Biocatalytic Membrane Based on Polydopamine Coating: A Platform for Studying Immobilization Mechanisms

Co-Immobilization of Alcalase/Dispase for Production of Selenium-Enriched Peptide from Cardamine violifolia

Enzymatically derived selenium-enriched peptides from Cardamine violifolia (CV) can serve as valuable selenium supplements. However, the industrial application of free enzyme is impeded by its limited stability and reusability. Herein, this study explores the application of co-immobilized enzymes (Alcalase and Dispase) on amino resin for hydrolyzing CV proteins to produce selenium-enriched peptides. The successful enzyme immobilization was confirmed through scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). Co-immobilized enzyme at a mass ratio of 5:1 (Alcalase/Dispase) exhibited the smallest pore size (7.065 nm) and highest activity (41 U/mg), resulting in a high degree of hydrolysis of CV protein (27.2%), which was obviously higher than the case of using free enzymes (20.7%) or immobilized Alcalase (25.8%). In addition, after a month of storage, the co-immobilized enzyme still retained a viability level of 41.93%, showing fairly good stability. Encouragingly, the selenium-enriched peptides from co-immobilized enzyme hydrolysis exhibited uniform distribution of selenium forms, complete amino acid fractions and homogeneous distribution of molecular weight, confirming the practicality of using co-immobilized enzymes for CV protein hydrolysis.

Mussel-Inspired Polymer-Based Coating Technology for Antifouling and Antibacterial Properties

Zwitterionic coatings provide a promising antifouling strategy against biofouling adhesion. Quaternary ammonium cationic polymers can effectively kill bacteria on the surface, owing to their positive charges. This strategy can avoid the release of toxic biocides, which is highly desirable for constructing coatings for biomedical devices. The present work aims to develop a facile method by covalently grafting zwitterionic and cationic copolymers containing aldehydes to the remaining amine groups of self-polymerized dopamine. Reversible addition-fragmentation chain transfer polymerization was used to copolymerize either zwitterionic 2-methacryloyloxyethyl phosphorylcholine monomer (MPC) or cationic 2-(methacryloyloxy)ethyl trimethylammonium monomer (META) with 4-formyl phenyl methacrylate monomer (FPMA), and the formed copolymers poly(MPC-st-FPMA) and poly(META-st-FPMA) are denoted as MPF and MTF, respectively. MPF and MTF copolymers were then covalently grafted onto the amino groups of polydopamine-coated surfaces. PDA/MPF/MTF-coated surfaces exhibited antibacterial and antifouling properties against S. aureus, E. coli, and bovine serum albumin protein. In addition, they showed excellent viability of normal human lung fibroblast cells MRC-5. We expect the facile surface modification strategy discussed here to be applicable to medical device manufacturing.

Investigation of biosensing properties in magnetron sputtered metallized UV-curable polymer microneedle electrodes

Direct management and assessment of metal film properties applied to polymer microneedle (MN) biosensors remains difficult due to constraints inherent to their morphology. By simplifying the three-dimensional structure of MNs and adjusting the deposition time, different thicknesses of Au films were deposited on the UV-cured polymer planar and MN substrates. Several properties relevant to the biosensing of the Au films grown on the polymer surfaces were investigated. The results demonstrate the successful deposition of pure and stable Au nanoparticles onto the surface of UV-curable polymer materials. Initially, Au islands formed within the first minute of deposition; however, as the sputtering time extended, these islands transformed into Au nanoparticle films and disappeared. The hydrophilicity of the surface remains unchanged, while the surface resistance of the thin film decreases with increasing thickness, and the adhesion to the substrate decreases as the thickness increases. In short, a sputtering time of 5-6 min results in Au films with a thickness of 100-200 nm, which exhibit exceptional comprehensive biosensing performance. Additionally, MNs made of Au/UV-curable polymers and produced using magnetron sputtering maintain their original shape, enhance their mechanical characteristics, and gain new functionalities. The Au/UV-curable polymer MNs exhibited remarkable electrode performance despite being soaked in a 37 °C PBS solution for 14 days. These discoveries have important implications in terms of decreasing the dependence on valuable metals in MN biosensors, lowering production expenses, and providing guidance for the choice and design of materials for UV-curable polymer MN metallization films.

