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Designing a strategy for encasing enzymes and nanozymes in microreactors with spatial confinement in a way to improve the selectivity and activity of nanozymes is an exciting goal. In the present work, we report a facile route to encapsulate glucose oxidase (GOx) and poly(ethylenimine) (PEI)-conjugated magnetite nanoparticles (Fe 3 O 4 -PEI) in the hollow interior of hybrid microreactors. The microreactors are prepared by polyallylamine hydrochloride (PAH)-mediated silica (SiO 2 ) nanoparticle assembly on calcium carbonate (CaCO 3 ) particles as a removable core. By tuning both shape and phase (vaterite/calcite and pure calcite) of CaCO 3 , it allows generation of GOx and Fe 3 O 4 -PEI-encapsulated silica hollow microspheres (GOx-Fe 3 O 4 @SHS) and microcubes (GOx-Fe 3 O 4 @SHC). As observed, in a biomimetic cascade catalysis, the confined GOx in the microreactors is able to catalyze oxidation of glucose to gluconic acid and hydrogen peroxide (H 2 O 2 ), followed by the activation of H 2 O 2 by Fe 3 O 4 -PEI for the oxidation of the chromogenic substrate o -phenylenediamine (oPD) to 2,3-diaminophenazine. Comparison of the peroxidase-like activity of the encapsulated Fe 3 O 4 -PEI shows that the hollow microspheres (GOx-Fe 3 O 4 @SHS) result in activity 14 times higher than that of the hollow microcubes (GOx-Fe 3 O 4 @SHC), which in turn is corroborated to the differential loading capacity of GOx in microspheres and microcubes. The evaluation of kinetic parameters indicates a fivefold increase in the catalytic constant ( k cat ) of Fe 3 O 4 -PEI confined in hollow microspheres (GOx-Fe 3 O 4 @SHS) compared to the mixture comprising free GOx and Fe 3 O 4 -PEI in solution. It suggests that the confined space in the microreactors allows the tandem reactions of GOx and Fe 3 O 4 -PEI to take place in close proximity, leading to an improved overall activity. This indeed is seen in the k cat obtained for Fe 3 O 4 @SHS (GOx added externally during the assay), which is 14 times lower than that of GOx-Fe 3 O 4 @SHS.

Spatial confinement of glucose oxidase (GOx) in the hollow interior of a bioinspired matrix via polyamine mediated silica nanoparticle assembly under environmentally benign conditions is demonstrated herein. In a similarity to the biosilicification processes in diatoms, we use poly(allylamine hydrochloride) (PAH) to direct the assembly of silica nanoparticles on CaCO 3 spheres as the removable core. When this assembly process is performed on the CaCO 3 spheres, which are preloaded with GOx in a postsynthesis method, microspheres encapsulating GOx are formed. Interestingly, the encapsulated GOx in these microreactors exhibits activity with a Michaelis-Menten constant ( K M ) that is 2- to 3-fold less compared with the free enzyme in the solution. While the microenvironment of the organic (PAH)-inorganic (silica) hybrid system can be advantageous for the substrate to interact with enzyme, the effective pH in the vicinity of the entrapped enzyme may also be accountable for the improved activity, resulting in the lower apparent K M and enhanced specificity constant ( k cat / K M ). A 2-fold higher thermal stability of the encapsulated GOx compared with free GOx in solution further demonstrates the efficacy of the integrated architecture. Additionally, the PAH by virtue of its buffering capability allows the microspheres in imparting pH stability to the encapsulated GOx. Therefore, the method is not only a greener process for performing enzyme immobilization but also anticipated to aid in designing microreactors for enhanced enzyme activity.

Calcium carbonate (CaCO 3 )-based materials as feasible pH-sensitive drug carriers, which can actively dissolve in an acidic microenvironment of cancer cells, are finding increasing importance. This has drawn our interest in the development of a bioinspired polypeptide- mediated method to design calcium carbonate microspheres loaded with tetracycline (CaCO 3 -TC) with an aim to explore its safe application in cancer therapeutics. Its therapeutic application in cancer patients essentially demands its safety information on the normal cells. Herein our study presents the in vitro genetic toxicological information on CaCO 3 -TC using noncancerous mammalian CHO cells in comparison to bare TC at three different concentrations (100, 200, and 300 μM) selected based on the cytotoxicity data (MTT). Assessment of various end points like chromosome aberrations, micronucleus, mitotic index and effects on cell cycle distribution after 24 h post-treatment demonstrates a significant reduction in clastogenic ( P < 0.001), aneugenic potential ( P < 0.05), and nonmitotoxic nature of CaCO 3 -TC than that of bare TC. Noticeably, as inferred from the FACS analysis on cancer cells, G 2 /M phase accumulation in breast cancer cells (MDA-MB-231), and at G 1 phase in cervical cancer cells (HeLa) reveal its potential anticancer property. On the other hand, the genotoxicity studies illustrate protective effects of CaCO 3 -TC on noncancerous cells. While the pH-dependent dissolution property of the CaCO 3 matrix encasing tetracycline results in higher toxicity on cancer cells, the near neutral pH in the case of normal cells prevents complete dissolution of CaCO 3 thereby not allowing the encapsulated TC to adequately interact with the cells. Therefore, thus assembled CaCO 3 spheres not only provide a way for facile encapsulation of tetracycline under mild conditions but also result in an effective matrix for differential toxicity toward normal and cancer cells justifying its clinical development as a novel target-specific drug in therapeutic applications for metastatic cancers.

Herein we demonstrate a bioinspired method involving macromolecular assembly of anionic polypeptide with cationic peptide-oligomer that allows for in situ encapsulation of antibiotics like tetracycline in CaCO3 microstructure. In a single step one-pot process, the encapsulation of the drug occurs under desirable environmentally benign conditions resulting in drug loaded CaCO3 microspheres. While this tetracycline-loaded sample exhibits pH dependent in vitro drug-release profile and excellent antibacterial activity, the encapsulated drug or the dye-conjugated peptide emits fluorescence suitable for optical imaging and detection, thereby making it a multitasking material. The efficacy of tetracycline loaded calcium carbonate microspheres as pH dependent drug delivery vehicles is further substantiated by performing cell viability experiments using normal and cancer cell lines (in vitro). Interestingly, the pH-dependent drug release enables selective cytotoxicity toward cancer cell lines as compared to the normal cells, thus having the potential for further development of therapeutic applications.

Herein, we present an environmentally benign method capable of mineralization and deposition of nanomaterials to introduce antibacterial functionalities into cotton fabrics under mild conditions. Similar to the way in which many naturally occurring biominerals evolve around the living organism under ambient conditions, this technique enables flexible substrates like the cotton fabric to be coated with inorganic-based functional materials. Specifically, our strategy involves the use of long-chain polyamines known to be responsible in certain biomineralization processes, to nucleate, organize, and deposit nanostructured ZnO on cotton bandage in an aqueous solution under mild conditions of room temperature and neutral pH. The ZnO-coated cotton bandages as characterized by SEM, confocal micro-Raman spectroscopy, XRD, UV-DRS, and fluorescence microscopy demonstrate the importance of polyamine in generating a stable and uniform coating of spindle-shaped ZnO particles on individual threads of the fabric. As the coating process requires only mild conditions, it avoids any adverse effect on the thermal and mechanical properties of the substrate. Furthermore, the ZnO particles on cotton fabric show efficient antibacterial activity against both gram-positive and gram-negetive bacteria. Therefore, the developed polyamine mediated bioinspired coating method provides not only a facile and "green" synthesis for coating on flexible substrate but also the fabrication of antibacterial enabled materials for healthcare applications.