Enzyme-functionalized mesoporous silica for bioanalytical applications

Ultrabright fluorescent particles via physical encapsulation of fluorescent dyes in mesoporous silica: a mini-review

Harnessing the power of mesoporous silica to encapsulate organic fluorescent dyes has led to the creation of an extraordinary class of nanocomposite photonic materials. These materials stand out for their ability to produce the brightest fluorescent particles known today, surpassing even the luminosity of quantum dots of similar spectrum and size. The synthesis of these materials offers precise control over the shape and size of the particles, ranging from the nano to the multi-micron scale. Just physical encapsulation of the dyes opens new possibilities for mixing different dyes within individual particles, paving the way for nearly limitless multiplexing capabilities. Moreover, this approach lays the groundwork for the development of highly sensitive sensors capable of detecting subtle changes in temperature and acidity at the nanoscale, among other parameters. This mini-review highlights the mechanism of synthesis, explains the nature of ultrabrightness, and describes the recent advancements and future prospects in the field of ultrabright fluorescent mesoporous silica particles, showcasing their potential for various applications.

Microbial electrosynthesis of valuable chemicals from the reduction of CO2: a review

The present energy demand of the world is increasing but the fossil fuels are gradually depleting. As a result, the need for alternative fuels and energy sources is growing. Fuel cells could be one alternative to address the challenge. The fuel cell can convert CO2 to value-added chemicals. The potential of bio-fuel cells, specifically enzymatic fuel cells and microbial fuel cells, and the importance of immobilization technology in bio-fuel cells are highlighted. The review paper also includes a detailed explanation of the microbial electrosynthesis system to reduce CO2 and the value-added products during microbial electrosynthesis. Future research in bio-electrochemical synthesis for CO2 conversion is expected to prioritize enhancing biocatalyst efficiency, refining reactor design, exploring novel electrode materials, understanding microbial interactions, integrating renewable energy sources, and investigating electrochemical processes for carbon capture and selective CO2 reduction. The challenges and perspectives of bio-electrochemical systems in the application of CO2 conversion are also discussed. Overall, this review paper provides valuable insights into the latest developments and criteria for effective research and implementation in bio-fuel cells, immobilization technology, and microbial electro-synthesis systems.

Designing Ubiquitin-like protease 1 (Ulp1) based nano biocatalysts: A promising technology for SUMO fusion proteins

The SUMO proteases (Ulps), a group of cysteine proteases, are well known for their efficient ability to perform structure-based cleavage of SUMO tag from the protein of interest and generation of biotherapeutics with authentic N-terminus. However, the stability of Ulps has remained a challenge for the economical production of difficult-to-produce proteins in E. coli. Therefore, the present study aimed to establish the methodology for developing stable S. pombe Ulp1 preparation using different enzyme immobilization strategies. The whole-cell biocatalyst developed using the Pir1 anchor protein of Pichia cleaved the SUMO tag within 24 h of reaction incubation. The chemical immobilization using commercial epoxy and amino methacrylate beads significantly enhanced the operational reusability of SpUlp1 up to 24 cycles. Silica beads further improved the repetitive usage of the immobilized enzyme for 65 cycles. The SpUlp1 immobilization on laboratory-developed chitosan-coated iron oxide nanoparticles exhibited more than 90 % cleavage of SUMO tag from different substrates even after 100 consecutive reactions. Moreover, an effective SUMO tag removal was observed within 10 min of incubation. The operational stability of the immobilized enzyme was confirmed in a pH range of 5 to 13. The spherical nature of nanoparticles was confirmed by FESEM and TEM results. The successful chitosan coating and subsequent activation with glutaraldehyde were established via FT-IR. Furthermore, HRTEM, SAED, and XRD proved the crystalline nature of nanoparticles, while VSM confirmed the superparamagnetic behavior.

Glucose Oxidase Loading in Ordered Porous Aluminosilicates: Exploring the Potential of Surface Modification for Electrochemical Glucose Sensing

Enzymatic electrochemical sensors have become the leading glucose detection technology due to their rapid response, affordability, portability, selectivity, and sensitivity. However, the performance of these sensors is highly dependent on the surface properties of the electrode material used to store glucose oxidase and its ability to retain enzymatic activity under variable environmental conditions. Mesoporous thin films have recently attracted considerable attention as promising candidates for enzyme storage and activity preservation due to their well-defined nanoarchitecture and tunable surface properties. Herein, we systematically compare pathways for the immobilization of glucose oxidase (GOx) and their effectiveness in electrochemical glucose sensing, following modification protocols that lead to the electrostatic attraction (amino functionalization), covalent bonding (aldehyde functionalization), and electrostatic repulsion (oxygen plasma treatment) of the ordered porous aluminosilicate-coated electrodes. By direct comparison using a quartz crystal microbalance, we demonstrate that glucose oxidase can be loaded in a nanoarchitecture with a pore size of ∼50 nm and pore interconnections of ∼35 nm using the native aluminosilicate surface, as well as after amino or aldehyde surface modification, while oxygen plasma exposure of the native surface inhibits glucose oxidase loading. Despite a variety of routes for enzyme loading, quantitative electrochemical glucose sensing between 0 and 20 mM was only possible when the porous surface was functionalized with amino groups, which we relate to the role of surface chemistry in accessing the underlying substrate. Our results highlight the impact of rational surface modification on electrochemical biosensing performance and demonstrate the potential of tailoring porous nanoarchitecture surfaces for biosensing applications.

