A mediator-free phenol biosensor based on immobilizing tyrosinase to ZnO nanoparticles

Recent Advances in Applications of Oxidases and Peroxidases Polymer-Based Enzyme Biocatalysts in Sensing and Wastewater Treatment: A Review

Oxidase and peroxidase enzymes have attracted attention in various biotechnological industries due to their ease of synthesis, wide range of applications, and operation under mild conditions. Their applicability, however, is limited by their poor stability in harsher conditions and their non-reusability. As a result, several approaches such as enzyme engineering, medium engineering, and enzyme immobilization have been used to improve the enzyme properties. Several materials have been used as supports for these enzymes to increase their stability and reusability. This review focusses on the immobilization of oxidase and peroxidase enzymes on metal and metal oxide nanoparticle-polymer composite supports and the different methods used to achieve the immobilization. The application of the enzyme-metal/metal oxide-polymer biocatalysts in biosensing of hydrogen peroxide, glucose, pesticides, and herbicides as well as blood components such as cholesterol, urea, dopamine, and xanthine have been extensively reviewed. The application of the biocatalysts in wastewater treatment through degradation of dyes, pesticides, and other organic compounds has also been discussed.

Tyrosinase Immobilization Strategies for the Development of Electrochemical Biosensors-A Review

The development of enzyme biosensors has successfully overcome various challenges such as enzyme instability, loss of enzyme activity or long response time. In the electroanalytical field, tyrosinase is used to develop biosensors that exploit its ability to catalyze the oxidation of numerous types of phenolic compounds with antioxidant and neurotransmitter roles. This review critically examines the main tyrosinase immobilization techniques for the development of sensitive electrochemical biosensors. Immobilization strategies are mainly classified according to the degree of reversibility/irreversibility of enzyme binding to the support material. Each tyrosinase immobilization method has advantages and limitations, and its selection depends mainly on the type of support electrode, electrode-modifying nanomaterials, cross-linking agent or surfactants used. Tyrosinase immobilization by cross-linking is characterized by very frequent use with outstanding performance of the developed biosensors. Additionally, research in recent years has focused on new immobilization strategies involving cross-linking, such as cross-linked enzyme aggregates (CLEAs) and magnetic cross-linked enzyme aggregates (mCLEAs). Therefore, it can be considered that cross-linking immobilization is the most feasible and economical approach, also providing the possibility of selecting the reagents used and the order of the immobilization steps, which favor the enhancement of biosensor performance characteristics.

Cost-Effective Fiber Optic Solutions for Biosensing

In the last years, optical fiber sensors have proven to be a reliable and versatile biosensing tool. Optical fiber biosensors (OFBs) are analytical devices that use optical fibers as transducers, with the advantages of being easily coated and biofunctionalized, allowing the monitorization of all functionalization and detection in real-time, as well as being small in size and geometrically flexible, thus allowing device miniaturization and portability for point-of-care (POC) testing. Knowing the potential of such biosensing tools, this paper reviews the reported OFBs which are, at the moment, the most cost-effective. Different fiber configurations are highlighted, namely, end-face reflected, unclad, D- and U-shaped, tips, ball resonators, tapered, light-diffusing, and specialty fibers. Packaging techniques to enhance OFBs' application in the medical field, namely for implementing in subcutaneous, percutaneous, and endoscopic operations as well as in wearable structures, are presented and discussed. Interrogation approaches of OFBs using smartphones' hardware are a great way to obtain cost-effective sensing approaches. In this review paper, different architectures of such interrogation methods and their respective applications are presented. Finally, the application of OFBs in monitoring three crucial fields of human life and wellbeing are reported: detection of cancer biomarkers, detection of cardiovascular biomarkers, and environmental monitoring.

Harnessing the Potential of Biological Recognition Elements for Water Pollution Monitoring

Environmental monitoring of pollutants is an imperative first step to remove the genotoxic, embryotoxic, and carcinogenic toxins. Various biological sensing elements such as proteins, aptamers, whole cells, etc., have been used to track down major pollutants, including heavy metals, aromatic pollutants, pathogenic microorganisms, and pesticides in both environmental samples and drinking water, demonstrating their potential in a true sense. The intermixed use of nanomaterials, electronics, and microfluidic systems has further improved the design and enabled robust on-site detection with enhanced sensitivity. Through this perspective, we shed light on the advances in the field and entail recent efforts to optimize these systems for real-time, online sensing and on-site field monitoring.

