Charge State of Weak Polyelectrolyte Brushes Determines Salt-Dependent Swelling and Hysteretic Behavior

We investigate the combined effects of ionizable monomer fraction f, pH, and monovalent salt concentration Cs on the swelling of weak polyelectrolyte brushes (PEBs) by using in situ ellipsometry. Our system consists of random copolymers of basic (2-(dimethylamino)ethyl acrylate, DMAEA) and neutral (2-hydroxyethyl acrylate, HEA) monomers at varying fractions of ionizable monomer. Swelling of the brushes qualitatively follows the trends predicted by scaling laws for PEBs under different charge states but quantitatively deviates at specific ionic strengths and pH values. We posit these deviations stem from the lack of excluded volume effects and assumptions of strong chain stretching in current theoretical models. Most notably, we uncover a salt-dependent, nonmonotonic hysteretic behavior as weak PEB brushes are cycled from protonated to deprotonated and back. The nonmonotonic trend of hysteresis with salt can be explained by an interplay between the protonation facilitating effects of salt in the osmotic regime and the charge screening effects in the salted regime, which make charge distribution along weak PEBs more uniform. Our results provide insight into the mechanisms that determine whether polyelectrolytes exhibit weak versus strong polyelectrolyte behavior in various environmental conditions.

Buffer Effects in Zirconium-Based UiO Metal-Organic Frameworks (MOFs) That Influence Enzyme Immobilization and Catalytic Activity in Enzyme/MOF Biocatalysts

Novel biocatalysts that feature enzymes immobilized onto solid supports have recently become a major research focus in an effort to create more sustainable and greener chemistries in catalysis. Many of these novel biocatalyst systems feature enzymes immobilized onto metal-organic frameworks (MOFs), which have been shown to increase enzyme activity, stability, and recyclability in industrial processes. While the strategies used for immobilizing enzymes onto MOFs can vary, the conditions always require a buffer to maintain the functionality of the enzymes during immobilization. This report brings attention to critical buffer effects important to consider when developing enzyme/MOF biocatalysts, specifically for buffering systems containing phosphate ions. A comparative analysis of different enzyme/MOF biocatalysts featuring horseradish peroxidase and/or glucose oxidase immobilized onto the MOFs UiO-66, UiO-66-NH₂, and UiO-67 using a noncoordinate buffering system (MOPSO buffer) and a phosphate buffering system (PBS) show that phosphate ions can have an inhibitory effect. Previous studies utilizing phosphate buffers for enzyme immobilization onto MOFs have shown Fourier transform infrared (FT-IR) spectra that have been assigned stretching frequencies associated with enzymes after immobilization. Analyses and characterizations using zeta potential measurements, scanning electron microscopy, Brunauer-Emmett-Teller surface area, powder X-ray diffraction, Energy Dispersive X-ray Spectroscopy, and FT-IR show concerning differences in enzyme loading and activity based on the buffering system used during immobilization.

Nanostructured supports for multienzyme co-immobilization for biotechnological applications: Achievements, challenges and prospects

The synergistic combination of current biotechnological and nanotechnological research has turned to multienzyme co-immobilization as a promising concept to design biocatalysis engineering. It has also intensified the development and deployment of multipurpose biocatalysts, for instance, multienzyme co-immobilized constructs, via biocatalysis/protein engineering to scale-up and fulfil the ever-increasing industrial demands. Considering the characteristic features of both the loaded multienzymes and nanostructure carriers, i.e., selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness, multienzyme-based green biocatalysts have become a powerful norm in biocatalysis/protein engineering sectors. In this context, the current state-of-the-art in enzyme engineering with a synergistic combination of nanotechnology, at large, and nanomaterials, in particular, are significantly contributing and providing robust tools to engineer and/or tailor enzymes to fulfil the growing catalytic and contemporary industrial needs. Considering the above critics and unique structural, physicochemical, and functional attributes, herein, we spotlight important aspects spanning across prospective nano-carriers for multienzyme co-immobilization. Further, this work comprehensively discuss the current advances in deploying multienzyme-based cascade reactions in numerous sectors, including environmental remediation and protection, drug delivery systems (DDS), biofuel cells development and energy production, bio-electroanalytical devices (biosensors), therapeutical, nutraceutical, cosmeceutical, and pharmaceutical oriented applications. In conclusion, the continuous developments in nano-assembling the multienzyme loaded co-immobilized nanostructure carriers would be a unique way that could act as a core of modern biotechnological research.

