Dithiocarbamate to modify magnetic graphene oxide nanocomposite (Fe 3 O 4 -GO): A new strategy for covalent enzyme (lipase) immobilization to fabrication a new nanobiocatalyst for enzymatic hydrolysis of PNPD

Advancements in enzyme immobilization on magnetic nanomaterials: toward sustainable industrial applications

Enzymes are widely used in biofuels, food, and pharmaceuticals. The immobilization of enzymes on solid supports, particularly magnetic nanomaterials, enhances their stability and catalytic activity. Magnetic nanomaterials are chosen for their versatility, large surface area, and superparamagnetic properties, which allow for easy separation and reuse in industrial processes. Researchers focus on the synthesis of appropriate nanomaterials tailored for specific purposes. Immobilization protocols are predefined and adapted to both enzymes and support requirements for optimal efficiency. This review provides a detailed exploration of the application of magnetic nanomaterials in enzyme immobilization protocols. It covers methods, challenges, advantages, and future perspectives, starting with general aspects of magnetic nanomaterials, their synthesis, and applications as matrices for solid enzyme stabilization. The discussion then delves into existing enzymatic immobilization methods on magnetic nanomaterials, highlighting advantages, challenges, and potential applications. Further sections explore the industrial use of various enzymes immobilized on these materials, the development of enzyme-based bioreactors, and prospects for these biocatalysts. In summary, this review provides a concise comparison of the use of magnetic nanomaterials for enzyme stabilization, highlighting potential industrial applications and contributing to manufacturing optimization.

Enhancing biocatalyst performance through immobilization of lipase (Eversa® Transform 2.0) on hybrid amine-epoxy core-shell magnetic nanoparticles

Magnetic nanoparticles were functionalized with polyethylenimine (PEI) and activated with epoxy. This support was used to immobilize Lipase (Eversa® Transform 2.0) (EVS), optimization using the Taguchi method. XRF, SEM, TEM, XRD, FTIR, TGA, and VSM performed the characterizations. The optimal conditions were immobilization yield (I.Y.) of 95.04 ± 0.79 %, time of 15 h, ionic load of 95 mM, protein load of 5 mg/g, and temperature of 25 °C. The maximum loading capacity was 25 mg/g, and its stability in 60 days of storage showed a negligible loss of only 9.53 % of its activity. The biocatalyst demonstrated better stability at varying temperatures than free EVS, maintaining 28 % of its activity at 70 °C. It was feasible to esterify free fatty acids (FFA) from babassu oil with the best reaction of 97.91 % and ten cycles having an efficiency above 50 %. The esterification of produced biolubricant was confirmed by NMR, and it displayed kinematic viscosity and density of 6.052 mm2/s and 0.832 g/cm3, respectively, at 40 °C. The in-silico study showed a binding affinity of -5.8 kcal/mol between EVS and oleic acid, suggesting a stable substrate-lipase combination suitable for esterification.

Improvement of thermal-stability of chondroitinase ABCI immobilized on graphene oxide for the repair of spinal cord injury

Spinal cord injury healing has been shown to be aided by chondroitinase ABC I (cABCI) treatment. The transport of cABCI to target tissues is complicated by the enzyme's thermal instability; however, cABCI may be immobilized on nanosheets to boost stability and improve delivery efficiency. This investigation's goal was to assess the immobilization of cABC I on graphene oxide (GO). for this purpose, GO was produced from graphene using a modified version of Hummer's process. the immobilization of cABC I on GO was examined using SEM, XRD, and FTIR. The enzymatic activity of cABC I was evaluated in relation to substrate concentration. The enzyme was then surface-adsorption immobilized on GO, and its thermal stability was examined. As compared to the free enzyme, the results showed that the immobilized enzyme had a greater Km and a lower Vmax value. The stability of the enzyme was greatly improved by immobilization at 20, 4, 25, and 37 °C. For example, at 37 °C, the free enzyme retained 5% of its activity after 100 min, while the immobilized one retained 30% of its initial activity. The results showed, As a suitable surface for immobilizing cABC I, GO nano sheets boost the enzyme's stability, improving its capability to support axonal regeneration after CNC damage and guard against fast degradation.

Immobilized lipase for sustainable hydrolysis of acidified oil to produce fatty acid

Acidified oil is obtained from by-product of crops oil refining industry, which is considered as a low-cost material for fatty acid production. Hydrolysis of acidified oil by lipase catalysis for producing fatty acid is a sustainable and efficient bioprocess that is an alternative of continuous countercurrent hydrolysis. In this study, lipase from Candida rugosa (CRL) was immobilized on magnetic Fe₃O₄@SiO₂ via covalent binding strategy for highly efficient hydrolysis of acidified soybean oil. FTIR, XRD, SEM and VSM were used to characterize the immobilized lipase (Fe₃O₄@SiO₂-CRL). The enzyme properties of the Fe₃O₄@SiO₂-CRL were determined. Fe₃O₄@SiO₂-CRL was used to catalyze the hydrolysis of acidified soybean oil to produce fatty acids. Catalytic reaction conditions were studied, including amount of catalyst, reaction time, and water/oil ratio. The results of optimization indicated that the hydrolysis rate reached 98% under 10 wt.% (oil) of catalyst, 3:1 (v/v) of water/oil ratio, and 313 K after 12 h. After 5 cycles, the hydrolysis activity of Fe₃O₄@SiO₂-CRL remained 55%. Preparation of fatty acids from high-acid-value by-products through biosystem shows great industrial potential.

