Enzyme immobilization on electrospun polymer nanofibers: An overview

Functionalized electrospun poly(vinyl alcohol) nanofibers for on-chip concentration of E. coli cells

Positively and negatively charged electrospun poly(vinyl alcohol) (PVA) nanofibers were incorporated into poly(methyl methacrylate) (PMMA) microchannels in order to facilitate on-chip concentration of Escherichia coli K12 cells. The effects of fiber distribution and fiber mat height on analyte retention were investigated. The 3D morphology of the mats was optimized to prevent size-related retention of the E. coli cells while also providing a large enough surface area for analyte concentration. Positively charged nanofibers produced an 87% retention and over 80-fold concentration of the bacterial cells by mere electrostatic interaction, while negatively charged nanofibers reduced nonspecific analyte retention when compared to an empty microfluidic channel. In order to take advantage of this reduction in nonspecific retention, these negatively charged nanofibers were then modified with anti-E. coli antibodies. These proof-of-principle experiments showed that antibody-functionalized negatively charged nanofiber mats were capable of the specific capture of 72% of the E. coli cells while also significantly reducing nonspecific analyte retention within the channel as expected. The ease of fabrication and immense surface area of the functionalized electrospun nanofibers make them a promising alternative for on-chip concentration of analytes. The pore size and fiber mat morphology, as well as surface functionality of the fibers, can be tailored to allow for specific capture and concentration of a wide range of analytes.

Enzyme Immobilization: An Overview on Methods, Support Material, and Applications of Immobilized Enzymes

Immobilized enzymes can be used in a wide range of processes. In recent years, a variety of new approaches have emerged for the immobilization of enzymes that have greater efficiency and wider usage. During the course of the last two decades, this area has rapidly expanded into a multidisciplinary field. This current study is a comprehensive review of a variety of literature produced on the different enzymes that have been immobilized on various supporting materials. These immobilized enzymes have a wide range of applications. These include applications in the sugar, fish, and wine industries, where they are used for removing organic compounds from waste water. This study also reviews their use in sophisticated biosensors for metabolite control and in situ measurements of environmental pollutants. Immobilized enzymes also find significant application in drug metabolism, biodiesel and antibiotic production, bioremediation, and the food industry. The widespread usage of immobilized enzymes is largely due to the fact that they are cheaper, environment friendly, and much easier to use when compared to equivalent technologies.

Improved thermostable polyvinyl alcohol electrospun nanofibers with entangled naringinase used in a novel mini-packed bed reactor

Polyvinyl alcohol (PVA) electrospun nanofibers were produced using an electrospinning technique. Key parameters (e.g. collectors, distance from needle tip to collector, among others) that influence the structure and morphology of fibers were optimized. The naringinase entrapped in PVA nanofibers retained over 100% of its initial activity after 212h of operation, at 25°C. Chemical crosslinking with several boronic acids further increased the hydrolysis temperature (up to 85°C) and yielded nanofibers with thermal stability up to 121°C. A mini packed bed reactor (PBR) developed to establish the feasibility for continuous enzymatic operation, ran for 16days at 45°C. Highest naringenin biosynthesis was attained at a flow rate of 10mLh(-1). Highest volumetric (78molL(-1)h(-1)) and specific (26molh(-1)genzyme(-1)) productivities were attained at 30mLh(-1). The activity of NGase in electrospun nanofibers remained constant for almost 16days of operation at 10mLh(-1).

Multi-biofunction of antimicrobial peptide-immobilized silk fibroin nanofiber membrane: Implications for wound healing

An antimicrobial peptide motif (Cys-KR12) originating from human cathelicidin peptide (LL37) was immobilized onto electrospun SF nanofiber membranes using EDC/NHS and thiol-maleimide click chemistry to confer the various bioactivities of LL37 onto the membrane for wound care purposes. Surface characterizations revealed that the immobilization density of Cys-KR12 on SF nanofibers could be precisely controlled with a high reaction yield. The Cys-KR12-immobilized SF nanofiber membrane exhibited antimicrobial activity against four pathogenic bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa) without biofilm formation on the membrane surface. It also facilitated the proliferation of keratinocytes and fibroblasts and promoted the differentiation of keratinocytes with enhanced cell-cell attachment. In addition, immobilized Cys-KR12 significantly suppressed the LPS-induced TNF-α expression of monocytes (Raw264.7) cultured on the membrane. These results suggest that a Cys-KR12-immobilized SF nanofiber membrane, which has multiple biological activities, would be a promising candidate as a wound dressing material.