Development of a Multi-Enzymatic Biocatalytic System through Immobilization on High Quality Few-Layer bio-Graphene

In this work, we report the green production of few-layer bio-Graphene (bG) through liquid exfoliation of graphite in the presence of bovine serum albumin. Microscopic characterization evaluated the quality of the produced nanomaterial, showing the presence of 3-4-layer graphene. Moreover, spectroscopic techniques also confirmed the quality of the resulted bG, as well as the presence of bovine serum albumin on the graphene sheets. Next, for the first time, bG was used as support for the simultaneous covalent co-immobilization of three enzymes, namely β-glucosidase, glucose oxidase, and horseradish peroxidase. The three enzymes were efficiently co-immobilized on bG, demonstrating high immobilization yields and activity recoveries (up to 98.5 and 90%, respectively). Co-immobilization on bG led to an increase of apparent K_M values and a decrease of apparent V_max values, while the stability of the nanobiocatalysts prevailed compared to the free forms of the enzymes. Co-immobilized enzymes exhibited high reusability, preserving a significant part of their activity (up to 72%) after four successive catalytic cycles at 30 °C. Finally, the tri-enzymatic nanobiocatalytic system was applied in three-step cascade reactions, involving, as the first step, the hydrolysis of p-Nitrophenyl-β-D-Glucopyranoside and cellobiose.

Immobilization of a Bienzymatic System via Crosslinking to a Metal‐Organic Framework

A leading biotechnological advancement in the field of biocatalysis is the immobilization of enzymes on solid supports to create more stable and recyclable systems. Metal-organic frameworks (MOFs) are porous materials that have been explored as solid supports for enzyme immobilization. Composed of organic linkers and inorganic nodes, MOFs feature empty void space with large surface areas and have the ability to be modified post-synthesis. Our target enzyme system for immobilization is glucose oxidase (GOx) and chloroperoxidase (CPO). Glucose oxidase catalyzes the oxidation of glucose and is used for many applications in biosensing, biofuel cells, and food production. Chloroperoxidase is a fungal heme enzyme that catalyzes peroxide-dependent halogenation, oxidation, and hydroxylation. These two enzymes work sequentially in this enzyme system by GOx producing peroxide, which activates CPO that reacts with a suitable substrate. This study focuses on using a zirconium-based MOF, UiO-66-NH2, to immobilize the enzyme system via crosslinking with the MOF’s amine group on the surface of the MOF. This study investigates two different crosslinkers: disuccinimidyl glutarate (DSG) and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinidimide (NHS), providing stable crosslinking of the MOF to the enzymes. The two crosslinkers are used to covalently bond CPO and GOx onto UiO-66-NH2, and a comparison of the recyclability and enzymatic activity of the single immobilization of CPO and the doubly immobilized CPO and GOx is discussed through assays and characterization analyses. The DSG-crosslinked composites displayed enhanced activity relative to the free enzyme, and all crosslinked enzyme/MOF composites demonstrated recyclability, with at least 30% of the activity being retained after four catalytic cycles. The results of this report will aid researchers in utilizing CPO as a biocatalyst that is more active and has greater recyclability.

A Nanoconfined Four-Enzyme Cascade Simultaneously Driven by Electrical and Chemical Energy, with Built-in Rapid, Confocal Recycling of NADP(H) and ATP

The importance of energized nanoconfinement for facilitating the study and execution of enzyme cascades that feature multiple exchangeable cofactors is demonstrated by experiments with carboxylic acid reductase (CAR), an enzyme that requires both NADPH and ATP during a single catalytic cycle. Conversion of cinnamic acid to cinnamaldehyde by a package of four enzymes loaded into and trapped in the random nanopores of an indium tin oxide (ITO) electrode is driven and monitored through the simultaneous delivery of electrical and chemical energy. The electrical energy is transduced by ferredoxin NADP+ reductase, which undergoes rapid, direct electron exchange with ITO and regenerates NADP(H). The chemical energy provided by phosphoenolpyruvate, a fuel contained in the bulk solution, is cotransduced by adenylate kinase and pyruvate kinase, which efficiently convert the AMP product back into ATP that is required for the next cycle. The use of the two-kinase system allows the recycling process to be dissected to evaluate the separate roles of AMP removal and ATP supply during presteady-state and steady-state catalysis.

