A general strategy for protein immobilization in layered titanates: polyelectrolyte-assisted self-assembly

A general strategy was demonstrated here to immobilize proteins with various isoelectric points (IPs) in layered titanates. The immobilization of proteins with relative low IPs, such as bovine serum albumin (BSA) and lipase, in layered titanates was successfully by a novel polyelectrolyte-assisted electrostatic self-assembly technique, which is impossible by a conventional electrostatic self-assembly method. Lysozyme with relative high IP was detractively interacted with negative titanate nanosheets to form a bioinorganic composite. The native structures of proteins were retained after immobilizing although a significant difference in microstructures was observed among these composites. The amounts of immobilized proteins were up to ~68.3 wt.% for lysozyme, 37.2 wt.% for BSA and 21.5 wt.% for lipase. These composites were stable in the neutral and weakly acidic condition, and only releases <10% proteins in the pH<4 solution. The immobilized lysozyme and lipase exhibit excellent thermal stability, which retain their initial activities of about 70% at 70 °C for about 40 min. In addition, these composites are reusable, and the residual activities of immobilized enzymes are 68% for lysozyme and 61% for lipase after 10 recycles.