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

Cofactor-directed co-immobilization of dual-enzyme on functionalized montmorillonite with enhanced catalytic performance

Recently, multi-enzyme cascade catalysis has attracted increasing attention due to the advantages of integrating multiple enzymes, few side reactions and high catalytic efficiency. Herein, a novel dual-enzyme cascade system (GOx-FMt-HRP) was developed through cofactor-directed orientational co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP) onto functional montmorillonite (FMt). The presented method realizes the reconstitution of cofactors and apo-enzymes (enzymes without cofactors), which enables enzymes to be immobilized in specific orientations on the support, thereby effectively reducing changes in their conformation. The results proved that GOx-FMt-HRP exhibited better catalytic stability and reusability than GOx/FMt/HRP (enzymes were co-immobilization on FMt by physical adsorption) and a physical mixture of free enzymes (GOx + HRP). After storage for 1 month, the residual activities of GOx-FMt-HRP, GOx/FMt/HRP, and GOx + HRP were 79.3 %, 60.4 %, and 1.32 %, respectively. Furthermore, GOx-FMt-HRP retained over 74 % activity after 10 uses, which is higher than that of GOx/FMt/HRP (61 %). Moreover, the substrate channeling allowed the prepared GOx-FMt-HRP to show the highest catalytic efficiency for both glucose (2.80 S-1·mM-1) and TMB (3.87 S-1·mM-1), being approximately 2.6-fold and 2.1-fold higher than that of the GOx + HRP, respectively. This work develops a simple method for dual-enzyme co-immobilization, aiding sustainable enzyme catalysis.

Coimmobilized Dual Enzymes in a Continuous Flow Reactor for the Efficient Synthesis of Optically Pure γ/δ-Lactones

Enzyme catalysis is a promising method for producing chiral chemicals with high stereoselectivity under mild conditions. However, the traditional batch reaction suffers from low enzyme stability, low cofactor recycling, and poor enzyme reusability. Here, we present a continuous-flow method using coimmobilized dual enzymes for the synthesis of chiral γ-/δ-lactones, which are widely used in fragrances and flavors. Typically, a carbonyl reductase mutant SmCRM5 from Serratia marcescens, was coimmobilized by covalent binding with BmGDH, a glucose dehydrogenase capable of recovering and recycling the cofactor NADPH. After immobilization, SmCRM5 and BmGDH exhibited a 8.9-/8.7-fold increase in catalytic efficiency (kcat/Km) and a 57-/15-fold increase in half-life at 30 °C, respectively. We demonstrated that coimmobilized dual enzymes used in a continuous flow reactor showed a higher reaction rate and a higher space-time yield (1586 g·L-1 d-1) than free enzymes and immobilized enzymes in a batch reaction for the production of (R)-δ-decalactone. This continuous flow reactor can run continuously for more than 650 h with 99% ee and 80% conversion, and the total volume exceeds 1500 reactor volumes. The robustness of this continuous-flow immobilized enzyme system provides a green and efficient method for the synthesis of high value-added chiral chemicals.

Co-immobilization of crosslinked enzyme aggregates on lysozyme functionalized magnetic nanoparticles for enhancing stability and activity

Surface chemistry of carriers plays a key role in enzyme loading capacity, structure rigidity, and thus catalyze activity of immobilized enzymes. In this work, the two model enzymes of horseradish peroxidase (HRP) and glucose oxidase (GOx) are co-immobilized on the lysozyme functionalized magnetic core-shell nanocomposites (LYZ@MCSNCs) to enhance their stability and activity. Briefly, the HRP and GOx aggregates are firstly formed under the crosslinker of trimesic acid, in which the loading amount and the rigidity of the enzyme can be further increased. Additionally, LYZ easily forms a robust anti-biofouling nanofilm on the surface of SiO2@Fe3O4 magnetic nanoparticles with abundant functional groups, which facilitate chemical crosslinking of HRP and GOx aggregates with minimized inactivation. The immobilized enzyme of HRP-GOx@LYZ@MCSNCs exhibited excellent recovery activity (95.6 %) higher than that of the free enzyme (HRP&GOx). Specifically, 85 % of relative activity was retained after seven cycles, while 73.5 % of initial activity was also remained after storage for 33 days at 4 °C. The thermal stability and pH adaptability of HRP-GOx@LYZ@MCSNCs were better than those of free enzyme of HRP&GOx. This study provides a mild and ecofriendly strategy for multienzyme co-immobilization based on LYZ functionalized magnetic nanoparticles using HRP and GOx as model enzymes.