Water Pollutants p-Cresol Detection Based on Au-ZnO Nanoparticles Modified Tapered Optical Fiber

In this work, a localized plasmon-based sensor is developed for para-cresol (p-cresol) - a water pollutant detection. A nonadiabatic [Formula: see text] of tapered optical fiber (TOF) has been experimentally fabricated and computationally analyzed using beam propagation method. For optimization of sensor's performance, two probes are proposed, where probe 1 is immobilized with gold nanoparticles (AuNPs) and probe 2 is immobilized with the AuNPs along with zinc oxide nanoparticles (ZnO-NPs). The synthesized metal nanomaterials were characterized by ultraviolet-visible spectrophotometer (UV-vis spectrophotometer) and transmission electron microscope (HR-TEM). The nanomaterials coating on the surface of the sensing probe were characterized by a scanning electron microscope (SEM). Thereafter, to increase the specificity of the sensor, the probes are functionalized with tyrosinase enzyme. Different solutions of p-cresol in the concentration range of [Formula: see text] - [Formula: see text] are prepared in an artificial urine solution for sensing purposes. Different analytes such as uric acid, β -cyclodextrin, L-alanine, and glycine are prepared for selectivity measurement. The linearity range, sensitivity, and limit of detection (LOD) of probe 1 are [Formula: see text] - [Formula: see text], 7.2 nm/mM (accuracy 0.977), and [Formula: see text], respectively; and for probe 2 are [Formula: see text] - [Formula: see text], 5.6 nm/mM (accuracy 0.981), and [Formula: see text], respectively. Thus, the overall performance of probe 2 is quite better due to the inclusion of ZnO-NPs that increase the biocompatibility of sensor probe. The proposed sensor structure has potential applications in the food industry and clinical medicine.

Analytical performance of functional nanostructured biointerfaces for sensing phenolic compounds

Electrochemical biointerfaces are constructed with a wide range of nanomaterials and conducting polymers that strongly affect the analytical performance of biosensors. The analysis of progress toward electrochemical sensing platforms offers opportunities to provide devices for commercial use. The investigation of different methods for the synthesis of phenol biointerfaces leads to design challenges in the field of monitoring phenolic compounds. This paper review the innovative strategies and feature techniques in the construction of phenolic compound biosensors. The focus was made on the preparation methods of nanostructures and nanomaterials design for catalytic improvements of sensing interfaces. The paper also provides a comprehensive overview in the field of enzyme immobilization approaches at solid supports and technical formation of polymer nanocomposites, as well as applications of hybrid organic-inorganic nanocomposites in phenolic biosensors. This review also highlights the recent progress in the electrochemical detection of phenolic compounds and summarizes analytical performance parameters including sensitivity, storage stability, limit of detection, linear range, and Michaelis-Menten kinetic analysis. It also emphasizes advances from the past decade including technical challenges for the construction of suitable biointerfaces for monitoring phenolic compounds.

Promotion effect of Zn on 2D bimetallic NiZn metal organic framework nanosheets for tyrosinase immobilization and ultrasensitive detection of phenol

Environmental monitoring of pollutants is essential to guarantee the human health and maintain the ecosystem. The exploration of both simple and sensitive detection method has aroused widespread attentions. Herein, 2D bimetallic metal organic framework nanosheets (NiZn-MOF NSs) with tunable Ni/Zn ratios were synthesized, and for the first time employed to construct a tyrosinase biosensor. It is revealed that Zn element not only tuned the porosity structure and electronic structure of MOF NSs, but also modified their electrochemical activity. As a result, enzyme immobilization and electrochemical sensing performance of the NiZn-MOF NSs based biosensor were significantly enhanced by a suitable Zn addition. The fabricated tyrosinase biosensor exhibited excellent analytical detections, with a wide linear range from 0.08 μM to 58.2 μM, a high sensitivity of 159.3 mA M^-1, and an ultralow detection limit of 6.5 nM. In addition, the proposed biosensing approach also demonstrated good repeatability, superior selectivity, long-term stability, and high recovery for phenol detection in the real tap water samples.