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.

Developing Enzyme Immobilization with Fibrous Membranes: Longevity and Characterization Considerations

Fibrous membranes offer broad opportunities to deploy immobilized enzymes in new reactor and application designs, including multiphase continuous flow-through reactions. Enzyme immobilization is a technology strategy that simplifies the separation of otherwise soluble catalytic proteins from liquid reaction media and imparts stabilization and performance enhancement. Flexible immobilization matrices made from fibers have versatile physical attributes, such as high surface area, light weight, and controllable porosity, which give them membrane-like characteristics, while simultaneously providing good mechanical properties for creating functional filters, sensors, scaffolds, and other interface-active biocatalytic materials. This review examines immobilization strategies for enzymes on fibrous membrane-like polymeric supports involving all three fundamental mechanisms of post-immobilization, incorporation, and coating. Post-immobilization offers an infinite selection of matrix materials, but may encounter loading and durability issues, while incorporation offers longevity but has more limited material options and may present mass transfer obstacles. Coating techniques on fibrous materials at different geometric scales are a growing trend in making membranes that integrate biocatalytic functionality with versatile physical supports. Biocatalytic performance parameters and characterization techniques for immobilized enzymes are described, including several emerging techniques of special relevance for fibrous immobilized enzymes. Diverse application examples from the literature, focusing on fibrous matrices, are summarized, and biocatalyst longevity is emphasized as a critical performance parameter that needs increased attention to advance concepts from lab scale to broader utilization. This consolidation of fabrication, performance measurement, and characterization techniques, with guiding examples highlighted, is intended to inspire future innovations in enzyme immobilization with fibrous membranes and expand their uses in novel reactors and processes.

Engineering and application of polysaccharides and proteins-based nanobiocatalysts in the recovery of toxic metals, phosphorous, and ammonia from wastewater: A review

Global waste production is anticipated reach to 2.59 billion tons in 2030, thus accentuating issues of environmental pollution and health security. 37 % of waste is landfilled, 33 % is discharged or burned in open areas, and only 13.5 % is recycled, which makes waste management poorly efficient in the context of the circular economy. There is therefore a need for methods to recycle waste into valuable materials through resource recovery process. Progress in the field of recycling is strongly dependent on the development of efficient, stable, and reusable, yet inexpensive catalysts. In this case, a growing attention has been paid to development and application of nanobiocatalysts with promising features. The main purpose of this review paper is to: (i) introduce nanobiomaterials and describe their effective role in the preparation of functional nanobiocatalysts for the recourse recovery aims; (ii) provide production methods and the efficiency improvement of nanobaiocatalysts; (iii) give comprehensive description of valued resource recovery for reducing toxic chemicals from the contaminated environment; (iv) describe various technologies for the valued resource recovery; (v) state the limitation of the valued resource recovery; (vi) and finally economic importance and current scenario of nanobiocatalysts strategies applicable for the resource recovery processes.

Immobilization of Dextranase Obtained from the Marine Cellulosimicrobium sp. Y1 on Nanoparticles: Nano-TiO2 Improving Hydrolysate Properties and Enhancing Reuse

Dextranase is widely used in sugar production, drug synthesis, material preparation, and biotechnology, among other fields. The immobilization of dextranase using nanomaterials in order to make it reusable, is a hot research topic. In this study, the immobilization of purified dextranase was performed using different nanomaterials. The best results were obtained when dextranase was immobilized on titanium dioxide (TiO₂), and a particle size of 30 nm was achieved. The optimum immobilization conditions were pH 7.0, temperature 25 °C, time 1 h, and immobilization agent TiO₂. The immobilized materials were characterized using Fourier-transform infrared spectroscopy, X-ray diffractometry, and field emission gun scanning electron microscopy. The optimum temperature and pH of the immobilized dextranase were 30 °C and 7.5, respectively. The activity of the immobilized dextranase was >50% even after 7 times of reuse, and 58% of the enzyme was active even after 7 days of storage at 25 °C, indicating the reproducibility of the immobilized enzyme. The adsorption of dextranase by TiO₂ nanoparticles exhibited secondary reaction kinetics. Compared with free dextranase, the hydrolysates of the immobilized dextranase were significantly different, and consisted mainly of isomaltotriose and isomaltotetraose. The highly polymerized isomaltotetraose levels could reach >78.69% of the product after 30 min of enzymatic digestion.

Immobilization of lipase in chitosan-mesoporous silica material and pore size adjustment

Mesoporous silica MCM-41 was modified by carboxyl groups and assembled with chitosan to produce a novel nanocarrier for the immobilization of lipase. The prepared composite was grafted with silane coupling agent KH560 to decrease the pore size of the mesoporous material and prevent the loss of shed lipase molecules. According to the characterization of the material before and after modification and determination of related parameters, the residual activity of the lipase fixed in the CTS-MCM-41 carrier was 85 % after seven repeated use cycles. The grafting rate of MCM-41 and shrinkage effect were maximized when the concentration of KH560 was 5.0 %, and the modification was performed at 4 h at 70 °C. Using glutaraldehyde as the crosslinking agent, the optimal conditions for enzyme immobilization involved a mass ratio of the carrier to enzyme of 4:1, glutaraldehyde solution volume of 3 %, reaction time of 3 h, and reaction temperature of 45 °C. Overall, the proposed innovative carrier for the fixation of lipase is stable and can physically control the free enzyme in the pore. Moreover, the efficient miniature lipase reactor can promote large-scale industrial production.

