Multi-enzyme co-embedded organic-inorganic hybrid nanoflowers: synthesis and application as a colorimetric sensor

Cascade synthesis of a gold nanoparticle-network polymer composite

The multi-step, cascade synthesis of a self-supporting, hierarchically-structured gold nanoparticle hydrogel composite is described. The composite is spontaneously prepared from a non-covalent, lamellar lyotropic mesophase composed of amphiphiles that support the reactive constituents, a mixture of hydroxyl- and acrylate-end-derivatized PEO117-PPO47-PEO117 and [AuCl4](-). The reaction sequence begins with the auto-reduction of aqueous [AuCl4](-) by PEO117-PPO47-PEO117 which leads to both the production of Au NPs and the free radical initiated polymerization and crosslinking of the acrylate end-derivatized PEO117-PPO47-PEO117 to yield a network polymer. Optical spectroscopy and TEM monitored the reduction of [AuCl4](-), formation of large aggregated Au NPs and oxidative etching into a final state of dispersed, spherical Au NPs. ATR/FT-IR spectroscopy and thermal analysis confirms acrylate crosslinking to yield the polymer network. X-ray scattering (SAXS and WAXS) monitored the evolution of the multi-lamellar structured mesophase and revealed the presence of semi-crystalline PEO confined within the water layers. The hydrogel could be reversibly swollen without loss of the well-entrained Au NPs with full recovery of composite structure. Optical spectroscopy shows a notable red shift (Δλ ∼ 45 nm) in the surface plasmon resonance between swollen and contracted states, demonstrating solvent-mediated modulation of the internal NP packing arrangement.

Papain/Zn3(PO4)2 hybrid nanoflower: preparation, characterization and its enhanced catalytic activity as an immobilized enzyme

Flower-like papain/Zn₃(PO₄)₂ hybrid materials are synthesized via a facile, rapid and low-cost method in this study.

Fluorescence sensing of glucose using glucose oxidase incorporated into a fluorophore-containing PNIPAM hydrogel

We present a new composite material composed of pH sensitive fluorescent dyes in a poly(N-isopropylacrylamide)-based hydrogel and incorporating glucose oxidase (GOx), which provides a platform for fluorescence sensing of glucose.

Facile fabrication of silk protein sericin-mediated hierarchical hydroxyapatite-based bio-hybrid architectures: excellent adsorption of toxic heavy metals and hazardous dye from wastewater

Facilely fabricated silk protein sericin-mediated hierarchical hydroxyapatite hybrid architectures show excellent adsorption of toxic heavy metal ions of Pb(ii), Cd(ii) and Hg(ii) and a hazardous dye, Congo red (CR), from wastewater.

A new lipase–inorganic hybrid nanoflower with enhanced enzyme activity

A new hybrid nanoflower biocatalyst was synthesized using the organic component of Burkholderia cepacia lipase and inorganic component of calcium phosphate.

Synthesis of a glucose oxidase-conjugated, polyacrylamide-based, fluorescent hydrogel for a reusable, ratiometric glucose sensor

New emission color-changeable hydrogels containing glucose oxidase were synthesized to be used in glucose sensing.

Protein-templated cobaltous phosphate nanocomposites for the highly sensitive and selective detection of platelet-derived growth factor-BB

