Enzyme-mediated green synthesis of glycosaminoglycans and catalytic process intensification

Glycosaminoglycans (GAGs) are a family of structurally complex heteropolysaccharides that play pivotal roles in biological functions, including the regulation of cell proliferation, enzyme inhibition, and activation of growth factor receptors. Therefore, the synthesis of GAGs is a hot research topic in drug development. The enzymatic synthesis of GAGs has received widespread attention due to their eco-friendly nature, high regioselectivity, and stereoselectivity. The enhancement of the enzymatic synthesis process is the key to its industrial applications. In this review, we overviewed the construction of more efficient in vitro biomimetic synthesis systems of glycosaminoglycans and presented the different strategies to improve enzyme catalysis, including the combination of chemical and enzymatic methods, solid-phase synthesis, and protein engineering to solve the problems of enzyme stability, separation and purification of the product, preparation of structurally defined sugar chains, etc., and discussed the challenges and opportunities in large-scale green synthesis of GAGs.

A simple chemiluminescent method for the quantification of exosomes based on horseradish peroxidase adsorbed on two-dimensional nanomaterials

The development of simple methods for the isolation and quantification of exosomes in biological samples is important. By using the typical two-dimensional (2D) nanomaterials, graphene oxide (GO), the present work first studied the interaction of liposomes with the nanocomposites formed by adsorbing HRP on the GO surface and found the presence of liposomes led to the release of HRP from the GO surface to the solution phase triggering the luminol-H2O2 chemiluminescence (CL) reaction to emit light. Benefiting from the similarity of exosomes to liposomes in both composition and morphology aspects, the GO-HRP nanocomposites with a mass ratio of 120:1 and 160:1 were employed for the quantitative detection of exosomes in 100-fold diluted serum samples. The whole detection process took about 15 min and as low as 3.2 × 102 particles μL-1 of exosomes could be sensitively detected. In addition to GO-HRP nanocomposites, the CL responses of other nanocomposites obtained from adsorbing HRP on other 2D nanomaterials such as layered MoS2 for exosomes were also tested. MoS2-HRP exhibited similar behavior and the LODs for the detection of exosomes were 5.8 × 102 particles μL-1. The proposed assays were a biomarker-independent quantitative method that achieved the quantification of exosomes in serum samples directly without an isolation process.

Role of pretty nanoflowers as novel versatile analytical tools for sensing in biomedical and bioanalytical applications

In recent years, an encouraging breakthrough in the synthesis of immobilized enzymes in flower-shaped called "organic-inorganic hybrid nanoflowers (hNFs)" with greatly enhanced catalytic activity and stability were reported. Although, these hNFs were discovered by accident, the enzymes exhibited highly enhanced catalytic activities and stabilities in the hNFs compared with the free and conventionally immobilized enzymes. Herein, we rationally utilized the catalytic activity of the hNFs for analytical applications. In this comprehensive review, we covered the design and use of the hNFs as novel versatile sensors for electrochemical, colorimetric/optical and immunosensors-based detection strategies in analytical perspective.

Microperoxidase-11 functionalized nanozyme with enhanced peroxidase-mimicking activities for visual detection of cysteine

Various nanomaterials with peroxidase activity (nanozyme) have been designed for bio catalysis and biosensing, however, most of them need further design and modification of probe molecules for the specific binding reaction with targets. This results in a decrease in catalysis activity and hinders them to be perfect alternatives to natural enzyme in biosensing. In this work, an enhanced nanozyme was synthesized by functionalizing natural microperoxidase-11 (MP-11) on a hybrid graphene oxide-gold (GO-Au) material. The designed nanozyme showed an enhanced catalysis activity and realized a robust and efficient colorimetric detection of cysteine based on specific binding reaction between active iron center from MP-11 and thiol in cysteine. The enhanced properties show promising applications of complex nanozyme and provides a great opportunity for developing efficient sensing systems.

