Improved catalytic performance of carrier-free immobilized lipase by advanced cross-linked enzyme aggregates technology.

The cross-linked enzyme aggregates (CLEAs) are one of the technologies that quickly immobilize the enzyme without a carrier. In this study, ionic liquid with amino group (1-aminopropyl-3-methylimidazole bromide, FIL) was used as the novel functional surface molecule to modify CRL (Candida rugosa lipase, CRL). The enzymatic properties of CRL-FIL-CLEAs were investigated. The activity of CRL-FIL-CLEAs (5.51 U/mg protein) was 1.9 times higher than that of CRL-CLEAs (2.86 U/mg protein) without surface modification. After incubating in a centrifuge tube for 50 min at 60 °C, CRL-FIL-CLEAs still maintained 61% of its initial activity, while the value for CRL-CLEAs was only 22%. After repeated use for five times, compared with the 22% residual activity of CRL-CLEAs, the value of CRL-FIL-CLEAs was 51%. Based on the above results, it was indicated that this method provided a new idea for the effective synthesis of immobilized enzyme.

Lipase nanogel catalyzed synthesis of vitamin E succinate in non-aqueous phase.

BACKGROUND: In order to improve the stability of vitamin E and broaden its scope of application, an effective solution is to convert vitamin E into its derivatives. This work developed a new Candida rugosa lipase (CRL) nanogel based on modification of ionic liquid with vinyl functional groups. This novel CRL nanogel was used in the preparation process of vitamin E succinate based on the principle of non-aqueous enzymology. At the same time, various factors including enzyme concentration, substrate molar ratio, reaction temperature and reaction time, that affect the yield of vitamin E succinate were optimized and analyzed. RESULTS: Different solvents with various hydrophobicity parameters (LogP values) from -1.3 to 3.5 were studied, it was found that dimethyl sulfoxide (DMSO) had the lowest LogP value among organic solvents but vitamin E succinate had the highest yield in DMSO. Furthermore, the effect of different operating conditions, such as molar ratios of substrate, enzyme concentration, reaction temperature and reaction time was studied. Under the optimal process conditions (enzyme concentration 6 mg mL-1 , substrate molar ratio 4:1, reaction temperature 55 °C and reaction time 15 h), the product yield was 62.58 ± 1.16%. CRL and CRL nanogel were characterized using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). It was shown that CRL nanogel influenced the catalytic behavior of lipase significantly by changing the structure and surface properties of CRL. CONCLUSION: Novel lipase nanogel was an excellent biocatalyst for enzymatic synthesis of vitamin E succinate. © 2020 Society of Chemical Industry.

Enhancing electrochemical sensing for catechol by biomimetic oxidase covalently functionalized graphene oxide.

Catechol level is an important indicator for evaluating the quality of tea. Therefore, the exploration of a simple and efficient quantitative detection method for catechol has an important significance. In this study, functionalized graphene oxide was synthesized by chemically modifying the surface of graphene oxide. The prepared carrier was covalently combined with biomimetic oxidase iron porphyrin (FePP, the active center of horseradish peroxidase). Ionic liquid as covalent coupling agents was designed as electronic bridge between biomimetic oxidase and graphene oxide. The novel biomimetic biosensor provided a detection range of 50.0-1600.0 µmol/L by modulating under the optimal conditions of the reaction system (FePP concentration is 1.5 × 10-3 mol/L, pH 3.0, Nafion solution dosage 1% and temperature 25 °C), the detection limit is 0.09 µmol/L. The biosensor has excellent stability, repeatability and reproducibility, and is expected to be applied to the rapid detection of catechol in actual tea sample..

Acetylcholinesterase biosensors based on ionic liquid functionalized carbon nanotubes and horseradish peroxidase for monocrotophos determination.

