Biosensors based on novel peroxidases with improved properties in direct and mediated electron transfer

Review of Bacterial Nanocellulose-Based Electrochemical Biosensors: Functionalization, Challenges, and Future Perspectives

Electrochemical biosensing devices are known for their simple operational procedures, low fabrication cost, and suitable real-time detection. Despite these advantages, they have shown some limitations in the immobilization of biochemicals. The development of alternative materials to overcome these drawbacks has attracted significant attention. Nanocellulose-based materials have revealed valuable features due to their capacity for the immobilization of biomolecules, structural flexibility, and biocompatibility. Bacterial nanocellulose (BNC) has gained a promising role as an alternative to antifouling surfaces. To widen its applicability as a biosensing device, BNC may form part of the supports for the immobilization of specific materials. The possibilities of modification methods and in situ and ex situ functionalization enable new BNC properties. With the new insights into nanoscale studies, we expect that many biosensors currently based on plastic, glass, or paper platforms will rely on renewable platforms, especially BNC ones. Moreover, substrates based on BNC seem to have paved the way for the development of sensing platforms with minimally invasive approaches, such as wearable devices, due to their mechanical flexibility and biocompatibility.

Amperometric Biosensors Based on Direct Electron Transfer Enzymes

The accurate determination of analyte concentrations with selective, fast, and robust methods is the key for process control, product analysis, environmental compliance, and medical applications. Enzyme-based biosensors meet these requirements to a high degree and can be operated with simple, cost efficient, and easy to use devices. This review focuses on enzymes capable of direct electron transfer (DET) to electrodes and also the electrode materials which can enable or enhance the DET type bioelectrocatalysis. It presents amperometric biosensors for the quantification of important medical, technical, and environmental analytes and it carves out the requirements for enzymes and electrode materials in DET-based third generation biosensors. This review critically surveys enzymes and biosensors for which DET has been reported. Single- or multi-cofactor enzymes featuring copper centers, hemes, FAD, FMN, or PQQ as prosthetic groups as well as fusion enzymes are presented. Nanomaterials, nanostructured electrodes, chemical surface modifications, and protein immobilization strategies are reviewed for their ability to support direct electrochemistry of enzymes. The combination of both biosensor elements-enzymes and electrodes-is evaluated by comparison of substrate specificity, current density, sensitivity, and the range of detection.

Synthesizing Electrodes Into Electrochemical Sensor Systems

Electrochemical sensors that can determine single/multiple analytes remain a key challenge in miniaturized analytical systems and devices. In this study, we present in situ synthesis and modification of gold nanodendrite electrodes to create an electrochemical system for the analysis of hydrogen peroxide. The sensor system consisted of the reference and counter electrodes as well as the working electrode. Electrochemical reduction of graphene oxide, ErGO, on the thin-film gold and gold nanodendrite working electrodes was used to achieve an efficient sensor interface for the adsorption of a biomimetic electrocatalytic sensor material, Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin complex, with as high as 10^-10 mol cm^-2 surface coverage. The sensor system demonstrated a detection limit of 0.3 µM H₂O₂ in the presence of oxygen. Electrochemical determination of hydrogen peroxide in plant material in the concentration range from 0.09 to 0.4 µmol (gFW)^-1 using the electrochemical sensor system was shown as well as in vivo real-time monitoring of the hydrogen peroxide dynamics as a sign of abiotic stress (intense sunlight). Results of the electrochemical determination were in good agreement with the results of biochemical analysis with the spectrophotometric detection. We anticipate that this method can be extended for the synthesis and integration of multisensor arrays in analytical microsystems and devices for the quantification and real-time in vivo monitoring of other analytes and biomarkers.

Electrochemical Biosensors Employing Natural and Artificial Heme Peroxidases on Semiconductors

Heme peroxidases are widely used as biological recognition elements in electrochemical biosensors for hydrogen peroxide and phenolic compounds. Various nature-derived and fully synthetic heme peroxidase mimics have been designed and their potential for replacing the natural enzymes in biosensors has been investigated. The use of semiconducting materials as transducers can thereby offer new opportunities with respect to catalyst immobilization, reaction stimulation, or read-out. This review focuses on approaches for the construction of electrochemical biosensors employing natural heme peroxidases as well as various mimics immobilized on semiconducting electrode surfaces. It will outline important advances made so far as well as the novel applications resulting thereof.