High Internal Phase Pickering Emulsion Stabilized by Lipase-Coated ZIF-8 Nanoparticles towards Recyclable Biphasic Biocatalyst

High internal phase Pickering emulsion (Pickering HIPE) stabilized by enzyme-decorated metal-organic frameworks (MOFs) nanoparticles is developed for biphasic biocatalysts to enhance lipase catalysis and recycling. Specifically, enzyme decorated nanoparticles are prepared via ZIF-8 physisorption of a model lipase Candida antarctica Lipase B (CALB), named ZIF-8@CALB, to be both Pickering stabilizer and catalytic sites. An oil-in-water (o/w) Pickering HIPE with oil/water volume ratio of 3 could then be fabricated by homogenizing p-nitrophenyl palmitate (p-NPP) n-heptane solution into the ZIF-8@CALB aqueous dispersion. The biocatalytic hydrolysis of p-NPP is conducted by just standing the biphasic system at room temperature. The Pickering HIPE system achieves a product conversion of up to 48.9% within 0.5 h, whereas the p-NPP n-heptane solution system containing free CALB only achieves a stable product conversion of 6.8% for the same time. Moreover, the ZIF@CALB could be recovered by a simple centrifugation at 800 rpm, and then reused in the next cycle. The hydrolysis equilibrium conversion rate of p-NPP keeps over 40% for all 8 cycles, reflecting the high catalytic efficiency and recyclability of the Pickering HIPE. This study provides a new opportunity in designing Enzyme-MOFs-based Pickering interfacial biocatalyst for practical applications.

Effective immobilization of lactate dehydrogenase onto mesoporous silica

This study presents that covalent immobilization technique has been utilized for the immobilization of l-lactate dehydrogenase (l-LDH) from porcine on mesoporous silica. To develop mesoporous silica as support material for use in l-LDH immobilization, the particle surfaces were functionalized with 3-aminopropyltrimethoxysilane and further conjugated with glutaraldehyde. The effect of some parameters such as glutaraldehyde concentration, immobilization pH, initial enzyme concentration, and immobilization time was investigated and the optimum conditions for these parameters were determined as 1% (w/v), pH 8.0, 1 mg/ml, and 120 min, respectively. The maximum working pH and temperature for the oxidation of lactate to pyruvate reaction were determined as 10.0 and 35°C for free and 9.0 and 40°C for immobilized l-LDH, respectively. The kinetic parameters (K_m and V_max ) of l-LDH for the oxidation of lactate to pyruvate reaction were examined as 1.02 mM and 7.58 U/mg protein for free and 0.635 mM and 1.7 U/mg protein for immobilized l-LDH, respectively. Moreover, the immobilized l-LDH was 1.3-fold more stable than free l-LDH at 25°C according to calculated t_1/2 values. The immobilized l-LDH retained 80% of its initial activity in a batch reactor after 14 reuses.

Recent advances in the utilization of immobilized laccase for the degradation of phenolic compounds in aqueous solutions: A review

Phenolic compounds such as phenol, bisphenol A, 2,4-dichlorophenol, 2,4-dinitrophenol, 4-chlorophenol and 4-nitrophenol are well known to be highly detrimental to both human and living beings. Thus, it is of critical importance that suitable remediation technologies are developed to effectively remove phenolic compounds from aqueous solutions. Biodegradation utilizing enzymatic technologies is a promising biotechnological solution to sustainably address the pollution in the aquatic environment as caused by phenolic compounds under a defined environmentally optimized strategy and thus should be investigated in great detail. This review aims to present the latest developments in the employment of immobilized laccase for the degradation of phenolic compounds in water. The review first succinctly delineates the fundamentals of biological enzyme degradation along with a critical discussion on the myriad types of laccase immobilization techniques, which include physical adsorption, ionic adsorption, covalent binding, entrapment, and self-immobilization. Then, this review presents the major properties of immobilized laccase, namely pH stability, thermal stability, reusability, and storage stability, as well as the degradation efficiencies and associated kinetic parameters. In addition, the optimization of the immobilized enzyme, specifically on laccase immobilization methods and multi-enzyme system are critically discussed. Finally, pertinent future perspectives are elucidated in order to significantly advance the developments of this research field to a higher level.

Mesoporous Materials as Elements of Modern Drug Delivery Systems for Anti-Inflammatory Agents: A Review of Recent Achievements

Interest in the use of mesoporous materials as carriers of medicinal substances has been steadily increasing in the last two decades. Mesoporous carriers have application in the preparation of delivery systems for drugs from various therapeutic groups; however, their use as the carriers of anti-inflammatory agents is particularly marked. This review article, with about 170 references, summarizes the achievements in the application of mesoporous materials as the carriers of anti-inflammatory agents in recent years. This article will discuss a variety of mesoporous carriers as well as the characteristics of their porous structure that determine further use of these materials in the field of medical applications. Special attention will be paid to the progress observed in the construction of stimuli-responsive drug carriers and systems providing site-specific drug delivery. Subsequently, a review of the literature devoted to the use of mesoporous matrices as the carriers of anti-inflammatory drugs was carried out.