An Up-to-Date Review on the Remediation of Dyes and Phenolic Compounds from Wastewaters Using Enzymes Immobilized on Emerging and Nanostructured Materials: Promises and Challenges

Addressing the critical issue of water pollution, this review article emphasizes the need to remove hazardous dyes and phenolic compounds from wastewater. These pollutants pose severe risks due to their toxic, mutagenic, and carcinogenic properties. The study explores various techniques for the remediation of organic contaminants from wastewater, including an enzymatic approach. A significant challenge in enzymatic wastewater treatment is the loss of enzyme activity and difficulty in recovery post-treatment. To mitigate these issues, this review examines the strategy of immobilizing enzymes on newly developed nanostructured materials like graphene, carbon nanotubes (CNTs), and metal-organic frameworks (MOFs). These materials offer high surface areas, excellent porosity, and ample anchoring sites for effective enzyme immobilization. The review evaluates recent research on enzyme immobilization on these supports and their applications in biocatalytic nanoparticles. It also analyzes the impact of operational factors (e.g., time, pH, and temperature) on dye and phenolic compound removal from wastewater using these enzymes. Despite promising outcomes, this review acknowledges the challenges for large-scale implementation and offers recommendations for future research to tackle these obstacles. This review concludes by suggesting that enzyme immobilization on these emerging materials could present a sustainable, environmentally friendly solution to the escalating water pollution crisis.

Enzyme immobilization studied through molecular dynamic simulations

In recent years, simulations have been used to great advantage to understand the structural and dynamic aspects of distinct enzyme immobilization strategies, as experimental techniques have limitations in establishing their impact at the molecular level. In this review, we discuss how molecular dynamic simulations have been employed to characterize the surface phenomenon in the enzyme immobilization procedure, in an attempt to decipher its impact on the enzyme features, such as activity and stability. In particular, computational studies on the immobilization of enzymes using i) nanoparticles, ii) self-assembled monolayers, iii) graphene and carbon nanotubes, and iv) other surfaces are covered. Importantly, this thorough literature survey reveals that, while simulations have been primarily performed to rationalize the molecular aspects of the immobilization event, their use to predict adequate protocols that can control its impact on the enzyme properties is, up to date, mostly missing.

Multipoint Immobilization at Inert Center of Papain on Homo-Functional Diazo-Activated Silica Support: A Way of Restoring "Above Room-Temperature" Bio-Catalytic Sustainability

Although enzymes play a significant role in industrial applications, their potential usage at high-level efficiency, particularly above room temperature, has not yet been fully harnessed. It brings above room-temperature catalytic sustainability of an immobilized (imm.) bio-catalyst as a long pending issue to improve enzyme stability, activity, specificity, or selectivity, particularly the enantio-selectivity over the native-enzymes. At this juncture, in a robust methodology, a heterogeneous solid phase bio-catalyst, {Si(OSi)₄(H₂O)_1.03}_n=328{OSi(CH₃)₂-NH-C₆H₄-N═N}₄{papain}(H₂O)₂₅₁, has efficiently been prepared by immobilizing papain on homo-functionalized SG (silica-gel) via multipoint covalent attachment. The bio-catalyst is easy to be recovered and reused multiple times. The homo-functional -N═N⁺, which appears on the SG-surface, makes the multipoint diazo-links with the inert center of the tyrosine-moiety to couple the enzyme where all the amino, thiol, phenol, and so forth, groups of the protein, including those that belong to the active-site, remain intact. The immobilized enzyme (13.9 μmol g^-1) swims in pore-water within the pore-channel, remains stable up to 70 ± 5 °C, and exhibits wider temperature adaptability in performing its hydrolyzing activities. The relative activity, 78 ± 2% at 27 °C, remains quantitative for 60 days and can be reused for 60 cycles with 53% activity at room-temperature. The thermal (relative activity: 87%; incubated at 70 ± 5 °C for 24 h) and mechanical (relative activity: 92%; incubated at 2500 rpm for 2 h at 27 °C) stability was outstanding.

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.

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF-8 Modified by Ni2+ Ions

The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework-8 (ZIF-8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF-8 carrier by using Ni²⁺ ions as anchor (ZIF-8@PEP-Ni). By contrast, the direct coating of PEP on the surface of ZIF-8 (ZIF-8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF-8@PEP-Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm^-2 , which is much lower than the 690 and 919 mV overpotential values of ZIF-8@PEP and PEP, respectively.

Designing multifunctional biocatalytic cascade system by multi-enzyme co-immobilization on biopolymers and nanostructured materials