Functionalization of seawater reverse osmosis membrane with quorum sensing inhibitor to regulate microbial community and mitigate membrane biofouling

Membrane biofouling is a challenge to be solved for the stable operation of the seawater reverse osmosis (SWRO) membrane. This study explored the regulation mechanism of quorum sensing (QS) inhibition on microbial community composition and population-level behaviors in seawater desalination membrane biofouling. A novel antibiofouling SWRO membrane (MA_m) by incorporating one of quorum sensing inhibitors (QSIs), methyl anthranilate (MA) was prepared. It exhibited enhanced anti-biofouling performance than the exogenous addition of QSIs, showing long-term stability and alleviating 22 % decrease in membrane flux compared with the virgin membrane. The results observed that dominant bacteria Epsilon- and Gamma-proteobacteria (Shewanella, Olleya, Colwellia, and Arcobacter), which are significantly related to (P ≤ 0.01) the metabolic products (i.e., polysaccharides, proteins and eDNA), are reduced by over 80 % on the MA_m membrane. Additionally, the introduction of MA has a more significant impact on the QS signal-sensing pathway through binding to the active site of the transmembrane sensor receptor. It effectively reduces the abundance of genes encoding QS and extracellular polymeric substance (EPS) (exopolysaccharides (i.e., galE and nagB) and amino acids (i.e., ilvE, metH, phhA, and serB)) by up to 50 % and 30 %, respectively, resulting in a reduction of EPS by more than 50 %, thereby limiting the biofilm formation on the QSI-modified membrane. This study provides novel insights into the potential of QSIs to control consortial biofilm formation in practical SWRO applications.

Chemically Bonded Pepsin via Its Inert Center to Diazo Functionalized Silica Gel through Multipoint Attachment Mode: A Way of Restoring Biocatalytic Sustainability over "Wider pH" Range

Proteolytic enzymes play a pivotal role in the industry. Still, because of denaturation, the extensive applicability at their level of best catalytic efficiency over a more comprehensive pH range, particularly in alkaline conditions over pH 8, has not been fully developed. On the other hand, enzyme immobilization following a suitable protocol is a long pending issue that determines the conformational stability, specificity, selectivity, enantioselectivity, and activity of the native enzymes at long-range pH. As a bridge between these two findings, in an attempt at a freezing temperature 273-278 K at an alkaline pH, the diazo-functionalized silica gel (SG) surface has been used to rapidly diazo couple pepsin through its inert center, the O-carbon of the phenolic -OH of surface-occupied Tyr residues in a multipoint mode: when all the various protein groups, viz., amino, thiol, phenol, imidazole, carboxy, etc., in the molecular sequence including those belonging to the active sites, remain intact, the inherent inbuilt interactions among themselves remain. Thereby, the macromolecule's global conformation and helicity preserve the status quo. The dimension of the SG-enzyme conjugate confirms as {Si(OSi)4 (H2O)1.03}n {-O-Si(CH3)2-O-C6H4-N═N+}4·{pepsin}·yH2O; where the values of n and y have been determined respectively as 347 and 188. The material performs the catalytic activity much better at 7-8.5 than at pH 2-3.5 and continues for up to six months without any appreciable change.

Preparation of Ultrathin and Degradable Polymeric Films by Electropolymerization of 3-Amino-l-tyrosine

Bioderived polymers are one of many current research areas that promise a sustainable future. Due to their unique properties, the bioderived polymer polydopamine has been in the spotlight over the last decades. Its ability to adhere to virtually any surface and its stability over a wide pH range as well as in several organic solvents make it a suitable candidate for various applications like coatings and biosensors. However, strong light absorption over a broad range of wavelengths and high quenching efficiency limit its uses. Therefore, new bioderived polymers with similar features to polydopamine but without fluorescence quenching properties are highly desirable. Herein, the electropolymerization of a bioderived analog of dopamine, 3-amino-l-tyrosine, is demonstrated. The resulting polymer, poly(amino-l-tyrosine), exhibits several characteristics complementary to or even exceeding those of polydopamine and its analog, polynorepinephrine, rendering poly(amino-l-tyrosine) attractive for the development of sensors and photoactive devices. Cyclic voltammetry, spectro-electrochemistry, and electrochemical quartz crystal microbalance measurements are applied to study the electrodeposition of this material, and the resulting films are compared to polydopamine and polynorepinephrine. Impedance spectroscopy reveals increased ion permeability of poly(amino-l-tyrosine) compared to polydopamine and polynorepinephrine. Moreover, the reduced fluorescence quenching of poly(amino-l-tyrosine) supports its use as coating for biosensors and organic semiconductors.