Recent Advancements in Enzyme‐Incorporated Nanomaterials: Synthesis, Mechanistic Formation and Applications

Over the past decade, nanotechnology has been developed and employed across various entities. Among the numerous nanostructured material types, enzyme‐incorporated nanomaterials have shown great potential in various fields, as an alternative to biologically derived as well as synthetically developed hybrid structures. The mechanism of incorporating enzyme onto a nanostructure depends on several factors including the method of immobilization, type of nanomaterial, as well as operational and environmental conditions. The prospects of enzyme‐incorporated nanomaterials have shown promising results across various applications, such as biocatalysts, biosensors, drug therapy, and wastewater treatment. This is due to their excellent ability to exhibit chemical and physical properties such as high surface‐to‐volume ratio, recovery and/or reusability rates, sensitivity, response scale, and stable catalytic activity across wide operating conditions. In this review, the evolution of enzyme‐incorporated nanomaterials along with their impact on our society due to its state‐of‐the‐art properties, and its significance across different industrial applications are discussed. In addition, the weakness and future prospects of enzyme‐incorporated nanomaterials were also discussed to guide scientists for futuristic research and development in this field.

Selective immobilization of his-tagged phosphomannose isomerase on Ni chelated nanoparticles with good reusability and activity

In this paper, self-stable precipitation polymerization was used to prepare the enzyme-immobilized microsphere composite. Phosphomannose isomerase (PMI) with His-tag was successfully immobilized on Ni 2+ charged pyridine-derived particles. The maximum amount of PMI immobilized on such particles was ~ 184 mg/g. Compared with the free enzymes, the activity of the immobilized enzymes has been significantly improved. In addition, the immoblized enzymes showed a much better thermostability than free enzymes. At the same time, the immobilized enzymes can be reused for multiple reaction cycles. We have observed that the enzyme activity did not decrease significantly after 6 cycles of repeating usages. We conclude that the pyridine-derived particles can be used to selectively immobilize His-tagged enzymes, which can couple the enzyme purification and catalysis steps and improve the efficiency of enzyme-catalyzed industrial processes.

Adsorption of lysozyme into a charged confining pore

Several applications arise from the confinement of proteins on surfaces because their stability and biological activity are enhanced. It is also known that the way in which a protein adsorbs on the surface is important for its biological function since its active sites should not be obstructed. In this study, the adsorption properties of hen egg-white lysozyme, HEWL, into a negatively charged silica pore is examined by employing a coarse-grained model and constant-pH Monte Carlo simulations. The role of electrostatic interactions is taken into account via including the Debye-Hückel potentials into the Cα structure-based model. We evaluate the effects of pH, salt concentration, and pore radius on the protein preferential orientation and spatial distribution of its residues regarding the pore surface. By mapping the residues that stay closer to the pore surface, we find that the increase of pH leads to orientational changes of the adsorbed protein when the solution pH gets closer to the HEWL isoelectric point. Under these conditions, the pK_a shift of these important residues caused by the adsorption into the charged confining surface results in a HEWL charge distribution that stabilizes the adsorption in the observed protein orientation. We compare our observations to the results of the pK_a shift for HEWL available in the literature and to some experimental data.

Challenges and perspectives of the β-galactosidase enzyme

The enzyme β-galactosidase has great potential for application in the food and pharmaceutical industries due to its ability to perform the hydrolysis of lactose, a disaccharide present in milk and in dairy by-products. It can be used in free form, in batch processes, or in immobilized form, which allows continuous operation and provides greater enzymatic stability. The choice of method and support for enzyme immobilization is essential, as the performance of the biocatalyst is strongly influenced by the properties of the material used and by the interaction mechanisms between support and enzyme. Therefore, this review showed the main enzyme immobilization techniques, and the most used supports for the constitution of biocatalysts. Also, materials with the potential for immobilization of β-galactosidases and the importance of their biotechnological application are presented. KEY POINTS: • The main methods of immobilization are physical adsorption, covalent bonding, and crosslinking. • The structural conditions of the supports are determining factors in the performance of the biocatalysts. • Enzymatic hydrolysis plays an important role in the biotechnology industry.

Loading and Release of Charged and Neutral Fluorescent Dyes into and from Mesoporous Materials: A Key Role for Sensing Applications

The aim of this study is to determine the efficiency of loading and release of several zwitterionic, neutral, anionic and cationic dyes into/from mesoporous nanoparticles to find the optimum loading and release conditions for their application in detection protocols. The loading is carried out for MCM-41 type silica supports suspended in phosphate-buffered saline (PBS) buffer (pH 7.4) or in acetonitrile, involving the dyes (rhodamine B chloride, rhodamine 101 chloride, rhodamine 101 perchlorate, rhodamine 101 inner salt, meso-(4-hydroxyphenyl)-boron–dipyrromethene (BODIPY), sulforhodamine B sodium salt and fluorescein 27). As a general trend, rhodamine-based dyes are loaded with higher efficiency, when compared with BODIPY and fluorescein dyes. Between the rhodamine-based dyes, their charge and the solvent in which the loading process is carried out play important roles for the amount of cargo that can be loaded into the materials. The delivery experiments carried out in PBS buffer at pH 7.4 reveal for all the materials that anionic dyes are more efficiently released compared to their neutral or cationic counterparts. The overall best performance is achieved with the negatively charged sulforhodamine B dye in acetonitrile. This material also shows a high delivery degree in PBS buffer.