2D graphene-based advanced nanoarchitectonics for electrochemical biosensors: Applications in cancer biomarker detection

Low-cost, rapid, and easy-to-use biosensors for various cancer biomarkers are of utmost importance in detecting cancer biomarkers for early-stage metastasis control and efficient diagnosis. The molecular complexity of cancer biomarkers is overwhelming, thus, the repeatability and reproducibility of measurements by biosensors are critical factors. Electrochemical biosensors are attractive alternatives in cancer diagnosis due to their low cost, simple operation, and promising analytical figures of merit. Recently graphene-derived nanostructures have been used extensively for the fabrication of electrochemical biosensors because of their unique physicochemical properties, including the high electrical conductivity, adsorption capacity, low cost and ease of mass production, presence of oxygen-containing functional groups that facilitate the bioreceptor immobilization, increased flexibility and mechanical strength, low cellular toxicity. Indeed, these properties make them advantageous compared to other alternatives. However, some drawbacks must be overcome to extend their use, such as poor and uncontrollable deposition on the substrate due to the low dispersity of some graphene materials and irreproducibility of the results because of the differences in various batches of the produced graphene materials. This review has documented the most recently developed strategies for electrochemical sensor fabrication. It differs in the categorization method compared to published works to draw greater attention to the wide opportunities of graphene nanomaterials for biological applications. Limitations and future scopes are discussed to advance the integration of novel technologies such as artificial intelligence, the internet of medical things, and triboelectric nanogenerators to eventually increase efficacy and efficiency.

DNA flexible chain modified MOFs as a versatile platform for chemoenzymatic cascade reactions in glucose catalysis

Glucose oxidase (GOD) is widely used in the pharmaceutical industry, fermentation products and glucose biosensors for its essential role in catalyzing the conversion of glucose to gluconic acid and hydrogen peroxide (H2O2). As H2O2 is the by-product and will have a toxic effect on glucose oxidase, so introducing another enzyme that could consume H2O2 to form an enzymatic cascade reaction is a practical solution. However, this decision will lead to extra expenses and complex condition optimization such as the specific mass ratio, temperature and pH to improve the activity, stability and recyclability. Herein, we describe a mild and versatile strategy by anchoring GOD on carboxyl-activated MOF (Cu-TCPP(Fe)) through DNA-directed immobilization (DDI) technology. Robust MOF nanosheets were utilized as not only the carrier for the immobilization of GOD, but also a peroxidase-like catalyst for the decomposition of H2O2 to reduce its harmful impacts. In this work, the immobilized GOD retained 55.78% of its initial activity after being used for 7 times. More than 60% of the immobilized enzyme's catalytic activity was still maintained after 96 h of being stored at 50 ℃. This study provides a new idea for preparing immobilized enzymes with enhanced stability, fast diffusion and high activity, which can be used in fields such as biocatalysis and biotechnology.

Construction of co-immobilized multienzyme systems using DNA-directed immobilization technology and multifunctionalized nanoparticles

The multienzyme co-immobilization systems with high cascade catalytic efficiency and selectivity have attracted considerable attention. In this study, through DNA-directed immobilization (DDI) technology, two model enzymes, glucose oxidase (GOD) and horseradish peroxide (HRP) were co-immobilized on the multifunctional silica nanoparticles (DDI enzyme). In addition to the directional distribution promoted by DNA complementary chains, the multienzyme system allowed the control of the stoichiometric ratio of the enzymes by adjusting the ratio of amino/carboxyl groups. The optimal mole ratio of GOD/HRP was 1:2, while the protein loading amount could reach 8.06 mg·g-1. Compared with the conventional direct adsorption, the catalytic activity of the DDI enzyme was 2.49 times higher. Moreover, with the enhancement of thermal and mechanical stability, the DDI enzyme could still retain at least 50% of its initial activity after 12 cycles. Accompanied by an excellent response and good selectivity, the constructed multienzyme systems simultaneously showed the potential as a glucose detector. Therefore, based on the DDI technology, the highly efficient multienzyme co-immobilization system could be further extended for a wider range of research fields.

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.

