Enzyme hybrid nanoflowers and enzyme@metal-organic frameworks composites: fascinating hybrid nanobiocatalysts

Hybrid nanomaterials have recently emerged as a new interface of nanobiocatalysis, serving as a host platform for enzyme immobilization. Enzyme immobilization in inorganic crystal nanoflowers and metal-organic frameworks (MOFs) has sparked the bulk of scientific interest due to their superior performances. Many breakthroughs have been achieved recently in the preparation of various types of enzyme@MOF and enzyme-hybrid nanoflower composites. However, it is unfortunate that there are few reviews in the literature related to enzyme@MOF and enzyme-hybrid nanoflower composites and their improved synthesis strategies and their applications in biotechnology. In this review, innovative synthetic strategies for enzyme@MOF composites and enzyme-hybrid nanoflower composites are discussed. Enzyme@MOF composites and enzyme-hybrid nanoflower composites are reviewed in terms of biotechnological applications and potential research directions. We are convinced that a fundamental study and application of enzyme@MOF composites and enzyme-hybrid nanoflower composites will be understood by the reader as a result of this work. The summary of different synthetic strategies for enzyme@MOF composites and enzyme-hybrid nanoflower composites and the improvement of their synthetic strategies will also benefit the readers and provide ideas and thoughts in the future research process.

Immobilized Dipeptidase in Manganese Ion-Loaded Polyethylenimine-Induced Calcium Phosphate Nanocrystals for Carnosine Synthesis

Carnosine is a natural bioactive dipeptide with important physiological functions widely used in food and medicine. Dipeptidase (PepD) from Serratia marcescens can catalyze the reverse hydrolytic reaction of β-alanine with l-histidine to synthesize carnosine in the presence of Mn2+. However, it remains challenging to practice carnosine biosynthesis due to the low activity and high cost of the enzyme. Therefore, the development of biocatalysts with high activity and stability is of significance for carnosine synthesis. Here, we proposed to chelate Mn2+ to polyethylenimine (PEI) that induced rapid formation of calcium phosphate nanocrystals (CaP), and Mn-PEI@CaP was used for PepD immobilization via electrostatic interaction. Mn-PEI@CaP as the carrier enhanced the stability of the immobilized enzyme. Moreover, Mn2+ loaded in the carrier acted as an in situ activator of the immobilized PepD for facilitating the biocatalytic process of carnosine synthesis. The as-prepared immobilized enzyme (PepD-Mn-PEI@CaP) kept similar activity with free PepD plus Mn2+ (activity recovery, 102.5%), while exhibiting elevated thermal stability and pH tolerance. Moreover, it exhibited about two times faster carnosine synthesis than the free PepD system. PepD-Mn-PEI@CaP retained 86.8% of the original activity after eight cycles of batch catalysis without the addition of free Mn2+ ions during multiple cycles. This work provides a new strategy for the co-immobilization of PepD and Mn2+, which greatly improves the operability of the biocatalysis and demonstrates the potential of the immobilized PepD system for efficient carnosine synthesis.

One-step, reagent-free construction of nano-enzyme as visual and reusable biosensor for oxidase substrates

The substrates of oxidase are biologically essential substances that are closely associated with human physiological health. However, current biosensing methods suffer from tough recyclability and undesired denaturation of enzyme due to impurity interference. Herein, we have developed a visual and reusable biosensor for detecting substrate using glucose oxidase (GOx) as a model oxidase. GOx was immobilized onto gold nanoparticles (AuNPs) at -20 °C in one step without additional reagents. The resulting nano-enzyme generated coloimetric signals by coupling with horseradish peroxidase (HRP) using TMB as the substrate. Our results demonstrated that the immobilized GOx exhibited satisfactory sensitivity (0.68 μM) for glucose detection and higher inherent stability than free GOx under harsh conditions, enabling reliable detection of glucose in complex fluids (colored beverages and saliva). Furthermore, the nano-enzyme retained 80 % activity even after four cycles of catalytic oxidation. This strategy constructs a universal biosensor for substrates with nano-enzyme which rely only on intrinsic cysteine within the oxidase while avoiding functional handle modification.