Controllable Enzyme Immobilization via Simple and Quantitative Adsorption of Dendronized Polymer-Enzyme Conjugates Inside a Silica Monolith for Enzymatic Flow-Through Reactor Applications

Although many different methods are known for the immobilization of enzymes on solid supports for use in flow-through applications as enzyme reactors, the reproducible immobilization of predetermined amounts of catalytically active enzyme molecules remains challenging. This challenge was tackled using a macro- and mesoporous silica monolith as a support and dendronized polymer-enzyme conjugates. The conjugates were first prepared in an aqueous solution by covalently linking enzyme molecules and either horseradish peroxidase (HRP) or bovine carbonic anhydrase (BCA) along the chains of a water-soluble second-generation dendronized polymer using an established procedure. The obtained conjugates are stable biohybrid structures in which the linking unit between the dendronized polymer and each enzyme molecule is a bisaryl hydrazone (BAH) bond. Quantitative and reproducible enzyme immobilization inside the monolith is possible by simply adding a defined volume of a conjugate solution of a defined enzyme concentration to a dry monolith piece of the desired size. In that way, (i) the entire volume of the conjugate solution is taken up by the monolith piece due to capillary forces and (ii) all conjugates of the added conjugate solution remain stably adsorbed (immobilized) noncovalently without detectable leakage from the monolith piece. The observed flow-through activity of the resulting enzyme reactors was directly proportional to the amount of conjugate used for the reactor preparation. With conjugate solutions consisting of defined amounts of both types of conjugates, the controlled coimmobilization of the two enzymes, namely, BCA and HRP, was shown to be possible in a simple way. Different stability tests of the enzyme reactors were carried out. Finally, the enzyme reactors were applied to the catalysis of a two-enzyme cascade reaction in two types of enzymatic flow-through reactor systems with either coimmobilized or sequentially immobilized BCA and HRP. Depending on the composition of the substrate solution that was pumped through the two types of enzyme reactor systems, the coimmobilized enzymes performed significantly better than the sequentially immobilized ones. This difference, however, is not due to a molecular proximity effect with regard to the enzymes but rather originates from the kinetic features of the cascade reaction used. Overall, the method developed for the controllable and reproducible immobilization of enzymes in the macro- and mesoporous silica monolith offers many possibilities for systematic investigations of immobilized enzymes in enzymatic flow-through reactors, potentially for any type of enzyme.

The Impact of Glucose Oxidase Immobilization on Dendritic Gold Nanostructures on the Performance of Glucose Biosensors

In recent years, many efforts have been made to develop rapid, sensitive and user-friendly glucose biosensors for monitoring blood glucose concentration in patients. In this study, the electrochemical glucose biosensors based on graphite rod (GR) electrode electrochemically modified with dendritic gold nanostructures (DGNs) and glucose oxidase (GOx) were developed. Phenazine methosulfate was used as a soluble redox mediator. Three GOx immobilization methods: adsorption on DGNs and cross-linking with glutaraldehyde (GA) vapour (GA-GOx/DGNs/GR), covalent immobilization on DGNs modified with 11-mercaptoundecanoic acid self-assembled monolayer (SAM) (GOx-SAM/DGNs/GR) and covalent immobilization on SAM with additional cross-linking with GA vapour (GA-GOx-SAM/DGNs/GR), were used. It was determined that GA significantly improved the stability of the enzyme layer. The difference of maximal current generated during the enzymatic reaction (ΔI_max) equal to 272.06 ± 8.69 µA was obtained using a biosensor based on GA-GOx/DGNs/GR electrodes. However, the highest ΔI_max equal to 384.20 ± 16.06 µA was obtained using GA-GOx-SAM/DGNs/GR electrode. ΔI_max for biosensors based on the GA-GOx-SAM/DGNs/GR electrode was 1.41 times higher than for the GA-GOx/DGNs/GR, whereas the linear dynamic range from 0.1 to 10 mM was the same using all three GOx immobilization methods. The limit of detection using GA-GOx-SAM/DGNs/GR and GA-GOx/DGNs/GR electrodes was 0.019 and 0.022 mM, respectively. The ability to detect glucose in the serum by developed biosensors was evaluated.

