Changzhu Wu

Nanoparticle Cages for Enzyme Catalysis in Organic Media

Encapsulation of enzymes in Pickering emulsions results in a large interfacial area of the enzyme-containing aqueous phase for biocatalysis in organic media. This immobilization technique minimizes enzyme inactivation through stabilizing immiscible liquids by particles, facilitates separation processes, and significantly increases catalytic performance of both stable and vulnerable enzymes. Thus, a broad technical applicability can be envisioned.

Immobilization of lipase B within micron-sized poly-N-isopropylacrylamide hydrogel particles by solvent exchange

The aim of the present work is the use of a water soluble enzyme in an organic solvent, still with a pronounced catalytic activity. Therefore, lipase B from Candida antarctica (CalB) is immobilized within micron-sized thermosensitive p-NIPAM hydrogel particles using a solvent exchange from polar to organic solvents. The absorbed amount of CalB is investigated at different immobilization temperatures. Confocal laser scanning microscopy (CLSM) shows that CalB is homogeneously distributed within the polymer network. An enhanced specific activity of CalB in n-hexane is achieved after immobilization within the p-NIPAM microgels. In order to get information on the supply of the substrate depending on the temperature, the activity is determined at different reaction temperatures. Additionally, the system is stable in the organic solvent, namely n-hexane, and shows a good reusability.

Fibrous Networks with Incorporated Macrocycles: A Chiral Stimuli‐Responsive Supramolecular Supergelator and Its Application to Biocatalysis in Organic Media

A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis-urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low-molecular-weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol-gel phase transitions can be reversibly triggered by host-guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme-catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems.

Using Hydrogel Microparticles To Transfer Hydrophilic Nanoparticles and Enzymes to Organic Media via Stepwise Solvent Exchange

We present a simple and versatile approach of using hydrogel microparticles to transfer both inorganic hydrophilic nanoparticles (NPs) such as CdTe quantum dots and enzymes such as lipase B from Candida antarctica (CalB) to organic media and eventually encapsulate them in the gel microparticles by consecutive exchange of the water swollen in the hydrogel microparticles with water-miscible organic solvents and water-immiscible solvents. The entrapment of hydrophilic nanoparticles is due to their incompatibility with water-immiscible organic solvents soaked in the gel matrices and in the surrounding environment, so the present approach obviates the need for any chemical modification to the NP surface or to the hydrogel and furthermore does not require any size matching or chemical affinity of the NPs for the hydrogel networks. The solvent exchange process causes little change of the intrinsic properties of hydrophilic nanoparticles; CdTe quantum dots encapsulated in hydrogel microparticles, dispersed in water-immiscible organic solvents, remain strongly fluorescent, and CalB retains high catalytic activity. Of importance is that the hydrophilic nanoparticles encapsulated in the gel microparticles in organic media can be completely recovered in aqueous media via reversed solvent exchange. As a consequence, the present approach should hold immense promise for technical applications, especially in catalysis.

Enzymatically cross-linked hyperbranched polyglycerol hydrogels as scaffolds for living cells.

Although several strategies are now available to enzymatically cross-link linear polymers to hydrogels for biomedical use, little progress has been reported on the use of dendritic polymers for the same purpose. Herein, we demonstrate that horseradish peroxidase (HRP) successfully catalyzes the oxidative cross-linking of a hyperbranched polyglycerol (hPG) functionalized with phenol groups to hydrogels. The tunable cross-linking results in adjustable hydrogel properties. Because the obtained materials are cytocompatible, they have great potential for encapsulating living cells for regenerative therapy. The gel formation can be triggered by glucose and controlled well under various environmental conditions.

Optimized Biocatalytically Active Static Emulsions for Organic Synthesis in Nonaqueous Media

Literature reports biocatalytically active static emulsions (BASE) as promising systems for the preparation of biocatalysts designed for synthetic use in organic media. Their excellent catalytic performance is attributed to the numerous micropools of dissolved enzymes independently dispersed in silicone beads. Here, a systematic study of the structure and morphology of BASE and optimization in terms of bead size distribution and overall catalytic performance is presented. The study relies on beads obtained by using a novel preparation method that enables a considerably improved reproducibility of the particle size and catalytic activity in separate batches. A large interfacial area of 0.023 m2 g−1 material was calculated. The adjustment of bead composition increased the apparent catalytic activity of entrapped lipase A from Candida antarctica (CalA) to 0.71 U gBASE−1, which is almost twofold higher than that previously reported. The specific activity remained in the range of prototype BASE (0.21 U mgprotein−1), which nevertheless is about 53 times higher than that reported for CalA entrapped in a sol–gel.

