Horseradish peroxidase and toluidine blue covalently immobilized leak-free sol-gel composite biosensor for hydrogen peroxide

Recent trends using natural polymeric nanofibers as supports for enzyme immobilization and catalysis

All the disciplines of science, especially biotechnology, have given continuous attention to the area of enzyme immobilization. However, the structural support made by material science intervention determines the performance of immobilized enzymes. Studies have proven that nanostructured supports can maintain better catalytic performance and improve immobilization efficiency. The recent trends in the application of nanofibers using natural polymers for enzyme immobilization have been addressed in this review article. A comprehensive survey about the immobilization strategies and their characteristics are highlighted. The natural polymers, e.g., chitin, chitosan, silk fibroin, gelatin, cellulose, and their blends with other synthetic polymers capable of immobilizing enzymes in their 1D nanofibrous form, are discussed. The multiple applications of enzymes immobilized on nanofibers in biocatalysis, biosensors, biofuels, antifouling, regenerative medicine, biomolecule degradation, etc.; some of these are discussed in this review article.

Electrochemical Enzyme Sensor Based on the Two-Dimensional Metal-Organic Layers Supported Horseradish Peroxidase

Metal-organic frames (MOFs) have recently been used to support redox enzymes for highly sensitive and selective chemical sensors for small biomolecules such as oxygen (O₂), hydrogen peroxide (H₂O₂), etc. However, most MOFs are insulative and their three-dimensional (3D) porous structures hinder the electron transfer pathway between the current collector and the redox enzyme molecules. In order to facilitate electron transfer, here we adopt two-dimensional (2D) metal-organic layers (MOLs) to support the HRP molecules in the detection of H₂O₂. The correlation between the current response and the H₂O₂ concentration presents a linear range from 7.5 μM to 1500 μM with a detection limit of 0.87 μM (S/N = 3). The sensitivity, reproducibility, and stability of the enzyme sensor are promoted due to the facilitated electron transfer.

Peroxidase enzymes as green catalysts for bioremediation and biotechnological applications: A review

The fast-growing consumer demand drives industrial process intensification, which subsequently creates a significant amount of waste. These products are discharged into the environment and can affect the quality of air, degrade water streams, and alter soil characteristics. Waste materials may contain polluting agents that are especially harmful to human health and the ecosystem, such as the synthetic dyes, phenolic agents, polycyclic aromatic hydrocarbons, volatile organic compounds, polychlorinated biphenyls, pesticides and drug substances. Peroxidases are a class oxidoreductases capable of performing a wide variety of oxidation reactions, ranging from reactions driven by radical mechanisms, to oxygen insertion into CH bonds, and two-electron substrate oxidation. This versatility in the mode of action presents peroxidases as an interesting alternative in cleaning the environment. Herein, an effort has been made to describe mechanisms governing biochemical process of peroxidase enzymes while referring to H₂O₂/substrate stoichiometry and metabolite products. Plant peroxidases including horseradish peroxidase (HRP), soybean peroxidase (SBP), turnip and bitter gourd peroxidases have revealed notable biocatalytic potentialities in the degradation of toxic products. On the other hand, an introduction on the role played by ligninolytic enzymes such as manganese peroxidase (MnP) and lignin peroxidase (LiP) in the valorization of lignocellulosic materials is addressed. Moreover, sensitivity and selectivity of peroxidase-based biosensors found use in the quantitation of constituents and the development of diagnostic kits. The general merits of peroxidases and some key prospective applications have been outlined as concluding remarks.

A novel biosensor based on multienzyme microcapsules constructed from covalent-organic framework

Electrochemical biosensors based on enzymes modified electrode are attracting special attention due to their broad applications. However, the immobilization of enzymes on electrode is always an important challenge because it's not conducive to conformational expansion of enzymes and affects the bioactivity of enzymes accordingly. Although the imobilization of enzymes in micropores of crystalline covalent-organic framework (COF) and metal-organic framework (MOF) to construct electrochemical biosensors based on pore embedding can achive good reuslts, their micropores can still not guarantee that the enzyme's conformation is well extended. Herein, a multienzyme microcapsules (enzymes@COF) containing glucose oxidase, horseradish peroxidase and acetylcholinesterase with a 600 nm-sized cavity and a shell of COF was used to construct electrochemical biosensors. The 600 nm-sized cavity ensures free conformation expansion of encapsulated enzymes and the shell of COF with good chemical stablity protects encapsulated enzymes against external harsh environments. And the specific catalytic substrates of the enzymes can infiltrated into the microcapsule through the pores of COF shell. So, the biosensor based on enzymes@COF microcapsules demonstrated preeminent performances as compared with those of enzymes assembled on electrode. The detection limits were 0.85 μM, 2.81 nM, 3.0×10^-13 g/L, and the detection range were 2.83 μM-8.0 mM, 9.53 nM-7.0 μM, 10^-12 g/L-10^-8 g/L for glucose, H2O2 and malathion detection. This work shows that it is feasible to fabricate electrochemical sensors using enzymes@COF microcapsules.

