96-Well Chromatography With The Multiscreen(R) Assay System

Sample isolation and preparation often creates a bottleneck in the execution and automation of high throughput processes. To address this issue, Millipore has recently adapted its MultiScreen Assay System to perform chromatographic separations. This adaptation enables researchers to purify many samples simultaneously and provides a platform that facilitates automation. The MultiScreen approach has been used successfully to perform several types of chromatographic separation (for example, size exclusion, reverse phase, and cationic exchange) and presumably can be used with any standard chromatography matrix. Millipore Column Loader The MultiScreen Assay System, developed in 1989, consists of two components: disposable 96-well filtration plate assemblies and a vacuum manifold. The well bottoms of the plates are not closed off with plastic, as one would find in a standard 96-well plate; rather the wells are sealed with a filter. The filter, combined with the patented underdrain, allows the plates to hold liquid securely for up to several weeks at a time. When the plate is spun in a centrifuge or placed on the vacuum manifold, the solution is removed from the well by passing through the filter. Plates are offered with a variety of filters, but the most common one is Millipore's Durapure® filter, which has a very low binding affinity for most biological molecules so reaction mixes pass through the filter without sample loss. The design of the MultiScreen plates enables successive incubation and removal with several reagents and/or buffers. Transfer of solutions to a new microtiter plate is easily accomplished using the underdrain and vacuum manifold. In recent years, this platform has provided a convenient format for numerous biochemical and cell-based assays. Millipore has adapted this platform to provide an alternative to standard column chromatography. Any dry chromatographic matrix can be quickly loaded into the wells of the MultiScreen plates using the MultiScreen Column Loader. The column loader enables simultaneous equal loading of all 96-wells of the MultiScreen plate. For gel-based matrices, such as Sephadex, (Amersham Pharmacia Biotech) the matrix is swollen after it has been loaded into the wells. After loading and swelling, samples can be placed directly on the matrix in each well. For most chromatographic matrices, it is essential to use centrifugation, rather than the vacuum manifold, for packing and filtrate collection, otherwise the soft gel matrices crack and the samples bypass the matrix. According to Carolyn Lee, the senior marketing manager for the Multiwell products, separation in the MultiScreen plates is "a cost effective way to handle numerous samples." Larry Grocki, who is involved in sequencing mouse expressed sequence tags at Lexicon Genetics, has found the MultiScreen approach to be a very convenient method to purify DNA from the dye terminators after sequencing reactions. After sequencing reactions are performed with fluorescently labeled dideoxynucleotide terminators, it is essential to remove the excess dye terminators so that the sequencing gel runs correctly. This step can be a problem if many sequencing reactions are being performed. However, using the MultiScreen technique, 96 purifications can be done at once. Grocki finds that the MultiScreen plates are much more convenient than ethanol precipitation, which is the method his company used to use. In addition, he added that the "sequencing reactions are done in 96-well format so now robotics is used to transfer from the sequencing plate to the column plate, which has made everything easier overall." He has also just begun using the plates to remove dNTPs and primers after PCR purification. For separations using organic liquids, such as those used for reverse phase chromatography, Millipore has introduced MultiScreen Resist plates, which have solvent resistant plastic and filters. In conjunction with this adaptation of the MultiScreen plates for chromatography purposes, Millipore will introduce a new vacuum manifold in July. The new manifold will also be solvent resistant and, in addition, will allow collection in deep well 96- well plates. This modification will enable larger collection volumes for column chromatagraphy. For more information concerning MultiScreen Assays, contact Millipore at 1-800-MILLIPORE (645-5476) or www.millipore.com/multiscreen Paul Diehl is a freelance writer based in Perth Amboy, N.J. He can be reached at paul_vfocus@msn.com.

96-Well Chromatography With The Multiscreen(R) Assay System

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