Nanomaterial Constructs for Catalytic Applications in Biomedicine: Nanobiocatalysts and Nanozymes

Nanomaterials possess superior advantages due to their special geometries, higher surface area, and unique mechanical, optical, and physicochemical properties. Their characteristics make them great contributors to the development of many technological and industrial sectors. Therefore, novel nanomaterials have an increasing interest in many research areas including biomedicine such as chronic inflammations, disease detection, drug delivery, and infections treatment. Their relevant role is, in many cases, associated with an effective catalytic application, either as a pure catalyst (acting as a nanozyme) or as a support for catalytically active materials (forming nanobiocatalysts). In this review, we analyze the construction of nanozymes and nanobiocatalyst by different existing forms of nanomaterials including carbon-based nanomaterials, metal-based nanomaterials, and polymer-based nanocomposites. Then, we examine successful examples of such nanomaterials employed in biomedical research. The role played by nanomaterials in catalytic applications is analyzed to identify possible research directions toward the development of the field and the achievement of real practicability.

Graphical Abstract

Nanomaterial-based electrochemical enzymatic biosensors for recognizing phenolic compounds in aqueous effluents

With the rapid development of industrial society, phenolic pollutants already identified in water are severe threats to human health. Traditional detection techniques like chromatography are poor in the ability of cost-effectiveness and on-site detection. In recent years, electrochemical enzymatic biosensors have attracted increasing attention for use in the recognition of phenolic compounds, which is considered an effective strategy for the product transfer of portable analytical devices. Although electrochemical enzymatic biosensors provide a fast, accurate on-site detection technique, the difficulties of enzyme deactivation, poor stability and low sensitivity remain to be solved. Thus, effective immobilization methods of enzymes and nanomaterials with excellent properties have been extensively researched to obtain a high-sensitivity and high-stability biosensing platform. Simultaneous detection of multiple phenols may become the focus of further research. In this review, we provide an overview of recent progress toward electrochemical enzymatic biosensors for the detection of phenolic compounds, including enzyme immobilization approaches and advanced nanomaterials, especially nanocomposites with attractive properties such as good conductivity, high specific surface area, and porous structure. We will comprehensively discuss the features and mechanisms of the main enzymes adopted in the construction of different phenolic biosensors, as well as traditional methods (e.g., adsorption, covalent bonding, entrapment, encapsulation, cross-linking) of enzyme immobilization. The most effective method is based on the properties of enzymes, supports and application objective because there is no one-size-fits-all method of enzymatic immobilization. The emphasis will be given to various advanced nanomaterials, including their special nanostructures, preparation methods and performance. Finally, the main challenges in future research on electrochemical phenolic biosensors will be discussed to provide further perspectives for practical applications in dynamic and on-site monitoring. We believe this review will deliver an important inspiration for the construction of novel and high-performance electrochemical biosensors from enzyme selection to nanomaterial design for the detection of various hazardous materials. We believe this review will deliver an important inspiration on the construction of novel and high-performance electrochemical biosensors from the enzyme selection to the nanomaterial design for detections of various hazardous materials.

Preparation of photoluminescent and anticorrosive epoxy paints immobilized with nanoscale graphene from sugarcane bagasse agricultural waste

Sugarcane bagasse agricultural waste has been one of the most common solid pollutants worldwide. Thus, introducing a simple method to convert sugarcane bagasse into value-added materials has been highly significant. Herein, we develop a simple and green strategy to reprocess sugarcane bagasse as a starting material for the preparation of graphene oxide nanosheets toward the preparation of novel photoluminescent, hydrophobic, and anticorrosive epoxy nanocomposite coatings integrated with lanthanide-doped aluminate nanoparticles. Environmentally friendly graphene oxide (GO) nanostructures were provided by a single-step preparation procedure from sugarcane bagasse (SCB) agricultural waste using ferrocene-based oxidation under muffled conditions. The oxidized SCB nanostructures were applied as a drier, anticorrosion, and crosslinking agent for epoxy coatings. Different concentrations of pigment phosphor were applied onto the epoxy coating. The generated epoxy-graphene-aluminate (EGA) paints were then coated onto mild steel. The hydrophobic properties and hardness as well as resistance to scratch of the EGA paints were examined. The transparency and colorimetric screening of the EGA nanocomposite paints were determined by the absorption spectral analysis and CIE Lab parameters. The luminescent translucent paints demonstrated a bright green emission at 520 nm when excited at 372 nm. The anticorrosion properties of the painted steel submerged in NaCl_(aq) were inspected by the electrochemical impedance spectral (EIS) method. The EGA paints with phosphor (11% w/w) exhibited the most distinct anti-corrosion properties and long-persistent luminescence. The produced paints displayed high durability and photostability.