In recent decades, enzyme-based biocatalytic systems have garnered increasing interest in industrial and applied research for catalysis and organic chemistry. Many enzymatic reactions have been applied to sustainable and environmentally friendly production processes, particularly in the pharmaceutical, fine chemicals, and flavor/fragrance industries. However, only a fraction of the enzymes available has been stepped up towards industrial-scale manufacturing due to low enzyme stability and challenging separation, recovery, and reusability. In this context, immobilization and co-immobilization in robust support materials have emerged as valuable strategies to overcome these inadequacies by facilitating repeated or continuous batch operations and downstream processes. To further reduce separations, it can be advantageous to use multiple enzymes at once in one pot. Enzyme co-immobilization enables biocatalytic synergism and reusability, boosting process efficiency and cost-effectiveness. Several studies on multi-enzyme immobilization and co-localization propose kinetic advantages of the enhanced turnover number for multiple enzymes. This review spotlights recent progress in developing versatile biocatalytic cascade systems by multi-enzyme co-immobilization on environmentally friendly biopolymers and nanostructured materials and their application scope in the chemical and biotechnological industries. After a succinct overview of carrier-based and carrier-free immobilization/co-immobilizations, co-immobilization of enzymes on a range of biopolymer and nanomaterials-based supports is thoroughly compiled with contemporary and state-of-the-art examples. This study provides a new horizon in developing effective and innovative multi-enzymatic systems with new possibilities to fully harness the adventure of biocatalytic systems.

Recent advances of graphene-biomacromolecule nanocomposites in medical applications

In recent years, graphene-based composites have received increasing attention due to their high biocompatibility, large specific surface area, high electrical conductivity and unique mechanical properties. The combination of biomacromolecules and graphene provides a promising route for the preparation of novel graphene-based nanocomposites. Novel graphene-based nanocomposites with unique functions could be applied to medicine, biology, biosensors, environmental science, energy storage and other fields. Graphene-biomacromolecule nanocomposites have excellent biocompatibility, outstanding biofunctionality and low cytotoxicity, and have more advantages and development prospects than other traditional graphene-based materials in biological and biomedical fields. In this work, we summarize the research on the covalent and non-covalent interactions between different biomacromolecules (peptides, DNA/RNA, proteins and enzymes) and graphene, as well as the synthesis methods of novel functionalized graphene-biomacromolecule composites in recent years. We mainly introduce the recent advances (last 5 years) of graphene-biomacromolecule nanocomposites in medical applications, such as medical detection and disease treatment. We hope that this review will help readers to understand the methods and mechanisms of biomolecules modifying the surface of graphene, as well as the synthesis and application of graphene-based nanocomposites, which will promote the future developments of graphene-biomolecule composites in biomedicine, tissue engineering, materials engineering, and so on.

The Effect of Amino-Phosphate Interactions on the Biosensing Performance of Enzymatic Graphene Field-Effect Transistors

The interaction between polyamines and phosphate species is found in a wide range of biological and abiotic systems, yielding crucial consequences that range from the formation of supramolecular colloids to structure determination. In this work, the occurrence of phosphate-amino interactions is evidenced from changes in the electronic response of graphene field effect transistors (gFETs). First, the surface of the transistors is modified with poly(allylamine), and the effect of phosphate binding on the transfer characteristics is interpreted in terms of its impact on the surface charge density. The electronic response of the polyamine-functionalized gFETs is shown to be sensitive to the presence of different phosphate anions, such as orthophosphate, adenosine triphosphate, and tripolyphosphate, and a simple binding model is developed to explain the dependence of the shift of the Dirac point potential on the phosphate species concentration. Afterward, the impact of phosphate-amino interactions on the immobilization of enzymes to polyamine-modified graphene surfaces is investigated, and a decrease in the amount of anchored enzyme as the phosphate concentration increases is found. Finally, multilayer polyamine-urease biosensors are fabricated while increasing the phosphate concentration in the enzyme solution, and the sensing properties of the gFETs toward urea are evaluated. It is found that the presence of simple phosphate anions alters the nanoarchitecture of the polyelectrolyte-urease assemblies, with direct implications on urea sensing.

Modulating the adsorption orientation of methionine-rich laccase by tailoring the surface chemistry of single-walled carbon nanotubes

Achieving fast electron transfer process between oxidoreductase and electrodes is pivotal for the biocathode of enzymatic biofuel cells (EBFCs). However, in-depth understanding of the interplay mechanism between enzymes and electrode materials remains challenging when designing and constructing EBFCs. Herein, atomic-scale insight into the direct electron transfer (DET) behavior of Thermus thermophilus laccase (TtLac) with a special methionine-rich β-hairpin motif adsorbed on the carboxyl-functionalized carbon nanotube (COOH-CNT) and amino-functionalized carbon nanotube (NH₂-CNT) surfaces were disclosed by multi-scale molecular simulations. Simulation results reveal that electrostatic modification is an effective way to tune the DET behavior for TtLac on the modified-CNTs electrode surface. Surprisingly, the positively charged TtLac can be attracted by both negatively charged COOH-CNT and positively charged NH₂-CNT surfaces, yet only the latter is capable to trigger the DET process due to the 'lying-on' adsorption orientation. Specifically, the T1 copper site is near the methionine-rich β-hairpin motif, which is the key binding site for TtLac binding onto the NH₂-CNT surface via electrostatic interaction, π-π stacking and cation-π interaction. Moreover, TtLac on the NH₂-CNT surface undergoes less conformational changes than those on the COOH-CNT surface, which allows the laccase stability and catalytic efficiency to be well preserved. These findings provide a fundamental guidance for future design and fabrication of methionine-rich laccase-based EBFCs with high power output and long lifespan.

