4 °C preparation of ferrite nanoparticles having protein molecules immobilized on their surfaces

Trypsin, a proteolytic enzyme or a protein, was immobilized onto the surfaces of ferrite $({\mathrm{a Fe}}_3{\mathrm{O}}_4\mathrm{–\gamma }{\mathrm{Fe}}_2{\mathrm{O}}_3$ mixed solution) fine particles, ∼8 nm in size, during the process in which the particles were synthesized from an aqueous solution. The process was performed in the open air at a temperature as low as 4 °C and on near-neutral condition of $p\mathrm{H}\text{⩽9,}$ which is compatible with most of the bioactive molecules as well as trypsin. Therefore this technique is advantageous for preparing magnetite particles having biomolecules immobilized on their surfaces, which will be used for biomedical applications utilizing magnetic separation technique.