We synthesized novel Co3(PO4)2-based nanocomposites with 3D porous architectures via self-assembly; here, bovine serum albumin (BSA) and aptamer were used as organic phases to produce Co3(PO4)2@BSA and Co3(PO4)2@Apt nanocomposites, respectively. The formation mechanism of Co3(PO4)2-based nanocomposites was described based on characterizations of their physio-chemical performance, and the developed nanocomposites were applied as scaffold materials to construct a novel electrochemical aptasensor and detect platelet-derived growth factor-BB (PDGF-BB). The PDGF-BB targeting aptamer must be immobilized onto the Co3(PO4)2@BSA-modified electrode to detect PDGF-BB, whereas Co3(PO4)2@Apt-based aptasensor may be directly used to determine the target protein. Electrochemical impedance spectroscopy results showed that the developed Co3(PO4)2@BSA- and Co3(PO4)2@Apt-based aptasensors present highly sensitive detection ability toward PDGF-BB. Due to the special nanoflower structure, the Co3(PO4)2@BSA-based aptasensor features a detection limit of 3.7 pg mL(-1); while the limit of detection of the Co3(PO4)2@Apt-based aptasensor is 61.5 pg mL(-1), which is the possible bioactivity loss of the aptamer in Co3(PO4)2@Apt nanocomposite. The two detection limits obtained are still much lower than or comparable with those of previously reported aptasensors. The Co3(PO4)2@BSA- and Co3(PO4)2@Apt-based aptasensors showed high selectivity, stability, and applicability for detecting the desired protein. This finding indicates that the Co3(PO4)2-based nanocomposites could be used as an electrochemical biosensor for various detection procedures in the biomedical field.

Facile synthesis of enzyme-embedded magnetic metal-organic frameworks as a reusable mimic multi-enzyme system: mimetic peroxidase properties and colorimetric sensor

This work reports a facile and easily-achieved approach for enzyme immobilization by embedding glucose oxidase (GOx) in magnetic zeolitic imidazolate framework 8 (mZIF-8) via a de novo approach. As a demonstration of the power of such materials, the resulting GOx embedded mZIF-8 (mZIF-8@GOx) was utilized as a colorimetric sensor for rapid detection of glucose. This method was constructed on the basis of metal-organic frameworks (MOFs), which possessed very fascinating peroxidase-like properties, and the cascade reaction for the visual detection of glucose was combined into one step through the mZIF-8@GOx based mimic multi-enzyme system. After characterization by electron microscopy, X-ray diffraction, nitrogen sorption, fourier transform infrared spectroscopy and vibrating sample magnetometry, the as-prepared mZIF-8@GOx was confirmed with the robust core-shell structure, the monodisperse nanoparticle had an average diameter of about 200 nm and displayed superparamagnetism with a saturation magnetization value of 40.5 emu g(-1), it also exhibited a large surface area of 396.10 m(2) g(-1). As a peroxidase mimic, mZIF-8 was verified to be highly stable and of low cost, and showed a strong affinity towards H2O2. Meanwhile, the mZIF-8 embedded GOx also exhibited improved activity, stability and greatly enhanced selectivity in glucose detection. Moreover, the mZIF-8@GOx had excellent recyclability with high activity (88.7% residual activity after 12 times reuse).

Microgel coating of magnetic nanoparticles via bienzyme-mediated free-radical polymerization for colorimetric detection of glucose

This study describes a new strategy for the fabrication of magnetic core-shell microgels by free-radical polymerization triggered by the cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP). The mild polymerization around the interface of the magnetic nanoparticles permits the mild coating of the microgel layer with excellent characteristics for various applications in biocatalysis and medical diagnostics, as well as in clinical fields. The immobilized bienzyme within the microgel has a largely retained activity relative to the non-immobilized one. The confining effect of the microgel and the well designed distance between the two enzymes can benefit the diffusion of intermediates to the HRP active site. The final microgels can be incontestably employed as sensitive biosensors for colorimetric glucose detection.

