Protecting Enzymatic Activity via Zwitterionic Nanocapsulation for the Removal of Phenol Compound from Wastewater

Design of enzyme immobilized zwitterionic copolymer nanogels and its size effect on electrochemical reaction

For enzyme-based electrochemical devices, an improvement in electron transfer between the enzyme and electrode is important. Thus, we developed a nano-scaled hydrogel that includes an electron mediator and enzyme to realize nano-sized effects that enhance the functions. Three different chain lengths (short, medium, and long) of copolymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid N-hydroxysuccinimide ester (MNHS; poly(MPC-co-MNHS), PMS) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The PMS nanogels can bind to the amino ferrocene (AFc) of the electron mediator and glucose oxidase (GOD) as a catalyst. The mono-dispersive PMS nanogels approximately 200-250 nm in size bound with AFc were prepared with different polymer chain lengths and amounts of AFc (PMMFcX_Y%, X= 'degree of polymerization, 50, 75, 100' and Y= 'AFc feeding ratio against the amount of NHS group in the polymer chain, 50 %, 100 %'). The size of PMMFcX_Y% could be controlled by changing degree of polymerization or AFc feeding ratio. After the modification of GOD to PMMFcX_Y%, their size increased slightly from the original size (ca. 200-250 nm) to approximately 250-300 nm. The catalytic activity of nanogel in dispersed system was higher than that of microgel, indicating that nanogels could improve glucose transport in hydrogel layer. Compared to the catalytic reaction of the PMMFc 75_50 %-GOD nanogel-modified electrodes with that of microgel modified electrode, the current response was improved by decreasing the nanogel size, as evaluated by electrochemical measurements. These results revealed that the smaller nanogels could improve both glucose transport and electron transfer via mediator by smaller size, resulting higher efficiency of enzyme immobilized electrode.

A novel photo-enzyme platform based on non-metallic modified carbon nitride for removal of bisphenol A in water

A nonmetallic composite photocatalyst with 2D/2D structure was prepared by hydrothermal in-situ polymerization and used for the immobilization of cytochrome C (Cyt c). The photo-enzyme coupling system has a very high enzyme load, which can reach 528.29 mg g-1 after optimization. Compared with free Cyt c, Cytc/PEDOT/CN showed better enzymatic activity, stability and catalytic efficiency. Even after being stored at 100 °C for 60 min, the enzyme activity remained at 49.42 % and remained at 57.89 % after 8 cycles. Moreover, Cytc0.5/PEDOT3/CN showed excellent photocatalytic degradation performance in the degradation experiment of bisphenol A (BPA), reaching 68.22 % degradation rate within 60 min, which was 3.9 times higher than that of pure g-C3N4 and 1.61 times higher than that of pure PEDOT3/CN. This study shows that the introduction of conductive polymers is of great significance to the photo-enzyme coupling system and provides a new strategy for the treatment of phenol-containing wastewater.

Zwitterionic Targeting Doxorubicin -Loaded Micelles Assembled by Amphiphilic Dendrimers with Enhanced Antitumor Performance

Chemotherapy is the main method of treating malignant tumors in clinical treatment. However, the commonly used chemotherapeutic drugs have the disadvantages of high biological toxicity, poor water solubility, low targeting ability, and high side effects. Zwitterionic micelles assembled by amphiphilic dendrimers modified with zwitterionic groups and targeting ligand should largely overcome these shortcomings. Herein, the zwitterionic group and targeting peptide c(RGDfC) were modified on the surface of generation 2 poly(propylene imine) dendrimers (G2 PPI), which was conjugated with hydrophobic N-(2-mercaptoethyl) oleamide to form amphiphilic dendrimers (PPIMYRC). PPIMYRC self-assembled into micelles with doxorubicin (DOX) loaded in the interior of micelles to prepare DOX-loaded micelles (PPIMYRC-DOX micelles). The PPIMYRC-DOX micelles had great stability in fibrinogen and pH-responsive drug release. Furthermore, PPIMYRC-DOX micelles had higher cellular uptake rates than free DOX, resulting in higher cytotoxicity of PPIMYRC-DOX micelles than that of free DOX. More importantly, PPIMYRC-DOX micelles inhibited tumors much better than free DOX. The tumor inhibition rate of PPIMYRC-DOX micelles was as high as 93%. Taken together, PPIMYRC-DOX micelles were assembled by amphiphilic dendrimers with the zwitterionic and targeting groups, which enhanced the therapeutic effect of DOX and reduced its side effects. The prepared targeting nanodrug has great potential for further application in antitumor therapy.