Preparation of immobilized pepsin for extraction of collagen from bovine hide

In the extraction of collagens from mammalian tissues, the free pepsin used in the acid-pepsin extraction system is hard to recycle, and there is a risk of enzyme protein contamination in the extracted collagen products, which limits their applications. To solve this problem, an immobilized pepsin was successfully prepared via the covalent crosslinking of glutaraldehyde using a 3-aminopropyltriethoxysilane (APTES) surface modified silica clay as the support. The immobilized pepsin was applied for the extraction of collagen from bovine hide. The optimal immobilization process involves incubating pepsin with an initial concentration of 35 mg mL^-1 and glutaraldehyde with 5% activated APTES modified silica clay at 25 °C for 60 min, by which the loading amount of pepsin was 220 mg g^-1 and the activity of the immobilized pepsin was 4.2 U mg^-1. The collagen extracted using acetic acid and the immobilized pepsin method retained its complete triple helix structure. This research thus details an effective separation method using pepsin for extraction of collagen via an acetic acid-enzyme method, where the extracted collagen may be a candidate for use in biomaterial applications.

Bioinspired Lipase Immobilized Membrane for Improving Hesperidin Lipophilization

Lipophilization is a promising way to improve the bioavailability of flavonoids. However, the traditional enzymatic esterification methods are time-consuming, and present low yields and purity. Herein, a novel membrane-based lipophilization technology-bioinspired lipase immobilized membranes (BLIMs), including CAL-B@PES, CAL-B@PDA/PES and GA/CAL-B@PDA/PES- were fabricated to improve the antioxidant flavanone glycoside hesperidin lipophilization. Via reverse filtration, PDA coating and GA crosslinking, Candida antarctica lipase B (CAL-B) was stably immobilized on membrane to fabricate BLIMs. Among the three BLIMs, GA/CAL-B@PDA/PES had the greatest enzyme activity and enzyme loading, the strongest tolerance of changes in external environmental conditions (temperatures, pH, heating time, storage time and numbers of cycles) and the highest hesperidin esterification efficiency. Moreover, the optimal operating condition for GA/CAL-B@PDA/PES fabrication was the CAL-B concentration of 0.36 mg/mL, operation pressure of 2 bar, GA concentration of 5% and crosslinking time of 1 h. Afterwards, the hesperidin esterification process did not affect the micromorphology of BLIM, but clearly improved the BLIM permeability and esterified product efficiency. The present study reveals the fabrication mechanism of BLIMs and offers insights into the optimizing strategy that governs the membrane-based lipophilization technology process.

Cross-linked laminar graphene oxide membranes for wastewater treatment and desalination: A review

Two-dimensional (2D) lamellar graphene oxide (GO) membranes are emerging as attractive materials for molecular separation in water treatment because of their single atomic thickness, excellent hydrophilicity, large specific surface areas, and controllable properties. To yet, commercialization of GO laminar membranes has been hindered by their propensity to swell in hydrated conditions. Thus, chemical crosslinking of GO sheets with the polymer matrix is used to improve GO membrane hydration stability. This review focuses on pertinent themes such as how chemical crosslinking improves the hydration stability, separation performance, and antifouling properties of GO membranes.

Bacteria-Templated and Dual Enzyme-Powered Microcapsule Motors To Promote Thrombus Penetration and Thrombolytic Efficacy

Antithrombotic therapy is confronted with short half-lives of thrombolytic agents and high bleeding risks. Challenges remain in the development of drug delivery systems for thorough destruction of thrombi and timely restoration of blood flow while minimizing side effects. Herein, polydopamine capsule-like micromotors with urokinase (uPA) loadings and Arg-Gly-Asp (RGD) grafts (r-u@PCM) were constructed using rod-shaped bacteria as the template, and one single opening was created on each capsule through bacterial ghost (BG) formation. Glucose oxidase and catalase were encapsulated in the large cavity of microcapsules, and their successive oxidation of glucose produced O₂ bubbles, which ejected out through the single opening to propel the motion of r-u@PCM. In vitro targeting testing of r-u@PCM shows significant higher accumulations on the activated platelets than those without RGD grafts (u@PCM, 7 folds) or without enzyme loadings (r-u@PC, 11 folds). Compared with the major distribution of r-u@PC on the clot surface, r-u@PCM efficiently penetrates into clots with dense fibrin networks, and near-infrared (NIR) irradiation (r-u@PCM/NIR) promotes thrombus infiltration through increasing uPA release and thermolysis of the networks. Pharmacokinetic study shows that the loading of uPA in r-u@PCM extends the terminal half-life from 24 min to 5.5 h and the bioavailability increased 13 times. In a hindlimb venous thrombosis model, r-u@PCM/NIR treatment promotes uPA accumulations in thrombi and disrupts all the thrombi after 8 h with a full recovery of blood flows. Effective thrombolysis is also achieved even after reducing the uPA dose 5 times. Thus, this is the first attempt to fabricate rod-shaped microcapsule motors through a biologically derived method, including bacterial templating and BG formation-induced opening generation. r-u@PCM/NIR treatment promotes thrombolysis through the photothermal effect, self-propelled infiltration into thrombi, and accelerated local release of uPA, providing a prerequisite for reducing uPA dose and bleeding side effects.