In-situ dual-channel surface plasmon resonance fiber sensor for temperature-compensated detection of glucose concentration

External temperature variations inevitably affect the accuracy of surface plasmon resonance (SPR) biosensors. To that end, we propose an ultra-compact label-free dual-channel SPR fiber sensor (DSPRFS) that can simultaneously measure the glucose concentration and ambient temperature in real-time. The proposed sensor is based on a unique dual-channel structure fabricated by etching a side-hole fiber (SHF), and has significantly higher spatial sensitivity than traditional SPR biosensors. After coating with silver and zinc oxide films, one channel was filled with polydimethylsiloxane (PDMS) to sense the ambient temperature, and the other channel was immobilized with glucose oxidase (GOx) enzyme for glucose sensing. The proposed sensor is analyzed theoretically, fabricated and characterized. Glucose concentration sensitivity and temperature sensitivity of the manufactured sensor sample were found to be as high as 6.156 nm/mMand -1.604 nm/°C with limits of detection (LOD) of 16.24 µM and 0.06 °C, respectively. The proposed sensor has an extremely compact structure, enables temperature compensation, and is suitable for in-situ monitoring and high-precision sensing of glucose and other biological analytes.

Reed Membrane as a Novel Immobilization Matrix for the Development of an Optical Phenol Biosensor

Background:

Biocompatible and easily available immobilization matrix is vital for the construction of enzyme-based biosensor.

Methods:

Reed membrane was selected as a novel immobilization matrix to construct an optical phenol biosensor. Tyrosinase from mushroom was immobilized in a reed membrane using glutaraldehyde as a cross-linker. The detection scheme was based on the measurement of the color intensity of the adduct resulting from the reaction of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with the quinone produced from the oxidation of phenol by tyrosinase. The performance of such method including specificity, sensitivity, repeatability and practical use were validated.

Results:

The prepared biosensor demonstrated optimum performance at pH 6-7, temperature of 40°C and a linear response in the phenol concentration range of 5-100 μM. It also showed good operation stability for repeated measurements (over 200 times) and good storage stability after it had been kept at 4°C for 2 months.

Conclusion:

Reed membrane is a novel matrix for immobilization of enzyme. The prepared biosensor permits good sensitivity, reproducibility and stability. It is anticipated that reed membrane is a promising solid support for fabricating other enzyme-based biosensors.

Nanomaterial-Supported Enzymes for Water Purification and Monitoring in Point-of-Use Water Supply Systems

Increasing pollution of global water sources and challenges in rapid detection and treatment of the wide range of contaminants pose considerable burdens on public health. The issue is particularly critical in rural areas, where building of centralized water treatment systems and pipe infrastructure to connect dispersed populations is not always practical. Point-of-use (POU) water supply systems provide cost-effective and energy-efficient approaches to store, treat, and monitor the quality of water. Currently available POU systems have limited success in dealing with the portfolio of emerging contaminants, particularly those present at trace concentrations. A site-to-site variation in contaminant species and concentrations also requires versatile POU systems to detect and treat contaminants and provide on-demand clean water. Among different technologies for developing rapid and sensitive water purification processes and sensors, enzymes offer one of the potential solutions because of their strong activity and selectivity toward chemical substrates. Many enzyme-nanomaterial composites have recently been developed that enhance enzymes' stability and activity and expand their functionality, thus facilitating the application of nanosupported enzymes in advanced POU systems. In this Account, we highlight the strengths and limitations of nanosupported enzymes for their potential applications in POU systems for water treatment as well as detection of contaminants, even at trace levels. We first summarize the mechanisms by which silica, carbon, and metallic nanosupports improve enzyme stability, selectivity, and catalysis. The unique immobilization properties and potential advantages of novel bioderived nanosupports over non-bioderived nanomaterials are emphasized. We illustrate prospective applications of nanosupported enzymes in POU systems with different roles: water purification, disinfection, and contaminant sensing. For each type of application, nanosupported enzymes offer higher performance than free enzymes. Nanosupports prolong enzymes' lifetimes and improve the rates of contaminant removal by concentrating contaminants near the enzymes. Nanosupports also stabilize antimicrobial enzymes while facilitating their attachment to bacterial surfaces, thereby increasing their potential uses for disinfection and prevention of biofouling in water purification and storage devices. As enzyme-based electrochemical sensors rely on electrochemical reactions of enzymatically generated species, the ability of conductive nanosupports to enhance enzyme activity and stability and to promote transfer of electrons onto the electrode greatly improves the sensitivity and durability of electroenzymatic contaminant sensors. Despite the promising results in laboratory settings, the application of nanosupported enzymes in real-world POU systems requires the implementation of multiple enzyme combinations and strategies for minimizing health risks associated with unintended releases of nanomaterials. Finally, we identify multidisciplinary research gaps in the development of nanosupported enzyme treatment systems and provide frameworks for the early adopters to make informed decisions on whether and how to use such POU systems.