Random and Positional Immobilization of Multi-enzyme Systems

In recent years, three key techniques including random co-immobilization, positional co-immobilization, and compartmentalization for multi-enzyme immobilization were extensively considered. Herein, we investigate random co-immobilization and positional co-immobilization techniques for multi-enzyme systems in detail. We describe randomly co-immobilized glucose oxidase (GOx) and horseradish peroxidase (HRP) on reduced graphene oxide (rGO) as the most used methods. Materials and methods are presented in terms of preparation of GO and rGO as well as enzyme immobilization procedure. Moreover, the principles of positional co-immobilization have been reviewed, and the relevant methods based on microfluidic systems and DNA structure considering HRP and GOx enzymes have been individually studied. It is believed that the benefits of using the methods associated with random and specifically positional immobilized multi-enzyme systems include not only enhanced cascade enzymatic activity via manipulated surface such as microfluidic systems (including porous materials) and DNA structure but also improved enzyme stability and ease of recovery for recycle.

Large Changes in Protonation of Weak Polyelectrolyte Brushes with Salt Concentration-Implications for Protein Immobilization

We report for the first time that the protonation behavior of weak polyelectrolyte brushes depends very strongly on ionic strength. The pKa changes by one pH step per order of magnitude in salt concentration. For low salt concentrations (∼1 mM), a very high pH is required to deprotonate a polyacidic brush and a very low pH is required to protonate a polybasic brush. This has major consequences for interactions with other macromolecules, as the brushes are actually almost fully neutral when believed to be charged. We propose that many previous studies on electrostatic interactions between polyelectrolytes and proteins have, in fact, looked at other types of intermolecular forces, in particular, hydrophobic interactions and hydrogen bonds.

Co-immobilization of an Enzyme System on a Metal-Organic Framework to Produce a More Effective Biocatalyst

In many respects, enzymes offer advantages over traditional chemical processes due to their decreased energy requirements for function and inherent greener processing. However, significant barriers exist for the utilization of enzymes in industrial processes due to their limited stabilities and inability to operate over larger temperature and pH ranges. Immobilization of enzymes onto solid supports has gained attention as an alternative to traditional chemical processes due to enhanced enzymatic performance and stability. This study demonstrates the co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP) as an enzyme system on Metal-Organic Frameworks (MOFs), UiO-66 and UiO-66-NH2, that produces a more effective biocatalyst as shown by the oxidation of pyrogallol. The two MOFs utilized as solid supports for immobilization were chosen to investigate how modifications of the MOF linker affect stability at the enzyme/MOF interface and subsequent activity of the enzyme system. The enzymes work in concert with activation of HRP through the addition of glucose as a substrate for GOx. Enzyme immobilization and leaching studies showed HRP/GOx@UiO-66-NH2 immobilized 6% more than HRP/GOx@UiO-66, and leached only 36% of the immobilized enzymes over three days in the solution. The enzyme/MOF composites also showed increased enzyme activity in comparison with the free enzyme system: the composite HRP/GOx@UiO-66-NH2 displayed 189 U/mg activity and HRP/GOx@UiO-66 showed 143 U/mg while the free enzyme showed 100 U/mg enzyme activity. This increase in stability and activity is due to the amine group of the MOF linker in HRP/GOx@UiO-66-NH2 enhancing electrostatic interactions at the enzyme/MOF interface, thereby producing the most stable biocatalyst material in solution. The HRP/GOx@UiO-66-NH2 also showed long-term stability in the solid state for over a month at room temperature.

Electrostatic Interaction-Induced Formation of Enzyme-on-MOF as Chemo-Biocatalyst for Cascade Reaction with Unexpectedly Acid-Stable Catalytic Performance

Combining biocatalytic and chemocatalytic reactions in a one-pot reaction not only avoids the tedious isolation of intermediates during the reactions but also provides a desirable alternative to extend the range of catalytic reactions. Here, we report a facile strategy to immobilize an enzyme, glucose oxidase (GOx), on PCN-222(Fe) induced by electrostatic interaction in which PCN-222(Fe) serves as both a support and chemocatalyst. The immobilization was confirmed through ζ potential measurement, confocal laser scanning microscopy, Fourier transform infrared spectrometry, and UV-vis spectroscopy. This chemo-biocatalyst was applied to a cascade reaction to catalyze glucose oxidation and ABTS (ABTS = 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (or pyrogallol) oxidation. The catalytic kinetics studies show that these chemo-biocatalytic cascade reactions obey the Michaelis-Menten equation, which indicates that the cascade reactions follow the typical enzymatic dynamic regulation process. Interestingly, GOx/PCN-222(Fe) exhibits an exceptional acid-stable catalytic performance as evidenced by circular dichroism spectroscopy where no significant structure change was observed toward acidic solutions with different pH values. GOx/PCN-222(Fe) also displays desirable recyclability since no significant loss of conversion rates was found after six repeated reactions. This work presents a convenient strategy to construct metal-organic framework based chemo-biocatalysts, which may find potential applications in sensing and nanomachines.