Bovine Serum Albumin - Hydroxyapatite Nanoflowers as Potential Local Drug Delivery System of Ciprofloxacin

Introduction

Hybrid nanoflowers are structures consisting of organic (enzymes, proteins, nucleic acids) and inorganic components (mostly metal phosphates) with a flower-like hierarchical structure. Novel hybrid nanoflowers based on bovine serum albumin (BSA) and hydroxyapatite (HA) were obtained and characterized. Study on BSA-HA nanoflowers as potential drug delivery system is reported for the first time.

Methods

Embedding ciprofloxacin in the structure of hybrid nanoflowers was confirmed by ATR-FTIR and thermogravimetric analysis. The inorganic phase of the nanoflowers was determined by X-ray diffraction. UV‒Vis spectroscopy was used to evaluate the release profiles of ciprofloxacin from nanoflowers in buffer solutions at pH 7.4 and 5. The agar disk diffusion method was used to study the antibacterial activity of the synthesized nanoflowers against Staphylococcus aureus and Pseudomonas aeruginosa.

Results

Bovine serum albumin - hydroxyapatite nanoflowers were obtained with diameters of ca. 1-2 µm. The kinetics of ciprofloxacin release from nanoflowers were described by the Korsmeyer-Peppas model. The antibacterial activity of the synthesized nanoflowers was demonstrated against S. aureus and P. aeruginosa, two main pathogens found in osteomyelitis.

Conclusion

The formulated nanoflowers may act as an efficient local antibiotic delivery system. Due to the use of nonhazardous, biodegradable components and benign synthesis, hybrid nanoflowers are very promising drug delivery systems that could be applied in the treatment of skeletal system infections.

Novel biocatalysts based on enzymes in complexes with nano- and micromaterials

In today's world, there is a wide array of materials engineered at the nano- and microscale, with numerous applications attributed to these innovations. This review aims to provide a concise overview of how nano- and micromaterials are utilized for enzyme immobilization. Enzymes act as eco-friendly biocatalysts extensively used in various industries and medicine. However, their widespread adoption faces challenges due to factors such as enzyme instability under different conditions, resulting in reduced effectiveness, high costs, and limited reusability. To address these issues, researchers have explored immobilization techniques using nano- and microscale materials as a potential solution. Such techniques offer the promise of enhancing enzyme stability against varying temperatures, solvents, pH levels, pollutants, and impurities. Consequently, enzyme immobilization remains a subject of great interest within both the scientific community and the industrial sector. As of now, the primary goal of enzyme immobilization is not solely limited to enabling reusability and stability. It has been demonstrated as a powerful tool to enhance various enzyme properties and improve biocatalyst performance and characteristics. The integration of nano- and microscale materials into biomedical devices is seamless, given the similarity in size to most biological systems. Common materials employed in developing these nanotechnology products include synthetic polymers, carbon-based nanomaterials, magnetic micro- and nanoparticles, metal and metal oxide nanoparticles, metal-organic frameworks, nano-sized mesoporous hydrogen-bonded organic frameworks, protein-based nano-delivery systems, lipid-based nano- and micromaterials, and polysaccharide-based nanoparticles.

Trypsin/Zn3(PO4)2 Hybrid Nanoflowers: Controlled Synthesis and Excellent Performance as an Immobilized Enzyme

Immobilized enzymes are a significant technological approach to retain enzyme activity and reduce enzyme catalytic cost. In this work, trypsin-incorporated Zn3(PO4)2 hybrid nanoflowers were prepared via mild precipitation and coordination reactions. The controllable preparation of hybrid nanoflowers was achieved by systematically investigating the effects of the raw-material ratio, material concentration and reaction temperature on product morphology and physicochemical properties. The enzyme content of hybrid nanoflowers was about 6.5%, and the maximum specific surface area reached 68.35 m2/g. The hybrid nanoflowers exhibit excellent catalytic activity and environmental tolerance compared to free trypsin, which was attributed to the orderly accumulation of nanosheets and proper anchoring formation. Further, the enzyme activity retention rate was still higher than 80% after 12 repeated uses. Therefore, trypsin/Zn3(PO4)2 hybrid nanoflowers—which combine functionalities of excellent heat resistance, storage stability and reusability—exhibit potential industrial application prospects.