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties-their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components-especially in the area of sensing-but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs' widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes.

Anaerobic Digestion of Lignocellulosic Waste Materials

Nowadays, the climate mitigation policies of EU promote the energy production based on renewable resources. Anaerobic digestion (AD) constitutes a biochemical process that can convert lignocellulosic materials into biogas, used for chemical products isolation or energy production, in the form of electricity, heat or fuels. Such practices are accompanied by several economic, environmental and climatic benefits. The method of AD is an effective method of utilization of several different low-value and negative-cost highly available materials of residual character, such as the lignocellulosic wastes coming from forest, agricultural or marine biomass utilization processes, in order to convert them into directly usable energy. Lignin depolymerization remains a great challenge for the establishment of a full scale process for AD of lignin waste. This review analyzes the method of anaerobic digestion (biomethanation), summarizes the technology and standards involved, the progress achieved so far on the depolymerization/pre-treatment methods of lignocellulosic bio-wastes and the respective residual byproducts coming from industrial processes, aiming to their conversion into energy and the current attempts concerning the utilization of the produced biogas. Substrates’ mechanical, physical, thermal, chemical, and biological pretreatments or a combination of those before biogas production enhance the hydrolysis stage efficiency and, therefore, biogas generation. AD systems are immensely expanding globally, especially in Europe, meeting the high demands of humans for clean energy.

Graphene and Graphene Oxide as a Support for Biomolecules in the Development of Biosensors

Graphene and graphene oxide have become the base of many advanced biosensors due to their exceptional characteristics. However, lack of some properties, such as inertness of graphene in organic solutions and non-electrical conductivity of graphene oxide, are their drawbacks in sensing applications. To compensate for these shortcomings, various methods of modifications have been developed to provide the appropriate properties required for biosensing. Efficient modification of graphene and graphene oxide facilitates the interaction of biomolecules with their surface, and the ultimate bioconjugate can be employed as the main sensing part of the biosensors. Graphene nanomaterials as transducers increase the signal response in various sensing applications. Their large surface area and perfect biocompatibility with lots of biomolecules provide the prerequisite of a stable biosensor, which is the immobilization of bioreceptor on transducer. Biosensor development has paramount importance in the field of environmental monitoring, security, defense, food safety standards, clinical sector, marine sector, biomedicine, and drug discovery. Biosensor applications are also prevalent in the plant biology sector to find the missing links required in the metabolic process. In this review, the importance of oxygen functional groups in functionalizing the graphene and graphene oxide and different types of functionalization will be explained. Moreover, immobilization of biomolecules (such as protein, peptide, DNA, aptamer) on graphene and graphene oxide and at the end, the application of these biomaterials in biosensors with different transducing mechanisms will be discussed.

Recent nanobiotechnological advancements in lignocellulosic biomass valorization: A review

Increase in human population, rapid industrialization, excessive utilization of fossil fuel utilization and anthropogenic activities have caused serious threats to the environment in terms of greenhouse gas emissions (GHGs), global warming, air pollution, acid rain, etc. This destruction in sustainability can be averted by a paradigm shift in the fuel production from fossil resources to bioenergy. Amongst different forms of bioenergy, lignocellulosic biomass can be utilized as an attractive substrate for the production of several high-value products owing to its renewability, easy availability, and abundance. Additionally, utilization of these waste biomasses reduces the environmental hazards associated with its disposal. Impedance of lignin and crystalline nature of cellulose pose major bottlenecks in biomass based energy. Though, several physio-chemicals processes are recommended as mitigation route but none of them seems to be promising for large scale application. In recent years, a right fusion of biological treatment combined with nanotechnology for efficient pretreatment and subsequent hydrolysis of biomass by ubiquitous enzymes seems to be promising alternative. In addition, to overcome these difficulties, nanotechnology-based methods have been recently adopted in catalytic valorization of lignocellulosic biomass. The present review has critically discussed the application of nano-biotechnology in lignocellulosic biomass valorization in terms of pretreatment and hydrolysis. A detailed discussion on the application of various nanoparticles in these processes, enzyme immobilization and end-production utilization is presented in this review. Finally, the review emphasizes the major challenges of this process along with different routes and recommendations to address the issues.