Recent Developments in Carriers and Non-Aqueous Solvents for Enzyme Immobilization

Immobilization techniques are generally based on reusing enzymes in industrial applications to reduce costs and improve enzyme properties. These techniques have been developing for decades, and many methods for immobilizing enzymes have been designed. To find a better immobilization method, it is necessary to review the recently developed methods and have a clear overview of the advantages and limitations of each method. This review introduces the recently reported immobilization methods and discusses the improvements in enzyme properties by different methods. Among the techniques to improve enzyme properties, metal–organic frameworks, which have diverse structures, abundant organic ligands and metal nodes, offer a promising platform.

Stable Immobilization of Enzymes in a Macro- and Mesoporous Silica Monolith

Horseradish peroxidase isoenzyme C (HRP) and Engyodontium album proteinase K (proK) were immobilized inside macro- and mesoporous silica monoliths. Stable immobilization was achieved through simple noncovalent adsorption of conjugates, which were prepared from a polycationic, water-soluble second generation dendronized polymer (denpol) and the enzymes. Conjugates prepared from three denpols with the same type of repeating unit (r.u.), but different average lengths were compared. It was shown that there is no obvious advantage of using denpols with very long chains. Excellent results were achieved with denpols having on average 750 or 1000 r.u. The enzyme-loaded monoliths were tested as flow reactors. Comparison was made with microscopy glass coverslips onto which the conjugates were immobilized and with glass micropipettes containing adsorbed conjugates. High enzyme loading was achieved using the monoliths. Monoliths containing immobilized denpol-HRP conjugates exhibited good operational stability at 25 °C (for at least several hours), and good storage stability at 4 °C (at least for weeks) was demonstrated. Such HRP-containing monoliths were applied as continuous flow reactors for the quantitative determination of hydrogen peroxide in aqueous solution between 1 μM (34 ng/mL) and 50 μM (1.7 μg/mL). Although many methods for immobilizing enzymes on silica surfaces exist, there are only a few approaches with porous silica materials for the development of flow reactors. The work presented is a promising contribution to this field of research toward bioanalytical and biosynthetic applications.

Bioconversion of xylose to xylonic acid via co-immobilized dehydrogenases for conjunct cofactor regeneration

Enzymatic cofactor-dependent conversion of monosaccharides can be used in the bioproduction of value-added compounds. In this study, we demonstrate co-immobilization of xylose dehydrogenase (XDH, EC 1.1.1.175) and alcohol dehydrogenase (ADH, EC 1.1.1.1) using magnetite-silica core-shell particles for simultaneous conversion of xylose into xylonic acid (XA) and in situ cofactor regeneration. The reaction conditions were optimized by factorial design, and were found to be: XDH:ADH ratio 2:1, temperature 25 °C, pH 7, and process duration 60 min. Under these conditions enzymatic production of xylonic acid exceeded 4.1 mM and was more than 25% higher than in the case of a free enzymes system. Moreover, the pH and temperature tolerance as well as the thermo- and storage stability of the co-immobilized enzymes were significantly enhanced. Co-immobilized XDH and ADH make it possible to obtain higher xylonic acid concentration over broad ranges of pH (6-8) and temperature (15-35 °C) as compared to free enzymes, and retained over 60% of their initial activity after 20 days of storage. In addition, the half-life of the co-immobilized system was 4.5 times longer, and the inactivation constant (k_D = 0.0141 1/min) four times smaller, than those of the free biocatalysts (k_D = 0.0046 1/min). Furthermore, after five reaction cycles, immobilized XDH and ADH retained over 65% of their initial properties, with a final biocatalytic productivity of 1.65 mM of xylonic acid per 1 U of co-immobilized XDH. The results demonstrate the advantages of the use of co-immobilized enzymes over a free enzyme system in terms of enhanced activity and stability.

Surface modification by assembling: a modular approach based on the match in nanostructures

A modular strategy is described to construct a multi-biofunctional and conductive membrane based on the assembling of a nanostructured substrate and functional nanoparticles.