Metal-Organic Enzyme Nanogels as Nanointegrated Self-Reporting Chemobiosensors

A fluorometric glucose biosensor based on fine-tuned chemoenzymatic nanohybrids is herein proposed. The successful integration of an engineered glucose oxidase enzyme and an optically responsive polymeric nanogel in a single entity has led to the fabrication of a highly efficient glucose chemobiosensor. The optical responsiveness has been achieved by the loading of preactivated polymeric hydrogel with fluorescent lanthanide, i.e., cerium (III), cations. A comprehensive investigation of the responsiveness of the biomaterial revealed the interplay between the oxidation state of the cerium lanthanide and the fluorescence emission of the polymer. Finally, a full structural, chemical, and biochemical characterization of the reported system supports the chemobiosensors as robust, specific, and sensitive materials that could be utilized to faithfully quantify the amount of glucose in tear fluids.

Phenoxyl mediators improve enzymatic degradation of organic pollutants: Effect and mechanism

A mediation strategy can effectively overcome the low reaction activity of enzymes with nonspecific substrates. In this study, we demonstrated how phenol compounds can mitigate the substrate limitation of HRP in catalytic degradation of various organic pollutants. In a classical HRP/H₂O₂ system, phenol and natural phenolic compounds (4-HBA & pHBA), exhibited up to over 100-fold enhancement in eliminating organic dyes and persistent antibiotics while the loading is only 2-5 wt%. A combination of molecular modelling, docking and frontier orbital energy analysis was employed to elucidate the catalytic performance and mechanism. We revealed that (1) generating phenoxyl radicals required the proximity of mediators to the HRP active centre, and (2) the subsequent efficient radical transfer to pollutants was determined by the large energy gap between the SOMO energy of phenoxyl radicals and the HOMO energy of phenols. When considering phenols as pollutants, we showed a synergistic effect on catalytic degradation of phenols, dyes, and tetracycline with a removal efficiency of 71-92 %. Overall, this work not only demonstrates that phenoxyl mediators can overcome the lower efficiency and substrate-specificity limitations of the HRP/H₂O₂ system but also revealed their structure-mediation relationship, implying great potential in the biodegradation of diverse pollutants and their mixtures.

Polymeric Nanocapsule Enhances the Peroxidase-like Activity of Fe3O4 Nanozyme for Removing Organic Dyes

Peroxidase-like nanozymes are nanoscale materials that can closely mimic the activity of natural peroxidase for a range of oxidation reactions. Surface coating with polymer nanogels has been considered to prevent the aggregation of nanozymes. For a long time, the understanding of polymer coating has been largely limited to its stabilization effect on the nanozyme in aqueous media, while little is known about how polymer coating plays a role in interaction with substrates and primary oxidants to dictate the catalytic process. This work reported a facile sequential modification of Fe3O4 nanoparticles to polyacrylamide coated nanozymes, and as low as 112 mg/L samples with only 5 mg/L Fe3O4 could nearly quantitatively (99%) remove a library of organic dyes with either H2O2 or Na2S2O8 as primary oxidants. The catalytic results and molecular simulation provide both experimental and computational evidence that the hydrogen bonding interaction between the reactant and nanozymes is key for the high local concentration hence catalytic efficiency. We envision that this work, for the first time, provides some insights into the role of polymer coating in enhancing the catalytic activity of nanozyme apart from the well-known water dispersity effect.

Verteporfin-loaded supramolecular micelles for enhanced cisplatin-based chemotherapy via autophagy inhibition