Multi-enzyme co-immobilized nano-assemblies: Bringing enzymes together for expanding bio-catalysis scope to meet biotechnological challenges

Co-immobilization of multi-enzymes has emerged as a promising concept to design and signify bio-catalysis engineering. Undoubtedly, the existence and importance of basic immobilization methods such as encapsulation, covalent binding, cross-linking, or even simple adsorption cannot be ignored as they are the core of advanced co-immobilization strategies. Different strategies have been developed and deployed to green the twenty-first century bio-catalysis. Moreover, co-immobilization of multi-enzymes has successfully resolved the limitations of individual enzyme loaded constructs. With an added value of this advanced bio-catalysis engineering platform, designing, and fabricating co-immobilized enzymes loaded nanostructure carriers to perform a particular set of reactions with high catalytic turnover is of supreme interest. Herein, we spotlight the emergence of co-immobilization strategies by bringing multi-enzymes together with various types of nanocarriers to expand the bio-catalysis scope. Following a brief introduction, the first part of the review focuses on multienzyme co-immobilization strategies, i.e., random co-immobilization, compartmentalization, and positional co-immobilization. The second part comprehensively covers four major categories of nanocarriers, i.e., carbon based nanocarriers, polymer based nanocarriers, silica-based nanocarriers, and metal-based nanocarriers along with their particular examples. In each section, several critical factors that can affect the performance and successful deployment of co-immobilization of enzymes are given in this work.

Effect of Triton X-100 on the Activity and Selectivity of Lipase Immobilized on Chemically Reduced Graphene Oxides

The effect of support hydrophobicity on lipase activity and substrate selectivity was investigated with and without Triton X-100 (TX-100). Lipases from Thermomyces lanuginosa (TL) and Alcaligenes sp. (QLM) were immobilized on graphene oxide (GO) and a range of chemically reduced graphene oxides (CRGOs) with different levels of surface hydrophobicity. Activity assays using 4-hydroxy-N-propyl-1,8-naphthalimide (NAP) esters of varying chain lengths (NAP-butyrate (NAP-B), NAP-octanoate (NAP-O), and NAP-palmitate (NAP-P)) showed that the activity of immobilized QLM and TL decreased by more than 60% on GO and 80% on CRGO (2 h), with activity decreasing further as surface hydrophobicity of the CRGOs increased. Across the hydrophobicity range of GO/CRGOs, the substrate selectivity of QLM shifted from more readily hydrolyzing NAP-P to NAP-B, while TL retained its substrate selectivity for NAP-O. Lipase TL was also shown to desorb from GO and 2 h CRGO when mixed with NAP-O and NAP-P, whereas QLM did not. Circular dichroism analyses of the lipase α-helix content correlate to the observed activity data, with decreases in the α-helical content (40% in TL and 20% in QLM relative to free lipase) consistent with decreases in activity after immobilization on GO. α-Helical content decreased even further as the surface hydrophobicity of CRGOs increased. Attenuated total reflectance-Fourier transform infrared spectroscopy also showed significant changes to the lipase secondary structure upon immobilization. The addition of TX-100 into the activity assay modified the substrate selectivity of immobilized QLM, improving the activity against NAP-O (90%) and NAP-P (67%) compared to the activity measured without TX-100. It was shown that TX-100 primarily affected the activity of QLM by interacting with the ester substrate and the lipase itself. This study provides an improved understanding of how support hydrophobicity and the presence of TX-100 can affect activity/selectivity of lipases immobilized on hydrophobic supports.

Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: a review

Population increase and industrialization has resulted in high energy demand and consumptions, and presently, fossil fuels are the major source of staple energy, supplying 80% of the entire consumption. This has contributed immensely to the greenhouse gas emission and leading to global warming, and as a result of this, there is a tremendous urgency to investigate and improve fresh and renewable energy sources worldwide. One of such renewable energy sources is biogas that is generated by anaerobic fermentation that uses different wastes such as agricultural residues, animal manure, and other organic wastes. During anaerobic digestion, hydrolysis of substrates is regarded as the most crucial stage in the process of biogas generation. However, this process is not always efficient because of the domineering stableness of substrates to enzymatic or bacteria assaults, but substrates' pretreatment before biogas production will enhance biogas production. The principal objective of pretreatments is to ease the accessibility of the enzymes to the lignin, cellulose, and hemicellulose which leads to degradation of the substrates. Hence, the use of pretreatment for catalysis of lignocellulose substrates is beneficial for the production of cost-efficient and eco-friendly process. In this review, we discussed different pretreatment technologies of hydrolysis and their restrictions. The review has shown that different pretreatments have varying effects on lignin, cellulose, and hemicellulose degradation and biogas yield of different substrate and the choice of pretreatment technique will devolve on the intending final products of the process.