Biofunctionalized "Kiwifruit-Assembly" of Oxidoreductases in Mesoporous ZnO/Carbon Nanoparticles for Efficient Asymmetric Catalysis

A mesoporous ZnO/carbon composite is designed for coimmobilization of two oxidoreductases involving a novel "kiwifruit-assembly" pattern. The coimmobilization of (S)-carbonyl reductase II-glucose dehydrogenase on nanoparticles (SCRII-GDH_nano ) exhibits 40-50% higher specific activity than the free enzyme and significantly improves stabilities of enzymes to heat, pH and solvents. It performs asymmetric catalysis of 75 × 10^-3 m substrate with a perfect yield of 100% and an excellent enantioselectivity of 99.9% within 1 h. SCRII-GDH_nano gives an over 72% yield and 99.9% enantioselectivity after it is reused for ten times. Even with a highly concentrated (400 × 10^-3 m) substrate, it shows about 60% yield and 99.9% enantioselectivity within 4 h. SCRII-GDH_nano presents 4.5-8.0-fold higher productivity in 2.0-8.0-fold shorter reaction time than the free enzyme. This work provides a general, facile, and unique approach for the immobilization of two oxidoreductases and gives high catalytic efficiency, long-term and good recycling stabilities by triggering radical proton-coupled electron transfer.

NH2Fe3O4@SiO2 supported peroxidase catalyzed H2O2 for degradation of endocrine disrupter from aqueous solution: Roles of active radicals and NOMs

In this work, magnetic Fe₃O₄ was utilized to immobilize horseradish peroxidase (IM-HRP) in order to improve its stability and reusability by crosslinking method process with glutaraldehyde. The physicochemical properties of NH₂Fe₃O₄@SiO₂ and IM-HRP were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Thermo-gravimetric Analysis (TGA) and Transmission electron microscopy (TEM). The thermal stability of immobilized-HRP was considerably improved in comparison with free counterpart. The catalytic performance of IM-HRP for estrogens removal from aqueous solution was evaluated, it was found that the presence of natural organic matters (NOM) have no significant effects on E2 removal and the E2 enzyme-degradation reached around 80% when pH = 7.0 with 0.552 × 10^-3 ratio of IM-HRP/H₂O_2. In addition, the active radicals responsible for estrogens degradation were identified with electro-spin resonance spectra (ESR). It was found that immobilization process on Fe₃O₄ showed no adverse effects on catalytic performance on HRP, estrogens degradation could be fitted well with pseudo-second kinetic equation. Estrogens degradation efficiency was reduced in the presence of humic substances. Both O₂^- and OH were detected in IM-HRP catalyzed H₂O₂ system and radicals quenching test indicated O₂^- played a more important role in estrogens removal. IM-HRP exhibited excellent stability and E2 removal efficiency could reach 45.41% after use seven times. Therefore, HRP enzymes immobilized on NH₂Fe₃O₄@SiO₂ by cross-linking method in glutaraldehyde solutions was an effective way to improve stability and reusability of HRP, and which could avoid potential secondary pollution in water environment caused by free HRP after treatment.

High Activity and Convenient Ratio Control: DNA-Directed Coimmobilization of Multiple Enzymes on Multifunctionalized Magnetic Nanoparticles

The development of new methods for fabricating artificial multienzyme systems has attracted much interest because of the potential applications and the urgent need for multienzyme catalysts. Controlling the enzyme ratio is critical for improving the cooperative enzymatic activity in multienzyme systems. Herein, we introduce a versatile strategy for fabricating a multienzyme system by coimmobilizing horseradish peroxidase (HRP) and glucose oxidase (GOx) on magnetic nanoparticles multifunctionalized with dopamine derivatives through DNA-directed immobilization. This multienzyme system exhibited precise enzyme ratio control, high catalytic efficiency, magnetic retrievability, and enhanced stability. The enzyme ratio was conveniently adjusted, as required, by regulating the quantity of functional groups on the multifunctionalized nanoparticles. The optimal mole ratio of GOx/HRP was 2:1. The Michaelis constant K_m and specificity constant (k_cat/K_m, where k_cat is the catalytic rate constant) of the multienzyme system were 1.41 mM and 5.02 s^-1 mM^-1, respectively, which were approximately twice the corresponding values of free GOx&HRP. The increased bioactivity of the multienzyme system was ascribed to the colocalization of the involved enzymes and the promotion of DNA-directed immobilization. Given the wide variety of possible enzyme associations and the high efficiency of this strategy, we believe that this work provides a new route for the fabrication of artificial multienzyme systems and can be extended for a wide range of applications in diagnosis, biomedical devices, and biotechnology.