IR780-doped cobalt ferrite nanoparticles@poly(ethylene glycol) microgels as dual-enzyme immobilized micro-systems: Preparations, photothermal-responsive dual-enzyme release, and highly efficient recycling

To solve the problems of separating dual enzymes from the carriers of dual-enzyme immobilized micro-systems and greatly increase the carriers' recycling times, photothermal-responsive micro-systems of IR780-doped cobalt ferrite nanoparticles@poly(ethylene glycol) microgels (CFNPs-IR780@MGs) are prepared. A novel two-step recycling strategy is proposed based on the CFNPs-IR780@MGs. First, the dual enzymes and the carriers are separated from the reaction system as a whole via magnetic separation. Second, the dual enzymes and the carriers are separated through photothermal-responsive dual-enzyme release so that the carriers can be reused. Results show that CFNPs-IR780@MGs is 281.4 ± 9.6 nm with a shell of 58.2 nm, and the low critical solution temperature is 42 °C, and the photothermal conversion efficiency increases from 14.04% to 58.41% by doping 1.6% of IR780 into the CFNPs-IR780 clusters. The dual-enzyme immobilized micro-systems and the carriers are recycled 12 and 72 times, respectively, and the enzyme activity remains above 70%. The micro-systems can realize whole recycling of the dual enzymes and carriers and further recycling of the carriers, thus providing a simple and convenient recycling method for dual-enzyme immobilized micro-systems. The findings reveal the micro-systems' important application potential in biological detection and industrial production.

DNA-directed coimmobilization of multiple enzymes on organic-inorganic hybrid DNA flowers

The artificial multienzyme systems developed by mimicking nature has attracted much interest. However, precisely controlled compositions and ratios of multienzymatic co-immobilization systems are still limited by the indistinguishable nature of enzymes. Herein, a strategy for fabricating DNA-directed immobilization of horseradish peroxidase (HRP) and glucose oxidase (GOx) on hybrid DNA nanoflowers (GOx-HRP@hDFs) is presented. The preparation of micron-sized hybrid DNA flowers (hDFs) begins with the predetermined repeatable polymer-like DNA sequences which contained two strands. The hDFs structure is generated through one-pot rolling circle amplification (RCA) and self-assembly with magnesium pyrophosphate inorganic crystals. Based on the rigid-base pairing, GOx and HRP conjugated with sequences complementary to strands would be anchored to the predesigned locations, respectively. By adjusting the loading amount/ratio of enzymes properly, the maximal catalytic efficiency can be precisely regulated. The reaction activity of GOx-HRP@hDFs was 7.4 times higher than that of the free GOx-HRP under the optimal mole ratio (GOx/HRP 4:1). In addition, this multienzyme catalyst system exhibits excellent precision, specificity, reproducibility, and long-term storage stability when applied to real human blood samples. The preceding results validate that GOx-HRP@hDFs are promising candidates for personal diabetes detection.

Application of Nucleic Acid Frameworks in the Construction of Nanostructures and Cascade Biocatalysts: Recent Progress and Perspective

Nucleic acids underlie the storage and retrieval of genetic information literally in all living organisms, and also provide us excellent materials for making artificial nanostructures and scaffolds for constructing multi-enzyme systems with outstanding performance in catalyzing various cascade reactions, due to their highly diverse and yet controllable structures, which are well determined by their sequences. The introduction of unnatural moieties into nucleic acids dramatically increased the diversity of sequences, structures, and properties of the nucleic acids, which undoubtedly expanded the toolbox for making nanomaterials and scaffolds of multi-enzyme systems. In this article, we first introduce the molecular structures and properties of nucleic acids and their unnatural derivatives. Then we summarized representative artificial nanomaterials made of nucleic acids, as well as their properties, functions, and application. We next review recent progress on constructing multi-enzyme systems with nucleic acid structures as scaffolds for cascade biocatalyst. Finally, we discuss the future direction of applying nucleic acid frameworks in the construction of nanomaterials and multi-enzyme molecular machines, with the potential contribution that unnatural nucleic acids may make to this field highlighted.

Cascade chiral amine synthesis catalyzed by site-specifically co-immobilized alcohol and amine dehydrogenases

Sustainable and efficient production of chiral amines was realized with an oriented co-immobilized dual-enzyme system via SiBP-tag.