Addressing the Selectivity of Enzyme Biosensors: Solutions and Perspectives

Enzymatic biosensors enjoy commercial success and are the subject of continued research efforts to widen their range of practical application. For these biosensors to reach their full potential, their selectivity challenges need to be addressed by comprehensive, solid approaches. This review discusses the status of enzymatic biosensors in achieving accurate and selective measurements via direct biocatalytic and inhibition-based detection, with a focus on electrochemical enzyme biosensors. Examples of practical solutions for tackling the activity and selectivity problems and preventing interferences from co-existing electroactive compounds in the samples are provided such as the use of permselective membranes, sentinel sensors and coupled multi-enzyme systems. The effect of activators, inhibitors or enzymatic substrates are also addressed by coupled enzymatic reactions and multi-sensor arrays combined with data interpretation via chemometrics. In addition to these more traditional approaches, the review discusses some ingenious recent approaches, detailing also on possible solutions involving the use of nanomaterials to ensuring the biosensors' selectivity. Overall, the examples presented illustrate the various tools available when developing enzyme biosensors for new applications and stress the necessity to more comprehensively investigate their selectivity and validate the biosensors versus standard analytical methods.

Silica Capsules Templated from Metal-Organic Frameworks for Enzyme Immobilization and Catalysis

Inspired by the unique biological microenvironments of eukaryotic cells, hollow capsules are promising to immobilize enzymes due to their advantages for physical protection and improved activity of enzymes. Herein, we report a facile method to fabricate silica (SiO₂) capsules using zeolitic imidazole framework-8 nanoparticles (ZIF-8 NPs) as templates for enzyme immobilization and catalysis. Enzyme-encapsulated SiO₂ capsules are obtained by encapsulation of enzymes in ZIF-8 NPs and subsequent coating of silica layers, followed by the removal of templates in a mild condition (i.e., ethylenediaminetetraacetic acid (EDTA) solution). The enzyme (i.e., horseradish peroxidase, HRP) activity in SiO₂ capsules is improved more than 15 times compared to that of enzyme-loaded ZIF-8 NPs. Enzymes in SiO₂ capsules maintain a high relative activity after being subjected to high temperature, enzymolysis, and recycling compared to free enzymes. In addition, multienzymes (e.g., glucose oxidase and HRP) can also be coencapsulated within SiO₂ capsules to show a reaction with a high cascade catalytic efficacy. This work provides a versatile strategy for enzyme immobilization and protection with potential applications in biocatalysis.

Magnetic graphene oxide nanocomposites as an effective support for lactase immobilization with improved stability and enhanced photothermal enzymatic activity

Magnetic graphene oxide-immobilized lactase with high loading capacity, improved stabilities, and photothermal enhancement of activity has been reported.

Molecular mechanism of direct electron transfer in the robust cytochrome-functionalised graphene nanosystem

Molecular mechanism of DET between graphene and cytochrome c depends on the metal in the bio-organic interface: Co enhances the cathodic current via electron hopping from graphene to haem, whereas Ni exerts the opposite effect via tunnelling.

Polyelectrolyte-functionalized reduced graphene oxide wrapped helical POMOF nanocomposites for bioenzyme-free colorimetric biosensing

For the sake of effective colorimetric sensing-pattern, a sensitive colorimetric sensor was conceived based on polyoxometalates based metal-organic frameworks (POMOFs) and polydiallyldimethylammonium chloride functionalized reduced graphene oxide (PDDA-rGO) for the first time, in which PDDA as a "glue" molecule turns rGO nanosheets into general platforms for bonding POMOFs nanoparticles. Herein, a new POMOF compound with fascinating helices-on-helices feature, [Ni₄(Trz)₆(H₂O)₂][SiW₁₂O₄₀]^.4H₂O (Trz = 1,2,4-triazole) (abbreviated as Ni₄SiW₁₂), was synthesized and characterized, then PDDA-rGO sheet as dispersive and conductive material was successfully introduced to Ni₄SiW₁₂ fabricating new PDDA-rGO/Ni₄SiW₁₂-n nanocomposites, (abbreviated as PMPG-n). The resulting PMPG-n nanocomposites as peroxidase mimetic show excellent catalytic activities under extreme condition (pH value 2.5), attributed to the nature and synergies from POMs, MOFs and PDDA-rGOs. Note that the peroxidase-like activity of PMPG-1 (the mass ratio of Ni₄SiW₁₂ to PDDA-rGO is 1:1) exhibits higher sensitivity (1-60 μM), faster response (10 min) and the lowest limit of detection (2.07 μM) among all reported materials to citric acid (CA) to date. This work opens up new application prospects in colorimetric sensing system for food quality control and safety, biotechnology and clinical diagnosis.