p-Co-BDC/AuNPs-based multiple signal amplification for ultra-sensitive electrochemical determination of miRNAs

In this work, we report AuNPs-decorated pyrolyzed Co-BDC nanosheets (p-Co-BDC/AuNPs) as high-performance electrocatalyst for developing an electrochemical platform. p-Co-BDC/AuNPs as a new electrocatalyst showed superior electrocatalytic activity towards the electrochemical oxidation of methylene blue (MB). Besides, magnetic p-Co-BDC/AuNPs can be well immobilized on the magnetic glassy carbon electrode without further assistance. The oxidation of MB can be reduced by ascorbic acid. Inspired by this phenomenon, an electrochemical biosensor was constructed based on multiple signal amplification for the diagnosis of miRNAs. Firstly, p-Co-BDC/AuNPs enhanced the electrochemical oxidation of MB. Then, strand displacement amplification reaction can form lots of double helix structure DNA to embed more MB molecules. Finally, ascorbic acid in the electrolyte was utilized to reduce the oxidation of MB and improve the electrochemical signal of MB electro-oxidation. The linear detection range for the detection of miRNAs is 100 aM to 10 nM, and the limit of detection is 86 aM. Furthermore, the constructed biosensor also displayed satisfactory selectivity, good reproducibility, and excellent recovery in the detection of real samples. We are convinced that our proposed multiple signal amplification strategy will provide more promising methods for the diagnosis of cancer.

Catalase biosensor based on the PAni/cMWCNT support for peroxide sensing

Polymeric-based composites can contribute to enhancing the detection, stability, and performance of enzymatic biosensors, due to their high structural stability, conductivity, and biocompatibility. This work presents the fabrication of a nanocomposite of polyaniline (PAni)/gold nanoparticles (AuNP)/carboxylated multiwalled carbon nanotubes (cMWCNT) as functional support for covalently linked catalase (CAT) enzyme. PAni was electropolymerized on a screen-printed carbon electrode (SPCE) and decorated with AuNP to improve charge transfer properties. CAT was bonded through amide formation using the carboxylic groups of cMWCNT, resulting in PAni/AuNP/cMWCNT/CAT biosensor. The structural and electroactive characteristics of the nanocomposite were studied by SEM, FT-IR, and cyclic voltammetry. The optimal performance was achieved after CAT immobilization over PAni/AuNP/cMWCNT/nanocomposite, showing improved analytical features such as a fast amperometric response of 1.28 s, a wide detection range from 0.01 to 6.8 mM, a correlation coefficient (R 2) of 0.9921, a low detection limit of 2.34 µM, and an average recovery rate of 99.6% when evaluated in milk samples. Additionally, the bioelectrode showed excellent selectivity and retained bioactivity after 30 days of storage. Such remarkable performance proved the synergistic effects of both the high surface area of the cMWCNT and AuNP and the inherent PAni electroactivity, yielding direct electron transfer from CAT.

Hydrogels and Their Role in Biosensing Applications

Hydrogels play an important role in the field of biomedical research and diagnostic medicine. They are emerging as a powerful tool in the context of bioanalytical assays and biosensing. In this context, this review gives an overview of different hydrogels and the role they adopt in a range of applications. Not only are hydrogels beneficial for the immobilization and embedding of biomolecules, but they are also used as responsive material, as wearable devices, or as functional material. In particular, the scientific and technical progress during the last decade is discussed. The newest hydrogel types, their synthesis, and many applications are presented. Advantages and performance improvements are described, along with their limitations.

Direct electrochemistry of covalently immobilized hemoglobin on a naphthylimidazolium butyric acid ionic liquid/MWCNT matrix

Monitoring the concentration levels of hydrogen peroxide (H₂O₂) is significant in both clinical and industrial applications. Herein, we develop a facile biosensor for the detection of H₂O₂ based on direct electron transfer of hemoglobin (Hb), which was covalently immobilized on a hydrophobic naphthylimidazolium butyric acid ionic liquid (NIBA-IL) over a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) to obtain an Hb/NIBA-IL/MWCNT/GCE. Highly water-soluble Hb protein was firmly immobilized on NIBA-IL via stable amide bonding between the free NH₂ groups of Hb and COOH groups of NIBA-IL via EDC/NHS coupling. Thus fabricated biosensor showed a well resolved redox peak with a cathodic peak potential (E_pc) at -0.35 V and anodic peak potential (E_pa) at -0.29 V with a formal potential (E°') of -0.32 V, which corresponds to the deeply buried Fe^III/Fe^II redox centre of Hb, thereby direct electrochemistry of Hb was established. Further, the modified electrode demonstrated very good electrocatalytic activity towards H₂O₂ reduction and showed a wide linear range of detection from 0.01 to 6.3 mM with a limit of detection and sensitivity of 3.2 μM and 111 μA mM^-1 cm^-2, respectively. Moreover, the developed biosensor displayed high operational stability under dynamic conditions as well as during continuous potential cycles and showed reliable reproducibility. The superior performance of the fabricated biosensor is attributed to the effective covalent immobilization of Hb on the newly developed highly conducting and biocompatible NIBA-IL/MWCNT/GCE platform.

