Catalase immobilized in polypeptide/silica nanocomposites via emulsion and biomineralization with improved activities.

Polypeptide-mediated silica mineralization is an attractive approach to prepare polypeptide/silica nanocomposites for enzyme immobilization. Herein, a facile approach for in situ immobilization of catalase (CAT) in polypeptide/silica nanocomposites is developed via the preparation of cross-linked polypeptide/enzyme microgels using an emulsion process followed by silica mineralization. The efficient protein immobilization under benign condition (25-28 °C, pH 7.0, 0.05 N) was evidenced by high immobilization yield (> 99%) and no protein leakage. Our data showed that the immobilized CAT exhibited prolonged reusability and storage stability compared to free one, suggesting that the composite networks not only provide suitable microenvironments to facilitate enzymatic reactions but also confine the enzyme macromolecules to prevent subunit dissociation. Star-shaped topology exhibited better coverage onto the enzyme than linear counterpart, leading to the superior reusability (relative activity >95% for 30 cycling number) and storage stability (relative activity >95% for 60 days) of the immobilized CAT (~ 14 mg/g of support). The substrate affinity and enzymatic reaction rate for the immobilized CAT were also influenced by silica content and polypeptide topology. This strategy may provide a feasible and inexpensive approach to fabricate polypeptide/silica nanocomposites, which would be promising materials in biotechnological fields such as enzyme immobilization.

Green synthesis of gold nanoparticle/gelatin/protein nanogels with enhanced bioluminescence/biofluorescence.

Here we report the green synthesis of gelatin/protein hybrid nanogels containing gold nanoparticles (AuNPs) that collectively exhibit metal-enhanced luminescence/fluorescence (MEL/MEF). The gelatin/protein nanogels, prepared by genipin cross-linking of preformed gelatin/protein polyion complexes (PICs), exhibited sizes ranging between 50 and 200 nm, depending on the weight ratio of gelatin and protein. These nanogels serve as reducing and stabilizing agents for the AuNPs, allowing for nucleation in a gel network that exhibits colloidal stability and MEL/MEF. AuNP/gelatin/HRP and AuNP/gelatin/LTF nanogels presented an ~11-fold enhancement of bioluminescence in an HRP-luminol system and a ~50-fold fluorescence enhancement when compared to free LTF in cell uptake experiments. These hybrid nanogels show promise for optically enhanced diagnosis and other therapeutic applications.