3D Printed Polylactic Acid Well-Plate for Multi-enzyme Immobilization

3D printing is lately utilized in biological sciences under the scope to develop customized scaffolds that will host biomolecules, either whole cells or parts of them, like enzymes. In the present work, we present a protocol to modify the surface of 3D printed polylactic acid (PLA) well-plates with the aim to co-immobilize multiple enzymes that will perform cascade reactions. Detailed steps to design and print the final models are described. The developed protocol for surface modification is based on coating with chitosan biopolymer and covalent immobilization of the enzymes β-glucosidase, glucose oxidase, and peroxidase via glutaraldehyde cross-linking. Enzymatic activity measurements indicative of the catalytic performance of the system are also presented.

Recent Advances in Emerging Metal- and Covalent-Organic Frameworks for Enzyme Encapsulation

Enzyme catalysis enables complex biotransformation to be imitated. This biomimetic approach allows for the application of enzymes in a variety of catalytic processes. Nevertheless, enzymes need to be shielded by a support material under challenging catalytic conditions due to their intricate and delicate structures. Specifically, metal-organic frameworks and covalent-organic frameworks (MOFs and COFs) are increasingly popular for use as enzyme-carrier platforms because of their excellent tunability in structural design as well as remarkable surface modification. These porous organic framework capsules that host enzymes not only protect the enzymes against harsh catalytic conditions but also facilitate the selective diffusion of guest molecules through the carrier. This review summarizes recent progress in MOF-enzyme and COF-enzyme composites and highlights the pore structures tuned for enzyme encapsulation. Furthermore, the critical issues associated with interactions between enzymes and pore apertures on MOF- and COF-enzyme composites are emphasized, and perspectives regarding the development of high-quality MOF and COF capsules are presented.

Multienzyme nanoassemblies: from rational design to biomedical applications

Multienzyme nanoassemblies (MENAs) that combine the functions of several enzymes into one entity have attracted widespread research interest due to their improved enzymatic performance and great potential for multiple applications. Considerable progress has been made to design and fabricate MENAs in recent years. This review begins with an introduction of the up-to-date strategies in designing MENAs, mainly including substrate channeling, compartmentalization and control of enzyme stoichiometry. The desirable properties that endow MENAs with important applications are also discussed in detail. Then, the recent advances in utilizing MENAs in the biomedical field are reviewed, with a particular focus on biosensing, tumor therapy, antioxidant and drug delivery. Finally, the challenges and perspectives for development of versatile MENAs are summarized.

Mimicking natural strategies to create multi-environment enzymatic reactors: From natural cell compartments to artificial polyelectrolyte reactors

Engineering microenvironments for sequential enzymatic reactions has attracted specific interest within different fields of research as an effective strategy to improve the catalytic performance of enzymes. While in industry most enzymatic reactions occur in a single compartment carrier, living cells are however able to conduct multiple reactions simultaneously within confined sub-compartments, or organelles. Engineering multi-compartments with regulated environments and transformation properties enhances enzyme activity and stability and thus increases the overall yield of final products. In this review, we discuss current and potential methods to fabricate artificial cells for sequential enzymatic reactions, which are inspired by mechanisms and metabolic pathways developed by living cells. We aim to advance the understanding of living cell complexity and its compartmentalization and present solutions to mimic these processes in vitro. Particular attention has been given to layer-by-layer assembly of polyelectrolytes for developing multi-compartments. We hope this review paves the way for the next steps toward engineering of smart artificial multi-compartments with adoptive stimuli-responsive properties, mimicking living cells to improve catalytic properties and efficiency of the enzymes and enhance their stability.

Nature Inspired Multienzyme Immobilization: Strategies and Concepts

In a biological system, the spatiotemporal arrangement of enzymes in a dense cellular milieu, subcellular compartments, membrane-associated enzyme complexes on cell surfaces, scaffold-organized proteins, protein clusters, and modular enzymes have presented many paradigms for possible multienzyme immobilization designs that were adapted artificially. In metabolic channeling, the catalytic sites of participating enzymes are close enough to channelize the transient compound, creating a high local concentration of the metabolite and minimizing the interference of a competing pathway for the same precursor. Over the years, these phenomena had motivated researchers to make their immobilization approach naturally realistic by generating multienzyme fusion, cluster formation via affinity domain-ligand binding, cross-linking, conjugation on/in the biomolecular scaffold of the protein and nucleic acids, and self-assembly of amphiphilic molecules. This review begins with the discussion of substrate channeling strategies and recent empirical efforts to build it synthetically. After that, an elaborate discussion covering prevalent concepts related to the enhancement of immobilized enzymes' catalytic performance is presented. Further, the central part of the review summarizes the progress in nature motivated multienzyme assembly over the past decade. In this section, special attention has been rendered by classifying the nature-inspired strategies into three main categories: (i) multienzyme/domain complex mimic (scaffold-free), (ii) immobilization on the biomolecular scaffold, and (iii) compartmentalization. In particular, a detailed overview is correlated to the natural counterpart with advances made in the field. We have then discussed the beneficial account of coassembly of multienzymes and provided a synopsis of the essential parameters in the rational coimmobilization design.