A review on the immobilization of pepsin: A Lys-poor enzyme that is unstable at alkaline pH values

Pepsin is a protease used in many different applications, and in many instances, it is utilized in an immobilized form to prevent contamination of the reaction product. This enzyme has two peculiarities that make its immobilization complex. The first one is related to the poor presence of primary amino groups on its surface (just one Lys and the terminal amino group). The second one is its poor stability at alkaline pH values. Both features make the immobilization of this enzyme to be considered a complicated goal, as most of the immobilization protocols utilize primary amino groups for immobilization. This review presents some of the attempts to get immobilized pepsin biocatalyst and their applications. The high density of anionic groups (Asp and Glu) make the anion exchange of the enzyme simpler, but this makes many of the strategies utilized to immobilize the enzyme (e.g., amino-glutaraldehyde supports) more related to a mixed ion exchange/hydrophobic adsorption than to real covalent immobilization. Finally, we propose some possibilities that can permit not only the covalent immobilization of this enzyme, but also their stabilization via multipoint covalent attachment.

Bioremoval of estrogens by laccase immobilized onto polyacrylonitrile/polyethersulfone material: Effect of inhibitors and mediators, process characterization and catalytic pathways determination

The presence of micropollutants in water, wastewater and soil are a global problem due to their persistent effect on ecosystems and human health. Although there are many methods of removal of environmental pollutants, they are often ineffective for degradation of pharmaceuticals, including estrogens. In presented work we proposed fabrication of electrospun material from polyacrylonitrile/polyethersulfone (PAN/PES) as a support for laccase immobilization by covalent binding. Oxidoreductase was attached to the electrospun fibers using polydopamine as a linker and produced system was used for degradation of two estrogens: 17β-estradiol (E2) and 17α-ethynylestradiol (EE2). It was shown that 92% of E2 and 100% of EE2 were degraded after 24 h of the process. Moreover, the effect of surfactants, metal ions and mediators on conversion efficiencies of estrogens was investigated and it was confirmed that immobilized enzyme possessed higher resistance to inhibitory agents as well as thermal and storage stability, compared to its native form. Finally, estrogenic activities of E2 and EE2 solutions decreased around 99% and 87%, respectively, after enzymatic conversion, that corresponds to significant reduction of the total organic carbon and formation of low-toxic final products of estrogens degradation.

Biocatalytic membranes for combating the challenges of membrane fouling and micropollutants in water purification: A review

Over the last few years, the list of water contaminants has grown tremendously due to many anthropogenic activities. Various conventional technologies are available for water and wastewater treatment. However, micropollutants of emerging concern (MEC) are posing a great threat due to their activity at trace concentration and poor removal efficiency by the conventional treatment processes. Advanced technology like membrane technology can remove MEC to some extent. However, issues like the different chemical properties of MEC, selectivity, and fouling of membranes can affect the removal efficiency. Moreover, the concentrate from the membrane filtration may need further treatment. Enzymatic degradation of pollutants and foulants is one of the green approaches for removing various contaminants from the water as well as mitigating membrane fouling. Biocatalytic membranes (BCMs), in which enzymes are immobilized on membranes, combines the advantages of membrane separation and enzymatic degradation. This review article discussed various commonly used enzymes in BCMs for removing MEC and fouling. The majorly used enzymes were oxidoreductases and hydrolases for removing MEC, antifouling, and self-cleaning ability. The various BCM synthesis processes based on entrapment, crosslinking, and binding have been summarized, along with the effects of the addition of the nanoparticles on the performances of the BCMs. The scale-up, commercial viability, challenges, and future direction for improving BCMs have been discussed and shown bright possibilities for these new generation membranes.

Facile mussel-inspired polydopamine-coated 3D-printed bioreactors for continuous flow biocatalysis

Enantiopure alcohol production by a flow system of 3D-printed bioreactor with immobilized Geotrichum candidum acetophenone reductase (GcAPRD).

