The amino-modified γ-Fe2O3 nanoparticles could also react to folic acid to form a covalent linkage in the presence of 1-hydroxy-1H-benzotriazole, benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate and N-ethyl-N-(1-methylethyl)-2-propanamine [27].