Green synthesis of rGO-AgNP composite using Curcubita maxima extract for enhanced photocatalytic degradation of the organophosphate pesticide chlorpyrifos

In this study, Curcubita maxima leaves are used as a novel source for green synthesis of reduced graphene oxide - silver nanoparticle composite in a single pot. Characterization of the novel phyto source-driven composite was performed by UV-visible spectroscopy, Fourier transform infrared analysis, X-ray diffraction analysis, and field emission scanning electron microscopic methods. The assessment of degradation effect of chlorpyrifos by the synthesized nanocomposite was performed. The photocatalytic activity of the composite was demonstrated through two different processes as adsorption under room temperature and photocatalysis in the presence of sunlight. Different parameters such as pH, time, photocatalyst dose and pesticide concentration were optimized. The adsorption isotherms governing the photocatalytic adsorption process were investigated to predict the adsorption capacity of the synthesized nanocomposite. In addition, the results of antimicrobial activity of the nanocomposite against gram-positive, gram-negative bacteria and antifungal activity were also been found to be highly promising to utilize this composite for the removal of microbial contaminations in wastewater treatment.

Performance of novel GO-Gly/HNTs and GO-GG/HNTs nanocomposites for removal of Pb(II) from water: optimization based on the RSM-CCD model

For the first time, in this study, two novel glycogen-graphene oxide/halloysite nanotubes (GO-Gly/HNTs) and guar gum-graphene oxide/halloysite nanotubes (GO-GG/HNTs) nanocomposites were synthesized as the adsorbents for removal of Pb(II) from water, and the ionic liquid was used in the synthesis as a green solvent. According to the SEM, TEM, EDS, BET, zeta potential, FTIR, and XRD results, GO-Gly/HNTs and GO-GG/HNTs were synthesized successfully. Response surface methodology (RSM) was applied to optimize the experimental conditions. Nanocomposites followed the Langmuir equilibrium model and were best fitted to the pseudo-second-order model. According to the thermodynamic model, the adsorption process was endothermic. Due to several features, these two novel nanocomposites can be considered the proper candidate for Pb(II) removal from water and wastewater. First, these nanocomposites have good adsorption capacity for Pb(II) removal, which is 219 mg/g for GO-Gly/HNTs and 315 mg/g for GO-GG/HNTs. Moreover, nanocomposites can be recycled with proper adsorption capacity after four repeated cycles. These materials can be used to remove Pb(II) from water in the presence of other contaminants because nanocomposites have selective tendency toward Pb(II) in the presence of other pollutants such as Cd²⁺, Cu²⁺, Cr²⁺, and Co²⁺. In addition, the presence of Ca²⁺, Mg²⁺, Na⁺, and K⁺ improve Pb(II) removal. Finally, possible mechanisms for each nanocomposite were represented.

Hydroxyapatite/Glycyrrhizin/Lithium-Based Metal-Organic Framework (HA/GL/Li-MOF) Nanocomposite as Support for Immobilization of Thermomyces lanuginosus Lipase

The hydroxyapatite/glycyrrhizin/lithium-based metal-organic framework (HA/GL/Li-MOF) nanocomposites were synthesized via the hydrothermal method in the presence of lecithin and glycyrrhizin. Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) were applied for characterization of the fabricated nanocomposites. The HA/GL/Li-MOF and Li-MOF nanocomposites were employed as support for immobilization of Thermomyces lanuginosus lipase (TLL). The Plackett-Burman and Box-Behnken designs were used for screening and optimizing of variables affecting the immobilization conditions, respectively. The optimum specific activity of immobilized TLL on HA/GL/Li-MOF and Li-MOF nanocomposites (41.8 ± 1.2 U/mg and 39.4 ± 3.1 U/mg, respectively) was predictably determined at support concentration of 0.5 mg/mL, glutaraldehyde concentration of 5 mM, and enzyme activity of 20 U/mg, while the specific activities of TLL@ HA/GL/Li-MOF and TLL@Li-MOF were experimentally found to be 39.5 ± 3.7 U/mg and 38.5 ± 2.3 U/mg, respectively. The stability results showed that the TLL@ HA/GL/Li-MOF has suitable stability against pH and thermal denaturation. However, the immobilized TLL on Li-MOF represented lower stability compared with that of the HA/GL/Li-MOF. The immobilized TLL on HA/GL/Li-MOF maintained near 70% of its original activity after 15 days' storage and during 5 runs of application. In addition, TLL@HA/GL/Li-MOF exhibited higher enzyme-substrate affinity (K_m, 10.1 mM) compared to that of TLL@Li-MOF (K_m, 23.4 mM). Therefore, these findings demonstrated the potential use of HA/GL/Li-MOF nanocomposites for enzyme immobilization.