STATEMENT OF SIGNIFICANCE

This research article reports various bioactivities of an antimicrobial peptide on electrospun silk fibroin nanofiber membrane. Recently, human cathelicidin peptide LL37 has been extensively explored as an alternative antibiotic material. It has not only a great antimicrobial activity but also a wide variety of bioactivities which can facilitate wound healing process. Especially, many studies on immobilization of LL37 or its analogues have shown the immobilization technique could improve performance of wound dressing materials or tissue culture matrices. Nevertheless, so far studies have only focused on the bactericidal effect of immobilized peptide on material surface. On the other hand, we tried to evaluate multi-biofunction of immobilized antimicrobial peptide Cys-KR12, which is the shortest peptide motif as an analogue of LL37. We fabricated silk fibroin nanofiber membrane as a model wound dressing by electrospinning and immobilized the antimicrobial peptide. As a result, we confirmed that the immobilized peptide can play multi-role in wound healing process, such as antimicrobial activity, facilitation of cell proliferation and keratinocyte differentiation, and inhibition of inflammatory cytokine expression. These findings have not been reported and can give an inspiration in wound-care application.

Encapsulated Hydrogels by E-beam Lithography and Their Use in Enzyme Cascade Reactions

Electron beam (e-beam) lithography was employed to prepare one protein immobilized hydrogel encapsulated inside another by first fabricating protein-reactive hydrogels of orthogonal reactivity and subsequently conjugating the biomolecules. Exposure of thin films of eight arm star poly(ethylene glycol) (PEG) functionalized with biotin (Biotin-PEG), alkyne (Alkyne-PEG) or aminooxy (AO-PEG) end-groups to e-beam radiation resulted in cross-linked hydrogels with the respective functionality. It was determined via confocal microscopy that a nominal size exclusion effect exists for streptavidin immobilized on Biotin-PEG hydrogels of feature sizes ranging from 5 to 40 μm. AO-PEG was subsequently patterned as an encapsulated core inside a contiguous outer shell of Biotin-PEG. Similarly, Alkyne-PEG was patterned as a core inside an AO-PEG shell. The hydrogel reactive end-groups were conjugated to dyes or proteins of complementary reactivity, and the three-dimensional (3-D) spatial orientation was determined for both configurations using confocal microscopy. The enzyme glucose oxidase (GOX) was immobilized in the core of the encapsulated Alkyne-PEG core/ AO-PEG shell architecture, and horseradish peroxidase (HRP) was conjugated to the shell periphery. Bioactivity for the HRP-GOX enzyme pair was observed in this encapsulated configuration by demonstrating that the enzyme pair was capable of enzyme cascade reactions.

Immobilisation of cyclodextrin glucanotransferase into polyvinyl alcohol (PVA) nanofibres via electrospinning

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Fabrication of enzyme-carrying polymeric nanofibers by electrospinning.

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PVA nanofibers structure and size were not affected by the addition of enzyme.

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The electrospun CGTase/PVA nanofibers show excellent immobilisation efficiency.

Immobilisation of cyclodextrin glucanotransferase (CGTase) on nanofibres was demonstrated. CGTase solution (1% v/v) and PVA (8 wt%) solution were mixed followed by electrospinning (−9 kV, 3 h). CGTase/PVA nanofibres with an average diameter of 176 ± 46 nm were successfully produced. The nanofibres that consist of immobilised CGTase were crosslinked with glutaraldehyde vapour. A CGTase/PVA film made up from the same mixture and treated the same way was used as a control experiment. The immobilised CGTase on nanofibres showed superior performance with nearly a 2.5 fold higher enzyme loading and 31% higher enzyme activity in comparison with the film.

Manipulation of nanofiber-based β-galactosidase nanoenvironment for enhancement of galacto-oligosaccharide production

The nanoenvironment of nanobiocatalysts, such as local hydrophobicity, pH and charge density, plays a significant role in optimizing the enzymatic selectivity and specificity. In this study, Kluyveromyces lactis β-galactosidase (Gal) was assembled onto polystyrene nanofibers (PSNFs) to form PSNF-Gal nanobiocatalysts. We proposed that local hydrophobicity on the nanofiber surface could expel water molecules so that the transgalactosylation would be preferable over hydrolysis during the bioconversion of lactose, thus improve the galacto-oligosaccharides (GOS) yield. PSNFs were fabricated by electro-spinning and the operational parameters were optimized to obtain the nanofibers with uniform size and ordered alignment. The resulting nanofibers were functionalized for enzyme immobilization through a chemical oxidation method. The functionalized PSNF improved the enzyme adsorption capacity up to 3100 mg/g nanofiber as well as enhanced the enzyme stability with 80% of its original activity. Importantly, the functionalized PSNF-Gal significantly improved the GOS yield and the production rate was up to 110 g/l/h in comparison with 37 g/l/h by free β-galactosidase. Our research findings demonstrate that the localized nanoenvironment of the PSNF-Gal nanobiocatalysts favour transgalactosylation over hydrolysis in lactose bioconversion.