Recent developments on rapid detection of main constituents in milk: a review

Milk is a good source of quality fats, proteins, carbohydrates, minerals, and vitamins. Determining milk constituents is very important in dairy production and is usually conducted by means of physical or chemical processes in laboratories. These methods are time-consuming and cannot satisfy the need in practice. Developing simple, quick, cost-effective, reliable, and sensitive methods on the detection of main constituents in milk is useful for dairy farmers, manufacturers and consumers. In last decades, many rapid detection techniques such as chromatography, spectroscopy, dielectric properties, and sensors, have emerged and shown great potential in the detection of main constituents in liquid milk. In this review, the rapid detection techniques applied to determine the main constituents in milk have been reviewed. Meanwhile, the potential advantages and limitations of these techniques and recommendations for future research have also been proposed.

Activity adaptability of a DhHP-6 peroxidase-mimic in wide pH and temperature ranges and solvent media

Deuterohemin-β-Ala-His-Thr-Val-Glu-Lys (DhHp-6): peroxidase with high activity.

Camel hydatidosis diagnostic kit: optimization of turnip and horseradish peroxidase conjugates using glutaraldehyde method

Echinococcosis/hydatidosis is one of the most important parasitic zoonotic diseases in the world. Cystic echinococcosis increases public health and socio-economic concern due to considerable morbidity rates that give rise to elevated economic losses both in the public health part and in the farm animal field. The enzyme linked immunosorbent assay (ELISA) is consider the more accurate tool for diagnosis of hydatidosis in camels. In the present study, affinity purified Echinococcus granulosus (E. granulosus) antigens (APA) were purified from crude hydatide E. granulosus germinal layer proteins for detection of E. granulosus antibodies in infected camels, using affinity matrix (camel IgGs coupled to CNBr-activated Sepharose). The electrophoretic profile of the APA showed that it was separated into two bands; one major band of 130 kDa and one minor band at 55 kDa. These antigens were used successfully as specific coating antigenic proteins in detection of echinococcosis in camel. In a trial to prepare an anti-camel IgGs peroxidase conjugate; peroxidase enzyme was purified from turnip roots (TPOD) using ammonium sulfate precipitation and affinity chromatography on phenyl Sepharose CL-4B. The purified TPOD showed a major band at 35 kDa. Rabbit anti-camel IgG antibodies (AC IgGs) were prepared then purified using affinity chromatography on Protein G-Sepharose. The TPOD, and commercial HRP for comparison, enzymes were conjugated to AC IgGs using 1%, 5% and 10% glutaraldehyde. The results revealed that the HRP was much better than TPOD in conjugation with AC-IgG antibodies and the 10% glutaraldehyde concentration was the most efficient concentration with ELISA titer 1:50.

Ficus sycomorus latex: An efficient alternative Egyptian source for horseradish peroxidase in labeling with antibodies for immunodiagnostic kits

Aim:

In view of various peroxidase applications, the searching for new sources of unique peroxidase properties is highly desirable. The present study aims to evaluate the efficiency of the peroxidase of locally grown sycamore latex (POL) for conjugation with antibodies and to study the conjugate optimal conditions, storage stability, and affinity toward different substrates as compared with commercial horseradish peroxidase (HRP).

Materials and Methods:

Anti-mouse antibodies were prepared in rabbits and purified by protein A sepharose affinity column chromatography. The POL and HRP conjugates were prepared by one-step glutaraldehyde coupling method. The reactivity of the prepared conjugates was examined using the enzyme-linked immunosorbent assay (ELISA). The optimal enzymatic conditions, storage stability, and affinity toward substrates were also determined for both the conjugates.

