Magnetic carboxymethyl chitosan nanoparticles with immobilized metal ions for lysozyme adsorption

Nearly monodispersed and functional carboxymethyl chitosan nanoparticles (Fe3O4 (PEG + CM–CTS)) (about 15 nm) which prepared by chemical coprecipitating were treated with Zn (II), Cu (II) and Fe (III) ions solutions to obtain immobilized metal affinity magnetic nanoparticles (IMAN) (short as Fe3O4 (PEG + CM–CTS) @ Zn (II), Fe3O4 (PEG + CM–CTS) @ Cu (II) and Fe3O4 (PEG + CM–CTS) @ Fe (III) nanoparticles). The presented synthetic technology is simple, cost effective and allows to preparing the high-quality superparamagnetic IMAN in a large scale. The as-prepared nanoparticles were conveniently applied for lysozyme adsorption. In lysozyme adsorption study, the results obtained emphasize the role of pH and ionic strength in governing the extent and mechanism of affinity interactions which using IMAN as the carriers. The adsorption kinetic models (the pseudo-second-order) were used to analyze the experimental data, the results indicated that the pseudo-second-order equation is the appropriate equation to predict the adsorption capacity of lysozyme for these three tested magnetic carriers. The adsorption equilibrium of lysozyme onto the IMAN fitted well with the Langmuir model. The maximum equilibrium adsorption capacity of the Fe3O4 (PEG + CM–CTS) @ Zn (II), Fe3O4 (PEG + CM–CTS) @ Cu (II) and Fe3O4 (PEG + CM–CTS) @ Fe (III) nanoparticles were calculated to be 200 mg/g, 185.19 mg/g and 232.56 mg/g, respectively. Fluorescence analysis demonstrated that Fe3O4 (PEG + CM–CTS) @ Zn (II) and Fe3O4 (PEG + CM–CTS) @ Fe (III) nanoparticles may not cause the conformational change and denaturation for the lysozyme, but the lysozyme which desorbed from Fe3O4 (PEG + CM–CTS) @ Cu (II) underwent some subtle change in comparison with the original lysozyme. These results are expected to open up a new application of superparamagnetic nanoparticles as well as a new possibility for the lysozyme separation. Additionally, it is worth noting that, since the preparation, surface functionality and affinity separation process of the magnetic nanoparticles is low cost, nontoxic and reusable, the application of the superparamagnetic nanoparticles may find much potential in protein separation and purification.