Store › SiR-NHS ester 1mg Image 1 of 1 SiR-NHS ester 1mg $765.00 Quantity: Add To Cart Added! SiR-NHS ester is the active ester form of SiR. SiR-NHS ester reacts with amines to form stable covalent amide bond. SiR-NHS ester is the active ester form of SiR. SiR-NHS ester reacts with amines to form stable covalent amide bond.