Hi. I am using EDC-NHS chemistry to modify PLGA surfaces using proteins. Is there a certain reaction time for the amine reactive NHS ester after which it becomes inactive (or less reactive) and does not aid in further protein binding to the surface?
It depends on the pH of the reaction medium and its temperature, at high pH the half-life of the ester is probably a few minutes, but within those minutes the reaction is also favored.
As Omar said, it depends, also depends on your solvent. Since you're working with proteins we're assuming water or aqueous buffer. I've found that at pH 7 and 25C the reaction is more or less complete within an hour. In some protein conjugation manuals (http://www.funakoshi.co.jp/data/datasheet/PCC/26099.pdf) they recommend 30 mins at RT and longer at lower temperatures.
Yes. I am using PBS. Is there any way to increase the stability and time of this reaction?
Keep it cold, since you cannot use organic solvents. You can also use sulfo-NHS instead of NHS.
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