With the development of science and technology, biosensors are applied in more and more fields, especially in clinical detection field. Immobilization of enzymes and proteins on activated supports permits the simplification of the biosensor design, which is a key technology for successful realization of enzyme-based biosensing processes. Innovative nanomaterials offer an exciting opportunity to address the challenges in immobilization of enzyme because of their large specific surface area and unique structure, which results in improved enzyme loading and enzyme activity compared to that of conventional materials. Recent breakthroughs in nano and hybrid technology have made various materials more affordable hosts for enzyme immobilization. Various enzymes have been immobilized on silica nanoparticles with multiple morphologies, including porous silica, mesoporous silica and Onion-like silica. Immobilization of the enzymes on gold nanoparticles is believed to help the protein to assume a favorable orientation and to make possible conducting channels between the prosthetic groups and the gold nanoparticle surface. Immobilized enzymes on magnetic nanoparticles exhibit high stability and can be easily separated from the reaction medium using a magnetic field.

However, many state-of-the-art immobilization methods afford high-quality stabilized enzyme systems by post-immobilization of enzymes on pre-synthesized nanomaterials, namely, by a multi-step route, which is always very tedious and complex. The reasons include that the preparation of nanomaterials is often conducted under rigorous conditions, e.g., high acidity, high temperature, and/or utilization of organic solvents, under which the enzymes may suffer severe deactivation. What’s more, these methods often need some organic solvent or cross-linking agent, such as glutaraldehyde, during the immobilization process of enzyme. Thus, greater efforts are needed for manipulation of enzyme immobilization. Up to now, success on facile and efficient one-step preparation of nanomaterials-enzyme conjugates is very challenging and such success has not been achieved yet. 

Scientists of TIPC,CAS develop a simple and environmentally-friendly method to prepare enzyme-zinc ferrite (Urease/ZnFe₂O₄) nanocomposites. The synthetic process is triggered through a biological mineralization process of decomposition of urea catalyzed by urease under mild conditions. During the growth of ZnFe₂O₄, urease molecules are immobilized by original ZnFe₂O₄ nanoparticles through electrostatic adsorption and covalent conjugation. And as a consequence, the bioactive Urease/ZnFe₂O₄ nanoparticle composites are assembled. The soft magnetic property of ZnFe₂O₄ endows the bioactive nanocomposites unique separable features for magnetic recycling. Our method overcomes the disadvantages of multi-step reaction and the use of organic solvent or cross-linking agent. The Urease/ZnFe₂O₄ nanocomposites can be used in biosensor to achieve sensitive detection of urea. This novel route is expected to endow the nanomaterials with new properties for various interesting applications.