Synthesis of gold nanoparticles supported on functionalized nanosilica using deep eutectic solvent for an electrochemical enzymatic glucose biosensor

Engineering of nanoparticle (NP) surfaces offers an effective approach for the development of enzymatic biosensors or microbial fuel cells with a greatly enhanced direct electron transport process. However, lack of control over the surface functionalization process and the operational instability of the immobilized enzymes are serious issues. Herein, we demonstrate a facile and green deep eutectic solvent (DES)-mediated synthetic strategy for efficient amine-surface functionalization of silicon dioxide and to integrate small gold nanoparticles (AuNPs) for a glucose biosensor. Owing to the higher viscosity of the DES, it provides uniform surface functionalization and further coupling of the AuNPs on the SiO₂ support with improved stability and dispersion. The amine groups of the functionalized Au-SiO₂NPs were covalently linked to the FAD-center of glucose oxidase (GOx) through glutaraldehyde as a bifunctional cross-linker, which promotes formation of "electrical wiring" with the immobilized enzymes. The Au-SiO₂NP/GOx/GC electrode exhibits direct electron transfer (DET) for sensing of glucose with a sensitivity of 9.69 μA mM^-1, a wide linear range from 0.2 to 7 mM and excellent stability. The present green DES-mediated synthetic approach expands the possibilities to support different metal NPs on SiO₂ as a potential platform for biosensor applications.

A Review of Recent Developments of Mesoporous Materials

This personal account concerns novel recent discoveries in the area of mesoporous materials. Most of the papers discussed have been published within the last two to three years. A major emphasis of most of these papers is the synthesis of unique mesoporous materials by a variety of synthetic methods. Many of these articles focus on the control of the pore sizes and shapes of mesoporous materials. Synthetic methods of various types have been used for such control of porosity including soft templating, hard templating, nano-casting, electrochemical methods, surface functionalization, and trapping of species in pores. The types of mesoporous materials range from carbon materials, metal oxides, metal sulfides, metal nitrides, carbonitriles, metal organic frameworks (MOFs), and composite materials. The vast majority of recent publications have centered around biological applications with a majority dealing with drug delivery systems. Several other bio-based articles on mesoporous systems concern biomass conversion and biofuels, magnetic resonance imaging (MRI) studies, ultrasound therapy, enzyme immobilization, antigen targeting, biodegradation of inorganic materials, applications for improved digestion, and antitumor activity. Numerous nonbiological applications of mesoporous materials have been pursued recently. Some specific examples are photocatalysis, photo-electrocatalysis, lithium ion batteries, heterogeneous catalysis, extraction of metals, extraction of lanthanide and actinide species, chiral separations and catalysis, capturing and the mode of binding of carbon dioxide (CO₂ ), optical devices, and magneto-optical devices. Of this latter class of applications, heterogeneous catalysis is predominant. Some of the types of catalytic reactions being pursued include hydrogen generation, selective oxidations, aminolysis, Suzuki coupling and other coupling reactions, oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and bifunctional catalysis. For perspective, there have been over 40,000 articles on mesoporous materials published in the last 4 years and about 1388 reviews. By no means is this personal account thorough or all inclusive. One objective has been to choose a variety of articles of different types to obtain a flavor of the breadth of diversity involved in the area of mesoporous materials.

Separated Immobilization of Incompatible Enzymes on Polymer Substrate via Visible Light Induced Living Photografting Polymerization

The use of the mixed catalytic system with several enzymes can provide multiple benefits in terms of the cost, simplification of a multistep reaction, and effectiveness of complex chemical reactions. Although study of different enzyme coimmobilization systems has attracted increasing attention in recent years, separately immobilizing enzymes which can not coexist on one support is still one of the great challenges. In this paper, a simple and effective strategy was introduced to separately encapsulate incompatible trypsin and transglutaminase (TGase) into different poly(ethylene glycol) (PEG) network layer grafted on low-density polyethylene (LDPE) film via visible light induced living photografting polymerization. As a proof of concept, this dual-enzyme separately loaded film was used to catalyze the synthesis of a new target antitumor drug LTV-azacytidine. The final results demonstrated that this strategy could maintain higher activities of both enzymes than the mixed coimmobilization method. And the mass spectra analysis results demonstrated that LTV-azacytidine was successfully synthesized. We believe that this facile and mild separately immobilizing incompatible enzyme strategy has great application potential in the field of biocatalysis.