Harnessing the biocatalytic attributes and applied perspectives of nanoengineered laccases-A review

In the recent past, numerous new types of nanostructured carriers, as support matrices, have been engineered to advance the traditional enzyme immobilization strategies. The current research aimed to develop a robust enzyme-based biocatalytic platform and its effective deployment in the industrial biotechnology sectors at large and catalysis area, in particular, as low-cost biocatalytic systems. Suitable coordination between the target enzyme molecules and surface pendent multifunctional entities of nanostructured carriers has led an effective and significant contribution in myriad novel industrial, biotechnological, and biomedical applications. As compared to the immobilization on planar two-dimensional (2-D) surface, the unique physicochemical, structural and functional attributes of nano-engineered matrices, such as high surface-to-volume ratio, surface area, robust chemical and mechanical stability, surface pendant functional groups, outstanding optical, thermal, and electrical characteristics, resulted in the concentration of the immobilized entity being substantially higher, which is highly requisite from applied bio-catalysis perspective. Besides inherited features, nanostructured materials-based enzyme immobilization aided additional features, such as (1) ease in the preparation or green synthesis route, (2) no or minimal use of surfactants and harsh reagents, (3) homogeneous and well-defined core-shell nanostructures with thick enzyme shell, and (4) nano-size can be conveniently tailored within utility limits, as compared to the conventional enzyme immobilization. Moreover, the growing catalytic needs can be fulfilled by multi-enzymes co-immobilization on these nanostructured materials-based support matrices. This review spotlights the unique structural and functional attributes of several nanostructured materials, including carbon nanotubes, graphene, and its derivate constructs, nanoparticles, nanoflowers, and metal-organic frameworks as robust matrices for laccase immobilization. The later half of the review focuses on the applied perspective of immobilized laccases for the degradation of emergent contaminants, biosensing cues, and lignin deconstruction and high-value products.

Design and Construction of an Effective Expression System with Aldehyde Tag for Site-Specific Enzyme Immobilization

In recent years, the development and application of site-specific immobilization technology for proteins have undergone significant advances, which avoids the unwanted and random covalent linkage between the support and active site of protein in the covalent immobilization. Formylglycine generating enzyme (FGE) can transform the cysteine from a conversed 6-amino-acid sequence CXPXR into formylglycine with an aldehyde group (also termed as “aldehyde tag”). Based on the frame of pET-28a, the His-tags were replaced with aldehyde tags. Afterward, a set of plasmids were constructed for site-specific covalent immobilization, their His-tags were knock out (DH), or were replaced at different positions: N-terminal (NQ), C-terminal (CQ), or both (DQ) respectively. Three different enzymes, thermophilic acyl aminopeptidase (EC 3.4.19.1) from Sulfolobus tokodaii (ST0779), thermophilic dehalogenase (EC 3.8.1.2) from Sulfolobus tokodaii (ST2570), and Lipase A (EC 3.1.1.3) from Bacillus subtilis (BsLA) were chosen as model enzymes to connect with these plasmid systems. The results showed that different aldehyde-tagged enzymes can be successfully covalently attached to different carriers modified with an amino group, proving the universality of the method. The new immobilized enzyme also presented better thermostability and reutilization than those of the free enzyme.

A Biosensor for the Detection of Acetylcholine and Diazinon

Acetylcholine is a neurotransmitter and a neuromodulator found in the autonomic, peripheral and central nervous systems. Diazinon is a pesticide with toxic effects on humans, such as the inhibition of acetylcholine. In this paper, a biosensor is proposed for the detection of acetylcholine (range 70 - 1000 μM) and diazinon (range 0.3 - 20000 ppb). This biosensor combines a pH-sensitive layer of reduced graphene oxide functionalized with 4-aminobenzoic acid and acetylcholinesterase. This enzyme was immobilized on reduced graphene oxide and it catalyzed the conversion of acetylcholine into choline and acetic acid, locally decreasing the pH value and triggering the sensor response. The limit of detection for the acetylcholine and diazinon were 70 μM and 0.3 ppb, respectively.

Advances in nanomaterial application in enzyme-based electrochemical biosensors: a review

Electrochemical enzyme-based biosensors are one of the largest and commercially successful groups of biosensors. Integration of nanomaterials in the biosensors results in significant improvement of biosensor sensitivity, limit of detection, stability, response rate and other analytical characteristics. Thus, new functional nanomaterials are key components of numerous biosensors. However, due to the great variety of available nanomaterials, they should be carefully selected according to the desired effects. The present review covers the recent applications of various types of nanomaterials in electrochemical enzyme-based biosensors for the detection of small biomolecules, environmental pollutants, food contaminants, and clinical biomarkers. Benefits and limitations of using nanomaterials for analytical purposes are discussed. Furthermore, we highlight specific properties of different nanomaterials, which are relevant to electrochemical biosensors. The review is structured according to the types of nanomaterials. We describe the application of inorganic nanomaterials, such as gold nanoparticles (AuNPs), platinum nanoparticles (PtNPs), silver nanoparticles (AgNPs), and palladium nanoparticles (PdNPs), zeolites, inorganic quantum dots, and organic nanomaterials, such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon and graphene quantum dots, graphene, fullerenes, and calixarenes. Usage of composite nanomaterials is also presented.