Carbonaceous materials for removal and recovery of phosphate species: Limitations, successes and future improvement

The carbonaceous materials have gained significant interest for the phosphorus species remediation and recovery in the last decade. Carbonaceous materials present many unique features, such as cost effective, availability, environmentally friendly, and high removal efficiency that make them a promising adsorbent. In this review, the recent application of carbonaceous materials including activated carbon (AC), graphene and graphene oxide (GO), lignin, carbon nanotubes (CNTs), and gC₃N₄ for phosphate removal and recovery were comprehensively summarized. The kinetics and isotherm models, removal mechanisms, and effects of operating parameters are reported. The reusability, lifetime of carbonaceous materials, and impact of modification were also considered. The modified carbonaceous materials have significantly high phosphate adsorption capacity compared to unmodified adsorbents. Namely, MgO-functionalized lignin-based bio-charcoal exhibited a 906.8 mg g^-1 of capacity as the highest one among other reviewed materials. The modification of carbonaceous materials with various elements has been presented to improve the surface functional groups, surface area and charge, and pore volume and size. Among these loaded elements, iron has been effectively used to provide a prospect for magnetic recovery of the adsorbent as well as increase phosphate adsorption. Furthermore, the phosphate recovery methods, phosphate removal efficiency of carbonaceous materials, the limitations, important gaps in the literature, and future studies to enhance applicability of carbonaceous materials in real scale are also discussed.

Nanobiocatalyst consisting of immobilized α-amylase on montmorillonite exhibiting enhanced enzymatic performance based on the allosteric effect

Enzyme immobilization on nanostructured substrates is an emerging method for the efficient development of nanobiocatalysts to enhance enzymatic performance. In this study, a novel α-amylase nanobiocatalytic system was constructed based on the allosteric activation of the enzyme and its immobilization on a natural nanostructured mineral montmorillonite. The strategy of allosteric modulation and immobilization, equipped the immobilized α-amylase with higher catalytic activity and greater stability (compared to those of free α-amylase) over a broad range of pH values (4.5-9.0) and temperatures (30-80 °C). Kinetic experiments revealed that although the immobilized α-amylase possessed a considerably lower affinity for its substrate, its catalytic activity was higher than that of free α-amylase, likely owing to allosteric modulation. Thus, this study demonstrates a convenient and environmentally benign immobilization strategy to construct a nanobiocatalytic α-amylase system that exploits the phenomenon of allosteric activation of the enzyme and lays the foundation for further industrial applications.

Expanding the bio-catalysis scope and applied perspectives of nanocarrier immobilized asparaginases

l-asparaginase is an essential enzyme in medicine and a well-known chemotherapeutic agent. This enzyme's importance is not limited to its use as an anti-cancer agent; it also has a wide variety of medicinal applications. Antimicrobial properties, prevention of infectious disorders, autoimmune diseases, and canine and feline cancer are among the applications. Apart from the healthcare industry, its importance has been identified in the food industry as a food manufacturing agent to lower acrylamide levels. When isolated from their natural habitats, they are especially susceptible to different denaturing conditions due to their protein composition. The use of an immobilization technique is one of the most common approaches suggested to address these limitations. Immobilization is a technique that involves fixing enzymes to or inside stable supports, resulting in a heterogeneous immobilized enzyme framework. Strong support structures usually stabilize the enzymes' configuration, and their functions are maintained as a result. In recent years, there has been a lot of curiosity and focus on the ability of immobilized enzymes. The nanomaterials with ideal properties can be used to immobilize enzymes to regulate key factors that determine the efficacy of bio-catalysis. With applications in biotechnology, immunosensing, biomedicine, and nanotechnology sectors have opened a realm of opportunities for enzyme immobilization.

Magnetic and GRPR-targeted reduced graphene oxide/doxorubicin nanocomposite for dual-targeted chemo-photothermal cancer therapy

Herein, we design a rGO-based magnetic nanocomposite by decorating rGO with citrate-coated magnetic nanoparticles (CMNP). The magnetic rGO (mrGO) was modified by phospholipid-polyethylene glycol to prepare PEGylated mrGO, for conjugating with gastrin-releasing peptide receptor (GRPR)-binding peptide (mrGOG). The anticancer drug doxorubicin (DOX) was bound to mrGO (mrGOG) by π-π stacking for drug delivery triggered by the low pH value in the endosome. The mrGOG showed enhanced photothermal effect under NIR irradiation, endorsing its role for dual targeted DOX delivery. With efficient DOX release in the endosomal environment and heat generation from light absorption in the NIR range, mrGOG/DOX could be used for combination chemo-photothermal therapy after intracellular uptake by cancer cells. We characterized the physico-chemical as well as biological properties of the synthesized nanocomposites. The mrGOG is stable in biological buffer solution, showing high biocompatibility and minimum hemolytic properties. Using U87 glioblastoma cells, we confirmed the magnetic drug targeting effect in vitro for selective cancer cell killing. The peptide ligand-mediated targeted delivery increases the efficiency of intracellular uptake of both nanocomposite and DOX up to ~3 times due to the over-expressed GRPR on U87 surface, leading to higher cytotoxicity. The increased cytotoxicity using mrGOG over mrGO was shown from a decreased IC₅₀ value (0.70 to 0.48 μg/mL) and an increased cell apoptosis rate (19.8% to 47.1%). The IC₅₀ and apoptosis rate changed further to 0.19 μg/mL and 76.8% in combination with NIR laser irradiation, with the photothermal effect supported from upregulation of heat shock protein HSP70 expression. Using U87 tumor xenograft model created in nude mice, we demonstrated that magnetic guidance after intravenous delivery of mrGOG/DOX could significantly reduce tumor size and prolong animal survival over free DOX and non-magnetic guided groups. Augmented with NIR laser treatment for 5 min, the anti-cancer efficacy significantly improves with elevated cell apoptosis and reduced cell proliferation. Together with safety profiles from hematological as well as major organ histological analysis of treated animals, the mrGOG nanocomposite is an effective nanomaterial for combination chemo-photothermal cancer therapy.

