Enhanced immobilization of hexa-arginine-tagged esterase on gold nanoparticles using mixed self-assembled monolayers

Mixed self-assembled monolayers (MSAMs) composed of diverse ligands offer a mechanism for the specific binding of biomolecules onto solid surfaces. In this study, we examined the formation of MSAMs on gold nanoparticles (AuNPs) and the immobilization of hexa-arginine-tagged esterase (Arg(6)-esterase) on the surfaces of the resulting particles. The functionalization of AuNPs with MSAMs was achieved by introducing a mixture of tethering and shielding ligands into an AuNP solution. The formation of self-assembled monolayers (SAMs) on the AuNP surface was characterized by UV/visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. Arg(6)-esterase was immobilized in a highly specific manner onto AuNPs treated with mixed SAMs (MSAM-AuNPs) by providing a shielding ligand which reduce the non-specific adsorption of enzymes caused by hydrophobic interaction compared to AuNPs treated with single-component SAMs (SSAM-AuNPs). Moreover, Arg(6)-esterase immobilized on MSAM-AuNPs showed substantially enhanced catalytic activity up to an original activity compared to that on SSAM-AuNPs (58%).