Biofunctionalized "Kiwifruit-Assembly" of Oxidoreductases in Mesoporous ZnO/Carbon Nanoparticles for Efficient Asymmetric Catalysis

A mesoporous ZnO/carbon composite is designed for coimmobilization of two oxidoreductases involving a novel "kiwifruit-assembly" pattern. The coimmobilization of (S)-carbonyl reductase II-glucose dehydrogenase on nanoparticles (SCRII-GDH_nano ) exhibits 40-50% higher specific activity than the free enzyme and significantly improves stabilities of enzymes to heat, pH and solvents. It performs asymmetric catalysis of 75 × 10^-3 m substrate with a perfect yield of 100% and an excellent enantioselectivity of 99.9% within 1 h. SCRII-GDH_nano gives an over 72% yield and 99.9% enantioselectivity after it is reused for ten times. Even with a highly concentrated (400 × 10^-3 m) substrate, it shows about 60% yield and 99.9% enantioselectivity within 4 h. SCRII-GDH_nano presents 4.5-8.0-fold higher productivity in 2.0-8.0-fold shorter reaction time than the free enzyme. This work provides a general, facile, and unique approach for the immobilization of two oxidoreductases and gives high catalytic efficiency, long-term and good recycling stabilities by triggering radical proton-coupled electron transfer.

Aspergillus niger PA2 Tyrosinase Covalently Immobilized on a Novel Eco-Friendly Bio-Composite of Chitosan-Gelatin and Its Evaluation for L-DOPA Production

Tyrosinase (EC 1.14.18.1) a copper-containing monooxygenase, isolated from a fungal isolate Aspergillus niger PA2 was subjected for immobilization onto a composite consisting of chitosan and gelatin biopolymers. The homogeneity of the chitosan-gelatin biocomposite film was characterized by X-ray diffraction analyses. To evaluate immobilization efficiency, chitosan-gelatin-Tyr bio-composite films were analyzed by field emission scanning electron microscopy, atomic force microscopy and UV-spectroscopy. The rough morphology of the film led to a high loading of enzyme and it could retain its bioactivity for a longer period. The enzyme adsorbed onto the film exhibited 72% of its activity after 10 days and exhibited good repeatability for up to nine times, after intermittent storage. Moreover, the immobilized enzyme exhibited broader pH and temperature profile as compared to free counterpart. Immobilized enzyme was further evaluated for the synthesis of L-DOPA (2,4-dihydroxy phenylalanine) which is a precursor of dopamine and a potent drug for the treatment of Parkinson's disease and for myocardium neurogenic injury.

Amperometric Biosensor Based on Zirconium Oxide/Polyethylene Glycol/Tyrosinase Composite Film for the Detection of Phenolic Compounds

A phenolic biosensor based on a zirconium oxide/polyethylene glycol/tyrosinase composite film for the detection of phenolic compounds has been explored. The formation of the composite film was expected via electrostatic interaction between hexacetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), and zirconium oxide nanoparticles casted on screen printed carbon electrode (SPCE). Herein, the electrode was treated by casting hexacetyltrimethylammonium bromide on SPCE to promote a positively charged surface. Later, zirconium oxide was mixed with polyethylene glycol and the mixture was dropped cast onto the positively charged SPCE/CTAB. Tyrosinase was further immobilized onto the modified SPCE. Characterization of the prepared nanocomposite film and the modified SPCE surface was investigated by scanning electron microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Cyclic voltamogram (CV). The developed biosensor exhibits rapid response for less than 10 s. Two linear calibration curves towards phenol in the concentrations ranges of 0.075–10 µM and 10–55 µM with the detection limit of 0.034 µM were obtained. The biosensor shows high sensitivity and good storage stability for at least 30 days.