Ternary biogenic silica/magnetite/graphene oxide composite for the hyperactivation of Candida rugosa lipase in the esterification production of ethyl valerate

Oil palm leaves (OPL) silica (SiO₂) can replace the energy-intensive, commercially produced SiO₂. Moreover, the agronomically sourced biogenic SiO₂ is more biocompatible and cost-effective enzyme support, which properties could be improved by the addition of magnetite (Fe₃O₄) and graphene oxide (GO) to yield better ternary support to immobilize enzymes, i.e., Candida rugosa lipase (CRL). This study aimed to optimize the Candida rugosa lipase (CRL immobilization onto the ternary OPL-silica-magnetite (Fe₃O₄)-GO (SiO₂/Fe₃O₄/GO) support, for use as biocatalyst for ethyl valerate (EV) production. Notably, this is the first study detailing the CRL/SiO₂/Fe3O4/GO biocatalyst preparation for rapid and high yield production of ethyl valerate (EV). AFM and FESEM micrographs revealed globules of CRL covalently bound to GL-A-SiO₂/Fe₃O₄/GO; similar to Raman and UV-spectroscopy results. FTIR spectra revealed amide bonds at 3478 cm^-1 and 1640 cm^-1 from covalent interactions between CRL and GL-A-SiO₂/Fe₃O₄/GO. Optimum immobilization conditions were 4% (v/v) glutaraldehyde, 8 mg/mL CRL, at 16 h stirring in 150 mM NaCl at 30 °C, offering 24.78 ± 0.26 mg/g protein (specific activity = 65.24 ± 0.88 U/g). The CRL/SiO₂/Fe₃O₄/GO yielded 77.43 ± 1.04 % of EV compared to free CRL (48.75 ± 0.70 %), verifying the suitability of SiO₂/Fe₃O₄/GO to hyperactivate and stabilize CRL for satisfactory EV production.

A three-dimensional nerve guide conduit based on graphene foam/polycaprolactone

In this study, a novel nerve guide conduit was developed, based on a three-dimensional (3D) graphene conductive core grown, by chemical vapor deposition (CVD) coupled with a polycaprolactone (PCL) polymer coating. Firstly, the monolithic 3D-graphene foam (3D-GF) was synthesized on Ni foam templates via inductive heating CVD, subsequently, Ni/Graphene samples were dipped successively in PCL and cyclododecane (CDD) solutions prior to the removal of Ni from the 3D-GF/PCL scaffold in FeCl₃. Our results showed that the electrical conductivity of the polymer composites reached to 25 S.m^-1 after incorporation of 3D-GF. Moreover, the mechanical properties of 3D-GF/PCL composite scaffold were enhanced with respect to the same geometry of PCL scaffolds. The wettability, surface porosity, and morphology did not show any significant changes, while the PC12 cell proliferation and extension were increased for the developed 3D-GF/PCL nanocomposite. It can be concluded that 3D-GF/PCL nanocomposites could be good candidates to utilize as a versatile system for the engineering of peripheral nerve tissue.

Protein morphology drives the structure and catalytic activity of bio-inorganic hybrids

Bio-hybrid materials have received a lot of attention in view of their bio-mimicking nature. One such biomimetic material with catalytic activity are the protein derived floral nanohybrid. Copper phosphate coordinated flakes can be curated to distinct floral morphology using proteins. Structurally two different proteins with similar size and with no known enzymatic activity are used to evaluate the role of protein structure and morphology, on the structure-activity relationship of the developed hybrid nanoflowers. Globular protein BSA and bacterial microcompartment domain protein PduBB' are selected. PduBB' because of self-assembling nature forms extended sheets, whereas BSA lacks specific assembly. The developed hybrid NFs differ in their morphology and also in their mimicry as a biological catalyst. The present investigation highlights the importance of the quaternary structure of proteins in tailoring the structure and function of the h-NFs. The results in this manuscript will motivate and guide designing, engineering and selection of glue material for fabricating biomacromolecule derived biohybrid material to mimic natural enzymes of potential industrial application.