Oriented immobilization of enzyme-DNA conjugates on magnetic Janus particles for constructing a multicompartment multienzyme system with high activity and stability

Various organelles (e.g., mitochondria and chloroplasts) have a multicompartment structure, providing superior function of material transformation, selective segregation and energy conversion. Enlightened by the elegant evolution of nature, intended isolation of the biochemical process by cooperative multicompartments in cells has become an appealing blueprint to construct bioreactors. In this study, we develop a "soft separation" way to establish a delicate multicompartment multienzyme system (MMS) with polyphenol-encapsulated enzyme-DNA conjugates, which are anchored on magnetic Janus particles, providing a biomimetic catalysis network with the model cascade reactions in confinement. The well-designed MMS exhibits preferable bioactivity benefitting from the dependable DNA bridges and the oriented immobilization of enzymes, while the polyphenol shell further protects the anchored enzymes from exterior attacks, such as heat and enzymatic degradation. Moreover, by applying the MMS as nanomotors, the asymmetrical distribution of enzymes on Janus particles is found to improve mutual elevation between the self-driven locomotion and enzyme-mediated reactions, delivering enhanced dispersal ability and bioactivity. Owing to the excellent enzymatic activity, promoted stability and satisfying biocompatibility, the assembled MMS is proved to be promising for the in vitro and intracellular sensing of glucose, showing significant potential for biochemical analysis applications.

Size-Tunable Metal-Organic Framework-Coated Magnetic Nanoparticles for Enzyme Encapsulation and Large-Substrate Biocatalysis

Immobilizing enzymes on nanoparticles (NPs) enhances the cost-efficiency of biocatalysis; however, when the substrates are large, it becomes difficult to separate the enzyme@NP from the products while avoiding leaching or damage of enzymes in the reaction medium. Metal-organic framework (MOF)-coated magnetic NPs (MNPs) offer efficient magnetic separation and enhanced enzyme protection; however, the involved enzymes/substrates have to be smaller than the MOF apertures. A potential solution to these challenges is coprecipitating metal/ligand with enzymes on the MNP surface, which can partially bury (protect) the enzyme below the composite surface while exposing the rest of the enzyme to the reaction medium for catalysis of larger substrates. Here, to prove this concept, we show that using Ca²⁺ and terephthalic acid (BDC), large-substrate enzymes can be encapsulated in CaBDC-MOF layers coated on MNPs via an enzyme-friendly, aqueous-phase one-pot synthesis. Interestingly, we found that using MNPs as the nuclei of crystallization, the composite size can be tuned so that nanoscale composites were formed under low Ca²⁺/BDC concentrations, while microscale composites were formed under high Ca²⁺/BDC concentrations. While the microscale composites showed significantly enhanced reusability against a non-structured large substrate, the nanoscale composites displayed enhanced catalytic efficiency against a rigid, crystalline-like large substrate, starch, likely due to the improved diffusivity of the nanoscale composites. To our best knowledge, this is the first report on aqueous-phase one-pot synthesis of size-tunable enzyme@MOF/MNP composites for large-substrate biocatalysis. Our platform can be applied to immobilize other large-substrate enzymes with enhanced reusability and tunable sizes.

Immobilization of Multi-Enzymes on Support Materials for Efficient Biocatalysis

Multi-enzyme biocatalysis is an important technology to produce many valuable chemicals in the industry. Different strategies for the construction of multi-enzyme systems have been reported. In particular, immobilization of multi-enzymes on the support materials has been proved to be one of the most efficient approaches, which can increase the enzymatic activity via substrate channeling and improve the stability and reusability of enzymes. A general overview of the characteristics of support materials and their corresponding attachment techniques used for multi-enzyme immobilization will be provided here. This review will focus on the materials-based techniques for multi-enzyme immobilization, which aims to present the recent advances and future prospects in the area of multi-enzyme biocatalysis based on support immobilization.