Cisplatin (CDDP) is one of the most successful chemotherapeutic agents for cancer therapy. However, CDDP can activate pro-survival autophagy, which inhibits the therapeutic efficacy of CDDP. Herein, autophagy inhibitor verteporfin (VTPF) is integrated into CDDP-conjugated micelles to address this issue. The CDDP-conjugated micelles are prepared by host-guest interaction of zwitterionic poly(2-(methacryloyloxy)ethyl phosphorylcholine)-co-poly(2-(methacryloyloxy)ethyl adamantane-1-carboxylate) (P(MPC-co-MAd)) and CDDP conjugated β-cyclodextrin (CD-CDDP). VTPF is then physically encapsulated into the supramolecular micelles by hydrophobic interaction. Due to the zwitterionic corona of the supramolecular micelles, the micelles are stable in different media. CDDP and VTPF could be released in a reductive environment. CDDP-activated autophagy could be inhibited by VTPF, which is fully characterized by western blot, fluorescence imaging, and transmission electron microscopy (TEM). Moreover, the outstanding therapeutic efficacy of CDDP and VTPF co-loaded micelles is validated both in vitro and in vivo. This research not only provides a new strategy to fabricate CDDP delivery systems by supramolecular self-assembly, but also presents an innovative way to enhance cisplatin-based chemotherapy via autophagy inhibition.

Zwitterionic Nanocapsules with Salt- and Thermo-Responsiveness for Controlled Encapsulation and Release

Intelligent polymer nanocapsules that can not only encapsulate substances efficiently but also release them in a controllable manner hold great potential in many applications. To date, although intensive efforts have been made to develop intelligent polymer nanocapsules, how to construct the well-defined core/shell structure with high stability via a straightforward method remains a considerable challenge. In this work, the target novel zwitterionic nanocapsules (ZN_Cs) with a stable hollow structure were synthesized by inverse reversible addition fragmentation transfer (RAFT) miniemulsion interfacial polymerization. The shell gradually grew from the water/oil interface due to the interfacial polymerization, accompanied by the cross-linking of the polyzwitterionic networks, where the core/shell structure could be well-tuned by adjusting the precursor compositions. The resultant ZN_Cs exhibited a salt-/thermo-induced swelling behavior through the phase transition of the external zwitterionic polymers. To further investigate the functions of ZN_Cs, different substances, such as methyl orange and bovine serum albumin (BSA), were encapsulated into the ZN_Cs with a high encapsulation efficiency of 89.3 and 93.6%, respectively. Interestingly, the loaded substances can be controllably released in aqueous solution triggered by salt or temperature variations, and such responsiveness also can be utilized to bounce off the bacteria adhered on target surfaces. We believe that these designed salt- and thermo-responsive intelligent polymer nanocapsules with well-defined core/shell structures and antifouling surfaces should be a promising platform for biomedical and saline related applications.

Weaving Enzymes with Polymeric Shells for Biomedical Applications

Enzyme therapeutics have received increasing attention due to their high biological specificity, outstanding catalytic efficiency, and impressive therapeutic outcomes. Protecting and delivering enzymes into target cells while retaining enzyme catalytic efficiency is a big challenge. Wrapping of enzymes with rational designed polymer shells, rather than trapping them into large nanoparticles such as liposomes, have been widely explored because they can protect the folded state of the enzyme and make post-functionalization easier. In this review, the methods for wrapping up enzymes with protective polymer shells are mainly focused on. It is aimed to provide a toolbox for the rational design of polymeric enzymes by introducing methods for the preparation of polymeric enzymes including physical adsorption and chemical conjugation with specific examples of these conjugates/hybrid applications. Finally, a conclusion is drawn and key points are emphasized.

Polyethylene Glycol Crowder's Effect on Enzyme Aggregation, Thermal Stability, and Residual Catalytic Activity

Protein stability and performance in various natural and artificial systems incorporating many other macromolecules for therapeutic, diagnostic, sensor, and biotechnological applications attract increasing interest with the expansion of these technologies. Here we address the catalytic activity of lysozyme protein (LYZ) in the presence of a polyethylene glycol (PEG) crowder in a broad range of concentrations and temperatures in aqueous solutions of two different molecular mass PEG samples (M_w = 3350 and 10000 g/mol). The phase behavior of PEG-protein solutions is examined by using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), while the enzyme denaturing is monitored by using an activity assay (AS) and circular dichroism (CD) spectroscopy. Molecular dynamic (MD) simulations are used to illustrate the effect of PEG concentration on protein stability at high temperatures. The results demonstrate that LYZ residual activity after 1 h incubation at 80 °C is improved from 15% up to 55% with the addition of PEG. The improvement is attributed to two underlying mechanisms. (i) Primarily, the stabilizing effect is due to the suppression of the enzyme aggregation because of the stronger PEG-protein interactions caused by the increased hydrophobicity of PEG and lysozyme at elevated temperatures. (ii) The MD simulations showed that the addition of PEG to some degree stabilizes the secondary structures of the enzyme by delaying unfolding at elevated temperatures. The more pronounced effect is observed with an increase in PEG concentration. This trend is consistent with CD and AS experimental results, where the thermal stability is strengthened with increasing of PEG concentration and molecular mass. The results show that the highest stabilizing effect is approached at the critical overlap concentration of PEG.