Facile Method To Prepare Microcapsules Inspired by Polyphenol Chemistry for Efficient Enzyme Immobilization

In this study, a method inspired by polyphenol chemistry is developed for the facile preparation of microcapsules under mild conditions. Specifically, the preparation process includes four steps: formation of the sacrificial template, generation of the polyphenol coating on the template surface, cross-linking of the polyphenol coating by cationic polymers, and removal of the template. Tannic acid (TA) is chosen as a representative polyphenol coating precursor for the preparation of microcapsules. The strong interfacial affinity of TA contributes to the formation of polyphenol coating through oxidative oligomerization, while the high reactivity of TA is in charge of reacting/cross-linking with cationic polymer polyethylenimine (PEI) through Schiff base/Michael addition reaction. The chemical/topological structures of the resultant microcapsules are simultaneously characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), etc. The wall thickness of the microcapsules could be tailored from 257±20 nm to 486±46 nm through changing the TA concentration. The microcapsules are then utilized for encapsulating glucose oxidase (GOD), and the immobilized enzyme exhibits desired catalytic activity and enhanced pH and thermal stabilities. Owing to the structural diversity and functional versatility of polyphenols, this study may offer a facile and generic method to prepare microcapsules and other kinds of functional porous materials.

Organic-inorganic hybrid nanoflowers: types, characteristics, and future prospects

Organic-inorganic hybrid nanoflowers, a newly developed class of flower-like hybrid nanoparticles, have received much attention due to their simple synthesis, high efficiency, and enzyme stabilizing ability. This article covers, in detail, the types, structural features, mechanism of formation, and bio-related applications of hybrid nanoflowers. The five major types of hybrid nanoflowers are discussed, i.e., copper-protein, calcium-protein, and manganese-protein hybrid nanoflowers, copper-DNA hybrid nanoflowers, and capsular hybrid nanoflowers. The structural features of these nanoflowers, such as size, shape, and protein ratio generally determine their applications. Thus, the specific characteristics of hybrid nanoflowers are summarized in this review. The interfacial mechanism of nanoflower formation is examined in three steps: first, combination of metal ion and organic matter; second, formation of petals; third, growth of nanoflowers. The explanations provided herein can be utilized in the development of innovative approaches for the synthesis of hybrid nanoflowers for prospective development of a plethora of hybrid nanoflowers. The future prospects of hybrid nanoflowers in the biotechnology industry, medicine, sensing, and catalysis are also discussed.

Ultrafast sonochemical synthesis of protein-inorganic nanoflowers

We developed a simple but efficient method to synthesize protein-inorganic hybrid nanostructures with a flower-like shape (nanoflowers), which relies on sonication to facilitate the synthesis of the nanoflowers. With this technique, we synthesized nanoflowers containing laccase as a model protein and copper phosphate within 5 minutes at room temperature. The resulting laccase nanoflowers yielded greatly enhanced activity, stability, and reusability, and their usefulness was successfully demonstrated by applying them in the colorimetric detection of epinephrine. The strategy developed could be used to rapidly synthesize nanoflowers for various applications in biosensor and enzyme catalysis and would expand the utilization of nanoflowers in diverse fields of biotechnology.

Artificial Peroxidase/Oxidase Multiple Enzyme System Based on Supramolecular Hydrogel and Its Application as a Biocatalyst for Cascade Reactions

Inspired by delicate structures and multiple functions of natural multiple enzyme architectures such as peroxisomes, we constructed an artificial multiple enzyme system by coencapsulation of glucose oxidases (GOx) and artificial peroxidases in a supramolecular hydrogel. The artificial peroxidase was a functional complex micelle, which was prepared by the self-assembly of diblock copolymer and hemin. Compared with catalase or horseradish peroxidase (HRP), the functional micelle exhibited comparable activity and better stability, which provided more advantages in constructing a multienzyme with a proper oxidase. The hydrogel containing the two catalytic centers was further used as a catalyst for green oxidation of glucose, which was a typical cascade reaction. Glucose was oxidized by oxygen (O2) via the GOx-mediated reaction, producing toxic intermediate hydrogen peroxide (H2O2). The produced H2O2 further oxidized peroxidase substrates catalyzed by hemin-micelles. By regulating the diffusion modes of the enzymes and substrates, the artificial multienzyme based on hydrogel could successfully activate the cascade reaction, which the soluble enzyme mixture could not achieve. The hydrogel, just like a protective covering, protected oxidases and micelles from inactivation via toxic intermediates and environmental changes. The artificial multienzyme could efficiently achieve the oxidation task along with effectively eliminating the toxic intermediates. In this way, this system possesses great potentials for glucose detection and green oxidation of a series of substrates related to biological processes.