Highly sensitive detection of multiple antibiotics based on DNA tetrahedron nanostructure-functionalized magnetic beads

Functional DNAs-functionalized magnetic beads (MBs) offer great potential in bioanalysis field because of their target recognition and magnetic separation functions. However, the recognition capability and hybridization affinity of DNA probes often suffer from limited available space, poor probe conformation and non-selective adsorption. To overcome these limitations, we herein used aptamer-pendant DNA tetrahedron nanostructure-functionalized MBs (TETapt-tet MBs) to develop a target-response fluorescence method with tetracycline (TET) as a model. In the absence of TET, 6-carboxy-X-rhodamine-labeled complementary DNAs (ROX-cDNAs) were assembled on the surface of MBs. Upon the addition of target TET, the ROX-cDNAs were separated and released from the MBs to generate fluorescence signal. The limit of detection and limit of quantification for TET were found to be 6 pg mL^-1 and 20 pg mL^-1, respectively. Compared with ssDNA-functionalized MBs surface, the designed DNA tetrahedron nanostructure-based surface could decrease the hybridization time and reduce false positives, ensuring the accuracy of TET detection in complex samples. The presented method was successfully employed for TET detection in honey samples. Moreover, this functionalization strategy could be extended to detect multiple antibiotics by simply substituting different aptamer sequences. Therefore, the proposed method has great potential in the field of food safety and public health.

Construction of a Multienzymatic Cascade Reaction System of Coimmobilized Hybrid Nanoflowers for Efficient Conversion of Starch into Gluconic Acid

Introducing an efficient method for the rapid conversion of starch into gluconic acid is desirable to solve the current problems existing in traditional gluconic acid preparation processes. In this study, a robust and easy-to-use multienzymatic cascade reaction system of coimmobilized GA@GOx hybrid nanoflowers with a specific spatial distribution of enzymes by compartmentalization was constructed and applied to catalyze starch to gluconic acid in one pot. In the preparation processes, the glucose oxidase (GOx) hybrid nanoflowers were first synthesized via a self-assembly mechanism, and then, glucoamylase (GA) was adsorbed on the surface of GOx hybrid nanoflowers through the interaction of Cu²⁺ and amino acids of GA. The optimum preparation conditions and reaction parameters of the GA@GOx hybrid nanoflowers had been investigated. In addition, the morphology, composition, and crystallization of the GA@GOx hybrid nanoflowers had been fully studied. Based on the lower K_m, the GA@GOx hybrid nanoflowers with compartmentalization had a better effect of the substrate channeling on the catalytic efficiency. The final results indicated that the overall enzyme activity of the GA@GOx hybrid nanoflowers increased by 1.5 times, and the conversion efficiency was 92.12% within 80 min significantly superior to the free multienzyme system, which showed the outstanding conversion of starch into gluconic acid in one pot.

Metal-Organic Framework in Situ Post-Encapsulating DNA-Enzyme Composites on a Magnetic Carrier with High Stability and Reusability

In recent years, metal-organic frameworks (MOFs) have been extensively studied as candidate enzyme immobilization platforms. However, conventional MOF-enzyme composites usually exhibit low controllability and reusability. In this study, a novel and stable strategy for enzyme immobilization was designed by use of ZIF-8 to encapsulate in situ DNA-enzyme composites on the surface of magnetic particles (MPs). The mechanism of in situ encapsulation was discussed in detail. It was found that immobilized enzymes were involved in the growth of ZIF-8, and the DNA cross-linking agents promoted the growth of ZIF-8 on the surface of MP. The thermal, chemical, and physical stabilities of horseradish peroxidase (HRP) were all significantly enhanced after in situ encapsulation. Most importantly, this strategy was proven to be a general platform that can be used to stabilize various proteins. The in situ encapsulation strategy was expanded to immobilize a cascade of enzymes, and ZIF-8@MP_GOx-HRP possessed high selectivity and a wide linear range (25-500 μM) for glucose detection.