Evaluating enzyme stabilizations in calcium carbonate: Comparing in situ and crosslinking mediated immobilization

Enzyme immobilization using inorganic materials has been shown to preserve enzyme activity improving and improve their practical applications in biocatalytic process designs. Proper immobilization methods have been used to obtain high recycling and storage stability. In this study, we compared the activity and stability of in situ or crosslink-immobilized enzymes in a CaCO₃ biomineral carrier. More than 30% of the initial enzyme activity was preserved for both the systems after 180 days upon 15 activity measurements at room temperature, confirming the improved stability of these enzyme systems (100 mM phosphate buffer, pH 8.0); however, differences in enzyme loading, activity, and characteristics were observed for each of these methods. Each system exhibited efficacy of 80% and 20%, respectively. Based on the same amount of immobilized enzyme (0.2 mg), the specific activities of hydrolysis of p-nitrophenyl butyrate substrate at room temperature of in situ immobilized carboxyl esterase (CE) and crosslinked CE were 11.37 and 7.63 mM min^-1 mg^-1, respectively (100 mM phosphate buffer, pH 8.0). Moreover, based on the kinetic behavior, in situ immobilized CE exhibited improved catalytic efficiency (Vmax Km^-1) of the enzyme, exhibiting 4-fold higher activity and efficiency values than those of the CE immobilized in CaCO₃. This is the first study to describe the stabilization of enzymes in CaCO₃ and compare the enzyme kinetics and efficiencies between in situ immobilization and crosslinking in CaCO₃ carriers.

Immobilized lipases-based nano-biocatalytic systems - A versatile platform with incredible biotechnological potential

Lipases belong to α/β hydrolases that cause hydrolytic catalysis of triacylglycerols to release monoacylglycerols, diacylglycerols, and glycerol with free fatty acids. Lipases have a common active site that contains three amino acid residues in a conserved Gly-X-Ser-X-Gly motif: a nucleophilic serine residue, an acidic aspartic or glutamic acid residue, and a basic histidine residue. Lipase plays a significant role in numerous industrial and biotechnological processes, including paper, food, oleochemical and pharmaceutical applications. However, its instability and aqueous solubility make application expensive and relatively challenging. Immobilization has been considered as a promising approach to improve enzyme stability, reusability, and survival under extreme temperature and pH environments. Innumerable supporting material in the form of natural polymers and nanostructured materials is a crucial aspect in the procedure of lipase immobilization used to afford biocompatibility, stability in physio-chemical belongings, and profuse binding positions for enzymes. This review outlines the unique structural and functional properties of a large number of polymers and nanomaterials as robust support matrices for lipase immobilization. Given these supporting materials, the applications of immobilized lipases in different industries, such as biodiesel production, polymer synthesis, additives, detergent, textile, and food industry are also discussed.

Nanobiocatalysts for Biodiesel Synthesis through Transesterification—A Review

Converting useless feedstock into biodiesel by utilizing the process of transesterification has been regarded as an alternative approach recently used to address the fuel and energy resources shortage issues. Nanobiocatalysts (NBCs), containing the biological component of lipase enzyme immobilized on nanomaterials (NMs), have also been presented as an advanced catalyst to effectively carry out the process of transesterification with appreciable yields. This study highlights the fundamentals associated with NBCs and the transesterification reaction catalyzed by NBCs for summarizing present academic literature reported in this research domain in recent years. Classification of the NBCs with respect to the nature of NMs and immobilization methods of lipase enzyme is also provided for organizing the recently documented case studies. This review is designed to act as a guideline for the researchers aiming to explore this domain of biodiesel production via NBCs as well as for the scholars looking to expand on this field.

Assessment of GO/ZnO nanocomposite for solar-assisted photocatalytic degradation of industrial dye and textile effluent

An ecofriendly and solar light-responsive graphene oxide wrapped zinc oxide nanohybrid has been synthesized hydrothermally using lemon and honey respectively as chelating and complexing agents. By tuning the reaction conditions, a heterostructure between GO and ZnO has been formed during synthesis. The photocatalytic activity of the synthesized nanohybrid was investigated by degradation of hazardous organic textile dye (methylene blue) as well as wastewater under natural solar light. The nanohybrid exhibited excellent photocatalytic activity towards degradation (~ 89%) of methylene blue (MeB). Furthermore, along with decolorization, 71% of mineralization was also achieved. Interestingly, the nanohybrid has been found to be reusable up to 4 cycles without significant loss of photocatalytic activity. Along with this, the physicochemical parameters of the wastewater generated from textile industry have been also monitored before and after exposure to nanohybrid. The results revealed significant reduction in chemical oxygen demand (COD) (96.33%), biochemical oxygen demand (BOD) (96.23%), and total dissolved solids (TDS) (20.85%), suggesting its potential applicability in textile wastewater treatment.

