acids. Liquid toner droplets of amino acids spread on the support, limiting spot density, and droplet evaporation can disturb coupling chemistry.”

    PEPperPRINT’s answer was to abandon inkjets and upgrade to a laser-printing approach. The resulting instrumentation is based on a conventional color laser printer, but instead of accommodating four-color ink cartridges, the printer uses 20 amino-acid toner units.

    “Our current laser-printer technology can spot at a 20-fold higher density than other state-of-the-art technologies, and by next year we hope to have developed a new system that will increase printing speed and spot density by another factor of four.”

    The process itself involves mounting the surface-modified glass slide onto a linear stage that drives the slide under the printer units with micrometer accuracy. Printing the first “layer” of amino-acid toners takes just one minute. The slide is then heated, to melt all the amino-acid toners at once to intiate coupling, followed by routine washing and deprotection steps. It can then undergo the next round of printing.

    PEPperPRINT believes that one of the major advantages of its laser-printer system is that the activated amino acids are embedded in solid toner particles, rather than in a liquid. This essentially immobilizes the amino acids in a stable state, so they can be stored within the toner for months without degradation, significantly reducing material costs and wastage.

    “The heating process after each round of printing raises the temperature just above the melting point of the amino acids, which isn’t high enough to cause evaporation,” Dr. Stadler continued. “And because the toner matrix has an oily consistency, it doesn’t spread on the slide surface. This is a key feature that allows us to achieve much higher spot densities.”

    PEPperPRINT is using the laser-printing technology to offer custom peptide chips, on both object slides and scalable glass slides. “The flexibility of the laser printing process means the cost is kept low however many chips are ordered, and whether we print a number of identical or completely different chips,” Dr. Stadler stressed. “In 2010 we aim to launch a web platform, PEPSlide®, which will allow customers to design their peptide chips on their own PC and send them through via the Internet, directly to the printing instrumentation.”

    In addition to its custom chip service, PEPperPRINT also offers peptide and peptidomimetic screening services for applications including biomarker discovery, antibody/enzyme profiling, diagnostic imaging, and drug development.

    “We can design individualized peptide arrays of up to 156,000 spots per slide for a wide range of screening applications. The combination of the system’s throughput, flexibility, and array density means that R&D can cost effectively use peptide arrays for sequential, iterative rounds of screening, for example to find and optimize high-affinity binders to target or probe proteins of interest.”

    “Proteome research is now provided with a highly efficient tool that PEPperPRINT expects to play a similar role as DNA chips in genome research do today,” Dr. Stadler concluded.

    “After starting the operative business in 2009, PEPperPRINT is going to establish both product lines, the customized peptide microarrays, and the iterative high-throughput screening routine, in the market in 2010. The next steps will include pilot studies with selected pharma companies and the launch of PEPSlide for the global web-based distribution of peptide chips.” 

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