Portable Enzyme-Paper Biosensors Based on Redox-Active CeO2 Nanoparticles

Portable, nanoparticle (NP)-enhanced enzyme sensors have emerged as powerful devices for qualitative and quantitative analysis of a variety of analytes for biomedicine, environmental applications, and pharmaceutical fields. This chapter describes a method for the fabrication of a portable, paper-based, inexpensive, robust enzyme biosensor for the detection of substrates of oxidase enzymes. The method utilizes redox-active NPs of cerium oxide (CeO2) as a sensing platform which produces color in response to H2O2 generated by the action of oxidase enzymes on their corresponding substrates. This avoids the use of peroxidases which are routinely used in conjunction with glucose oxidase. The CeO2 particles serve dual roles, as high surface area supports to anchor high loadings of the enzyme as well as a color generation reagent, and the particles are recycled multiple times for the reuse of the biosensor. These sensors are small, light, disposable, inexpensive, and they can be mass produced by standard, low-cost printing methods. All reagents needed for the analysis are embedded within the paper matrix, and sensors stored over extended periods of time without performance loss. This novel sensor is a general platform for the in-field detection of analytes that are substrates for oxidase enzymes in clinical, food, and environmental samples.

Zinc oxide thin film based nonenzymatic electrochemical sensor for the detection of trace level catechol

In the present work, a novel zinc oxide thin film based nonenzymatic, electrochemical sensor is developed for the detection of catechol.

A novel bioassay based gold nanoribbon biosensor to aid the preclinical evaluation of anticancer properties

In this manuscript we have attempted to develop a novel biosensor based on Au nanoribbons (AuNRs). Initially, Quercetin stabilized AuNPs were prepared and dityrosine peptides was used as a structure directing agent for the synthesis of AuNRs.

An Electrochemical Glucose Sensor Based on Zinc Oxide Nanorods

A glucose electrochemical sensor based on zinc oxide (ZnO) nanorods was investigated. The hydrothermal sol–gel growth method was utilized to grow ZnO nanorods on indium tin oxide-coated glass substrates. The total active area of the working electrode was 0.3 × 0.3 cm² where titanium metal was deposited to enhance the contact. Well aligned hexagonal structured ZnO nanorods with a diameter from 68 to 116 nm were obtained. The excitonic peak obtained from the absorbance spectroscopy was observed at ~370 nm. The dominant peak of Raman spectroscopy measurement was at 440 cm⁻¹, matching with the lattice vibration of ZnO. The uniform distribution of the GO_x and Nafion membrane that has been done using spin coating technique at 4000 rotations per minute helps in enhancing the ion exchange and increasing the sensitivity of the fabricated electrochemical sensor. The amperometric response of the fabricated electrochemical sensor was 3 s. The obtained sensitivity of the fabricated ZnO electrochemical sensor was 10.911 mA/mM·cm² and the lower limit of detection was 0.22 µM.

Novel ferrocene-anchored ZnO nanoparticle/carbon nanotube assembly for glucose oxidase wiring: application to a glucose/air fuel cell

Glucose oxidase (GOx) is immobilized on ZnO nanoparticle-modified electrodes. The immobilized glucose oxidase shows efficient mediated electron transfer with ZnO nanoparticles to which the ferrocenyl moiety is π-stacked into a supramolecular architecture. The constructed ZnO-Fc/CNT modified electrode exhibits high ferrocene surface coverage, preventing any leakage of the π-stacked ferrocene from the newly described ZnO hybrid nanoparticles. The use of the new architecture of ZnO supported electron mediators to shuttle electrons from the redox centre of the enzyme to the surface of the working electrode can effectively bring about successful glucose oxidation. These modified electrodes evaluated as a highly efficient architecture provide a catalytic current for glucose oxidation and are integrated in a specially designed glucose/air fuel cell prototype using a conventional platinum-carbon (Pt/C) cathode at physiological pH (7.0). The obtained architecture leads to a peak power density of 53 μW cm(-2) at 300 mV for the Nafion® based biofuel cell under "air breathing" conditions at room temperature.