Long-term and excessive use of monocrotophos (MPs) pesticide leads to an accumulation of MPs residues in agricultural products. Electrochemical biosensor technology was developed as a simple and efficient method for detecting MPs. However, commercial acetylcholinesterase (AChE) sensors are not applied in practical MPs detection due to poor stability and reliability. In this study, the advantages of functionalized carbon nanotubes (Cl/MWCNTs) and a bi-enzyme system (horseradish peroxidase (HRP)/AChE) were combined, a novel bi-enzyme electrode (Cl/MWCNTs/HRP/AChE/GCE) was constructed. Under optimal conditions, the bi-enzyme sensor had a wide detection range of 1.0 × 10-11 to 1.0 × 10-7 mol/L and low detection limit of 4.5 × 10-12 mol/L. The proposed AChE biosensor exhibited excellent stability and sensitivity for MPs determination and presented a promising tool for monitoring food safety.

Biomimetic oxidase sensor based on functionalized surface of carbon nanotubes and iron prophyrins for catechol detection.

A novel and highly stable biomimetic oxidase sensor system was designed for catehol detection. FePP used as biomimetic horseradish peroxidase (HRP) was immobilized onto modified multi-walled carbon nanotubes (MWCNTs). Functional groups such as -OH, -NH2 and -COOH were introduced onto the surface of MWCNTs to provide biomimetic microenvironment for iron porphyrins (FePP). Stable biomimetic enzyme electrode has been developed to detect catechol as a simple, economical and efficient method. At optimal condition, the detection limit of OH-MWCNTs/FePP/Nafion was 3.754 × 10- 6 M. After stored at - 4 °C for 35 days, the oxidation current value still maintained 98.3% of initial activity. In repetitive nature test, relative standard deviation (RSD) of oxidation current remained within 1.0% after ten consecutive measurements in the same concentration of catechol solution, while most of reported oxidase sensor was within 2.0% under the same condition.

Acetylcholinesterase biosensor based on functionalized surface of carbon nanotubes for monocrotophos detection.

Monocrotophos (Ops) has been widely used as pesticide in crop production but simultaneously could accumulate in the nature and seriously impact food safety and human health. It is necessary to develop a high sensitivity biosensor for accurate and fast detection of OPs. In this study, multi-walled carbon nanotubes (MWCNTs) were selected as acetylcholinesterase (AChE) carrier and their surface was modified by introducing different functional groups (-SH, -NH2, -Cl, -OH), hydrophobic alkyl groups (-CH3, -(CH2)2CH3, -(CH2)7CH3, -(CH2)15CH3) and ionic liquids (-IL1, -IL2). The interaction mechanism of MWCNTs functionalized surface and AChE has been revealed by studying characteristics of AChE immobilized on different carrier surface. Finally, compared with reported references and above other modifiers, we found that MWCNTs surface modified by -IL1 was the best carrier for AChE and the detection limit of IL1-MWCNTs/AChE/GCE was 3.3 × 10-11 M. At optimum reaction condition (pH 7.0, AChE loading 0.25 U, Inhibition time 14 min), storability test indicated reactivity of IL1-MWCNTs/AChE/GCE remained above 98.5% within two weeks. For real vegetable sample detection, the recoveries of IL1-MWCNTs/AChE/GCE were found to be between 90.0% and 104%. These results demonstrated novel biosensors could act as device of high sensitivity for accurate and fast detection of OPs.

Quick separation and enzymatic performance improvement of lipase by ionic liquid-modified Fe3O4 carrier immobilization.

To promote the activity and stability of immobilized porcine pancreatic lipase (PPL), novel carrier was combined with special immobilization method. Enzymatic activity was enhanced after immobilized onto ionic liquid modified magnetic Fe3O4 by electrostatic adsorption. Activity of immobilized enzyme (PPL-IM/BF4-Fe3O4@CA) reached 596 U/g PPL. Through the combination of electrostatic adsorption and embedding immobilization methods, we improve binding force between the carrier and enzyme, and further enhance the efficiency and stability of immobilized enzyme. The activity of PPL-IM/BF4-Fe3O4@CA after repeated third use was 78%. After storage at room temperature for 5 days, the residual activity was 89%. Enzymatic properties and catalytic kinetics of immobilized enzymes were studied, and the effect mechanism of ionic liquid modified Fe3O4 on PPL was revealed. The effect of ionic liquid on the carrier structure was investigated by characterization of XRD, FT-IR, SEM and TG. The mechanism and enzymatic properties of immobilized PPL via electrostatic adsorption and embedding were analyzed. A novel and efficient immobilized PPL was developed.