Biomimetic reusable microfluidic reactors with physically immobilized RuBisCO for glucose precursor production

Reusable RuBisCO-immobilized microfluidic reactors are used to synthesize the glucose precursor from CO2 and restore >95% of activity after refreshing.

Conjugated Organic Photothermal Films for Spatiotemporal Thermal Engineering

With the growth of photoenergy harvesting and thermal engineering, photothermal materials (PTMs) have attracted substantial interest due to their unique functions such as localized heat generation, spatiotemporal thermal controllability, invisibility, and light harvesting capabilities. In particular, π-conjugated organic PTMs show advantages over inorganic or metallic PTMs in thin film applications due to their large light absorptivity, ease of synthesis and tunability of molecular structures for realizing high NIR absorption, flexibility, and solution processability. This review is intended to provide an overview of organic PTMs, including both molecular and polymeric PTMs. A description of the photothermal (PT) effect and conversion efficiency (η_PT ) for organic films is provided. After that, the chemical structure and optical properties of organic PTMs are discussed. Finally, emerging applications of organic PT films from the perspective of spatiotemporal thermal engineering principles are illustrated.

An enzymatic membrane reactor for oligodextran production: Effects of enzyme immobilization strategies on dextranase activity

An enzymatic membrane reactor (EMR) with immobilized dextranase provides an excellent opportunity for tailoring the molecular weight (Mw) of oligodextran to significantly improve product quality. However, a highly efficient EMR for oligodextran production is still lacking and the effect of enzyme immobilization strategy on dextranase hydrolysis behavior has not been studied yet. In this work, a functional layer of polydopamine (PDA) or nanoparticles made of tannic acid (TA) and hydrolysable 3-amino-propyltriethoxysilane (APTES) was first coated on commercial membranes. Then cross-linked dextranase or non-cross-linked dextranase was loaded onto the modified membranes using incubation mode or fouling-induced mode. The fouling-induced mode was a promising enzyme immobilization strategy on the membrane surface due to its higher enzyme loading and activity. Moreover, unlike the non-cross-linked dextranase that exhibited a normal endo-hydrolysis pattern, we surprisingly found that the cross-linked dextranase loaded on the PDA modified surface exerted an exo-hydrolysis pattern, possibly due to mass transfer limitations. Such alteration of hydrolysis pattern has rarely been reported before. Based on the hydrolysis behavior of the immobilized dextranase in different EMRs, we propose potential applications for the oligodextran products. This study presents a unique perspective on the relation between the enzyme immobilization process and the immobilized enzyme hydrolysis behavior, and thus opens up a variety of possibilities for the design of a high-performance EMR.

Enhancing bio-catalytic performance of lipase immobilized on ionic liquids modified magnetic polydopamine

In this study, imidazolium-based ionic liquid with [tf₂N]^- as the anion was successfully grafted to magnetic polydopamine nanoparticles (MPDA). The prepared materials were well characterized and used as supports for lipase immobilization. The immobilized lipase (PPL-ILs-MPDA) exhibited excellent activity and stability. The specific activity of PPL-ILs-MPDA was 2.15 and 1.49 folds higher than that of free PPL and PPL-MPDA. In addition, after 10 rounds of reuse, the residual activity of PPL-ILs-MPDA was 86.2 % higher than that of PPL-MPDA (75.4 %). Furthermore, the kinetic assay indicated that the affinity between PPL-ILs-MPDA and substrate had increased. Analysis of the secondary structure using circular dichroism was used to explain the mechanism underlying the improvement in the performance of PPL-ILs-MPDA. In addition, the immobilized lipase can be easily separated from the reaction system with a magnet. The observations regarding the development of new supports for lipase immobilization may provide new ideas regarding further studies in this field.

Facile fabrication of antibacterial and antiviral perhydrolase-polydopamine composite coatings

In situ generation of antibacterial and antiviral agents by harnessing the catalytic activity of enzymes on surfaces provides an effective eco-friendly approach for disinfection. The perhydrolase (AcT) from Mycobacterium smegmatis catalyzes the perhydrolysis of acetate esters to generate the potent disinfectant, peracetic acid (PAA). In the presence of AcT and its two substrates, propylene glycol diacetate and H₂O₂, sufficient and continuous PAA is generated over an extended time to kill a wide range of bacteria with the enzyme dissolved in aqueous buffer. For extended self-disinfection, however, active and stable AcT bound onto or incorporated into a surface coating is necessary. In the current study, an active, stable and reusable AcT-based coating was developed by incorporating AcT into a polydopamine (PDA) matrix in a single step, thereby forming a biocatalytic composite onto a variety of surfaces. The resulting AcT-PDA composite coatings on glass, metal and epoxy surfaces yielded up to 7-log reduction of Gram-positive and Gram-negative bacteria when in contact with the biocatalytic coating. This composite coating also possessed potent antiviral activity, and dramatically reduced the infectivity of a SARS-CoV-2 pseudovirus within minutes. The single-step approach enables rapid and facile fabrication of enzyme-based disinfectant composite coatings with high activity and stability, which enables reuse following surface washing. As a result, this enzyme-polymer composite technique may serve as a general strategy for preparing antibacterial and antiviral surfaces for applications in health care and common infrastructure safety, such as in schools, the workplace, transportation, etc.