Results:

The POL showed higher percent recovery (98%) than HRP (78%) over the initial activity after conjugation process. The POL and HRP conjugates showed ELISA titers of 1:120 and 1:80, respectively, demonstrating high binding affinity of POL-conjugate. The POL-conjugate showed high thermal stability up to 70°C compared with HRP-conjugate up to 40°C. After conjugation, POL had wide pH stability (5.0-8.0) compared with HPR (4.5-6.0). Both of the prepared conjugates had a high affinity toward the substrates used in immunoassays with lower K_m values. The POL-conjugate showed high storage stability for its enzymatic activity and ELISA titer compared with HRP-conjugate after 1 year at −20°C.

Conclusion:

The POL of Ficus sycomorus latex is an efficient source for labeling antibodies and could be utilized in immunodiagnostic kits.

Interprotein Coupling Enhances the Electrocatalytic Efficiency of Tobacco Peroxidase Immobilized at a Graphite Electrode

Covalent immobilization of enzymes at electrodes via amide bond formation is usually carried out by a two-step protocol, in which surface carboxylic groups are first activated with the corresponding cross-coupling reagents and then reacted with protein amine groups. Herein, it is shown that a modification of the above protocol, involving the simultaneous incubation of tobacco peroxidase and the pyrolytic graphite electrode with the cross-coupling reagents produces higher and more stable electrocatalytic currents than those obtained with either physically adsorbed enzymes or covalently immobilized enzymes according to the usual immobilization protocol. The remarkably improved electrocatalytic properties of the present peroxidase biosensor that operates in the 0.3 V ≤ E ≤ 0.8 V (vs SHE) potential range can be attributed to both an efficient electronic coupling between tobacco peroxidase and graphite and to the formation of intra- and intermolecular amide bonds that stabilize the protein structure and improve the percentage of anchoring groups that provide an adequate orientation for electron exchange with the electrode. The optimized tobacco peroxidase sensor exhibits a working concentration range of 10-900 μM, a sensitivity of 0.08 A M(-1) cm(-2) (RSD 0.05), a detection limit of 2 μM (RSD 0.09), and a good long-term stability, as long as it operates at low temperature. These parameter values are among the best reported so far for a peroxidase biosensor operating under simple direct electron transfer conditions.

Site-directed mutagenesis of tobacco anionic peroxidase: Effect of additional aromatic amino acids on stability and activity

Tobacco anionic peroxidase (TOP) is known to effectively catalyze luminol oxidation without enhancers, in contrast to horseradish peroxidase (HRP). To pursue structure-activity relationship studies for TOP, two amino acids have been chosen for mutation, namely Thr151, close to the heme plane, and Phe140 at the entrance to the active site pocket. Three mutant forms TOP F140Y, T151W and F140Y/T151W have been expressed in Escherichia coli, and reactivated to yield active enzymes. Single-point mutations introducing additional aromatic amino acid residues at the surface of TOP exhibit a significant effect on the enzyme catalytic activity and stability as judged by the results of steady-state and transient kinetics studies. TOP T151W is up to 4-fold more active towards a number of aromatic substrates including luminol, whereas TOP F140Y is 2-fold more stable against thermal inactivation and 8-fold more stable in the reaction course. These steady-state observations have been rationalized with the help of transient kinetic studies on the enzyme reaction with hydrogen peroxide in a single turnover regime. The stopped-flow data reveal (a) an increased stability of F140Y Compound I towards hydrogen peroxide, and thus, a higher operational stability as compared to the wild-type enzyme, and (b) a lesser leakage of oxidative equivalents from TOP T151W Compound I resulting in the increased catalytic activity. The results obtained show that TOP unique properties can be further improved for practical applications by site-directed mutagenesis.

Simple approach for the immobilization of horseradish peroxidase on poly-l-histidine modified reduced graphene oxide for amperometric determination of dopamine and H2O2

In this work, immobilization of horseradish peroxidase (HRP) on poly-l-histidine (P-l-His) modified reduced graphene oxide (RGO) was demonstrated.

Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO3-). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H2O2. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO3- film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H2O2 with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO3-/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM-1 cm-2), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.

Prospects of Organic Conducting Polymer Modified Electrodes: Enzymosensors

Organic conducting polymer modified electrodes (OCPMEs) have emerged as potential candidates for electrochemical biosensors due to their easy preparation methods along with unique properties, like stability in air and being compatible with biological molecules in a neutral aqueous solution. OCPMEs are playing an important role in the improvement of public health and environment for the detection of desired analytes with high sensitivity and specificity. In this paper, we highlight the prospects of OCMEs-based electrochemical enzymosensors.

