Enhanced reusability of hexa-arginine-tagged esterase immobilized on gold-coated magnetic nanoparticles

Gold-coated magnetic nanoparticle (GMP) was manufactured and used as a carrier for the immobilization of hexa-arginine-tagged esterase (Arg6-esterase). The formation of gold shell on the magnetic nanoparticle (Fe2O3) was performed by an iterative reduction method using hydroxylamine as a reductant. The surface of the GMP was further functionalized with mercapto-hexadecanoic acid (MHA) to tether the positively charged Arg6-esterase effectively. The enzymatic activity of the immobilized Arg6-esterase was investigated by monitoring the dissociation rate of its colorimetric substrate, p-nitrophenol butyrate (pNPB). Although the immobilized enzyme exhibited a lower activity (∼60%) compared to the free one, its original activity was found to be retained even after seven times repetitive uses by magnetic decantation.