Review of large-pore mesostructured cellular foam (MCF) silica and its applications

The unique properties of mesostructured cellular foam (MCF) silica such as, large pore size, continuous three-dimensional (3D) pore system and hydrothermal robust materialallow favorable conditions for incorporating active sites to produce modified MCF silica as catalysts, biocatalysts and adsorbents. Recently, the modified MCF silicas were reported to be efficient catalysts for the hydrogenation of phenylacetylene, heck coupling reaction of arylboronic acid, etc. Biocatalysts derived from modified MCF silicas were found to be a potential to convert glucose to gluconic acid, hydrolysis of N-benzoyl-DLarginine-p-nitroanilide (BAPNA) and casein, transesterification of racemic 1 phenyl- ethanol and hydrolytic, etc. Several separation processes such as CO2 capture and adsorption of L-tryptophan, lysozyme and bovine serum were sucessfully conducted using adsorbents derived from modified MCF silicas. This paper reviews the synthesis of the MCF silica material and the incorporation of active sites or immobilization of enzymes in the MCF silica material. Additionally, a detailed understanding of the characterization of the modified MCF silicas, which includes pore size, active sites/enzymes sizes, amount of active sites/enzymes bound with the MCF silica, was also discussed to obtain their potentialities as catalysts, biocatalysts and adsorbents. The review also describes recent progress on the applications of the MCF silica.

Characterization of enzyme-immobilized catalytic support and its exploitation for the degradation of methoxychlor in simulated polluted soils

Chiral mesoporous silica (SiO₂) with helical structure was synthesized by using anionic surfactants as template. Pre-prepared graphene oxide (GO) was then loaded onto SiO₂ to synthesize composite carrier chial-meso-SiO₂@GO for the immobilization of laccase. The enzyme activity, thermostability, acid stability, and repeatability of the immobilized enzyme were significantly improved after immobilization. The chial-meso-SiO₂@GO-immobilized laccase was then used for the degradation of MXC in aqueous phase. The degradation conditions, including temperature, time, pH, MXC concentration, and the dose of immobilized enzyme for cellulosic hydrolysis, were optimized. The optimum conditions for degradation of methoxychlor were selected as pH 4.5, MXC concentration 30 mg/L, immobilized enzyme dose 0.1 g, the maximum MXC removal of over 85% and the maximum degradation rate of 50.75% were achieved after degradation time of six h at temperature of 45 °C. In addition, the immobilized cellulase was added into the immobilized laccase system to form chial-meso-SiO₂@GO-immobilized compound enzyme with the maximum MXC degradation rate of 59.58%, higher than that of 50.75% by immobilized laccase. An assessment was made for the effect of chial-meso-SiO₂@GO-immobilized compound enzyme on the degradation of MXC in soil phase. For three contaminated soils with MXC concentration of 25 mg/kg, 50 mg/kg, and 100 mg/kg, the MXC removals were 93.0%, 85.8%, and 65.1%, respectively. According to the GC-MS analyses, it was inferred that chial-meso-SiO₂@GO-immobilized compound enzyme had a different degradation route with that of chial-meso-SiO₂@GO-immobilized laccase. The hydrolysis by immobilized cellulase might attack at a weak location of the MXC molecule with its free radical OH and ultimately removed three chlorine atoms from MXC molecule, leading to generating small molecular amount of degradation product.

Enzyme Entrapment in Amphiphilic Myristyl-Phenylalanine Hydrogels

Supramolecular amino acid and peptide hydrogels are functional materials with a wide range of applications, however, their ability to serve as matrices for enzyme entrapment have been rarely explored. Two amino acid conjugates were synthesized and explored for hydrogel formation. These hydrogels were characterized in terms of strength and morphology, and their ability to entrap enzymes while keeping them active and reusable was explored. It was found that the hydrogels were able to successfully entrap two common and significant enzymes-horseradish peroxidase and -amylase-thus keeping them active and stable, along with inducing recycling capabilities, which has potential to further advance the industrial biotransformation field.

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

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

Highly active enzymes immobilized in large pore colloidal mesoporous silica nanoparticles

Carbonic anhydrase and horseradish peroxidase are immobilized inside the ordered material by click reactions. Colorimetric assays prove their catalytic activity.

Synthesis of functional ionic liquid modified magnetic chitosan nanoparticles for porcine pancreatic lipase immobilization

We developed magnetic chitosan nanoparticles (CS‑Fe₃O₄) with mean diameter of 15-20 nm. Subsequently, these inorganic-organic composite nanoparticles were modified using an imidazole-based functional ionic liquid (IL). The prepared support (IL‑CS‑Fe₃O₄), which was used to immobilize porcine pancreatic lipase (PPL), was characterized using Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM), thermogravimetry (TG), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Circular dichroism (CD) was used to analyze the secondary structure of immobilized PPL. The immobilized PPL (PPL‑IL‑CS‑Fe₃O₄) exhibited 1.93-fold higher specific activity than PPL‑CS-Fe₃O₄ when triacetin was used as the substrate, and showed 95 mg/g of lipase immobilization capacity and 382% of activity recovery. The residual activity of PPL‑IL‑CS‑Fe₃O₄ was above 60% of the initial activity after incubation at 50 °C for 6 h, as was higher than that of PPL‑CS‑Fe₃O₄ which showed 40% of the initial activity. In addition, PPL‑IL‑CS‑Fe₃O₄ retained 84.6% of the initial activity after 10 cycles, whereas PPL‑CS‑Fe₃O₄ retained only 75.5% activity. Furthermore, the kinetic parameters, apparent K_m and V_max of PPL‑IL‑CS‑Fe₃O₄ were 2.51 mg/mL and 1.395 U/mg respectively, these results indicated that the immobilized PPL had better affinity towards the substrate, especially when the nanoparticles were modified by functional IL. Besides, the magnetic chitosan nanoparticles loaded with PPL were easily recovered. A novel, efficient, and practical method for enzyme immobilization was developed.