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.

Amides and Heparin-Like Polymer Co-Functionalized Graphene Oxide Based Core @ Polyethersulfone Based Shell Beads for Bilirubin Adsorption

Excessive bilirubin in the body of patient with liver dysfunction or metabolic obstruction may cause jaundice with irreversible brain damage, and new type of adsorbent for bilirubin is under frequent investigation. Herein, graphene oxide based core @ polyethersulfone-based shell beads are fabricated by phase inversion method, amides and heparin-like polymer are introduced to functionalize the core-shell beads. The beads are successfully prepared with obvious core-shell structure, adequate thermostability and porous shell. Clotting times and protein adsorption are investigated to inspect the hemocompatibility property of the beads. The adsorption of bilirubin is systematically investigated by evaluating the effects of contacting time, initial concentration and temperature on the adsorption, which exhibits improved bilirubin adsorption amount for the beads with amides contained cores or/and shells. It is worth believing that the amides and heparin-like polymer co-functionalized core-shell beads may be utilized in the field of hemoperfusion for bilirubin adsorption.

From Graphite to Laccase Biofunctionalized Few-Layer Graphene: A "One Pot" Approach Using a Chimeric Enzyme

A chimeric enzyme based on the genetic fusion of a laccase with a hydrophobin domain was employed to functionalize few-layer graphene, previously exfoliated from graphite in the presence of the hydrophobin. The as-produced, biofunctionalized few-layer graphene was characterized by electrochemistry and Raman spectroscopy, and finally employed in the biosensing of phenols such as catechol and dopamine. This strategy paves the way for the functionalization of nanomaterials by hydrophobin domains of chimeric enzymes and their use in a variety of electrochemical applications.

Synthesis of lutein esters using a novel biocatalyst of Candida antarctica lipase B covalently immobilized on functionalized graphitic carbon nitride nanosheets

Lutein scavenges free radicals and inhibits vision damage caused by photo oxidation, while decomposing easily with light and heat. Its stability and bioavailability can be tremendously improved by lutein ester synthesis. However, green and efficient esterification preparation methods are urgently needed. In this study, which used functionalized graphitic carbon nitride nanosheets (g-C₃N₄-Ns) as the immobilized carrier, a novel biocatalyst was designed and prepared to accommodate Candida antarctica lipase B (CALB), considerably enhancing the performance. It was characterized by TEM, XRD, FTIR, XPS, TGA, and BET to demonstrate successful preparation and then applied to catalyze esterification between lutein and succinate anhydride in dimethyl formamide (DMF) solvent resulting in a conversion rate up to 92% at 50 °C in 60 h, 34% more than free CALB under the same conditions. We believe this is the highest esterification rate in lutein esters synthesis and it has great potential to facilitate eco-friendly and efficient preparation.

Reduction of nitroarenes by magnetically recoverable nitroreductase immobilized on Fe3O4 nanoparticles

Enzymes as catalysts have attracted significant attention due to their excellent specificity and incomparable efficiency, but their practical application is limited because these catalysts are difficult to separate and recover. A magnetically recoverable biocatalyst has been effectively prepared through the immobilization of a nitroreductase (oxygen-insensitive, purified from Enterobacter cloacae) onto the Fe3O4 nanoparticles. The magnetic nanoparticles (MNPs) were synthesized by a coprecipitation method in an aqueous system. The surfaces of the MNPs were modified with sodium silicate and chloroacetic acid (CAA). Using 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) through a covalent binding, nitroreductase was loaded onto the modified magnetic carriers through covalent coupling, and thus, a magnetically recoverable biocatalyst was prepared. The free and immobilized nitroreductase activity was also investigated by the reduction of p-nitrobenzonitrile using nicotinamide adenine dinucleotide phosphate (NAPDH) as a cofactor. The activity of the immobilized enzyme was able to maintain 83.23% of that of the free enzyme. The prepared enzyme can easily reduce substituted nitrobenzene to substituted aniline at room temperature and atmospheric pressure, and the yield is up to 60.9%. Most importantly, the loaded nitroreductase carriers can be easily separated and recycled from the reaction system using an externally applied magnetic field. The magnetically recoverable biocatalyst can be recycled and reused 7 times while maintaining high activities and the activity of the magnetic catalyst can be maintained at more than 85.0% of that of the previous cycle. This research solves the recovery problem encountered in industrial applications of biocatalysts and presents a clean and green method of preparing substituted aniline.