Immobilized enzymes in inorganic hybrid nanoflowers for biocatalytic and biosensing applications

Enzyme immobilization has been accepted as a powerful technique to solve the drawbacks of free enzymes such as limited activity, stability and recyclability under harsh conditions. Different from the conventional immobilization methods, enzyme immobilization in inorganic hybrid nanoflowers was executed in a biomimetic mineralization manner with the advantages of mild reaction conditions, and thus it was beneficial to obtain ideal biocatalysts with superior characteristics. The key factors influencing the formation of enzyme-based inorganic hybrid nanoflowers were elucidated to obtain a deeper insight into the mechanism for achieving unique morphology and improved properties of immobilized enzymes. To date, immobilized enzymes in inorganic hybrid nanoflowers have been successfully applied in biocatalysis for preparing medical intermediates, biodiesel and biomedical polymers, and solving the environmental or food industrial issues such as the degradation of toxic dyes, pollutants and allergenic proteins. Moreover, they could be used in the development of various biosensors, which provide a promising platform to detect toxic substances in the environment or biomarkers associated with various diseases. We hope that this review will promote the fundamental research and wide applications of immobilized enzymes in inorganic hybrid nanoflowers for expanding biocatalysis and biosensing.

Understanding intricacies of bioinspired organic-inorganic hybrid nanoflowers: A quest to achieve enhanced biomolecules immobilization for biocatalytic, biosensing and bioremediation applications

The immobilization of biomolecules has been a subject of interest for scientists for a long time. The organic-inorganic hybrid nanoflowers are a new class of nanostructures that act as a host platform for the immobilization of such biomolecules. It provides better practical applicability to these functional biomolecules while also providing superior activity and reusability when catalysis is involved. These nanostructures have a versatile and straightforward synthesis process and also exhibit enzyme mimicking activity in many cases. However, this facile synthesis involves many intricacies that require in-depth analysis to fully attain its potential as an immobilization technique. A complete account of all the factors involving the synthesis process optimisation is essential to be studied to make it commercially viable. This paper explores all the different aspects of hybrid nanoflowers which sets them apart from the conventional immobilization techniques while also giving an overview of its wide range of applications in industries.

Enzyme-Loaded Flower-Shaped Nanomaterials: A Versatile Platform with Biosensing, Biocatalytic, and Environmental Promise

As a result of their unique structural and multifunctional characteristics, organic-inorganic hybrid nanoflowers (hNFs), a newly developed class of flower-like, well-structured and well-oriented materials has gained significant attention. The structural attributes along with the surface-engineered functional entities of hNFs, e.g., their size, shape, surface orientation, structural integrity, stability under reactive environments, enzyme stabilizing capability, and organic-inorganic ratio, all significantly contribute to and determine their applications. Although hNFs are still in their infancy and in the early stage of robust development, the recent hike in biotechnology at large and nanotechnology in particular is making hNFs a versatile platform for constructing enzyme-loaded/immobilized structures for different applications. For instance, detection- and sensing-based applications, environmental- and sustainability-based applications, and biocatalytic and biotransformation applications are of supreme interest. Considering the above points, herein we reviewed current advances in multifunctional hNFs, with particular emphasis on (1) critical factors, (2) different metal/non-metal-based synthesizing processes (i.e., (i) copper-based hNFs, (ii) calcium-based hNFs, (iii) manganese-based hNFs, (iv) zinc-based hNFs, (v) cobalt-based hNFs, (vi) iron-based hNFs, (vii) multi-metal-based hNFs, and (viii) non-metal-based hNFs), and (3) their applications. Moreover, the interfacial mechanism involved in hNF development is also discussed considering the following three critical points: (1) the combination of metal ions and organic matter, (2) petal formation, and (3) the generation of hNFs. In summary, the literature given herein could be used to engineer hNFs for multipurpose applications in the biosensing, biocatalysis, and other environmental sectors.

