From: Avian Diseases Vol 28, No. 4 October-December 1982

Technical Aids in Avian Serology.
3. A Rapid-Access Storage System for Frozen Sera

P.F.McMullin

Veterinary Diagnostic Laboratory MSD Agvet Caixa Postal 878 Brazil 13100

 

Summary

  A system for storing frozen serum samples using hollow plastic cards is described. This system offers improved economy of materials and storage spaceand also facilitates rapid retrieval of samples.
 

Research Note

  Official diagnostic laboratories commonly freeze sera from routine accessions for future reference. Material collected for specific serological surveys should be likewise stored. Such sera collected over a period of years can be very useful in retrospective epidemiological investigations when previously unknown infectious diseases are described. The main limitation on the size of such collections of sera is the amount of freezer space available. Glass vials and ampules have been commonly used to store sera but they occupy a lot of space if stored in boxes which allow rapid identification and retrieval of samples. Plastic microtitration plates have many advantagesover conventional methods: They are compact and facilitate the identification of individual sera by a grid system (1). Their main disadvantage is the necessity to thaw up to 96 samples at one time resulting in unnecessary freeze-thaw cycles for many sera. Other disadvantages are the small well capacity (maximum 275 mcl) and the rather high cost of plates in some countries.

In view of these disadvantages a method of serum storage using hollow plastic cards was developed.

The corrugated plastic card used (Polionda 3mm, Tuffy Habib S.A. Rio de Janeiro Brazil) appears as a linear series of hexagons in cross section, each of which represents a compartment in which serum can be stored. This laboratory has had good results with cards of 5 x x cms(for 10 samples, 0.5ml in each). The cards may be siliconised by immersiojn in 0.35% polysiloxane (24 Emulsion, Dow Corning, Sao Paulo Brazil). One of the open edges of each card is sealed with heat and pressure. One corner of the opposite edge is removed to facilitate orientation of the card within the filing system. Figure 1 shows a storage card ready for use.

  Figure 1 Storage card ready for use.

The larger the dimension of the X axis, the larger the volume that can be stored in each compartment. The larger the dimension in the Y axis, the larger the number of samples that can be stored in each card.

  Filing boxes may be made from wood or other material and notches can be cut in their sides. Boxes designed to store photographic slides may be acquired in specialised shops and are ideal for the size of card described.

Sera should be carefully placed in each compartment with Pasteur pipettes, beginning at the bottom to avoid air bubble formation (Fig.2). A few drops of melted paraffin may be used to seal the end of each compartment. Each card should be properly identified and its contents registered in a book before placing them in the storage box at -20 C (Fig. 3).

  Figure 2. Storage card ready for use (right) and already loaded with sera and identified.
  Figure 3. A photographic slide box may be used to file the cards. This box holds 1600-2000 serum samples . On the left is the number of microtitration plates needed to hold a similar number of samples.
  The shape of the storage cards results in rapid freezing and thawing of samples and efficient use of available space. Samples can be removed from the storage cards by means of a Pasteur pipette or plunger-type micropipette.
 

References

  1. Whittemore, A.D. and J.E. Williams Microsystem for collecting and shipping diagnostic sera. Appl. Microbiol. 24:671-672 1972