Co-localization of proteins with defined sequential order and controlled stoichiometric ratio on magnetic nanoparticles

Co-immobilization of enzymes used in cascade reactions is important for improving the overall catalytic efficiency. In this work, we employed scaffoldins as a bridge and succeeded in a highly-ordered co-localization of multiple proteins on magnetic nanoparticles with a loading capacity of ∼0.831 μmol g^-1 supports.

Preparation and Applications of Dendronized Polymer-Enzyme Conjugates

Dendronized polymer-enzyme conjugates are large, water-soluble macromolecular structures built from a linear, fully synthetic, dendronized polymer (denpol), and several copies of enzyme molecules covalently bound to the peripheral functional groups of the denpol. Since denpol chains comprise repeating units with regularly branched side chains (dendrons), denpols have a cylindrical shape and are much thicker than conventional linear polymers. Depending on the dendron generation and chemical structure, denpols may have a large number of functional groups on their surface, exposed to the aqueous medium in which they are dissolved. Enzymes (and also other molecules) can be attached to these functional groups, for example, via a stable bis-aryl hydrazone (BAH) bond. The dendronized polymer scaffold might also serve as a nanoarmor and stabilize the delicate enzymes. One of the denpols which can be used for the preparation of denpol-enzyme conjugates is de-PG2. It has a poly(methacrylate) backbone and consists of second-generation dendrons with four peripheral amino groups in each repeating unit. The synthesis of de-PG2 and the preparation of a de-PG2 conjugate carrying BAH-linked proteinase K (proK), as an example, are described here for applications in the field of enzyme immobilization on solid surfaces. The nanoarmored enzyme-polymer conjugate indicated high stability and retention of enzymatic activity.

Immobilization of lysozyme proteins on a hierarchical zeolitic imidazolate framework (ZIF-8)

A hierarchical zeolitic imidazolate framework-8 containing micropores and mesopores showed superior adsorption activity than micro-ZIF-8 towards enzyme proteins.

Magnetic metal–organic frameworks as scaffolds for spatial co-location and positional assembly of multi-enzyme systems enabling enhanced cascade biocatalysis

Magnetic metal–organic frameworks have been prepared as scaffolds for spatial co-location and positional assembly of multi-enzymes enabling enhanced cascade biocatalysis.

Enzymatic reactions in confined environments

Within each biological cell, surface- and volume-confined enzymes control a highly complex network of chemical reactions. These reactions are efficient, timely, and spatially defined. Efforts to transfer such appealing features to in vitro systems have led to several successful examples of chemical reactions catalysed by isolated and immobilized enzymes. In most cases, these enzymes are either bound or adsorbed to an insoluble support, physically trapped in a macromolecular network, or encapsulated within compartments. Advanced applications of enzymatic cascade reactions with immobilized enzymes include enzymatic fuel cells and enzymatic nanoreactors, both for in vitro and possible in vivo applications. In this Review, we discuss some of the general principles of enzymatic reactions confined on surfaces, at interfaces, and inside small volumes. We also highlight the similarities and differences between the in vivo and in vitro cases and attempt to critically evaluate some of the necessary future steps to improve our fundamental understanding of these systems.

One pot three-component reaction for covalent immobilization of enzymes: application of immobilized lipases for kinetic resolution of rac-ibuprofen

A one pot three-component reaction was used for the covalent immobilization of CALB and RML on epoxy-functionalized supports.

Stable and Simple Immobilization of Proteinase K Inside Glass Tubes and Microfluidic Channels

Engyodontium album proteinase K (proK) is widely used for degrading proteinaceous impurities during the isolation of nucleic acids from biological samples, or in proteomics and prion research. Toward applications of proK in flow reactors, a simple method for the stable immobilization of proK inside glass micropipette tubes was developed. The immobilization of the enzyme was achieved by adsorption of a dendronized polymer-enzyme conjugate from aqueous solution. This conjugate was first synthesized from a polycationic dendronized polymer (denpol) and proK and consisted, on average, of 2000 denpol repeating units and 140 proK molecules, which were attached along the denpol chain via stable bis-aryl hydrazone bonds. Although the immobilization of proK inside the tube was based on nonspecific, noncovalent interactions only, the immobilized proK did not leak from the tube and remained active during prolonged storage at 4 °C and during continuous operation at 25 °C and pH = 7.0. The procedure developed was successfully applied for the immobilization of proK on a glass/PDMS (polydimethylsiloxane) microchip, which is a requirement for applications in the field of proK-based protein analysis with such type of microfluidic devices.