Organic-Inorganic Hybrid Nanoflower Production and Analytical Utilization: Fundamental to Cutting-Edge Technologies

Over the past decade, science has experienced a growing rise in nanotechnology with ground-breaking contributions. Through various laborious technologies, nanomaterials with different architectures from 0 D to 3 D have been synthesized. However, the 3 D flower-like organic-inorganic hybrid nanomaterial with the most direct one-pot green synthesis method has attracted widespread attention and instantly become research hotspot since its first allusion in 2012. Mild synthesis procedure, high surface-to-volume ratio, enhanced enzymatic activity and stability are the main factor for its rapid development. However, its lower mechanical strength, difficulties in recovery from the reaction system, lower loading capacity, poor reusability and accessibility of enzymes are fatal, which hinders its wide application in industry. This review first discusses the selection of non-enzymatic biomolecules for the synthesis of hybrid nanoflowers followed by the innovative advancements made in organic-inorganic hybrid nanoflowers to overcome aforementioned issues and to enhance their extensive downstream applications in transduction technologies. Besides, the role of hybrid nanoflower has been successfully utilized in many fields including, water remediation, biocatalyst, pollutant adsorption and decolourization, nanoreactor, biosensing, cellular uptake and others, accompanied with several quantification technologies, such as ELISA, electrochemical, surface plasmon resonance (SPR), colorimetric, and fluorescence were comprehensively reviewed.

Zr-based acid-stable nucleotide coordination polymers: An excellent platform for acidophilic enzymes immobilization

Acidophilic enzymes play an important role in special industrial catalytic reactions. In this work, we reported Zr-based acid-stable nucleotide coordination polymers (CPs) for efficiently improving acidophilic enzymes immobilization. Among all tested metal ions, the Zr⁴⁺/AMP CPs exhibited the highest acid stability and enzyme affinity. As a typical acidophilic enzyme, the immobilized Chloroperoxidase by Zr⁴⁺/AMP CPs displayed robust reusability in the asymmetric synthesis of modafinil, remained 95.7% of conversion rate and 99.1% enantiomeric excess (e.e.) value. This work displayed a novel acid-stable bioorganic and inorganic hybrid nanomaterial for acidophilic enzymes immobilization.

Recyclable thermophilic hybrid protein-inorganic nanoflowers for the hydrolysis of milk lactose

Thermostable β-galactosidase (TmLac) has been immobilized as hybrid inorganic-protein nanoflowers using salts of Cu²⁺, Mn²⁺, Zn²⁺, Co²⁺ and Ca²⁺ as the inorganic component. The incorporation efficiency of enzyme into the nanoflowers was higher than 95% for a protein concentration of 0.05 mg/mL. The structure, activity and recyclability of the nanoflowers with different chemical composition were analyzed. Ca²⁺, Mn²⁺ and Co²⁺ nanoflowers showed a level of lactase activity equivalent to their same content of free enzyme. Cu²⁺nanoflowers showed only marginal enzyme activity in agreement with the inhibitory effect of this cation on the enzyme. TmLac nanoflowers provide an efficient methodology for enzyme immobilization and recyclability. TmLac-Ca²⁺ nanoflowers presented the best properties for lactose hydrolysis both in buffered and in milk, and could be reused in five consecutive cycles.

Dual-enzyme and NADPH co-embedded organic–inorganic hybrid nanoflowers prepared using biomimetic mineralization for the asymmetric synthesis of (R)-(−)-pantolactone

A SA-coated hNF composite was designed to co-immobilize dual enzymes and coenzyme NADP⁺ for the asymmetric synthesis of d-(−)-pantolactone.

Engineering enzyme-coupled hybrid nanoflowers: The quest for optimum performance to meet biocatalytic challenges and opportunities

The current industrial revolution signifies the high-value of biocatalysis engineering. Over the past decade, multiple micro- and nanostructured materials have been attempted for immobilization of enzymes to improve their catalytic properties. Conventional immobilization strategies result in improved stability, while insolubilized enzymes generally lost their activity compared to free counterparts. Recently, a new generation organic-inorganic hybrid nanoflowers with unique properties have received great attention as a novel and incentive immobilization approach owing to their simple fabrication, high biocatalytic efficiency, and enzyme stabilizing capability. The hybrid nanoflowers biocatalytic system implicates metal ions and biomolecules (enzymes). In contrast to free or conventionally immobilized enzymes, single enzyme or multi enzyme-incorporated flowers-like hybrid nanoconstructs demonstrated elevated catalytic activities and stabilities over a very broader range of experimental conditions, i.e., pHs, temperatures and salt concentration. This review discusses the recent developments in the fabrication strategies to diversifying nanoflowers, types, characteristics, and applications of organic-inorganic hybrid nanoflowers as a host platform to engineer different kinds of enzymes with requisite functionalities for biocatalysis applications in different sectors of the modern world. Based on experimental and theoretical literature data, the review is wrapped up with concluding remarks and an outlook in terms of upcoming challenges and prospects for their scale-up applications.

