Enzyme- or Au Nanoparticle-Loaded Fe3+-Ion-Cross-Linked Carboxymethyl Cellulose Hydrogel Microcapsules: Functional...

The synthesis of catalytic nanoassemblies or microassemblies emulating native enzymes attracts scientific interest. Here, we introduce the synthesis and characterization of Fe3+-bridged methacrylate carboxymethyl cellulose, Fe3+-MACMC, microcapsules (MCs) as catalytic carriers emulating native peroxidase activities. These are reflected by the H2O2-catalyzed oxidation of tetramethylbenzidine, TMB, to TMB+• or the H2O2-catalyzed oxidation of dopamine to aminochrome by the Fe3+-MACMC MCs. Integration of glucose oxidase (GOx) or Au nanoparticles (AuNPs, 1.9 ± 0.5 nm) into the MC boundaries enables the operation of oxidase/peroxidase biomimetic cascades by the engineered MCs. In these systems, aerobic oxidation of d-glucose by GOx, or of d-/l-glucose by AuNPs, yields gluconic acid and H2O2. The resulting H2O2 mediates the Fe3+-MACMC MC-catalyzed oxidation of TMB to the colored TMB+• (λ = 652 nm), providing a colorimetric signal for probing the catalytic cascades. By molecular imprinting of d- or l-glucose binding sites into the MC boundaries, enhanced aerobic oxidation of d-glucose by the GOx-functionalized MCs, or of d-/l-glucose by the AuNP-modified MCs, is accomplished. The enhanced activities of the molecular imprinted MCs are attributed to enhanced binding of the reactive substrate to the imprinted sites ("molarity effect"). In addition, imprinting of d- or l-glucose sites into the MC boundaries yields chiral binding sites, enabling the chiroselective-cascaded oxidation of d- or l-glucose by the imprinted MCs. Furthermore, imprinting of l- or d-DOPA sites into the Fe3+-MACMC MC boundaries enables the H2O2-mediated, enantioselective oxidation of l-/d-DOPA to dopachrome by the peroxidase-mimicking Fe3+-MACMC MCs.