Reversible immobilization of glucoamylase onto magnetic carbon nanotubes functionalized with dendrimer

Magnetic carbon nanotubes (MCNTs) with necklace-like nanostructures was prepared via hydrothermal method, and hyperbranched poly(amidoamine) (PAMAM) was grafted on the surface of MCNTs on the basis of the Michael addition of methyl acrylate and the amidation of the resulting ester with a large excess of ethylenediamine (EDA), which could achieve generational growth under such uniform stepwise reactions. The terminal -NH(2) groups from the dendritic PAMAM were reacted with differently functionalized groups to form functionalized MCNTs. Subsequently, enzyme was immobilized on the functionalized MCNTs through adsorption, covalent bond, and metal-ion affinity interactions. The immobilization of glucoamylase, hereby chosen as model enzyme, onto the differently functionalized MCNTs is further demonstrated and assessed based on its activity, thermal stability, as well as reusability. Besides ease in recovery by magnetic separation, the immobilized glucoamylase on functionalized MCNTs offers superior stability and reusability, without compromising the substrate specificity of free glucoamylase. Furthermore, the results indicate that the metal-chelate dendrimer offers an efficient route to immobilize enzymes via metal-ion affinity interactions. The applicability of the regenerated supports in the current study is relevant for the conjugation of other enzymes beyond glucoamylase.