Environmental applications of chitosan and its derivatives

Chitosan originates from the seafood processing industry and is one of the most abundant of bio-waste materials. Chitosan is a by-product of the alkaline deacetylation process of chitin. Chemically, chitosan is a polysaccharide that is soluble in acidic solution and precipitates at higher pHs. It has great potential for certain environmental applications, such as remediation of organic and inorganic contaminants, including toxic metals and dyes in soil, sediment and water, and development of contaminant sensors. Traditionally, seafood waste has been the primary source of chitin. More recently, alternative sources have emerged such as fungal mycelium, mushroom and krill wastes, and these new sources of chitin and chitosan may overcome seasonal supply limitations that have existed. The production of chitosan from the above-mentioned waste streams not only reduces waste volume, but alleviates pressure on landfills to which the waste would otherwise go. Chitosan production involves four major steps, viz., deproteination, demineralization, bleaching and deacetylation. These four processes require excessive usage of strong alkali at different stages, and drives chitosan's production cost up, potentially making the application of high-grade chitosan for commercial remediation untenable. Alternate chitosan processing techniques, such as microbial or enzymatic processes, may become more cost-effective due to lower energy consumption and waste generation. Chitosan has proved to be versatile for so many environmental applications, because it possesses certain key functional groups, including - OH and -NH2 . However, the efficacy of chitosan is diminished at low pH because of its increased solubility and instability. These deficiencies can be overcome by modifying chitosan's structure via crosslinking. Such modification not only enhances the structural stability of chitosan under low pH conditions, but also improves its physicochemical characteristics, such as porosity, hydraulic conductivity, permeability, surface area and sorption capacity. Crosslinked chitosan is an excellent sorbent for trace metals especially because of the high flexibility of its structural stability. Sorption of trace metals by chitosan is selective and independent of the size and hardness of metal ions, or the physical form of chitosan (e.g., film, powder and solution). Both -OH and -NH2 groups in chitosan provide vital binding sites for complexing metal cations. At low pH, -NH3 + groups attract and coagulate negatively charged contaminants such as metal oxyanions, humic acids and dye molecules. Grafting certain functional molecules into the chitin structure improves sorption capacity and selectivity for remediating specific metal ions. For example, introducing sulfur and nitrogen donor ligands to chitosan alters the sorption preference for metals. Low molecular weight chitosan derivatives have been used to remediate metal contaminated soil and sediments. They have also been applied in permeable reactive barriers to remediate metals in soil and groundwater. Both chitosan and modified chitosan have been used to phytoremediate metals; however, the mechanisms by which they assist in mobilizing metals are not yet well understood. In addition, microbes have been used in combination with chitosan to remediate metals (e.g., Cu and Zn) in contaminated soils. Chitosan has also been used to remediate organic contaminants, such as oil-based wastewater, dyes, tannins, humic acids, phenols, bisphenoi-A, p-benzoquinone, organo-phosphorus insecticides, among others. Chitosan has also been utilized to develop optical and electrochemical sensors for in-situ detection of trace contaminants. In sensor technology, naturally-derived chitosan is used primarily as an immobilizing agent that results from its enzyme compatibility, and stabilizing effect on nanoparticles. Contaminant-sensing agents, such as enzymes, microbes and nanoparticles, have been homogeneously immobilized in chitosan gels by using coagulating (e.g., alginate, phosphate) or crosslinking agents (e.g., GA, ECH). Such immobilization maintains the stability of sensing elements in the chitosan gel phase, and prevents inactivation and loss of the sensing agent. In this review, we have shown that chitosan, an efficient by-product of a waste biomaterial, has great potential for many environmental applications. With certain limitations, chitosan and its derivatives can be used for remediating contaminated soil and wastewater. Notwithstanding, further research is needed to enhance the physicochemical properties of chitosan and mitigate its deficiencies.