Electrochemical H2O2 biosensor based on horseradish peroxidase encapsulated protein nanoparticles with reduced graphene oxide-modified gold electrode

In this study, an electrochemical biosensor composed of a horseradish peroxidase (HRP)-encapsulated protein nanoparticles (HEPNP) was fabricated for the sensitive and selective detection of H₂O₂. The HEPNP has a three-dimensional structure that can contain a large amount of HRP; therefore, HEPNP can amplify the electrochemical signals necessary for the detection of H₂O₂. Furthermore, reduced graphene oxide (rGO) was used to increase the efficiency of electron transfer from the HEPNP to an electrode, which could enhance the electrochemical signal. This biosensor showed a sensitive electrochemical performance for detection of H₂O₂ with signals in the range from 0.01-100 μM, and it could detect low concentrations up to 0.01 μM. Furthermore, this biosensor was operated against interferences from glucose, ascorbic acid, and uric acid. In addition, this fabricated H₂O₂ biosensor showed selective detection performance in human blood serum. Therefore, the proposed biosensor could promote the sensitive and selective detection of H₂O₂ in clinical applications.

A comprehensive review on incredible renewable carriers as promising platforms for enzyme immobilization & thereof strategies

Enzymes are the highly versatile bio-catalysts having the potential for being employed in biotechnological and industrial sectors to catalyze biosynthetic reactions over a commercial point of view. Immobilization of enzymes has improved catalytic properties, retention activities, thermal and storage stabilities as well as reusabilities of enzymes in synthetic environments that have enthralled significant attention over the past few years. Dreadful efforts have been emphasized on the renewable and synthetic supports/composite materials to reserve their inherent characteristics such as biocompatibility, non-toxicity, accessibility of numerous reactive sites for profitable immobilization of biological molecules that often serve diverse applications in the pharmaceutical, environmental, and energy sectors. Supports should be endowed with unique physicochemical properties including high specific surface area, hydrophobicity, hydrophilicity, enantioselectivities, multivalent functionalization which professed them as competent carriers for enzyme immobilization. Organic, inorganic, and nano-based platforms are more potent, stable, highly recovered even after used for continuous catalytic processes, broadly renders the enzymes to get efficiently immobilized to develop an inherent bio-catalytic system that displays higher activities as compared to free-counter parts. This review highlights the recent advances or developments on renewable and synthetic matrices that are utilized for the immobilization of enzymes to deliver emerging applications around the globe.

Gold Nanoparticle-Redox Ionic Liquid based Nanoconjugated Matrix as a Novel Multifunctional Biosensing Interface

Creation of interfaces with a prudent design for the immobilization of biomolecules is substantial in the construction of biosensors for real-time monitoring. Herein, an adept biosensing interface was developed using a nanoconjugated matrix and has been employed toward the electrochemical determination of hydrogen peroxide (H₂O₂). The anionic gold nanoparticle (AuNP) was electrostatically tethered to cationic redox ionic liquid (IL), to which the horseradish peroxidase (HRP) enzyme was covalently immobilized to form a nanobioconjugate. The anthracene-substituted, aldehyde-functionalized redox IL (CHO-AIL) was judiciously designed with the (i) imidazolium cation for electrostatic interaction with AuNPs, (ii) anthracene moiety to mediate the electron transfer, and (iii) free aldehydic group for covalent bonding with a free amine group of the enzyme. Thus, the water-soluble HRP is effectively bonded to the CHO-AIL on a glassy carbon electrode (GCE) via imine bond formation, which resulted in the formation of the HRP-CHO-AIL/GCE. Electrochemical investigations on the HRP-CHO-AIL/GCE reveal highly stable and distinct redox peaks for the anthracene/anthracenium couple at a formal potential (E°') of -0.47 V. Electrostatic tethering of anionic AuNPs to the HRP-CHO-AIL promotes the electron transfer process in the HRP-CHO-AIL/AuNPs/GCE, as observed by the reduction in the formal potential to -0.42 V along with the enhancement in peak currents. The HRP-CHO-AIL/AuNPs/GCE has been explored toward the electrocatalytic detection of H₂O₂, and the modified electrode demonstrated a linear response toward H₂O₂ in the concentration range of 0.02-2.77 mM with a detection limit of 3.7 μM. The developed biosensor ascertained predominant selectivity and sensitivity in addition to remarkable stability and reproducibility, corroborating the suitableness of the platform for the effectual biosensing of H₂O₂. The eminent performance realized with our biosensor setup is ascribed to the multifunctional efficacy of this newly designed nanobioconjugate.