Iron Complexes Anchored onto Magnetically Separable Graphene Oxide Sheets: An Excellent Catalyst for the Synthesis of Dihydroquinazoline-Based Compounds

In this work, a green, sustainable, and efficient protocol for the syntheses of dihydroquinazoline derivatives is proposed. Initially, three Schiff base complexes of iron containing the ligand (2,2-dimethylpropane-1,3-diyl)bis(azanylylidene)bis(methanylylidene)bis(2,4-Xphenol), where X = Cl (complex 1)/Br (complex 2)/I (complex 3), were synthesized, fully characterized, and used in the desired syntheses. Complex 1 excelled as a catalyst, closely followed by complexes 2 and 3. DFT calculations helped in rationalizing the role of the halide substituent in the ligand backbone as a relevant factor in the catalytic superiority of complex 1 over complexes 2 and 3 for the synthesis of the dihydroquinazoline derivatives. Finally, to facilitate catalyst recoverability and reusability, complex 1 was immobilized on GO@Fe₃O₄@APTES (GO, graphene oxide; APTES, 3-aminopropyltriethoxysilane) to generate GO@Fe₃O₄@APTES@FeL¹ (GOTESFe). GOTESFe was thoroughly characterized through scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy and efficiently used for the synthesis of dihydroquinazoline derivatives. GOTESFe could be magnetically recovered and reused up to five cycles without compromising its catalytic efficiency. Therefore, immobilization of the chosen iron complex onto magnetic GO sheets offers an extremely competent route in providing a blueprint of a readily recoverable, reusable, robust, and potent catalyst for the synthesis of dihydroquinazoline-based compounds.

Production and use of immobilized lipases in/on nanomaterials: A review from the waste to biodiesel production

As a highly efficient and environmentally friendly biocatalyst, immobilized lipase has received incredible interest among the biotechnology community for the production of biodiesel. Nanomaterials possess high enzyme loading, low mass transfer limitation, and good dispersibility, making them suitable biocatalytic supports for biodiesel production. In addition to traditional nanomaterials such as nano‑silicon, magnetic nanoparticles and nano metal particles, novel nanostructured forms such as nanoflowers, carbon nanotubes, nanofibers and metal-organic frameworks (MOFs) have also been studied for biodiesel production in the recent years. However, some problems still exist that need to be overcome in achieving large-scale biodiesel production using immobilized lipase on/in nanomaterials. This article mainly presents an overview of the current and state-of-the-art research on biodiesel production by immobilized lipases in/on nanomaterials. Various immobilization strategies of lipase on various advanced nanomaterial supports and its applications in biodiesel production are highlighted. Influential factors such as source of lipase, immobilization methods, feedstocks, and production process are also critically discussed. Finally, the current challenges and future directions in developing immobilized lipase-based biocatalytic systems for high-level production of biodiesel from waste resources are also recommended.

TiO2 Sol-Gel Coated PAN/O-MMT Multi-Functional Composite Nanofibrous Membrane Used as the Support for Laccase Immobilization: Synergistic Effect between the Membrane Support and Enzyme for Dye Degradation

Removal of a triphenylmethane dye (crystal violet, CV) by a simultaneous enzymatic-photocatalytic-adsorption treatment was investigated in this work. A desirable synergistic effect on dye treatment was achieved by decorating laccase (Lac) onto the surface of TiO₂ sol-gel coated polyacrylonitrile/organically modified montmorillonite (PAN/O-MMT) nanofibers prepared by electrospinning. The assembly of Lac on the surface of PAN/O-MMT/TiO₂ nanofibers was confirmed by confocal laser scanning microscope (CLSM). In comparison with free Lac, the immobilized Lac showed better pH, temperature and operational stabilities, reaching highest relative activity at an optimum pH of 3 and optimum temperature of 50 °C. Therefore, the immobilized Lac displayed a higher degradation efficiency of CV at an initial dye concentration of 100 mg/L, an optimum pH of 4.5 and temperature at 60 °C. Under UV illumination, the CV removal efficiency was further improved by ~20%. These results demonstrated that the Lac-immobilized PAN/O-MMT/TiO₂ composite nanofibers with a combined effect between the immobilized enzyme and the polymeric support have potential for industrial dye degradation.

Immobilization of Thermoalkalophilic Lipase from Bacillus atrophaeus FSHM2 on Amine-Modified Graphene Oxide Nanostructures: Statistical Optimization and Its Application for Pentyl Valerate Synthesis

Synthesis of (3-aminopropyl) triethoxysilane (APTES)-functionalized graphene oxide (GO) nanosheets, statistical optimization of conditions for immobilization of Bacillus atrophaeus lipase (BaL) on as-synthesized support, and application of the immobilized BaL for esterification of valeric acid were carried out in this investigation. The optimum specific activity of the immobilized BaL (81.60 ± 0.28 U mg^-1) was achieved at 3 mg mL^-1 of GO-NH₂, 50 mM of phosphate buffer, pH 7.0, 60 min sonication time, 100 mM glutaraldehyde, 25 U mL^-1 of enzyme, and 8 h immobilization time at 4 °C. The immobilized BaL retained about 90% of its initial activity after 10 days of storage. Moreover, about 70% of the initial activity of the immobilized BaL was retained after 10 cycles of application. The results of esterification studies exhibited that maximum pentyl valerate synthesis using the free BaL (34.5%) and the immobilized BaL (92.7%) occurred in the organic solvent medium (xylene) after 48 h of incubation at 60 °C.