Immobilization as a strategy for improving enzyme properties-application to oxidoreductases

The main objective of the immobilization of enzymes is to enhance the economics of biocatalytic processes. Immobilization allows one to re-use the enzyme for an extended period of time and enables easier separation of the catalyst from the product. Additionally, immobilization improves many properties of enzymes such as performance in organic solvents, pH tolerance, heat stability or the functional stability. Increasing the structural rigidity of the protein and stabilization of multimeric enzymes which prevents dissociation-related inactivation. In the last decade, several papers about immobilization methods have been published. In our work, we present a relation between the influence of immobilization on the improvement of the properties of selected oxidoreductases and their commercial value. We also present our view on the role that different immobilization methods play in the reduction of enzyme inhibition during biotechnological processes.

Zinc oxide nanoparticles based microfluidic immunosensor applied in congenital hypothyroidism screening

In this article, we present an innovative approach for congenital hypothyroidism (CHT) screening. This pathology is the most common preventable cause of mental retardation, affecting newborns around the world. Its consequences could be avoided with an early diagnosis through the thyrotropin (TSH) level measurement. To accomplish the determination of TSH, synthesized zinc oxide (ZnO) nanobeads (NBs) covered by chitosan (CH), ZnO-CH NBs, were covalently attached to the central channel of the designed microfluidic device. These beads were employed as platform for anti-TSH monoclonal antibody immobilization to specifically recognize and capture TSH in neonatal samples without any special pretreatment. Afterwards, the amount of this trapped hormone was quantified by horseradish peroxidase (HRP)-conjugated anti-TSH antibody. HRP reacted with its enzymatic substrate in a redox process, which resulted in the appearance of a current whose magnitude was directly proportional to the level of TSH in the neonatal sample. The structure and morphology of synthesized ZnO-CH NBs were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The calculated detection limits for electrochemical detection and the enzyme-linked immunosorbent assay procedure were 0.00087 μUI mL(-1) and 0.015 μUI mL(-1), respectively, and the within- and between-assay coefficients of variation were below 6.31% for the proposed method. According to the cut-off value for TSH neonatal screening, a reasonably good limit of detection was achieved. These above-mentioned features make the system advantageous for routine clinical analysis adaptation.

Mesoporous carbon nitride based biosensor for highly sensitive and selective analysis of phenol and catechol in compost bioremediation

Herein, we reported here a promising biosensor by taking advantage of the unique ordered mesoporous carbon nitride material (MCN) to convert the recognition information into a detectable signal with enzyme firstly, which could realize the sensitive, especially, selective detection of catechol and phenol in compost bioremediation samples. The mechanism including the MCN based on electrochemical, biosensor assembly, enzyme immobilization, and enzyme kinetics (elucidating the lower detection limit, different linear range and sensitivity) was discussed in detail. Under optimal conditions, GCE/MCN/Tyr biosensor was evaluated by chronoamperometry measurements and the reduction current of phenol and catechol was proportional to their concentration in the range of 5.00 × 10(-8)-9.50 × 10(-6)M and 5.00 × 10(-8)-1.25 × 10(-5)M with a correlation coefficient of 0.9991 and 0.9881, respectively. The detection limits of catechol and phenol were 10.24 nM and 15.00 nM (S/N=3), respectively. Besides, the data obtained from interference experiments indicated that the biosensor had good specificity. All the results showed that this material is suitable for load enzyme and applied to the biosensor due to the proposed biosensor exhibited improved analytical performances in terms of the detection limit and specificity, provided a powerful tool for rapid, sensitive, especially, selective monitoring of catechol and phenol simultaneously. Moreover, the obtained results may open the way to other MCN-enzyme applications in the environmental field.

Microbial tyrosinases: promising enzymes for pharmaceutical, food bioprocessing, and environmental industry

Tyrosinase is a natural enzyme and is often purified to only a low degree and it is involved in a variety of functions which mainly catalyse the o-hydroxylation of monophenols into their corresponding o-diphenols and the oxidation of o-diphenols to o-quinones using molecular oxygen, which then polymerizes to form brown or black pigments. The synthesis of o-diphenols is a potentially valuable catalytic ability and thus tyrosinase has attracted a lot of attention with respect to industrial applications. In environmental technology it is used for the detoxification of phenol-containing wastewaters and contaminated soils, as biosensors for phenol monitoring, and for the production of L-DOPA in pharmaceutical industries, and is also used in cosmetic and food industries as important catalytic enzyme. Melanin pigment synthesized by tyrosinase has found applications for protection against radiation cation exchangers, drug carriers, antioxidants, antiviral agents, or immunogen. The recombinant V. spinosum tryosinase protein can be used to produce tailor-made melanin and other polyphenolic materials using various phenols and catechols as starting materials. This review compiles the recent data on biochemical and molecular properties of microbial tyrosinases, underlining their importance in the industrial use of these enzymes. After that, their most promising applications in pharmaceutical, food processing, and environmental fields are presented.

