Synthesis of silica nanospheres with Ni2+-iminodiacetic acid for protein separation

Silica (SiO₂) nanospheres (NSs) with immobilized metal ligands have been prepared for the affinity separation of proteins. First, SiO₂ NSs were prepared by controlled hydrolysis of tetraethoxysilane in a basic aqueous-ethanol solution. Then through reaction of iminodiacetic acid (IDA) with 3-glycidoxypropyltrimethoxysilane and immobilization of them onto the surfaces of above SiO₂ NSs, novel affinity adsorbents with IDA chelating groups were obtained. After chelating Ni²⁺ ions, the SiO₂–IDA–Ni²⁺ NSs were applied to separate his-tagged proteins directly from the mixture of lysed cells. The SiO₂–IDA–Ni²⁺ NSs present negligible nonspecific protein adsorption and high protein binding ability (28.3 mg/g).