Continuous flow biocatalysis

The continuous flow synthesis of active pharmaceutical ingredients, value-added chemicals, and materials has grown tremendously over the past ten years. This revolution in chemical manufacturing has resulted from innovations in both new methodology and technology. This field, however, has been predominantly focused on synthetic organic chemistry, and the use of biocatalysts in continuous flow systems is only now becoming popular. Although immobilized enzymes and whole cells in batch systems are common, their continuous flow counterparts have grown rapidly over the past two years. With continuous flow systems offering improved mixing, mass transfer, thermal control, pressurized processing, decreased variation, automation, process analytical technology, and in-line purification, the combination of biocatalysis and flow chemistry opens powerful new process windows. This Review explores continuous flow biocatalysts with emphasis on new technology, enzymes, whole cells, co-factor recycling, and immobilization methods for the synthesis of pharmaceuticals, value-added chemicals, and materials.

Enzyme-Based Ultrasensitive Electrochemical Biosensors for Rapid Assessment of Nitrite Toxicity: Recent Advances and Perspectives

In the present era of rapid international globalization and industrialization, intensive use of nitrite as a fertilizing agent in agriculture, preservative, dyeing agent, food additive and as corrosion inhibitor in industrial sectors is adversely effecting environment, natural habitats and human health. The issue of toxicity and carcinogenicity due to excessive ingestion of nitrites via the dietary intake has led to an imminent need for its efficient real-time monitoring in situ. Nitrite detection employing electrochemical biosensors has been gaining high credibility in the field of clinical research. Nitrite biosensors have emerged as an outstanding choice for portable point of care testing of nitrite quantification owing to the excellent properties, such as rapidity, miniaturization, ultra-low limits of detection, multiplexing and enhanced detection sensitivity. The article is enclosed with an interesting outlook on latest emerging trends in the development of nitrite biosensors utilizing nanomaterials, such as metal nanoparticles, carbon nanotubes, metal oxide nanoparticles, nanocomposites, polymers and biomaterials. The present review embarks on the highlights relevant to the nitrite quantification in real samples, then proceeds with a meticulous description of the most pertinent electrochemical nitrite biosensors, which have been proposed by adopting diverse materials and strategies of fabrication and finally end with the achievements and future outlook signifying the application of these nanoengineered biosensors for environmental surveillance and human safety.

Mice pancreatic islets protection from oxidative stress induced by single-walled carbon nanotubes through naringin

The growing use of carbon nanotubes (CNTs) emphasizes the importance of its potential toxic effects on the human health. Previous studies proved that CNTs caused oxidative stress and decreased cell viability. On the other hand, reactive oxygen species (ROS) and oxidative stress impaired β-cell functions and reduced the insulin secretion. However, there is not any study on the effects of CNTs on islets and β-cells. Therefore, the present study aimed to evaluate the effects of single-walled CNTs (SWCNTs) on oxidative stress in islets in addition to the protective effects of naringin (NRG) as an antioxidant . We examined the effects of SWCNTs and naringin on islets by 3,4 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay; measurement of insulin secretion, ROS, and malondialdehyde (MDA); activities of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) peroxidase (GSH-Px); and content of GSH and mitochondrial membrane potential (MMP). The MTT assay demonstrated that decreased viability of islets cells was dose-dependent with exposure to SWCNTs. Further studies revealed that SWCNTs decreased insulin secretion and MMP, induced the formation of ROS, increased the level of MDA, and decreased the activities of SOD, GSH-Px, and CAT and content of GSH. Furthermore, the pretreatment of islets with naringin significantly reverted back these changes. These findings revealed that SWCNTs might induce the oxidative stress to pancreatic islets, causing the occurrence of diabetes, and the protective effects of naringin that was mediated by augmentation of the antioxidant defense system of islets. Our research indicated the necessity for further in vivo and in vitro researches on the effects of SWCNTs and naringin on diabetes.

Functionally Active Membrane Proteins Incorporated in Mesostructured Silica Films

A versatile synthetic protocol is reported that allows high concentrations of functionally active membrane proteins to be incorporated in mesostructured silica materials. Judicious selections of solvent, surfactant, silica precursor species, and synthesis conditions enable membrane proteins to be stabilized in solution and during subsequent coassembly into silica-surfactant composites with nano- and mesoscale order. This was demonstrated by using a combination of nonionic ( n-dodecyl-β-d-maltoside or Pluronic P123), lipid-like (1,2-diheptanoyl- s n-glycero-3-phosphocholine), and perfluoro-octanoate surfactants under mild acidic conditions to coassemble the light-responsive transmembrane protein proteorhodopsin at concentrations up to 15 wt % into the hydrophobic regions of worm-like mesostructured silica materials in films. Small-angle X-ray scattering, electron paramagnetic resonance spectroscopy, and transient UV-visible spectroscopy analyses established that proteorhodopsin molecules in mesostructured silica films exhibited native-like function, as well as enhanced thermal stability compared to surfactant or lipid environments. The light absorbance properties and light-activated conformational changes of proteorhodopsin guests in mesostructured silica films are consistent with those associated with the native H+-pumping mechanism of these biomolecules. The synthetic protocol is expected to be general, as demonstrated also for the incorporation of functionally active cytochrome c, a peripheral membrane protein enzyme involved in electron transport, into mesostructured silica-cationic surfactant films.