DNA-targeted formation and catalytic reactions of DNAzymes for label-free ratiometric electrochemiluminescence biosensing

A label-free ratiometric electrochemiluminescence (ECL) sensing strategy for the sensitive detection of target DNA (T-DNA) was proposed on the basis of G-quadruplex/hemin-regulated ECL emissions of CdS quantum dots (QDs) and luminol with their common coreactant of H₂O₂. The ECL biosensor was constructed through stepwise assemblies of CdS QDs and hairpin DNA (H-DNA) on a glassy carbon electrode, and subsequent introduction of T-DNA resulted in the development of G-quadruplex/hemin DNAzymes via the specific recognition of T-DNA and H-DNA in the presence of hemin and K⁺ ions. The formed DNAzymes not only prompted the catalytic oxidation of hydroquinone followed by deposition of insoluble oxidation oligomers on the electrode surface to attenuate the cathodic ECL emission of CdS QDs but also triggered the catalytic oxidation of luminol to enhance the anodic ECL emission. The label-free ratiometric ECL biosensor for the detection of T-DNA showed a wide response range from 1 to 10,000 fM (10^-15 M) with a low detection limit of 0.2 fM and exhibited excellent selectivity against mismatched base sequences. This work provides a reliable and sensitive sensing platform for the detection of targets in analytical community by means of rational design of DNA sequences.

Enhancing the peroxidase-mimicking activity of hemin by covalent immobilization in polymer nanogels

A polymeric nanozyme that can closely mimic peroxidase is presented. The coordination between pendant hemins and primary amines together with the synergistic interactions between substrates and nanogels contribute to the enhanced catalytic activity.

Nanostructured materials for harnessing the power of horseradish peroxidase for tailored environmental applications

High catalytic efficiency, stereoselectivity, and sustainability outcomes of enzymes entice chemists for considering biocatalytic transformations to supplant conventional synthetic routes. As a green and versatile enzyme, horseradish peroxidase (HRP)-based enzymatic catalysis has been widely employed in a range of biological and chemical transformation processes. Nevertheless, like many other enzymes, HRP is likely to denature or destabilize in harsh realistic conditions due to its intrinsic fragile nature, which results in inevitably shortened lifespan and immensely high bioprocess cost. Enzyme immobilization has proven as a prospective strategy for improving their biocatalytic performance in continuous industrial processes. Nanostructured materials with huge accessible surface area, abundant porous structures, exceptional functionalities, and high chemical and mechanical stability have recently garnered intriguing research interests as novel kinds of supporting matrices for HRP immobilization. Many reported immobilized biocatalytic systems have demonstrated high catalytic performances than that to the free form of enzymes, such as enhanced enzyme efficiency, selectivity, stability, and repeatability due to the protective microenvironments provided by nanostructures. This review delineates an updated overview of HRP immobilization using an array of nanostructured materials. Furthermore, the general physicochemical aspects, improved catalytic attributes, and the robust practical implementations of engineered HRP-based catalytic cues are also discussed with suitable examples. To end, concluding remarks, challenges, and worthy suggestions/perspectives for future enzyme immobilization are also given.

Tunable Polymeric Scaffolds for Enzyme Immobilization

The number of methodologies for the immobilization of enzymes using polymeric supports is continuously growing due to the developments in the fields of biotechnology, polymer chemistry, and nanotechnology in the last years. Despite being excellent catalysts, enzymes are very sensitive molecules and can undergo denaturation beyond their natural environment. For overcoming this issue, polymer chemistry offers a wealth of opportunities for the successful combination of enzymes with versatile natural or synthetic polymers. The fabrication of functional, stable, and robust biocatalytic hybrid materials (nanoparticles, capsules, hydrogels, or films) has been proven advantageous for several applications such as biomedicine, organic synthesis, biosensing, and bioremediation. In this review, supported with recent examples of enzyme-protein hybrids, we provide an overview of the methods used to combine both macromolecules, as well as the future directions and the main challenges that are currently being tackled in this field.