Nanobiocatalysis: Nanostructured materials – a minireview

The field of nanobiocatalysis has experienced a rapid growth due to recent advances in nanotechnology. However, biocatalytic processes are often limited by the lack of stability of the enzymes and their short lifetime. Therefore, immobilization is key to the successful implementation of industrial processes based on enzymes. Immobilization of enzymes on functionalized nanostructured materials could give higher stability to nanobiocatalysts while maintaining free enzyme activity and easy recyclability under various conditions. This review will discuss recent developments in nanobiocatalysis to improve the stability of the enzyme using various nanostructured materials such as mesoporous materials, nanofibers, nanoparticles, nanotubes, and individual nanoparticles enzymes. Also, this review summarizes the recent evolution of nanostructured biocatalysts with an emphasis on those formed with polymers. Based on the synthetic procedures used, established methods fall into two important categories: “grafting onto” and “grafting from”. The fundamentals of each method in enhancing enzyme stability and the use of these new nanobiocatalysts as tools for different applications in different areas are discussed.

A review on non-electro nanofibre spinning techniques

A large surface area, scalable porosity, and versatility have made nanofibres one of the most widely investigated morphologies among the nanomaterials.

Electrospun fibers for oil–water separation

The increasing worldwide oil pollution intensifies the needs for new techniques of separation of oil from oily water.

Estrone removal by horseradish peroxidase immobilized on a nanofibrous support with Fe3O4 nanoparticles

The occurrence, fate, and removal of estrone (E₁) from environmental systems have attracted considerable research interests in recent years because of the potential risks of human and wildlife exposure to E₁.

An electrochemical biosensing platform based on 1-formylpyrene functionalized reduced graphene oxide for sensitive determination of phenol

A novel electrochemical biosensing platform is proposed. New tyrosinase-based biosensor can be used to detect phenols.

Recent advances in electrospun metal-oxide nanofiber based interfaces for electrochemical biosensing

Synthesis of various electrospun metal-oxide nanofibers and their application towards electrochemical enzymatic and enzyme-free biosensor platforms has been critically discussed.

Electrochemical biosensors based on nanofibres for cardiac biomarker detection: A comprehensive review

The vital importance of early and accurate diagnosis of cardiovascular diseases (CVDs) to prevent the irreversible damage or even death of patients has driven the development of biosensor devices for detection and quantification of cardiac biomarkers. Electrochemical biosensors offer rapid sensing, low cost, portability and ease of use. Over the past few years, nanotechnology has contributed to a tremendous improvement in the sensitivity of biosensors. In this review, the authors summarise the state-of-the-art of the application of one particular type of nanostructured material, i.e. nanofibres, for use in electrochemical biosensors for the ultrasensitive detection of cardiac biomarkers. A new way of classifying the nanofibre-based electrochemical biosensors according to the electrical conductance and the type of nanofibres is presented. Some key data from each article reviewed are highlighted, including the mechanism of detection, experimental conditions and the response range of the biosensor. The primary aim of this review is to emphasise the prospects for nanofibres for the future development of biosensors in diagnosis of CVDs as well as considering how to improve their characteristics for application in medicine.

Functionalized Nanofiber Meshes Enhance Immunosorbent Assays

Three-dimensional substrates with high surface-to-volume ratios and subsequently large protein binding capacities are of interest for advanced immunosorbent assays utilizing integrated microfluidics and nanosensing elements. A library of bioactive and antifouling electrospun nanofiber substrates, which are composed of high-molecular-weight poly(oxanorbornene) derivatives, is described. Specifically, a set of copolymers are synthesized from three 7-oxanorbornene monomers to create a set of water insoluble copolymers with both biotin (bioactive) and triethylene glycol (TEG) (antifouling) functionality. Porous three-dimensional nanofiber meshes are electrospun from these copolymers with the ability to specifically bind streptavidin while minimizing the nonspecific binding of other proteins. Fluorescently labeled streptavidin is used to quantify the streptavidin binding capacity of each mesh type through confocal microscopy. A simplified enzyme-linked immunosorbent assay (ELISA) is presented to assess the protein binding capabilities and detection limits of these nanofiber meshes under both static conditions (26 h) and flow conditions (1 h) for a model target protein (i.e., mouse IgG) using a horseradish peroxidase (HRP) colorimetric assay. Bioactive and antifouling nanofiber meshes outperform traditional streptavidin-coated polystyrene plates under flow, validating their use in future advanced immunosorbent assays and their compatibility with microfluidic-based biosensors.

