Nunc-Immuno Plates MaxiSorp F96 from one batch were used in all experiments, except in the batch to batch variation analysis. After exposing the plates to different temperatures for various periods of time, the surface stability was tested using Nunc's binding uniformity test (described in Nunc Bulletin No. 4, second edition 1997). In short, a mixture of enzyme-conjugated and unconjugated antibodies in carbonate buffer, pH 9.6, was added to each well (200 µl/well). After incubation overnight, each well was washed 3 times with PBS containing 0.05% Triton X-100.
Color development by substrate reaction was read on an Immuno Reader NJ 2000. The mean, standard deviation, and CV were calculated using in-house software on an IBM-AT computer.
Storage at the following temperatures was used to simulate various storage/transport conditions: +60°C, +37°C, +4°C, room temperature (+20°C), -70°C, and outdoor temperature variations.
Plates produced from 1982 to 1986 were compared in order to make sure that storage at room temperature did not change the binding properties of the MaxiSorp surfaces. The results from this batch to batch comparison are shown in Fig. 1. Seven different batches were tested, and only a slight variation in the binding capacity was observed.
This means that under Nunc's standard storage conditions at room temperature, MaxiSorp products can be kept in stock for at least 4 years without affecting the surface binding capacity.
All other results are expressed as a percentage of values obtained simultaneously from plates kept at room temperature.
Transport during winter in cold climates may lead to exposure to extremely low temperatures for short periods of time, e.g. during air transport. In Figure 2 are shown the results of plates stored at -70°C. Plates were stored for up to one month, and as indicated in the Figure, no significant change occurred when compared with plates stored at room temperature.
In hot climates the products may be exposed to temperatures well above +40°C for short or long time periods. The effect of exposure to high temperatures was demonstrated by storing plates at +60°C (results are shown in Figure 2). The signal level decreased by 30% after three days of storage but remained thereafter constant for the rest of the .observation period (42 days).
Plates stored at room temperature, +4°C, +37°C, and plates stored outdoor (packed in a plastic bag) were followed for more than one year. The results are shown in Figure 3.
There was no significant difference between the results obtained for plates stored at
+4°C, at room temperature, or outdoor. However, after being stored at +37°C for 150 days, the plates showed a 10% decrease in signal as compared to those at room temperature. But after this period no further decrease could be observed for up to one year of storage.
From these experiments it can be concluded that Nunc-Immuno MaxiSorp surfaces can be stored for at least one year at temperatures below +37°C without changing their high adsorption properties. Storage at +37°C will reduce the signal level by 10% during the first 150 days, but after that no further decrease can be observed.
Storage at high temperatures, even for short periods, should be avoided as the signal level decreases rapidly at +60°C. However, like plates stored at +37°C, the decrease in signal level will not continue, but will stop at a temperature specific level. For plates stored at +60°C, the signal level decreases to 70% of the value for plates stored at room temperature.
It should be noted that these studies were performed exclusively with IgG. The adsorption of other molecules might respond differently to storage temperature.