Electrochemical biosensors for on-chip detection of oxidative stress from immune cells

Seamless integration of biological components with electrochemical sensors is critical in the development of microdevices for cell analysis. The present paper describes the integration miniature Au electrodes next to immune cells (macrophages) in order to detect cell-secreted hydrogen peroxide (H(2)O(2)). Photopatterning of poly(ethylene glycol) (PEG) hydrogels was used to both immobilize horseradish peroxidase molecules onto electrodes and to define regions for cell attachment in the vicinity of sensing electrodes. Electrodes micropatterned in such a manner were enclosed inside poly(dimethylsiloxane) fluid conduits and incubated with macrophages. The cells attached onto the exposed glass regions in the vicinity of the electrodes and nowhere else on the non-fouling PEG hydrogel surface. A microfluidic device was converted into an electrochemical cell by placing flow-through Ag∕AgCl reference and Pt wire counter electrodes at the outlet and inlet, respectively. This microdevice with integrated H(2)O(2)-sensing electrodes had sensitivity of 27 μA∕cm(2) mM with a limit of detection of 2 μM. Importantly, this microdevice allowed controllable seeding of macrophages next to electrodes, activation of these cells and on-chip monitoring of H(2)O(2) release in real time. In the future, this biosensor platform may be utilized for monitoring of macrophage responses to pathogens or for the study of inflammatory signaling in micropatterned cell cultures.

Enzyme integrated silicate-Pt nanoparticle architecture: a versatile biosensing platform

A novel 3-D nanoarchitectured platform based on Pt nanoparticles (nPts) is developed for the sensing of sub-nanomolar levels of hydrogen peroxide and for the fabrication of amperometric biosensor for uric acid, cholesterol and glucose. The nPts have been immobilized on the thiol functional group containing sol-gel silicate 3-D network derived from 3-mercaptopropyltrimethoxysilane (MPTS). The nanoparticles on the 3-D architecture have size distribution between 7 and 10nm. The nPts on the platform efficiently catalyze the oxidation of H(2)O(2) at the potential of +0.45 V in the absence of enzymes and redox mediators. This nanoarchitectured platform is highly sensitive and can detect H(2)O(2) at sub-nanomolar levels (0.1 nM) in neutral solution. The nanoarchitectured platform does not suffer from interference due to other common easily oxidizable interfering agents. Excellent reproducibility, long-term storage and operational stability are observed. This platform is used to determine H(2)O(2) concentration in rainwater and for the fabrication of biosensors. Amperometric oxidase-based biosensing platforms are developed by integrating the enzymes and nPts with the silicate network for the sensing of uric acid cholesterol and glucose. The enzyme encapsulated 3-D architecture retains the enzymatic activity and efficiently detects enzymatically generated H(2)O(2) without any interference. These biosensors are stable and show excellent sensitivity and fast response time. A linear response was obtained for a wide concentration range of all analytes. The practical utilization of the biosensor for the measurement of uric acid, cholesterol and glucose in serum sample is demonstrated. The biological sample analysis was validated with clinical laboratory measurements.

Thermal stability of peroxidase from Chamaerops excelsa palm tree at pH 3

The structural stability of a peroxidase, a dimeric protein from palm tree Chamaerops excelsa leaves (CEP), has been characterized by high-sensitivity differential scanning calorimetry, circular dichroism and steady-state tryptophan fluorescence at pH 3. The thermally induced denaturation of CEP at this pH value is irreversible and strongly dependent upon the scan rate, suggesting that this process is under kinetic control. Moreover, thermally induced transitions at this pH value are dependent on the protein concentration, leading to the conclusion that in solution CEP behaves as dimer, which undergoes thermal denaturation coupled with dissociation. Analysis of the kinetic parameters of CEP denaturation at pH 3 was accomplished on the basis of the simple kinetic scheme N-->kD, where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N is the native state, and D is the denatured state, and thermodynamic information was obtained by extrapolation of the kinetic transition parameters to an infinite heating rate.