Self-assembled enzyme-inorganic hybrid nanoflowers and their application to enzyme purification

We report a novel method to synthesize organic-inorganic nanoflowers for crude soybean peroxidase (SBP) purification. A hierarchical flower-like spherical structure with hundreds of nanopetals was self-assembled by using crude SBP as the organic component and Cu3(PO4)2·3H2O as the inorganic component. The structure of the hybrid nanoflowers was confirmed by Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy, and the enzymatic activity of SBP embedded in the hybrid nanoflowers was evaluated using guaiacol as substrate. Compared with free crude SBP in solution, SBP embedded in hybrid nanoflowers exhibited enhanced enzymatic activity (∼446%). The hybrid nanoflowers also exhibited excellent reusability and reproducibility during cycle analysis. These results demonstrate that synthesis of hybrid nanoflowers is an effective enzyme purification strategy.

Polymeric Flower-Like Microparticles from Self-Assembled Cellulose Stearoyl Esters

Flower-like particles (FLPs) with hierarchical surface architectures have recently attracted considerable attention due to their potentially wide application range. Hitherto, nearly all FLPs were fabricated using inorganic compounds, while versatile organic polymers have not received sufficient attention yet. Herein, we show the construction of novel organic, polymeric FLPs with diameters of 2.5-5 μm using cellulose stearoyl esters (CSEs) by means of the crystallization of side chains. CSEs with degrees of substitution of approximately 3 were transformed into FLPs during the gradual precipitation of polymer chains from the mixture of their solutions in dichloromethane (DCM) and a nonsolvent, which is driven by the evaporation of DCM. Ordered petal-like nanostructures were formed on the particle surface through the crystallization of side chains. Finally, partially crystalline FLPs containing lamellar structures were obtained. Moreover, the formation process was strongly affected by the molecular weight of CSE, concentrations of CSE solutions and the volume ratio between DCM and nonsolvents.

Self-assembly of an organic–inorganic hybrid nanoflower as an efficient biomimetic catalyst for self-activated tandem reactions

An organic–inorganic hybrid nanoflower was prepared as an efficient biomimetic catalyst with excellent catalytic activity, durability and stability.

Controlled synthesis of peony-shaped photocatalyst grains of Ag3PO4/Zn3(PO4)2 by coprecipitation and recrystallization technology

Peony-shaped grains of a Ag₃PO₄/Zn₃(PO₄)₂ composite have been synthesized through a coprecipitation and recrystallization technology.

Cascade catalysis – strategies and challenges en route to preparative synthetic biology

In this feature article recent progress and future perspectives of cascade catalysis combining bio/bio or bio/chemo catalysts are presented.

An enzyme–inorganic hybrid nanoflower based immobilized enzyme reactor with enhanced enzymatic activity

Ca₃(PO₄)₂–ChT hybrid nanoflowers were synthesized by a facile approach. The nanoflowers exhibited an enhanced enzymatic activity and can be used as an immobilized enzyme reactor (IMER) for highly efficient protein digestion.

Metal–organic frameworks and inorganic nanoflowers: a type of emerging inorganic crystal nanocarrier for enzyme immobilization

By the methods of physical adsorption, covalent conjugation and self-assembly, enzymes can be immobilized on metal–organic frameworks (MOFs) and inorganic crystal nanoflowers with the great promise of enhancing enzyme stability, activity and even selectivity.

Hierarchical assembly of enzyme-inorganic composite materials with extremely high enzyme activity

We synthesized a composite material with a hierarchical flower-like structure and extremely high enzyme activity and found that the main factor affecting its catalytic activity was the material structure and not the actual enzyme weight percentage.

