We have never used NP-40 with our streptavidin beads; nevertheless, this detergent should be completely compatible with our beads. The literature is full of references in which NP-40 at a final concentration of 0.1% is used to wash streptavidin beads prior to addition of biotinylated molecules. In this regard, our streptavidin beads should be no different and fully compatible with the use of this detergent. The covalent bond used to immobilize streptavidin on the beads is not affected by the presence of this detergent. The only detergent that we definitely know destroys all biotin binding capacity is the denaturing ionic detergent SDS.