Biosensor Based on ZIF-67-HRP and MWCNTs Nanocomposite Modified Glass Carbon Electrode for the Detection of Luteolin in Vegetables.

Luteolin has various pharmacological properties, including anti-inflammatory, antioxidant, and antitumor characteristics. Due to its potential value in drugs and functional foods, it is important to develop an efficient method for detecting luteolin. In this work, the poor selectivity of existing luteolin nonenzymatic sensors was solved by translating the enzyme-catalyzed reaction from bulk solution to the surface of a horseradish peroxidase (HRP) modified electrode through an electrocatalytic oxidation process. Here, we modified the surface of a glassy carbon electrode (GCE) with metal-organic frameworks (MOFs; ZIF-67 here, abbreviated as ZIF), functional nanomaterials, and HRP and finally covered it with Nafion (NF). In this case, luteolin acts as a hydrogen donor, and the electrode acts as a hydrogen acceptor; the oxidation reaction occurs on the electrode surface. The use of ZIF-67 ensured the conformational stability of HRP to ensure the selectivity and anti-interference property, and SDS-dispersed multiwalled carbon nanotubes (MWCNTs) enhanced the electrode conductivity. The use of NF avoids shedding of the electrode material during the testing process. A UV-vis spectrophotometer was used to study the selectivity of luteolin by HRP and the compatibility between HRP and ZIF. The materials were characterized and analyzed by scanning electron microscopy and transmission electron microscopy. Due to the synergistic effect of these nanomaterials, the linear range of NF/ZIF-HRP/MWCNTs-SDS/GCE was 1.0 × 10-2 to 6.0 µM, with detection limits of 25.3 nM (S/N = 3). The biosensor showed long-term stability and reproducibility, with a relative standard deviation of 4.2% for the peak current (n = 5). Finally, the biosensor was successfully used to detect luteolin in carrots, celery, and cauliflower.

Glucose Biosensor Based on Glucose Oxidase Immobilized on BSA Cross-Linked Nanocomposite Modified Glassy Carbon Electrode.

Glucose sensors based blood glucose detection are of great significance for the diagnosis and treatment of diabetes because diabetes has aroused wide concern in the world. In this study, bovine serum albumin (BSA) was used to cross-link glucose oxidase (GOD) on a glassy carbon electrode (GCE) modified by a composite of hydroxy fullerene (HFs) and multi-walled carbon nanotubes (MWCNTs) and protected with a glutaraldehyde (GLA)/Nafion (NF) composite membrane to prepare a novel glucose biosensor. The modified materials were analyzed by UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), and cyclic voltammetry (CV). The prepared MWCNTs-HFs composite has excellent conductivity, the addition of BSA regulates MWCNTs-HFs hydrophobicity and biocompatibility, and better immobilizes GOD on MWCNTs-HFs. MWCNTs-BSA-HFs plays a synergistic role in the electrochemical response to glucose. The biosensor shows high sensitivity (167 µA·mM-1·cm-2), wide calibration range (0.01-3.5 mM), and low detection limit (17 µM). The apparent Michaelis-Menten constant Kmapp is 119 µM. Additionally, the proposed biosensor has good selectivity and excellent storage stability (120 days). The practicability of the biosensor was evaluated in real plasma samples, and the recovery rate was satisfactory.

Detection of Guanine and Adenine Using an Aminated Reduced Graphene Oxide Functional Membrane-Modified Glassy Carbon Electrode.

A new electrochemical sensor based on a Nafion, aminated reduced graphene oxide and chitosan functional membrane-modified glassy carbon electrode was proposed for the simultaneous detection of adenine and guanine. Fourier transform-infrared spectrometry (FTIR), transmission electron microscopy (TEM), and electrochemical methods were utilized for the additional characterization of the membrane materials. The prepared electrode was utilized for the detection of guanine (G) and adenine (A). The anodic peak currents to G and A were linear in the concentrations ranging from 0.1 to 120 µM and 0.2 to 110 µM, respectively. The detection limits were found to be 0.1 µM and 0.2 µM, respectively. Moreover, the modified electrode could also be used to determine G and A in calf thymus DNA.

Catalase immobilization: Current knowledge, key insights, applications, and future prospects - A review.

