Stability of magnetic bead IVD kits over time is important and should reflect the environment that is typically encountered by their reagents. For example, if the reagents will be frozen and thawed, stability should be addressed in these conditions. Magnetic beads, such as streptavidin beads, may behave heterogeneusly in different conditions, so these should be preserved when performing stability studies.
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The long-term behaviour can be very different for kits manufactured using covalent binding and the ones taking advantage of bio-activated surface (as biotin or streptvidin magnetic beads). Likewise, length of storage of the reagent should also be addressed while looking at stability. The following common reagent conditions should be considered when looking at stability of IVD kits:
1. Accelerated instability
Sometimes the kit can lose significant activity at 37ºC (approximately 20% activity loss after three days). This usually happens because the ligand is unstable. This accelerated instability is not acceptable in a CLIA IVD kit since many of the enzymes used in catalyzing the final reaction need to work at physiological temperatures.
2. Long-term stability issues
In order to test for long term stability, reference lots should always be stored at -20ºC and tested periodically. Long term stability, especially while stored frozen, is highly desirable since customers can purchase in quantity ahead of their demand and store the material until it is needed.
Long term stability is also important when considering cost issues – both cost of production and cost for the customer. The longer you can store your product, the larger your batches can be and the less your production cost will be.
3. Real-time stability issues
Ultimately, you would like to aim for your IVD kit to remain stable in the refrigerator (at 4ºC) for at least a year. This speaks once again to cost issues and consumer demand.
4. Bench top storage and delivery issues
It is reasonable to aim for room temperature stability of up to three months. This allows the end user to store reagents on their bench during a prolonged period of assays and also alleviates worries about instability during delayed delivery times.
5. Freeze/thaw and Heating/cooling cycles
You should aim for a loss of activity after freeze/thaw or heating/cooling cycles of less than 10% over time. Labs may overestimate what they need at any given time and need to re-freeze their inventory. In addition, you also want your product to be refractory to ambient environmental temperature variances.
When end users look at products to use in their assays, they look at ease of use, reliability, precision and of course, stability. If a product isn’t stable, the accuracy from one assay to another is in question and the product becomes useless to the end user. When proper steps are taken to guarantee stability in a variety of conditions, there will be great demand for your product.
Don't forget to check these posts from our blog in order to get a deeper insight into Chemiluminescent immunoassays:
- The Five Most Popular Magnetic Microsphere Currently for Chemiluminescent Immunoassays
- How to Select the Best Surface for Your Chemiluminescent Immunoassays
- Five Points to Consider when Selecting the Proper Magnetic Microsphere for Chemiluminescent Immunoassays