Tailor-made novel electrospun polystyrene/poly(d,l-lactide-co-glycolide) for oxidoreductases immobilization: Improvement of catalytic properties under extreme reaction conditions

Immobilized enzymes find applications in many areas such as pharmacy, medicine, food production and environmental protection. However, protecting these biocatalysts against harsh reaction conditions and retaining their enzymatic activity even after several biocatalytic cycles are major challenges. Properly selected supports and type of surface modifier therefore seem to be crucial for achieving high retention of catalytic activity of immobilized biomolecules. Here we propose production of novel composite electrospun fibers from polystyrene/poly(d,l-lactide-co-glycolide) (PS/PDLG) and its application as a support for immobilization of oxidoreductases such as alcohol dehydrogenase (ADH) and laccase (LAC). Two strategies of covalent binding, (i) (3-aminopropyl)triethoxysilane (APTES) with glutaraldehyde (GA) and (ii) polydopamine (PDA), were applied to attach oxidoreductases to PS/PDLG. The average fiber diameter was shown to increase from 1.252 µm to even 3.367 µm after enzyme immobilization. Effective production of PS/PDLG fibers and biomolecule attachment were confirmed by Fourier transform infrared spectroscopy analysis. The highest substrate conversion efficiency was observed at pH 6.5 and 5 for ADH and LAC, respectively, and at 25 °C for enzymes attached using the APTES + GA approach. Improvement of enzyme stabilization at high temperatures was confirmed in that relative activities of enzymes immobilized onto PS/PDLG fibers were over 20% higher than those of the free biomolecules, and enzyme leaching from the support using acetate and MES buffers was below 10 mg/g.

Geranyl Functionalized Materials for Site-Specific Co-Immobilization of Proteins

Different materials containing carboxylic groups have been functionalized with geranyl-amine molecules by using an EDC/NHS strategy. Chemical modification of the support was confirmed by XRD, UV-spectrophotometer, and FT-IR. This geranyl-functionalized material was successfully applied for four different strategies of site-selective immobilization of proteins at room temperature and aqueous media. A reversible hydrophobic immobilization of proteins (lipases, phosphoglucosidases, or tyrosinase) was performed in neutral pH in yields from 40 to >99%. An increase of the activity in the case of lipases was observed from a range of 2 to 4 times with respect to the initial activity in solution. When chemically or genetically functionalized cysteine enzymes were used, the covalent immobilization, via a selective thiol-alkene reaction, was observed in the presence of geranyl support at pH 8 in lipases in the presence of detergent (to avoid the previous hydrophobic interactions). Covalent attachment was confirmed with no release of protein after immobilization by incubation with hydrophobic molecules. In the case of a selenium-containing enzyme produced by the selenomethionine pathway, the selective immobilization was successfully yielded at acidic pH (pH 5) (89%) much better than at pH 8. In addition, when an azido-enzyme was produced by the azide-homoalanine pathway, the selective immobilization was successful at pH 6 and in the presence of CuI for the click chemistry reaction.

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.

Molecular Decoration of Ceramic Supports for Highly Effective Enzyme Immobilization-Material Approach

A highly effective method was developed to functionalize ceramic supports (Al₂O₃ powders and membranes) using newly synthesized spacer molecules. The functionalized materials were subsequently utilized for Candida antarctica lipase B enzyme immobilization. The objective is to systematically evaluate the impact of various spacer molecules grafted onto the alumina materials will affect both the immobilization of the enzymes and specific material surface properties, critical to enzymatic reactors performance. The enzyme loading was significantly improved for the supports modified with shorter spacer molecules, which possessed higher grafting effectiveness on the order of 90%. The specific enzyme activity was found to be much higher for samples functionalized with longer modifiers yielding excellent enantioselectivity >97%. However, the enantiomeric ratio of the immobilized lipase was slightly lower in the case of shorter spacer molecules.