Catalase (CAT), a ubiquitous enzyme in all oxygen-exposed organisms, effectively decomposes hydrogen peroxide (H2O2), a harmful by-product, into water and oxygen, mitigating oxidative stress and cellular damage, safeguarding cellular organelles and tissues. Therefore, CAT plays a crucial role in maintaining cellular homeostasis and function. Owing to its pivotal role, CAT has garnered considerable interest. However, many challenges arise when used, especially in multiple practical processes. "Immobilization", a widely-used technique, can help improve enzyme properties. CAT immobilization offers numerous advantages, including enhanced stability, reusability, and facilitated downstream processing. This review presents a comprehensive overview of CAT immobilization. It starts with discussing various immobilization mechanisms, support materials, advantages, drawbacks, and factors influencing the performance of immobilized CAT. Moreover, the review explores the application of the immobilized CAT in various industries and its prospects, highlighting its essential role in diverse fields and stimulating further research and investigation. Furthermore, the review highlights some of the world's leading companies in the field of the CAT industry and their substantial potential for economic contribution. This review aims to serve as a discerning, source of information for researchers seeking a comprehensive cutting-edge overview of this rapidly evolving field and have been overwhelmed by the size of publications.

Electrochemical biosensor based on functional nanomaterials and horseradish peroxidase for the determination of luteolin in peanut shell, honeysuckle and perilla.

Constructing a biosensor to detect luteolin content accurately is essential, especially considering its specific health benefits at certain concentrations. In this work, the reaction of HRP catalyzed luteolin could be successfully applied in electrocatalytic processes, the oxidation process of electron loss and dehydrogenation occurring on the electrode replaced the hydrogen receptor role of H2O2 in the HRP biocatalytic process. This oxidation reaction had an apparent current response, thus achieving accurate measurement of luteolin. On this biosensor, CTAB was used to disperse MWCNTs, and BSA was used to improve the hydrophobicity of MWCNTs, which was conducive to the subsequent AuNPs fixation of HRP. Three detection methods (LSV, DPV and SWV) for the detection of luteolin were compared and showed that SWV method had a wider linear range (1 × 10-8-2 × 10-5 M) and lower detection limit (8 × 10-10 M). The determination of luteolin in Traditional Chinese Medicine (TCM) by high performance liquid chromatography (HPLC) and biosensor was almost identical. Therefore, this biosensor could successfully replace HPLC in detecting luteolin in TCM.

Direct electrochemistry of hemoglobin immobilized on a functionalized multi-walled carbon nanotubes and gold nanoparticles nanocomplex-modified glassy carbon electrode.

Direct electron transfer of hemoglobin (Hb) was realized by immobilizing Hb on a carboxyl functionalized multi-walled carbon nanotubes (FMWCNTs) and gold nanoparticles (AuNPs) nanocomplex-modified glassy carbon electrode. The ultraviolet-visible absorption spectrometry (UV-Vis), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) methods were utilized for additional characterization of the AuNPs and FMWCNTs. The cyclic voltammogram of the modified electrode has a pair of well-defined quasi-reversible redox peaks with a formal potential of -0.270 ± 0.002 V (vs. Ag/AgCl) at a scan rate of 0.05 V/s. The heterogeneous electron transfer constant (ks) was evaluated to be 4.0 ± 0.2 s(-1). The average surface concentration of electro-active Hb on the surface of the modified glassy carbon electrode was calculated to be 6.8 ± 0.3 × 10(-10) mol cm(-2). The cathodic peak current of the modified electrode increased linearly with increasing concentration of hydrogen peroxide (from 0.05 nM to 1 nM) with a detection limit of 0.05 ± 0.01 nM. The apparent Michaelis-Menten constant (K(m)(app)) was calculated to be 0.85 ± 0.1 nM. Thus, the modified electrode could be applied as a third generation biosensor with high sensitivity, long-term stability and low detection limit.

MWCNTs-CTAB and HFs-Lac Nanocomposite-Modified Glassy Carbon Electrode for Rutin Determination.

