A Gel Sample Block Paul M. Taslimi Department of Chemistry and Biochemistry, Concordia University, 1455 DeMaisonneuve West, Montreal, Quebec, Canada H3G 1M8
DNA samples for analysis by agarose gel electrophoresis are usually prepared in 1.5-mL microcentrifuge tubes (Eppendorf tubes). Typically 15-20 KL samples are applied to wells on a horizontal agarose gel. Disadvantages of Microcentrifuge Tubes If a large number of samples are to be analyzed, the handling of individual tubes can became quite cumbersome. T h e tubes have to be numbered or labelled to avoid mix-ups. I f analysis is carried out routinely, the number of tubes used can became quite staggering. Considering the numbers of Eppendorftubes used in all bio-science labs, one can see how any method of reducing their numbers in terms of reducing waste may be worth consideration. The description of a simple device that will eliminate the necessity for the use of microcentrifuge tubes for preparation of most DNA samples follows. Features of a Better Apparatus The Block The apparatus is made from a small block of 114-in. (6.5 mm) Plexiglas into which two rows of wells are drilled using a 3-mm drill bit to a depth of 4 mm allowing samples of approximately 30 pL to be prepared. The dimensions of the block and the number of wells can vary according to the needs of the laboratory, but I have found that a block of
approximately 13-15 cm x 3 4 cm containing two rows of 8-10 wells to be quite convenient (Fig. 1).The wells can be numbered using the fine tip of a small engraving tool or a Tungsten carbide nib normally used for marking soft metal sheets for cutting. The Lid
A simple lid also can be made for the gel sample block using another piece of Plexiglas of the same dimensions over which a 2-mm thin strip of soft polyethylene foam, usually used to cover storage surfaces for glass apparatus, has been stuck. A thin layer of rubber adhesive or contact cement may be used for this purpose. For sealing, a strip of Parafilm slightly larger than the area of the gel sample block is placed over the block. The Plexiglas lid is placed over the Parafilm, and the whole assembly is clamped using 3 or 4 small spring-loaded paper clamps used for stationary (Fig. 2). The apparatus can be autoclaved if Teflon plastic is used for its construction and Silicon rubber used instead of the polyethylene foam. In this way RNA samples also can be prepared using the block. The Cleanup
It is i m p o r t a n t that t h e block be cleaned immedia t e l y a f t e r u s e t o a v o i d c o n t a m i n a t i o n of o t h e r samples. A rinse with lukewarm tap water, followed by distilled water, directed into individual wells, is sufficient.
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Plexiglas block Figure 1. The gel sample block and lid.
gel sample block Figure 2. Gel sample block assembled for storage of samples.
Volume 69 Number 1 January 1992
61