Hierarchical Micro- and Mesoporous Zn-Based Metal-Organic Frameworks Templated by Hydrogels: Their Use for Enzyme Immobilization and Catalysis of Knoevenagel Reaction

Encapsulation of enzymes in metal-organic frameworks (MOFs) is often obstructed by the small size of the orifices typical of most reported MOFs, which prevent the passage of larger-size enzymes. Here, the preparation of hierarchical micro- and mesoporous Zn-based MOFs via the templated emulsification method using hydrogels as a template is presented. Zinc-based hydrogels featuring a 3D interconnecting network are first produced via the formation of hydrogen bonds between melamine and salicylic acid in which zinc ions are well distributed. Further coordination with organic linkers followed by the removal of the hydrogel template produces hierarchical Zn-based MOFs containing both micropores and mesopores. These new MOFs are used for the encapsulation of glucose oxidase and horseradish peroxidase to prove the concept. The immobilized enzymes exhibit a remarkably enhanced increased operational stability and enzymatic activity with a k_cat /k_m value of 85.68 mm s^-1 . This value is 7.7-fold higher compared to that found for the free enzymes in solution, and 2.7-fold higher than enzymes adsorbed on conventional microporous MOFs. The much higher catalytic activity of the mesoporous conjugate for Knoevenagel reactions is demonstrated, since the large pores enable easier access to the active sites, and compared with that observed for catalysis using microporous MOFs.

An on-site bacterial detection strategy based on broad-spectrum antibacterial ε-polylysine functionalized magnetic nanoparticles combined with a portable fluorometer

A sensitive on-site bacterial detection strategy is presented that integrates the broad-spectrum capturing feature of ε-polylysine-functionalized magnetic nanoparticles with an in-house built portable fluorometer. Based on the electrostatic interaction, the functionalized magnetic nanoparticles (ε-PL-MNPs) were prepared for Gram-positive and Gram-negative bacterial separation and subsequent viable release. ε-PL-MNPs show a broad reactivity towards bacteria with the high capture efficiency from real-world sample media. They also enable controlled viable bacterial release with pH adjustment. Detection of bacteria is based on a combination of broad-spectrum capture with colorimetric and fluorimetric immunoassays. A portable fluorometer is built to enhance the applicability for sensitive on-site detection. A limit of detection of 98 CFU·mL^-1 is achieved that is comparable to that of a known spectrofluorometric method for E. coli DH5α. Graphical abstract Schematic presentation of bacterial capture using cationic polymer functionalized magnetic nanoparticles and general fluorometric immunoassay with portable fluorometer. The limit of detection is 98 CFU·mL^-1 for E. coli DH5α.

Enzymatic Cascade Catalysis in a Nanofiltration Membrane: Engineering the Microenvironment by Synergism of Separation and Reaction

Microenvironment plays a significant role in enzymatic catalysis, which directly influences enzyme activity and stability. It is important to regulate the enzyme microenvironment, especially for the liquid with unfavored properties (e.g., pH and dissolved oxygen). In this work, we propose a methodology that can regulate pH and substrate concentration for enzymatic catalysis by a biocatalytic membrane, which is composed of glucose oxidase (GOx) and horseradish peroxidase (HRP) co-immobilized in a polyamide nanofiltration (NF) membrane (i.e., beneath the separation layer). By virtue of the selective separation function of NF membrane and in situ production of organic acid/electron donor with GOx, a synergism effect of separation and reaction in the liquid/solid interface was manipulated for engineering the microenvironment of HRP to enhance its activity and stability for micropollutant removal in water. The outcome of this work not only provides a new methodology to precisely control enzymatic reaction but also offers a smart membrane system to efficiently and steadily remove the micropollutants in portable water.

Polydopamine-mediated synthesis of core–shell gold@calcium phosphate nanoparticles for enzyme immobilization

Constructing calcium phosphate (CaP)–gold (Au) nanocomposites for enzyme immobilization to overcome the bottleneck of loss of enzyme activity upon immobilization.

Self-assembly of a magnetic DNA hydrogel as a new biomaterial for enzyme encapsulation with enhanced activity and stability

A rationally designed strategy has been established to construct a magnetic DNA hydrogel for enzyme encapsulation through a programmable one-pot self-assembly approach.

Multifunctional magnetic particles for effective suppression of non-specific adsorption and coimmobilization of multiple enzymes by DNA directed immobilization

Zwitterion-functionalized magnetic particles can efficiently suppress non-specific adsorption of enzymes and can be used for coimmobilization of multienzymes by DNA directed immobilization.

Attachment of enzymes to hydrophilic magnetic nanoparticles through DNA-directed immobilization with enhanced stability and catalytic activity

An efficient enzyme immobilization strategy based on DNA directed immobilization on hydrophilic polydopamine (PDA) modified magnetic nanoparticles was developed in this study.