In vivo immobilization of an organophosphorus hydrolyzing enzyme on bacterial polyhydroxyalkanoate nano-granules

Background

Polyhydroxyalkanoate (PHA) are nano-granules naturally produced by bacteria. Two types of proteins, PHA synthase (PhaC) and phasins (PhaPs), are attached to the PHA surface by covalent and hydrophobic interactions. Utilizing these anchored proteins, functionalized PHA nano-granules displaying proteins of interest can be easily prepared by fermentation.

Results

In this study, a one-step fabrication method was developed for stable and efficient immobilization of an organophosphorus degrading enzyme on PHA nano-granules. The nano-biocatalysts were produced in recombinant Escherichia coli cells into which the polyhydroxyalkanoate synthesis pathway from Cupriavidus necator had been introduced. Two different strategies, covalent attachment and hydrophobic binding, were investigated by fusing bacterial organophosphorus anhydride hydrolase (OPAA4301) with PhaC and PhaP, respectively. Using both methods, the tetrameric enzyme successfully self-assembled and was displayed on the PHA surface. The display density of the target fused enzyme was enhanced to 6.8% of total protein on decorated PHA by combination of covalent and non-covalent binding modes. Immobilization of the enzyme on PHA granules resulted in higher catalytic efficiency, increased stability and excellent reusability. The k_cat values of the immobilized enzymes increased by threefold compared to that of the free enzyme. The pH stability under acidic conditions was significantly enhanced, and the immobilized enzyme was stable at pH 3.0–11.0. Furthermore, more than 80% of the initial enzyme activity retained after recycling ten times.

Conclusions

This study provides a promising approach for cost-efficient in vivo immobilization of a tetrameric organophosphorus degrading enzyme. The immobilization process expands the utility of the enzyme, and may inspire further commercial developments of PHA nano-biocatalysts. As revealed by our results, combination of covalent and non-covalent binding is recommended for display of enzymes on PHA granules.

Noncovalent Immobilization of Yarrowia lipolytica Lipase on Dendritic-Like Amino Acid-Functionalized Silica Nanoparticles

Immobilization of enzymes is a promising approach for the cost-effective application of enzymes. Among others, noncovalent but unleachable approaches for immobilization are one of the most favorable and crucial approaches. Herein, silica nanoparticles are modified by (3-aminopropyl)triethoxysilane (APTES) to generate amino-functionalized silica nanoparticles. Then, the amine functionalities are converted to bifunctional amino acid via post-modification that has zwitterionic properties. This nanostructure with the new functional theme is employed to immobilize Yarrowia lipolytica lipase at room temperature with no further post-modification or cross-linking. This immobilization method is further compared with the metal chelate-based immobilization approach on the same support. The biocatalytic activity of the immobilized lipase is examined under various conditions. The encapsulation of lipase through amino acid-functionalized silica nanoparticles exhibited enhanced stability for the immobilized lipase at higher temperatures and unneutral pHs.

Graphene oxide enabled long-term enzymatic transesterification in an anhydrous gas flux

Gas-phase enzymatic catalysis has been long pursued but not yet utilized in industrial processes due to many limitations. Herein, we report a hydroxyl-rich graphene oxide (GO) aerogel that can preserve the enzymatic activity and stability in an anhydrous gas flow by providing a water-like microenvironment. Lipase immobilized in the GO aerogel exhibits a 5 to 10-fold increase in apparent activity than the lyophilized lipase powder in transesterification of geraniol and vinyl acetate in the gas phase and maintains the initial activity for more than 500 h. The solid-state circular dichroism measurement confirms that the lipase keeps its native conformation in the aerogel, and the thermogravimetric analysis shows that water molecules essential for the lipase activity can be replaced by the hydroxyl groups at the GO surface. The versatility of this method is demonstrated for two other lipases with different structures, promising unprecedented applications of enzyme-GO aerogels to gas-phase enzymatic catalysis.

Implementing enzymatic reactions in gas phase has several limitations. Here, the authors report on a method to overcome these using graphene oxide aerogels to immobilize lipase, improve stability/lifetime and investigate the mechanism for improved function.

Euphorbia leaf extract-assisted sustainable synthesis of Au NPs supported on exfoliated GO for superior activity on water purification: reduction of 4-NP and MB

In the present work, the effect of graphene oxide (GO) architecture and synthesis of gold nanoparticles (Au_NPs) on the surface of GO by using Euphorbia leaf extract was investigated. The as-synthesized catalyst was utilized for reduction of 4-nitrophenol (4-NP) and methylene-blue (MB). The ethanol/water extract of the leaves of Euphorbia was found as a non-toxic, suitable, eco-friendly natural reducing agent in one-step generation of Au nanoparticles onto the GO. The catalyst was characterized by different analysis such as atomic force microscopy, powder X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, SEM-mapping, transmission electron microscopy, and atomic absorption spectrometry. The high catalytic performance of the surfactant exfoliated gold-GO (SE-Au_NPs/GO) towards the reduction of 4-NP to 4-aminophenol (4-AP) and reduction of MB to leucomethylene blue (LMB) under mild conditions, in water and at room temperature, was exhibited. Graphical abstract.