Performance Study of the Immobilized Tyrosinase Using Dopamine-Coated Fe ₃ O ₄ Nanoparticles

Focused on the synthesize of an immobilized tyrosinase (TYR) with high loading, fast response, high activity, easy recovery, simple preparation, as well as environmental protection, this work designed the structure of the novel carrier as follows: Firstly, Fe 3 O 4 nanoparticles was prepared by the reverse microemulsion technology, and then it was coated with polydopamine (DA) to endow it with excellent biocompatibility while avoiding the oxidation of Fe 3 O 4 . Secondly, glutaraldehyde (GA) was graft on the coating layer by Schiff base reaction to obtain Fe 3 O 4 @PDA-GA MNPs. Finally, based on the Schiff base reaction with the unreacted aldehyde group of glutaraldehyde, Tyrosinase was immobilized on the carrier by covalent bonding to obtain immobilized sample, Fe 3 O 4 @PDA-GA-TYR MNPs. Condition investigation found that the best performance of immobilized TYR was achieved at an enzyme solution concentration of 3.00 mg/mL, pH of 7.0, immobilization time of 20 hours, and a temperature of 35 °C. Under the optimal condition, enzyme activity (EA), enzyme loading capacity (ELC), and enzyme activity retention ratio (EAR) reached 16046 U/g, 56 mg/g, and 80.4%, respectively. Compared with free TYR, the reusability, operational reliability, and stable in storage immobilized TYR were evaluated, results showed that the im-mobilized TYR improve above properties at a large degree.