Hydrogen Peroxide Sensors for Biomedical Applications

Hydrogen peroxide (H2O2) is an important molecule within the human body, but many of its roles in physiology and pathophysiology are not well understood. To better understand the importance of H2O2 in biological systems, it is essential that researchers are able to quantify this reactive species in various settings, including in vitro, ex vivo and in vivo systems. This review covers a broad range of H2O2 sensors that have been used in biological systems, highlighting advancements that have taken place since 2015.

Study of horseradish peroxidase and hydrogen peroxide bi-analyte sensor with boronate affinity-based molecularly imprinted film

A novel electrochemical horseradish peroxidase (HRP) sensor was developed based on boronate affinity-based electropolymerized polythionine (PTh) molecularly imprinted polymer (MIP) as specific recognition element for HRP on gold nanoparticles (AuNPs) modified glassy carbon electrode, in which PTh acted as the electrochemical probe for the sensor. The sensor was characterized by scanning electron microscopy and electron dispersive spectroscopy. Electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry were exploited for the study of the properties of the MIP sensor. The MIP sensor exhibited excellent linear response over the range of 2.0 × 10−10 mg/mL ∼ 1.0 × 10−7 mg/mL for HRP. In addition, with MIP film as HRP immobilized matrices, the sensor for the detection of H2O2 was developed with the MIP sensor based on the reduction of H2O2 catalyzed by HRP in the presence of electron mediator PTh. The sensor showed linear relationships between the current response and H2O2 concentration from 6.0 × 10−7 to 2.0 × 10−5 mol/L. HRP and H2O2 bi-analyte sensor based on MIP film was successfully developed in this work. The developed method can also be applicable for enzyme and its enzymatic substrate bi-analyte sensor.

Rationally designed naphthyl substituted amine functionalized ionic liquid platform for covalent immobilization and direct electrochemistry of hemoglobin

Herein, we have designed and demonstrated a facile and effective platform for the covalent anchoring of a tetrameric hemoprotein, hemoglobin (Hb). The platform comprises of naphthyl substituted amine functionalized gel type hydrophobic ionic liquid (NpNH₂-IL) through which the heme protein was covalently attached over a glassy carbon electrode (Hb-NpNH₂-IL/GCE). UV-vis and FT-IR spectral results confirmed that the Hb on NpNH₂-IL retains its native structure, even after being covalently immobilized on NpNH₂-IL platform. The direct electron transfer of redox protein could be realized at Hb-NpNH₂-IL/GCE modified electrode and a well resolved redox peak with a formal potential of −0.30 V and peak separation of 65 mV was observed. This is due to the covalent attachment of highly conducting NpNH₂-IL to the Hb, which facilitates rapid shuttling of electrons between the redox site of protein and the electrode. Further, the fabricated biosensor favoured the electrochemical reduction of bromate in neutral pH with linearity ranging from 12 to 228 µM and 0.228 to 4.42 mM with a detection limit and sensitivities of 3 µM, 430.7 µA mM⁻¹ cm⁻² and 148.4 µA mM⁻¹ cm⁻² respectively. Notably, the fabricated biosensor showed good operational stability under static and dynamic conditions with high selectivity and reproducibility.

Electrospun Chitosan-Gelatin Biopolymer Composite Nanofibers for Horseradish Peroxidase Immobilization in a Hydrogen Peroxide Biosensor

A biosensor based on chitosan-gelatin composite biopolymers nanofibers is found to be effective for the immobilization of horseradish peroxidase to detect hydrogen peroxide. The biopolymer nanofibers were fabricated by an electrospining technique. Upon optimization of synthesis parameters, biopolymers nanofibers, an average of 80 nm in diameter, were obtained and were then modified on the working electrode surface. The effects of the concentration of enzyme, pH, and concentration of the buffer and the working potential on the current response of the nanofibers-modified electrode toward hydrogen peroxide were optimized to obtain the maximal current response. The results found that horseradish peroxidase immobilization on chitosan-gelatin composite biopolymer nanofibers had advantages of fast response, excellent reproducibility, high stability, and showed a linear response to hydrogen peroxide in the concentration range from 0.1 to 1.7 mM with a detection limit of 0.05 mM and exhibited high sensitivity of 44 µA∙mM-1∙cm-2. The developed system was evaluated for analysis of disinfectant samples and showed good agreement between the results obtained by the titration method without significant differences at the 0.05 significance level. The proposed strategy based on chitosan-gelatin composite biopolymer nanofibers for the immobilization of enzymes can be extended for the development of other enzyme-based biosensors.