This heterobifunctional crosslinking reagent features a carboxylic acid group at one end and a reactive N-hydroxysuccinimide (NHS) ester at the other, separated by a flexible 12-methylene (C12) hydrocarbon spacer chain. It is primarily utilized in bioconjugation and protein modification, enabling the attachment of biomolecules such as proteins or peptides to substrates or other molecules. The NHS ester group facilitates the formation of stable amide bonds with primary amines (-NH₂), making it valuable for developing bioconjugates in research, diagnostics, and therapeutics. The free carboxylic acid (-COOH) can be further activated (e.g., via EDC/NHS coupling) for conjugation to other amines or surfaces. Additionally, it is used in surface functionalization of nanoparticles or polymers to improve biocompatibility or targeting in drug delivery. The long spacer provides optimal flexibility and distance, preserving the activity of conjugated biomolecules.