Development of a continuous-flow system with immobilized biocatalysts towards sustainable bioprocessing

Implementing immobilized biocatalysts in continuous-flow systems can enable a sustainable process through enhanced enzyme stability, better transport and process continuity as well as simplified recycle and downstream processing.

Biocatalytic membrane: Go far beyond enzyme immobilization

Biocatalytic membrane takes advantages of reaction-separation integration as well as enzyme immobilization, which has attracted increasing attentions in online detection and biomanufacturing. However, the high preparation cost, inferior comprehensive performance, and low stability limit its applications. Thus, besides enzyme immobilization, more efforts should be made in biocatalytic membrane configuration design for a specific application to enhance the synergistic effect of reaction and separation and improve its operating stability. This review summarized the recent progress on biocatalytic membrane preparation, discussed different membrane configurations for various applications, finally proposed several challenges and possible solutions, which provided directions and guides for the development and industrialization of biocatalytic membrane.

Catalytically Active Hollow Fiber Membranes with Enzyme-Embedded Metal-Organic Framework Coating

Metal-organic frameworks (MOFs) are suitable enzyme immobilization matrices. Reported here is the in situ biomineralization of glucose oxidase (GOD) into MOF crystals (ZIF-8) by interfacial crystallization. This method is effective for the selective coating of porous polyethersulfone microfiltration hollow fibers on the shell side in a straightforward one-step process. MOF layers with a thickness of 8 μm were synthesized, and fluorescence microscopy and a colorimetric protein assay revealed the successful inclusion of GOD into the ZIF-8 layer with an enzyme concentration of 29±3 μg cm^-2 . Enzymatic activity tests revealed that 50 % of the enzyme activity is preserved. Continuous enzymatic reactions, by the permeation of β-d-glucose through the GOD@ZIF-8 membranes, showed a 50 % increased activity compared to batch experiments, emphasizing the importance of the convective transport of educts and products to and from the enzymatic active centers.

Formation of glyco-functionalized interfaces for protein binding using polyphenolic glycoside

In this study, a polyphenolic glycoside (α-glucosyl rutin) was used to form glyco-functionalized interfaces for protein binding. α-Glucosyl rutin was coated onto precious metals, metal oxides, and synthetic polymers, including polyethylene and polytetrafluoroethylene with poor surface modifiability. The glyco-functionalized interfaces bound strongly and specifically to concanavalin A and Bauhinia purpurea lectin, which have different carbohydrate specificities. Competitive adsorption tests demonstrated that the binding sites for the abovementioned lectins were glucosyl and rhamnosyl residues, respectively. The glyco-functionalized interfaces maintained the protein binding ability after being stored in aqueous solution for 1 day and in air for 160 days. Once the glyco-functionalized interfaces were formed on gold, silicon dioxide, polystyrene, and polytetrafluoroethylene using α-glucosyl rutin, all the glyco-functionalized interfaces bound to concanavalin A rather than peanut agglutinin.

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.

Biomimetic dynamic membrane for aquatic dye removal

This study utilized physical adsorption and filtration of carbon nanotubes (CNTs) and laccases to fabricate biomimetic dynamic membrane (BDM) for the advanced treatment of dye wastewater. In BDM, the adsorption, enzymatic degradation and membrane separation demonstrated a synergism effect on pollutant removal. At first, the fabrication methods of BDM were investigated, and the mixed filtration for laccases and CNTs showed a better performance than the stepwise filtration. Furthermore, the operation parameters of BDM, including CNTs and laccase loading amounts, dye concentration, agitation speed and transmembrane pressure (TMP), were studied. Suitable CNTs and laccase amounts could reduce filtration resistance and increase catalysis efficiency, while moderate TMP and agitation speed were in favor of boosting the BDM structure for catalysis and permeability. Optimized operation parameters (CNT loading amount = 20 g m^-2, laccase loading amount = 74.6 g m^-2, agitation speed = 100 rpm, and TMP = 1.0 bar) sustained a high removal rate, and the flux was over 120 L m^-2 h^-1, even for 7 operation cycle' tests. BDM exhibited an excellent dye removal rate, stable flux and great antifouling capacity, on the ground that adsorption saturation and foulant may be alleviated "online and in-situ" by the enzymatic degradation. Afterwards, the bionic layer on BDM, after absorption saturation and catalyst deactivation, could be eliminated rapidly by carrying out a simple backwash cleaning operation, then a new one could be fabricated immediately. Therefore, BDM is a good candidate for functional membrane materials in future water treatment.