Rutin is a flavonoid glycoside compound, which is mainly transported via the blood circulation system in the human body. The monitoring of the blood concentration of rutin is of great significance in many fields such as pharmacology and pharmacokinetics. In this work, a biosensor based on multi-walled carbon nanotubes (MWCNTs), cetyltrimethylammonium bromide (CTAB), hydroxyl fullerenes (HFs), and laccase (Lac) nanocomposite-modified glassy carbon electrodes was constructed. The modified materials were characterized with a transmission electron microscope (TEM), cyclic voltammograms (CV), and electrochemical impedance spectroscopy (EIS). CTAB is used to disperse MWCNTs and improve hydrophilicity and biocompatibility of MWCNTs, while the use of Lac can enhance the oxidation of catechol structure in rutin, thus significantly improving the sensitivity and selectivity of the modified electrode. Linear sweep voltammetry (LSV) studies showed that the determination linear ranges of rutin were 0.1 µmol L-1 to 2 µmol L-1 and 2 µmol L-1 to 11 µmol L-1, with the determination limits of 30 nmol L-1 and 95.5 nmol L-1, respectively. The proposed biosensor can be used to detect rutin tablets and serum samples with high recovery, which indicates a good accuracy of this method, and the results are consistent with those measured by the traditional ultra-high performance liquid chromatography (UHPLC) method. Hence, this biosensor has potential practical application value in rutin drug quality testing and clinical blood drug concentration monitoring.

Steered molecular dynamic simulations of conformational lock of Cu, Zn-superoxide dismutase.

The conformational lock was a bio-thermodynamic theory to explain the characteristics of interfaces in oligomeric enzymes and their effects on catalytic activity. The previous studies on superoxide dismutases (Cu, Zn-SODs) showed that the dimeric structure contributed to the high catalytic efficiency and the stability. In this study, steered molecular dynamics simulations were used firstly to study the main interactions between two subunits of Cu, Zn-SODs. The decomposition process study showed that there were not only four pairs of hydrogen bonds but also twenty-five residue pairs participating hydrophobic interactions between A and B chains of SOD, and van der Waals interactions occupied a dominant position among these residue pairs. Moreover, the residue pairs of hydrogen bonds played a major role in maintaining the protein conformation. The analysis of the energy and conformational changes in the SMD simulation showed that there were two groups (two conformational locks) between A and B chains of SOD. The first group consisted of one hydrogen-bond residues pair and seven hydrophobic interactions residues pairs with a total average energy of -30.10 KJ/mol, and the second group of three hydrogen-bond residues pair and eighteen hydrophobic interactions residues pairs formed with a total average energy of -115.23 KJ/mol.

Glucose Oxidase Immobilized on a Functional Polymer Modified Glassy Carbon Electrode and Its Molecule Recognition of Glucose.

In the present study, a glucose oxidase (GluOx) direct electron transfer was realized on an aminated polyethylene glycol (mPEG), carboxylic acid functionalized multi-walled carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymer modified glassy carbon electrode (GCE). The amino groups in PEG, carboxyl groups in multi-walled carbon nanotubes, and IL may have a better synergistic effect, thus more effectively adjust the hydrophobicity, stability, conductivity, and biocompatibility of the composite functional polymer film. The composite polymer membranes were characterized by cyclic voltammetry (CV), ultraviolet-visible (UV-Vis) spectrophotometer, fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and transmission electron microscopy (TEM), respectively. In 50 mM, pH 7.0 phosphate buffer solution, the formal potential and heterogeneous electron transfer constant (ks) of GluOx on the composite functional polymer modified GCE were -0.27 V and 6.5 s-1, respectively. The modified electrode could recognize and detect glucose linearly in the range of 20 to 950 µM with a detection limit of 0.2 µM. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 143 µM. The IL/mPEG-fMWCNTs functional polymer could preserve the conformational structure and catalytic activity of GluOx and lead to high sensitivity, stability, and selectivity of the biosensors for glucose recognition and detection.

A novel self-assembled nano micelle as a highly efficient artificial peroxidase based on hexadecyl trimethyl ammonium bromide and cytochrome c.

A novel artificial peroxidase (AP) with highly catalytic efficiency was designed using hexadecyl trimethyl ammonium bromide (CTAB, 3 mM) nano-micelles and bovine heart cytochrome c (Cyt c, 0.5 µM) in 100 mM, pH 8.0 phosphate buffer at 25°C. The catalytic rate (kcat) and Michaelis-Menten (Km) of the AP were determined to be 0.311 ± 0.013 s(-1) and 8.64 ± 0.6 µM. The catalytic efficiency was 0.0360 ± 0.0020 µM(-1)s(-1) (about 50% the efficiency of native horseradish peroxidase). The Ultraviolet-visible spectrophotometer and Circular Dichroism techniques were applied to study the properties of the CTAB-Cyt c nano-micelle. Designed AP can be applied instead of native horseradish peroxidase.