Urease immobilized GO core@shell heparin-mimicking polymer beads with safe and effective urea removal for blood purification

Adsorbents are usually used to remove uremic toxins for blood purification. However, the removal of urea is still an intractable problem, since no effective material has been found for urea removal by physical adsorption. Here, urease immobilized graphene oxide core@shell heparin-mimicking polymer (U-GO-HMP) beads were designed, which exhibited good urea removal ability with a removal amount of about 635 mg/g and a removal ratio of about 80% from urea solution. In addition, urea could be removed from collected dialysate and the removal ratio could reach 60% within 480 min. Beyond that, the U-GO-HMP beads also showed good reusability with sustainable relative activity after 5 cycles. Furthermore, the U-GO-HMP beads exhibited good blood compatibility with low hemolysis ratio, suppressed complement activation and contact activation, as well as increased clotting times. It is worthy believing that the U-GO-HMP beads may have great potential in the field of blood purification for urea removal.

Immobilization and unbinding investigation of the antigen-antibody complex using theoretical and experimental techniques

Experimental results for the antibody known as immunoglobulin G - IgG interacting with phenobarbital were obtained via atomic force microscopy (AFM) and thereafter investigated using computer simulation modeling tools. Using molecular dynamics simulation and docking calculations, the energetically stable configurations of an immobilized antibody over a silicon surface were searched. Six stable configurations of the immobilized antibody over the silicon nitride surface covered by linker molecules were found. Although, only three of them (P1, P2, P5) maintained the Fragment antigen binding available for antigen interaction. Therefore, these configurations were equilibrated after reaching 100 ns molecular dynamics trajectory. The average interaction energy between the surface and the immunoglobulin G - IgG antibody in the P1, P2 and P5 configurations were -62.4 ± 2.4 kcal/mol; -54.3 ± 5.7 kcal/mol, and -360.9 ± 4.2 kcal/mol respectively. Phenobarbital was docked within the Fab domain of P1, P2, and P5 immobilized configurations and equilibrated with molecular dynamics for binding energy estimation. Then, steered molecular dynamics was performed to evaluate unbinding energy pathway between phenobarbital and IgG in each of the three-oriented IgG configurations. No significant differences were observed in the rupture force values (EP1 = 591 ± 13 pN, EP2 = 605 ± 18 pN, and EP5 = 610 ± 45 pN). In comparison, the average AFM experimental results were (641.6 ± 363.3 pN). Therefore, it is worth noting that P5 is the configuration with highest protein-surface interaction. Therefore, the force value calculated for the P5 orientation is statistically more favorable and it is the one to be compared to the experimental data. The agreement between experimental and theoretical results indicates a favorable presented for this study opening new perspectives for antigen-antibody evaluation.

Recombinant Escherichia coli BL21-pET28a-egfp Cultivated with Nanomaterials in a Modified Microchannel for Biofilm Formation

The application of whole cells as catalytic biofilms in microchannels has attracted increasing scientific interest. However, the excessive biomass formation and structure of biofilms in a reactor limits their use. A microchannel reactor with surface modification was used to colonize recombinant Escherichia coil BL21-pET28a-egfp rapidly and accelerated growth of biofilms in the microchannel. The segmented flow system of 'air/culture medium containing nanomaterials' was firstly used to modulate the biofilms formation of recombinant E. coil; the inhibitory effects of nanomaterials on biofilm formation were investigated. The results indicated that the segmental flow mode has a significant impact on the structure and development of biofilms. Using the channels modified by silane reagent, the culture time of biofilms (30 h) was reduced by 6 h compared to unmodified channels. With the addition of graphene sheets (10 mg/L) in Luria-Bertani (LB) medium, the graphene sheets possessed a minimum inhibition rate of 3.23% against recombinant E. coil. The biofilms cultivated by the LB medium with added graphene sheets were stably formed in 20 h; the formation time was 33.33% shorter than that by LB medium without graphene. The developed method provides an efficient and simple approach for rapid preparation of catalytic biofilms in microchannel reactors.