Congo Red Decolorization Using Textile Filters and Laccase-Based Nanocomposites in Continuous Flow Bioreactors

Removal of azo and diazo dye content from textile industry wastewaters is crucial due to their environmental impact. Here, we report on the use of the fungal laccase from Pycnoporus sanguineus CS43 immobilized on silica nanoparticles and entrapped in textile-based filters for the degradation of Congo Red. Laccase immobilization and synthesis of the nanocomposites were carried out by two different methods, one in the presence of acetone and the second using water as solvent. This led to a change in the hydrophobicity of the obtained biofilters. Successful preparation of the nanocomposites was confirmed via FTIR spectroscopy. Changes in the secondary structure of the enzyme were inspected through the second derivative of the FTIR spectra. Six different types of filter were fabricated and tested in a continuous flow bioreactor in terms of their decolorization capabilities of Congo Red. The results indicate removal efficiencies that approached 40% for enzymes immobilized on the more hydrophobic supports. Backscattered electron (BSE) images of the different filters were obtained before and after the decolorization process. Percentage of decolorization and activity loss were determined as a function of time until a plateau in decolorization activity was reached. Experimental data was used to recreate the decolorization process in COMSOL Multiphysics® (Stockholm, Sweden). These simulations were used to determine the proper combination of parameters to maximize decolorization. Our findings suggest that the treatment of textile-based filters with immobilized laccase in conjunction with hydrophobic nanocomposites provides a suitable avenue to achieve more efficient laccase dye decolorization (39%) than that obtained with similar filters treated only with free laccase (8%). Filters treated with silica-based nanocomposites and immobilized laccases showed an increase in their decolorization capability, probably due to changes in their wetting phenomena.

Entrapment of enzyme in the presence of proline: effective approach to enhance activity and stability of horseradish peroxidase

In this report, activity and stability of horseradish peroxidase (HRP) entrapped in polyacrylamide gel in the presence of proline (HEP) are compared with that of enzyme entrapped in absence of proline (HE). Within polyacrylamide (8%) beads, 80% entrapment yield for peroxidase was observed in the presence as well as absence of proline. The HEP (1.5 M proline) showed 170% higher activity compared to HE. HEP also showed significant increase in K _M, V _max and K _cat. At 8th cycle of use, HEP retained 40% of its activity, whereas HE retained only 10% of activity. In addition, in comparison with HE, HEP showed increased storage stability and thermo-stability. HEP showed higher activity compared to HE over an extensive range of pH (4-8), temperature (30-80 °C) and inhibitors such as NaN₃, Cd²⁺ and Pb²⁺. Our results suggest that peroxidase entrapment in polyacrylamide gel in the presence of proline can be a useful approach for increasing activity and stability of horseradish peroxidase.

Enzyme Immobilization in Polyelectrolyte Brushes: High Loading and Enhanced Activity Compared to Monolayers

Catalysis by enzymes on surfaces has many applications. However, strategies for efficient enzyme immobilization with preserved activity are still in need of further development. In this work, we investigate polyelectrolyte brushes prepared by both grafting-to and grafting-from with the aim to achieve high catalytic activity. For comparison, self-assembled monolayers that bind enzymes with the same chemical interactions are included. We use the model enzyme glucose oxidase and two kinds of polymers: anionic poly(acrylic acid) and cationic poly(diethylamino)methyl methacrylate. Surface plasmon resonance and spectroscopic ellipsometry are used for accurate quantification of surface coverage. Besides binding more enzymes, the "3D-like" brush environment enhances the specific activity compared to immobilization on self-assembled monolayers. For grafting-from brushes, multilayers of enzymes were spontaneously and irreversibly immobilized without conjugation chemistry. When the pH was between the pI of the enzyme and the p K_a of the polymer, binding was considerable (thousands of ng/cm² or up to 50% of the polymer mass), even at physiological ionic strength. However, binding was observed also when the brushes were neutrally charged. For acidic brushes (both grafting-to and grafting-from), the activity was higher for covalent immobilization compared to noncovalent. For grafting-from brushes, a fully preserved specific activity compared to enzymes in the liquid bulk was achieved, both with covalent (acidic brush) and noncovalent (basic brush) immobilization. Catalytic activity of hundreds of pmol cm^-2 s^-1 was easily obtained for polybasic brushes only tens of nanometers in dry thickness. This study provides new insights for designing functional interfaces based on enzymatic catalysis.