Direct electron transfer of horseradish peroxidase on a functional nanocomplex modified glassy carbon electrode.

Direct electron transfer of horseradish peroxidase (HRP) was achieved by immobilizing HRP on a functional nanocomplex modified glassy carbon (GC) electrode. The cyclic voltammograms (CVs) of the modified electrode have a pair of well-defined redox peaks with a formal potential (E°') of -26 ± 2 mV versus Ag/AgCl, in 0.05 M, pH7.0 phosphate buffer solution (PBS) at a scan rate of 0.05 V/s. The heterogeneous electron transfer constant (ks) was calculated to be 1.94 s-1. The modified electrode response toward hydrogen peroxide was linear in the concentrations ranging from 0.28 µM to 10 µM, with a detection limit of 0.28 µM. The apparent Michaelis-Menten constant (Kmapp) for H2O2 was 2.54 µM. Moreover, results of biochemical computation showed that the amino acid residues (Ala34, Arg38, Ser73, Arg75, Ala140, Pro141, Phe172, Gly173, Lys174, Phe179, Arg31, Ser35, Lys174, Gln176) of HRP may playa crucial role in the improvement of electron transport between electro-active site (heme group) of an HRP molecule and nanocomplex modified GC electrode.

Direct electrochemistry of glucose oxidase and glucose biosensing on a hydroxyl fullerenes modified glassy carbon electrode.

Direct electrochemistry of glucose oxidase (GOD) was achieved when GOD-hydroxyl fullerenes (HFs) nano-complex was immobilized on a glassy carbon (GC) electrode and protected with a chitosan (Chit) membrane. The ultraviolet-visible absorption spectrometry (UV-vis), transmission electron microscopy (TEM), and circular dichroism spectropolarimeter (CD) methods were utilized for additional characterization of the GOD, GOD-HFs and Chit/GOD-HFs. Chit/HFs may preserve the secondary structure and catalytic properties of GOD. The cyclic voltammograms (CVs) of the modified GC electrode showed a pair of well-defined quasi-reversible redox peaks with the formal potential (E°') of 353 ± 2 mV versus Ag/AgCl at a scan rate of 0.05 V/s. The heterogeneous electron transfer constant (ks) was calculated to be 2.7 ± 0.2s(-1). The modified electrode response to glucose was linear in the concentrations ranging from 0.05 to 1.0mM, with a detection limit of 5 ± 1 µM. The apparent Michaelis-Menten constant (Km(app)) was 694 ± 8 µM. Thus, the modified electrode could be applied as a third generation biosensor for glucose with high sensitivity, selectivity and low detection limit.

A highly efficient nano-cluster artificial peroxidase and its direct electrochemistry on a nano complex modified glassy carbon electrode.

A nano-cluster with highly efficient peroxide activity was constructed based on nafion (NF) and cytochrome c (Cyt c). UV-Vis spectrometry and transmission electron microscopy (TEM) methods were utilized for characterization of the nano-structured enzyme or artificial peroxidase (AP). The nano-cluster was composed of a Chain-Ball structure, with an average ball size of about 40 nm. The Michaelis-Menten (K(m)) and catalytic rate (k(cat)) constants of the AP were determined to be 2.5 ± 0.4 µM and 0.069 ± 0.001 s(-1), respectively, in 50 mM PBS at pH 7.0. The catalytic efficiency of the AP was evaluated to be 0.028 ± 0.005 µM(-1) s(-1), which was 39 ± 5% as efficient as the native horseradish peroxidase (HRP). The AP was also immobilized on a functional multi-wall carbon nanotube (MWNCTs)-gold colloid nanoparticles (AuNPs) nano-complex modified glassy carbon (GC) electrode. The cyclic voltammetry of AP on the nano complex modified GC electrode showed a pair of well-defined redox peaks with a formal potential (E°') of -45 ± 2 mV (vs. Ag/AgCl) at a scan rate of 0.05 V/s. The heterogeneous electron transfer rate constant (k(s)) was evaluated to be 0.65 s(-1). The surface concentration of electroactive AP on GC electrode (Γ) was 7 × 10(-10) mol cm(-2). The apparent Michaelis-Menten constant (K(m)(app)) was 0.23 nM.