Control and formation mechanism of extended nanochannel geometry in colloidal mesoporous silica particles

A large class of colloidal multi-micron mesoporous silica particles have well-defined cylindrical nanopores, nanochannels which self-assembled in the templated sol-gel process. These particles are of broad interest in photonics, for timed drug release, enzyme stabilization, separation and filtration technologies, catalysis, etc. Although the pore geometry and mechanism of pore formation of such particles has been widely investigated at the nanoscale, their pore geometry and its formation mechanism at a larger (extended) scale is still under debate. The extended geometry of nanochannels is paramount for all aforementioned applications because it defines accessibility of nanochannels, and subsequently, kinetics of interaction of the nanochannel content with the particle surrounding. Here we present both experimental and theoretical investigation of the extended geometry and its formation mechanism in colloidal multi-micron mesoporous silica particles. We demonstrate that disordered (and consequently, well accessible) nanochannels in the initially formed colloidal particles gradually align and form extended self-sealed channels. This knowledge allows to control the percentage of disordered versus self-sealed nanochannels, which defines accessibility of nanochannels in such particles. We further show that the observed aligning the channels is in agreement with theory; it is thermodynamically favored as it decreases the Gibbs free energy of the particles. Besides the practical use of the obtained results, developing a fundamental understanding of the mechanisms of morphogenesis of complex geometry of nanopores will open doors to efficient and controllable synthesis that will, in turn, further fuel the practical utilization of these particles.

Soybean peroxidase immobilized onto silica-coated superparamagnetic iron oxide nanoparticles: Effect of silica layer on the enzymatic activity

Peroxidase immobilization onto magnetic supports is considered an innovative strategy for the development of technologies that involves enzymes in wastewater treatment. In this work, magnetic biocatalysts were prepared by immobilization of soybean peroxidase (SBP) onto different silica-coated superparamagnetic iron oxide nanoparticles. The obtained magnetic biocatalysts were tested for the degradation of malachite green (MG), a pollutant often found in industrial wastewaters and with significant drawbacks for the human and environmental health. A deep physicochemical characterization of the materials was performed by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR-TEM) and magnetization measurements among others techniques. Results showed high immobilization yield of SBP onto nanomaterials with excellent properties for magnetic recoverability. A partial loss of activity with respect to free SBP was observed, compatible with the modification of the conformational structure of the enzyme after immobilization. The structural modification depended on the amount (and thickness) of silica present in the hybrid materials and the activity yield of 43% was obtained for the best biocatalyst. Thermal stability and reusability capacity were also evaluated.

Effects of TiO2 crystal structure on the luminescence quenching of [Ru(bpy)2(dppz)]2+-intercalated into DNA

The intercalation of [Ru(bpy)₂(dppz)]²⁺ labeled as Ru(II) (bpy=2,2'-bipyridine and dppz=dipyrido[3,2,-a:2',3'-c]phenazine) into herring sperm DNA leads to the formation of emissive Ru(II)-DNA dyads, which can be quenched by TiO₂ nanoparticles (NPs) and sol-gel silica matrices at heterogeneous interfaces. The calcinations temperature exhibits a remarkable influence on the luminescence quenching of the Ru(II)-DNA dyads by TiO₂ NPs. With increasing calcinations temperature in the range from 200 to 850°C, the anatase-to-rutile TiO₂ crystal structure transformation increases the average particle size and hydrodynamic diameter of TiO₂ and DNA@TiO₂. The anatase TiO₂ has the stronger ability to unbind the Ru(II)-DNA dyads than the rutile TiO₂ at room temperature. The TiO₂ NPs and sol-gel silica matrices can quench the luminescence of the Ru(II) complex intercalated into DNA by selectively capturing the negatively DNA and positively charged Ru(II) complex to unbind the dyads, respectively. This present results provide new insights into the luminescence quenching and competitive binding of dye-labeled DNA dyads by inorganic NPs.

Effective delivery of volatile biocides employing mesoporous silicates for treating biofilms

Nanoparticulate delivery of biocides has the potential to decrease levels of exposure to non-target organisms, and miminize long-term exposure that can promote the development of resistance. Silica nanoparticles are an ideal vehicle since they are inert, biocompatible, biodegradable, and thermally and chemically stable. Encapsulation of biocides within nanoparticulates can improve their stability and longevity and maximize the biocidal potential of hydrophobic volatile compounds. Herein, we have shown that the plant secondary metabolites allyl isothiocyanate and cinnamaldehyde demonstrated increased antimicrobial activity against Escherichia coli in planktonic form, when packaged into mesoporous silica nanoparticles. Furthermore, the biocide-loaded nanoparticles showed activity against Pseudomonas aeruginosa biofilms that have inherent resistance to antimicrobial agents. The delivery platform can also be expanded to traditional biocides and other non-conventional antimicrobial agents.

Self-assembly of multi-hierarchically structured spongy mesoporous silica particles and mechanism of their formation

Here we report on self-assembly of novel multi-hierarchically structured meso(nano)porous colloidal silica particles which have cylindrical pores of 4-6nm, overall size of ∼10μm and "cracks" of 50-200nm. These cracks make particles look like micro-sponges. The particles were prepared through a modified templated sol-gel self-assembly process. The mechanism of assembly of these particles is investigated. Using encapsulated fluorescent dye, we demonstrate that the spongy particles are advantageous to facilitate dye diffusion out of particles. This multi-hierarchically geometry of particles can be used to improve the particle design for multiple applications to control drug release, rate of catalysis, filtration, utilization of particles as hosts for functional molecules (e.g., enzymes), etc.