Polybiguanide (PHMB) loaded in PLA scaffolds displaying high hydrophobic, biocompatibility and antibacterial properties

Polyhexamethylenebiguanide hydrochloride (PHMB), a low molecular weight polymer related to chlorohexidine (CHX), is a well-known antibacterial agent. In this study, polylactide (PLA) nanofibers loaded with PHMB were produced by electrospinning to obtain 3D biodegradable scaffolds with antibacterial properties. PLA fibers loaded with CHX were used as control. The electrospun fibers were studied and analyzed by SEM, FTIR, DSC and contact angle measurements. PHMB and CHX release from loaded scaffolds was evaluated, as well as their antibacterial activity and biocompatibility. The results showed that the nanofibers became smoother and their diameter smaller with increasing the amount of loaded PHMB. This feature led to an increase of both surface roughness and hydrophobicity of the scaffold. PHMB release was highly dependent on the hydrophilicity of the medium and differed from that determined for CHX. Lastly, PHMB-loaded PLA scaffolds showed antibacterial properties since they inhibited adhesion and bacterial growth, and exhibited biocompatible characteristics for the adhesion and proliferation of both fibroblast and epithelial cell lines.

Nanobiocatalyst advancements and bioprocessing applications

The nanobiocatalyst (NBC) is an emerging innovation that synergistically integrates advanced nanotechnology with biotechnology and promises exciting advantages for improving enzyme activity, stability, capability and engineering performances in bioprocessing applications. NBCs are fabricated by immobilizing enzymes with functional nanomaterials as enzyme carriers or containers. In this paper, we review the recent developments of novel nanocarriers/nanocontainers with advanced hierarchical porous structures for retaining enzymes, such as nanofibres (NFs), mesoporous nanocarriers and nanocages. Strategies for immobilizing enzymes onto nanocarriers made from polymers, silicas, carbons and metals by physical adsorption, covalent binding, cross-linking or specific ligand spacers are discussed. The resulting NBCs are critically evaluated in terms of their bioprocessing performances. Excellent performances are demonstrated through enhanced NBC catalytic activity and stability due to conformational changes upon immobilization and localized nanoenvironments, and NBC reutilization by assembling magnetic nanoparticles into NBCs to defray the high operational costs associated with enzyme production and nanocarrier synthesis. We also highlight several challenges associated with the NBC-driven bioprocess applications, including the maturation of large-scale nanocarrier synthesis, design and development of bioreactors to accommodate NBCs, and long-term operations of NBCs. We suggest these challenges are to be addressed through joint collaboration of chemists, engineers and material scientists. Finally, we have demonstrated the great potential of NBCs in manufacturing bioprocesses in the near future through successful laboratory trials of NBCs in carbohydrate hydrolysis, biofuel production and biotransformation.

Immobilization of acetylcholinesterase on electrospun poly(acrylic acid)/multi-walled carbon nanotube nanofibrous membranes

The immobilized enzyme on nanofibrous samples maintained more than 90% of its original activity even after 10 cycles of reusing.

Effect of Cultivation Time and Medium Condition in Production of Bacterial Cellulose Nanofiber for Urease Immobilization

A new nanoporous biomatrix originated from bacterial resources has been chosen for urease immobilization. Urease has been immobilized on synthesized bacterial cellulose nanofiber since this enzyme has a key role in nitrogen metabolism.Gluconacetobacter xylinumATCC 10245 has been cultivated for synthesis of a nanofiber with the diameter of 30–70 nm. Different cultivation processes in the aspect of time and cultivation medium conditions were chosen to study the performance of immobilized enzyme on four types of bacterial cellulose nanofibers (BCNs). Urease immobilization into the nanofiber has been done in two steps: enzyme adsorption and glutaraldehyde cross-linking. The results showed that the immobilized enzymes were relatively active and highly stable compared to the control samples of free enzymes. Optimum pH was obtained 6.5 and 7 for different synthesized BCNs, while the optimum temperature for immobilized urease was 50°C. Finding of the current experiment illustrated that the immobilized enzyme in optimum condition lost its initial activity by 41% after 15 weeks.

A facile pathway to polyurea nanofiber fabrication and polymer morphology control in copolymerization of oxydianiline and toluene diisocyanate in acetone

Polyurea nanofibers, of high thermal stability and solvent resistance, were obtained through simple precipitation polymerization of TDI and ODA in acetone at 30 °C.

An environmentally-friendly enzyme-based nanofibrous membrane for 3,3′,5,5′-tetrabromobisphenol removal

Immobilization of HRP on NCC-incorporated CS/PVA membranes and its application in TBBPA removal.