A Highly Photostable Hyperbranched Polyglycerol-Based NIR Fluorescence Nanoplatform for Mitochondria-Specific Cell Imaging

Considering the critical role of mitochondria in the life and death of cells, non-invasive long-term tracking of mitochondria has attracted considerable interest. However, a high-performance mitochondria-specific labeling probe with high photostability is still lacking. Herein a highly photostable hyperbranched polyglycerol (hPG)-based near-infrared (NIR) quantum dots (QDs) nanoplatform is reported for mitochondria-specific cell imaging. Comprising NIR Zn-Cu-In-S/ZnS QDs as extremely photostable fluorescent labels and alkyl chain (C12 )/triphenylphosphonium (TPP)-functionalized hPG derivatives as protective shell, the tailored QDs@hPG-C12 /TPP nanoprobe with a hydrodynamic diameter of about 65 nm exhibits NIR fluorescence, excellent biocompatibility, good stability, and mitochondria-targeted ability. Cell uptake experiments demonstrate that QDs@hPG-C12 /TPP displays a significantly enhanced uptake in HeLa cells compared to nontargeted QDs@hPG-C12 . Further co-localization study indicates that the probe selectively targets mitochondria. Importantly, compared with commercial deep-red mitochondria dyes, QDs@hPG-C12 /TPP possesses superior photostability under continuous laser irradiation, indicating great potential for long-term mitochondria labeling and tracking. Moreover, drug-loaded QDs@hPG-C12 /TPP display an enhanced tumor cell killing efficacy compared to nontargeted drugs. This work could open the door to the construction of organelle-targeted multifunctional nanoplatforms for precise diagnosis and high-efficient tumor therapy.

Temperature Controlled Activity of Lipase B from Candida Antarctica after Immobilization within p-NIPAM Microgel Particles

Abstract The immobilization of lipase B from Candida antarctica (CalB) within micronsized poly-N-Isopropylacrylamide (p-NIPAM) microgel particles with a crosslinker content of 5% is reported. The immobilization of the enzyme was reached by an exchange from polar to organic solvents. After determining the embedded amount of CalB within the polymer network, an enhanced specific activity in n-hexane was obtained. Due to the thermoresponsibility of the polymer particles, the activity reaction was done at 25 ºC and 50 ºC. The results presented show that the reversible collapse of the microgel leads to a decreased activity with increasing temperature. Hence, p-NIPAM microgels display a good opportunity to tailor the activity of CalB. An interesting side effect is that CalB presents a suitable probe to estimate the mesh size of the polymer network, since it penetrates in the unlabeled form but not after labeling with FITC.

Active Antibacterial and Antifouling Surface Coating via a Facile One-Step Enzymatic Cross-Linking

Prevention of microbial contamination of surfaces is one of the biggest challenges for biomedical applications. Establishing a stable, easily produced, highly antibacterial surface coating offers an efficient solution but remains a technical difficulty. Here, we report on a new approach to create an in situ hydrogel film-coating on glass surfaces made by enzymatic cross-linking under physiological conditions. The cross-linking is catalyzed by horseradish peroxidase (HRP)/glucose oxidase (GOD)-coupled cascade reactions in the presence of glucose and results in 3D dendritic polyglycerol (dPG) scaffolds bound to the surface of glass. These scaffolds continuously release H2O2 as long as glucose is present in the system. The resultant polymeric coating is highly stable, bacterial-repellent, and functions under physiological conditions. Challenged with high loads of bacteria (OD540 = 1.0), this novel hydrogel and glucose-amended coating reduced the cell viability of Pseudomonas putida (Gram-negative) by 100% and Staphylococcus aureus (Gram-positive) by ≥40%, respectively. Moreover, glucose-stimulated production of H2O2 by the coating system was sufficient to kill both test bacteria (at low titers) with >99.99% efficiency within 24 h. In the presence of glucose, this platform produces a coating with high effectiveness against bacterial adhesion and survival that can be envisioned for the applications in the glucose-associated medical/oral devices.

Antimicrobial Efficacy and Cell Adhesion Inhibition of In Situ Synthesized ZnO Nanoparticles/Polyvinyl Alcohol Nanofibrous Membranes

Nanoparticle metal oxides are emerging as a new class of important materials in medical, agricultural, and industrial applications. In this context, free zinc oxide (ZnO) nanoparticles (NPs) have been increasingly shown with broad antimicrobial activities. However, biological properties of immobilized ZnO NPs on matrixes like nanofibrous membranes are still limited. In this study, in situ synthesized ZnO NPs/polyvinyl alcohol (PVA) nanofibrous membranes were fabricated by electrospinning with different zinc acetate concentrations. Characterization results indicated that, with 5 mM zinc acetate, uniform size ZnO NPs (~40 nm) were formed and evenly distributed on the membrane surface. The surfaces became more hydrophobic with higher concentration of zinc acetate. ZnO NPs/PVA nanofibrous membranes showed a broad spectrum of antimicrobial activities and cell adhesion inhibiting effects against four microorganisms including Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli, fungi Candida albicans, and spores of Aspergillus niger. Our data revealed that the major antimicrobial mechanism could be attributed to cell membrane damage and cellular internalization of ZnO NPs, while the hydrophobic surface of the membrane primarily contributed to the cell adhesion inhibition. This study suggests that ZnO NPs/PVA nanofibrous membranes could potentially be used as an effective antimicrobial agent to maintain agricultural and food safety.