M aterials that efficiently release biological molecules or therapeutic chemicals on demand using exposure to remotely controlled and safe external sources of energy, such as magnetic fields, could find applications for drug delivery 1 , biotechnology 2,3 and biosensors 4 . Because live tissue and synthetic polymers are not responsive to weak magnetic fields, the development of magnetic-field-responsive soft materials has been reported by combining magnetic nanoparticles and stimuli-responsive soft materials 5 . Magnetic nanoparticles interact with magnetic fields and transduce magnetic field energy into physical or chemical changes in the soft material. Materials that control enzymatic processes are one example of such soft materials. Enzymes are extensively used to change or degrade colloidal particles, capsules, and their assemblies to trigger release of the cargo via biocatalytic reactions 6,7 .In all eukaryotes, metabolic pathways are precisely organized and regulated. This precise control is based in part on the high selectivity of biocatalytic reactions and controlled transport of chemicals and biomacromolecules across membranes that compartmentalize cells, organelles and organs. Highly selective biocatalysis alone cannot orchestrate complex systems of biochemical reactions without the supporting role of signal-triggered synthesis, release, secretion, conversion and degrading processes that take place in different compartments in cells and organs. Despite being highly selective, enzymes cannot provide 100% selectivity. In particular, enzymes could interact with a number of substrates of a similar chemical structure (for example, proteases are highly promiscuous catalysts), be degraded by other enzymes or even by self-digestion upon secretion into a complex biological environment, or undergo undesired aggregation, crystallization or nonspecific adsorption, which would strongly damage the efficiency of the biocatalytic process. However, the overall high specificity of biocatalytic processes is strengthened by localizing the enzymatic reactions within a specific environment and spatial compartments.Inspired by this hierarchical design in live systems, diverse stimuli-responsive functional materials have been reported, involving various architectures that respond to changes in magnetic fields [8][9][10] . However, it remains challenging to create a reactive system that preserves enzyme molecules from destructive environments and undesired interactions while being able to initiate the designated reaction when needed. Different approaches have been developed to preserve enzymes for storage and delivery before activating them on demand in a magnetic field at the targeted location. A number of studies aimed at controlling the kinetics of biocatalytic reactions in model systems [11][12][13][14][15] have explored magnetic-field-triggered changes of the local concentration and mobility of enzymes. However, it is difficult to apply many of such approaches to live tissue because of limitations associated with degradat...

Herein, we report a conjugation strategy, where we utilize a poly­(ethylene oxide) cylindrical molecular brush architecture to design a self-assembled structure for thermal stabilization of enzymes. We demonstrate that the proposed architecture of the moderately stiff polymer ligand results in a significant improvement of biocatalytic activity and thermal stability of lysozyme and trypsin that retain their activity, even upon heating to 100 °C and above. The molecular brush is bound via epoxy functional groups to the amino groups of the lysine on the surface of the enzyme globule, promoting the formation of stiff and crowded cages around the enzymes and preventing the water molecules access to the enzyme and enzymes agglomeration. The molecular dynamic simulations show that the high concentration of poly­(ethylene oxide) in the vicinity of the enzyme is critical for their stability. Monitoring of lysozyme–molecular brush conjugates for 6 and 12 months in lyophilized form and in solution, respectively, has shown that the conjugation does not compromise the shelf life of the enzyme.

This work demonstrates the application of hyaluronan-conjugated nitrogen-doped carbon quantum dots (HA-nCQDs) for bioimaging of tumor cells and illustrates their potential use as carriers in targeted drug delivery. Quantum dots are challenging to deliver with specificity, which hinders their application. To facilitate targeted internalization by cancer cells, hyaluronic acid, a natural ligand of CD44 receptors, was covalently grafted on nCQDs. The HA-nCQD conjugate was synthesized by carbodiimide coupling of the amine moieties on nCQDs and the carboxylic acids on HA chains. Conjugated HA-nCQD retained sufficient fluorescence, although with 30% lower quantum efficiency than the original nCQDs. Confocal microscopy showed enhanced internalization of HA-nCQDs, facilitated by CD44 receptors. To demonstrate the specificity of HA-nCQDs toward human tumor cells, patient-derived breast cancer tissue with high-CD44 expression was implanted in adult mice. The tumors were allowed to grow up to 200–250 mm3 prior to the injection of HA-nCQDs. With either local or systemic injection, we achieved a high level of tumor specificity judged by a strong signal-to-noise ratio between the tumor and the surrounding tissue in vivo. Overall, the results show that HA-nCQDs can be used for imaging of CD44-specific tumors in preclinical models of human cancer and potentially used as carriers for targeted drug delivery into CD44-rich cells.