Synthesis of organic–inorganic hybrid microcapsules through in situ generation of an inorganic layer on an adhesive layer with mineralization-inducing capability

A facile and efficient route is developed to prepare (PDA–PEI)/titania hybrid microcapsules by in situ generation of an inorganic layer on an adhesive layer with mineralization-inducing capability under mild conditions.

Selective biomineralization of Co3(PO4)2-sponges triggered by His-tagged proteins: efficient heterogeneous biocatalysts for redox processes

Heterogeneous redox biocatalyts fabricated by mineralization of cobalt phosphate triggered by His-tag enzymes.

Facile synthesis of enzyme-inorganic hybrid nanoflowers and its application as a colorimetric platform for visual detection of hydrogen peroxide and phenol

This study reports a facile approach for the synthesis of horseradish peroxidise (HRP)-inorganic hybrid nanoflowers by self-assembly of HRP and copper phosphate (Cu3(PO4)2·3H2O) in aqueous solution. Several reaction parameters that affect the formation of the hybrid nanoflowers were investigated and a hierarchical flowerlike spherical structure with hundreds of nanopetals was obtained under the optimum synthetic conditions. The enzymatic activity of HRP embedded in hybrid naonflowers was evaluated based on the principle of HRP catalyzing the oxidation of o-phenylenediamine (OPD) in the presence of hydrogen peroxide (H2O2). The results showed that 506% enhancement of enzymatic activity in the hybrid nanoflowers could be achieved compared with the free HRP in solution. Taking advantages of the structural feature with catalytic property, a nanoflower-based colorimetric platform was newly designed and applied for fast and sensitive visual detection of H2O2 and phenol. The limits of detection (LODs) for H2O2 and phenol were as low as 0.5 μM and 1.0 μM by the naked-eye visualization, which meet the requirements of detection of both analytes in clinical diagnosis and environmental water. The proposed method has been successfully applied to the analysis of low-level H2O2 in spiked human serum and phenol in sewage, respectively. The recoveries for all the determinations were higher than 92.6%. In addition, the hybrid nanoflowers exhibited excellent reusability and reproducibility in cycle analysis. These primary results demonstrate that the hybrid nanoflowers have a great potential for applications in biomedical and environmental chemistry.

5,10,15,20-tetrakis(4-carboxyl phenyl)porphyrin-CdS nanocomposites with intrinsic peroxidase-like activity for glucose colorimetric detection

Here, we describe the design of a novel mimic peroxidase, nanocomposites composed by 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin (H2TCPP) and cadmium sulfide (CdS). The H2TCPP-CdS nanocomposites can catalyze oxidation of substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 and form a blue product which can be seen by the naked eye in 5 min. The mechanism of the catalytic reaction originated from the generation of hydroxyl radical (·OH), which is a powerful oxidizing agent to oxidize TMB to produce a blue product. Then, we developed a colorimetric method that is highly sensitive and selective to detect glucose, combined with glucose oxidase (GOx). The proposed method allowed the detection of H2O2 concentration in the range of 4×10(-6)-1.4×10(-5)M and glucose in the range of 1.875×10(-5)-1×10(-4)M with detectable H2O2 concentration as low as 4.6×10(-7)M and glucose as low as 7.02×10(-6)M, respectively. The results provided the theoretical basis of practical application in glucose detecting and peroxidase mimetic enzymes.

Horseradish peroxidase (HRP) as a tool in green chemistry

The horseradish peroxidase (HRP) potential in organic synthesis.

Facile synthesis of enzyme–inorganic hybrid nanoflowers and their application as an immobilized trypsin reactor for highly efficient protein digestion

Hybrid nanoflowers were synthesized by a novel approach. The nanoflowers exhibited an enhanced enzymatic activity and can be used as an immobilized enzyme reactor (IMER) for highly efficient protein digestion.