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August 01, 2010 (Vol. 30, No. 14)

Refining Automated Liquid Dispensing

New Instrumentation Aims to Make Process More Accurate and Reproducible

  • Multichannel Verification

    Liquid transfers were evaluated in-house using 10 previously determined optimization parameters, including air gap, blow out, aspiration and dispense speeds, overstroke, and tip height. These were subsequently evaluated using a multichannel verification technique—a dual-dye multichannel verification system that has been widely used in the automation field to calibrate liquid volumes from a variety of automation platforms. This system offers a systematic validation of the liquid-handling instrument and includes dye solutions (sample and diluent), a calibration plate, an orbital plate mixer, as well as spectrophotometric read-out and data-analysis software.

    The single-, 8-, and 12-channel heads were used to dispense three different volumes: 2, 3, and 30 µL, to evaluate accuracy over a wide range. In addition, the 96-channel head was used to dispense five volumes, from 0.5 to 30 µL, in order to determine that this new liquid handler can dispense liquids in a precise and accurate manner. The assessment of these parameters is critical to generate reliable data when using the instrument for automated applications.

    The accuracy of the Versette was initially confirmed via the following process:

    • Dye was dispensed at the selected volume into a 96-well plate.
    • The plate was shaken at 1,200 rpm for one minute and centrifuged at 1,700 rpm for one minute.
    • Spectrophotometric absorbance was measured.

    The coefficient of variation (%CV) and margins of error (%error) were subsequently calculated using multichannel verification system software.

  • Results

    Click Image To Enlarge +
    Versette performance data using multichannel verification system

    The data obtained, including the %CV and %error were directly compared for a wide range of volumes using the 1-, 8-, 12-, and 96-channel pipetting heads (Table).

    Consistent results were obtained from the Versette and the multichannel verification system, demonstrating that the volumes dispensed from this liquid-handling platform are accurate and precise. This is, in part, due to the pipetting mechanics, which are adjustable for improved accuracy. With five precalibrated liquid classes for adjustment between standard experimental solutions, performance can be optimized. Experimental error due to dispensing inaccuracies is, therefore, reduced.

  • Conclusion

    Automated liquid handling is an integral part of any HTS protocol. In order to maintain experimental integrity and ensure that precise data is obtained, all potential sources of error must be significantly reduced. As such, ensuring the accuracy and precision of any liquid volumes dispensed is of extreme importance.

    The modular Thermo Scientific Versette automation platform for liquid handling provides the functionality to dispense volumes from 0.1 to 1,250 µL in a precise and accurate manner. Compatible with 19 interchangeable pipetting heads, ranging from single to 384 channels, means a wide range of throughput requirements are easily met. As such, when used in the creation of dilution series, users can be confident that the occurrence of false positive or negative results is maintained at a minimum, while throughput can be maximized without any loss in precision.

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