Biocatalytic self-assembly on magnetic nanoparticles

Combining (bio-)catalysis and molecular self-assembly provides an effective approach for the production and processing of self-assembled materials, by exploiting catalysis to direct the assembly kinetics and hence control the formation of ordered nanostructures. Applications of (bio-)catalytic self-assembly in biologically interfacing systems and in nanofabrication have recently been reported. Inspired by self-assembly in biological cells, efforts to confine catalysts on flat or patterned surfaces to exert spatial control over molecular gelator generation and nanostructure self-assembly have also emerged. Building on our previous work in the area, we demonstrate in this report the use of enzymes immobilized onto magnetic nanoparticles (NPs) to spatially localize the initiation of peptide self-assembly into nanofibers around NPs. The concept is generalized for both an equilibrium biocatalytic system that forms stable hydrogels and a non-equilibrium system that normally has a preset lifetime. Characterization of the hydrogels shows that self-assembly occurs at the site of enzyme immobilization on the NPs, to give rise to gels with a “hub-and-spoke” morphology where the nanofibers are linked through the enzyme-NP conjugates. This NP-controlled arrangement of self-assembled nanofibers enables remarkable enhancements in the shear strength of both hydrogel systems, as well as a dramatic extension of the hydrogel stability in the non-equilibrium system. We are also able to show that the use of magnetic NPs enables external control of both the formation of the hydrogel and its overall structure by application of an external magnetic field. We anticipate that the enhanced properties and stimuli-responsiveness of our NP-enzyme system will have applications ranging from nanomaterial fabrication to biomaterials and biosensing.