Metal-Organic-Framework-Based Enzymatic Microfluidic Biosensor via Surface Patterning and Biomineralization

Recently, the biomineralization of enzyme in metal-organic-framework (enzyme-MOF) composite have shown a great potential to increase enzymes stability without compromising their activity; hence, it is desirable for its applications in biosensing devices. Nonetheless, most of the enzyme-MOF research has been focusing on enzyme encapsulation in particle form, which limits its synthesis flexibility for practical applications because of its requirement for postsynthesis immobilization onto solid support. Therefore, to develop a diagnostic device out of the biomineralized enzyme, surface patterning and integration of microfluidic system offers many advantages. In this work, mussel-inspired polydopamine/polyethyleneimine (PDA/PEI) coating is employed to pattern enzyme-MOF in microfluidic channels and exploit the wettability gradient for "pumpless transportation" effect. As a proof of concept, we combine a cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymes to detect glucose into a patterned zeolitic imidazole framework-8 (ZIF-8) thin film on a flexible polymeric substrate. The results show that the ZIF-8/GOx&HRP in situ composites on PDA/PEI patterns have good acid and thermal stability compared with samples without ZIF-8. ZIF-8/GOx&HRP in situ shows high selectivity toward glucose, linear sensitivity of 0.00303 Abs/μM, and the limit of detection of 8 μM glucose concentration. An unexpected benefit of this approach is the ability of the ZIF-8 thin-film structure to provide a diffusion limiting effect for substrate influx, thus, producing high range of linear response range (8 μM to 5 mM of glucose). This work provides insights into the spatial location of the enzymes in MOF thin films and the potential of such patterning techniques for MOF-based biosensors using other types of biological elements such as antibodies and aptamers.

Fabrication of an Anion-Exchange Membrane by Pore-Filling Using Catechol-1,4-Diazabicyclo-[2,2,2]octane Coating and Its Application to Reverse Electrodialysis

We have successfully exploited the Michael-type addition reaction between catechol and DABCO (1,4-diazabicyclo-[2,2,2]octane) molecules under alkaline conditions for the formation of new quaternary ammonium (QA) groups in an anion-exchange membrane. The anion-exchange membranes (AEMs) were prepared using the pore-filling method by addition of electrolytes (vinyl benzyl trimethylammonium chloride (VBTMA), dopamine methacrylamide (DMA) bearing a catechol group, and ethylene glycol diacrylate as a cross-linker) to a porous substrate. The formation of new QA groups by the reaction of DABCO with catechol components was confirmed by characterization of new peaks in the Fourier transform infrared spectra of the AEMs. The DABCO-bound AEM demonstrated a significant decrease in area resistance (0.4 Ω·cm²) and increase in permselectivity (94%). Furthermore, the electrochemical properties of the AEMs could be controlled by altering the concentrations of VBTMA and DMA and the formation of new bonds between DMA and DABCO. The calculated theoretical (4.31 W/m²) and practical (1.52 W/m²) power densities during a reverse electrodialysis (RED) process employing the membrane with the best properties (E2C1-DMA0.5-DABCO) were by 33 and 18% higher than those of a system utilizing a commercial membrane, Neosepta AMX (3.25 and 1.29 W/m²). Therefore, the AEM synthesized in this study is a good candidate for use in RED applications.

Bioinspired Peptide-Coated Superhydrophilic Poly(vinylidene fluoride) Membrane for Oil/Water Emulsion Separation

Polyvinylidene fluoride (PVDF) membranes are limited in the field of oil-in-water emulsion treatment because the intrinsic hydrophobicity of PVDF can cause serious membrane fouling. Here, a superhydrophilic PVDF membrane (PVDF@PDA-GSH) was fabricated using a facile, versatile, mussel-inspired method. The pristine PVDF membrane was coated with dopamine under mild alkaline conditions by a dip-coating method, followed by addition of glutathione (GSH) via a simple reaction. GSH was successfully coated onto the membrane surface and confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectrometry. Hierarchical surface structure and superhydrophilicity were examined by scanning electron microscopy and contact angle, respectively, giving the PVDF@PDA-GSH membrane excellent wettability and antifouling ability. The water flux of PVDF@PDA-GSH was several-fold higher than conventional filtration membranes, and the oil rejection ratio was nearly 99%. The PVDF@PDA-GSH membrane also showed favorable reusability because the flux recovery ratio (FRR) remained above 90% after five cycles. In general, these results indicated that this modification might provide a good method for the fabrication of superhydrophilic PVDF membranes with good prospects for water filtration applications.