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anna.moberg@ge.com  
#1 Posted : 03 July 2017 11:13:50(UTC)
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GE'anna.moberg@ge.com

Joined: 30/06/2017(UTC)
Posts: 3

A few years ago we were working on an assay for measurement of anti-drug antibodies in human plasma. Almost immediately we noticed that the non-specific binding from plasma “masked” the specific antibody binding and the sensitivity of our assay was low. Our goal was to achieve the detection limit required by FDA at that time (250-500 ng/ml) and initially we were far off. In order to enhance the sensitivity of our assay we knew we needed to decrease the non-specific binding from plasma and one way to accomplish this could be with a more suited buffer composition. So, we designed a multi-variant buffer study in which we looked at different buffer components, NaCl concentration, pH, detergents and additives. To be able to multiply and look at several buffers in parallel we performed the study on Biacore 4000, which is an excellent tool for this type of optimization. What we found was that the largest effect on assay sensitivity came from increasing the salt concentration. An increase in NaCl concentration from 0.15 M to 0.5 M had an enormous effect on the overall assay sensitivity. The non-specific binding was significantly reduced while the specific analyte binding remained more or less unaffected. This meant that the goal of reaching the FDA sensitivity requirement was passed with flying colors. The results also showed that salt concentrations higher than 0.5 had a negative impact on assay performance. The other parameters had little or no effect on sensitivity. So, for plasma assays on Biacore, a simple addition of NaCl to a total concentration of 0.5 M in regular HBS-EP+ buffer is my recommendation. The effect of the modified buffer was confirmed for seven different model molecules. Nice to see that sometimes problems can be overcome with the simplest of solutions. If you want to learn more check out the reference below. /Anna M, GEHC J Pharm Biomed Anal. 2013 May 5;78-79:224-32. doi: 10.1016/j.jpba.2013.02.018. Epub 2013 Feb 21.
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