Thermostable enzyme-immobilized magnetic responsive Ni-based metal–organic framework nanorods as recyclable biocatalysts for efficient biosynthesis of S-adenosylmethionine

A novel magnetic responsive Ni-based metal–organic framework material was developed to efficiently separate and immobilize thermal enzymes with high catalytic performance.

Polydopamine-mediated synthesis of core–shell gold@calcium phosphate nanoparticles for enzyme immobilization

Constructing calcium phosphate (CaP)–gold (Au) nanocomposites for enzyme immobilization to overcome the bottleneck of loss of enzyme activity upon immobilization.

Metal-nucleobase hybrid nanoparticles for enhancing the activity and stability of metal-activated enzymes

A novel strategy for enhancing the activity and stability of metal-activated enzyme methionine adenosyltransferase (MAT) by allosteric control and confinement of metal-nulceobase hybrid coordination.

Proximal Pocket Controls Alkene Oxidation Selectivity of Cytochrome P450 and Chloroperoxidase toward Small, Nonpolar Substrates

This paper examines the influence of the proximal pockets of cytochrome P450_CAM and chloroperoxidase (CPO) on the relative favorability of catalytic epoxidation and allylic hydroxylation of olefins, a type of alkene oxidation selectivity. The study employs quantum mechanical models of the active site to isolate the proximal pocket's influence on the barrier for the selectivity-determining step for each reaction, using cyclohexene and cis-β-methylstyrene as substrates. The proximal pocket is found to preference epoxidation by 2-5 kcal/mol, the largest value being for CPO, converting the active heme-thiolate moiety from being intrinsically hydroxylation-selective to being intrinsically epoxidation-selective. This theoretical study, the first to correctly predict these enzymes' preference for epoxidation of allylic substrates, strongly suggests that the proximal pocket is the key determinant of alkene oxidation selectivity. The selectivity for epoxidation can be rationalized in terms of the proximal pocket's modulation of the thiolate's electron "push" and consequent influence on the heme redox potential and the basicity of the trans ligand.

Synthesis of cross-linked protein-metal hybrid nanoflowers and its application in repeated batch decolorization of synthetic dyes

Herein, we report the preparation of a cross-linked protein-metal hybrid nanoflower (NF) system for laccase immobilization. The immobilized laccase showed effective encapsulation yield and activity recovery of 78.1% and 204%, respectively. The catalytic efficiency (k_catV_max^-1) of cross-linked NF (CL-NF) was 2.2-fold more than that of free laccase. The CL-NF also exhibited significantly higher stability towards pH and temperature changes. It exhibited excellent storage stability and tolerance towards solvents and inhibitors as compared with the free enzyme. After 10 cycles of reuses, the NF and CL-NF laccase showed 41.2% and 92.3% residual activity, respectively. The CL-NF showed high oxidation potential, 265% that of the free enzyme, towards phenolic compounds. The CL-NF laccase retained the residual decolorization efficiency of up to 84.6% for synthetic dyes under repeated batch conditions of 10 cycles. These results suggested that the preparation of CL-NF is an effective approach to enhance the enzymatic properties and has great potential in many industrial applications.

Recent advances in biomolecule immobilization based on self-assembly: organic-inorganic hybrid nanoflowers and metal-organic frameworks as novel substrates

In the past few years, the immobilization of biomolecules on hybrid nanoflowers and metal-organic frameworks (MOFs) via self-assembly synthesis has received much attention due to its simplicity, high efficiency, and a bright prospect of enhancing the stability, activity and even selectivity of biomolecules compared to conventional immobilization methods. In the synthesis of organic-inorganic hybrid nanoflowers, biomolecules used as organic components are simply mixed with metal ions which act as inorganic components to form flower-like nanocomposites, while in the self-assembly process of encapsulating biomolecules in MOFs (biomolecule@MOF composites), the biomolecules just need to be added to the precursor mixtures of MOFs, in which the biomolecules are therefore embedded in MOF crystals with small pores. In this review, we focus on the recent advances of these composites, especially in the synthesis strategies, mechanism and applications in biosensors, biomedicine, pollutant disposal, and industrial biocatalysis, and future perspectives are discussed as well.