Magnetic nanoparticles supported ionic liquids improve firefly luciferase properties

Ionic liquids as neoteric solvents, microwave irradiation, and alternative energy source are becoming as a solvent for many enzymatic reactions. We recently showed that the incubation of firefly luciferase from Photinus pyralis with various ionic liquids increased the activity and stability of luciferase. Magnetic nanoparticles supported ionic liquids have been obtained by covalent bonding of ionic liquids-silane on magnetic silica nanoparticles. In the present study, the effects of [γ-Fe2O3@SiO2][BMImCl] and [γ-Fe2O3@SiO2][BMImI] were investigated on the structural properties and function of luciferase using circular dichroism, fluorescence spectroscopy, and bioluminescence assay. Enzyme activity and structural stability increased in the presence of magnetic nanoparticles supported ionic liquids. Furthermore, the effect of ingredients which were used was not considerable on K(m) value of luciferase for adenosine-5'-triphosphate and also K(m) value for luciferin.

Realization of an efficient cholesterol biosensor using ZnO nanostructured thin film

A zinc oxide (ZnO) nanostructured thin film synthesized by a vapour phase transport technique on a platinum coated silicon (Pt/Si) substrate has been successfully utilized for the detection of cholesterol. Amperometric and photometric studies reveal that the prepared bioelectrode ChOx/ZnO/Pt/Si is highly sensitive to the detection of cholesterol over a wide concentration range, 0.12-12.93 mM (5-500 mg dl(-1)). The higher sensitivity is attributed to the large surface area of ZnO thin film for effective loading of ChOx besides its high electron communication capability. A relatively low value of the enzyme's kinetic parameter (Michaelis-Menten constant, 1.08 mM) indicates an enhanced affinity of the enzyme (ChOx) towards the analyte (cholesterol). The prepared bioelectrode is found to exhibit a long shelf life of more than 10 weeks, having negligible interference from the presence of other biomolecules present in human serum indicating potential application of the ZnO nanostructured thin film for cholesterol sensing.

Recennt Advances on Chitosan-Metal Oxide Nanoparticles and their Biological Application

There is a growing interest in the use of green resources for nanoparticle (NP) synthesis. Natural polymer, Chitosan (CH) has been employed as templates for the preparation of metal oxide NPs. They modify the surface characteristics of the nanometal oxides generated. In the presence of template CH, the spatial separation of the particles, enable the synthesis of highly crystalline, mono-dispersed particles of < 100 nm. The properties of metal oxides can be improved by combining with CH and the product can be employed for different applications. CH along with metal oxide NPs has recently been utilized as a stabilizing agent due to its excellent film-forming ability, mechanical strength, biocompatibility, non-toxicity, high permeability towards water, susceptibility to chemical modification and cost-effectiveness. Metal oxide NPs-CH based hybrid composites have attracted much interest for the development of desired biosensors, MRI agents, buffers, antibacterial agents etc.

Recent advances in ZnO nanostructures and thin films for biosensor applications: review

Biosensors have shown great potential for health care and environmental monitoring. The performance of biosensors depends on their components, among which the matrix material, i.e., the layer between the recognition layer of biomolecule and transducer, plays a crucial role in defining the stability, sensitivity and shelf-life of a biosensor. Recently, zinc oxide (ZnO) nanostructures and thin films have attracted much interest as materials for biosensors due to their biocompatibility, chemical stability, high isoelectric point, electrochemical activity, high electron mobility, ease of synthesis by diverse methods and high surface-to-volume ratio. ZnO nanostructures have shown the binding of biomolecules in desired orientations with improved conformation and high biological activity, resulting in enhanced sensing characteristics. Furthermore, compatibility with complementary metal oxide semiconductor technology for constructing integrated circuits makes ZnO nanostructures suitable candidate for future small integrated biosensor devices. This review highlights recent advances in various approaches towards synthesis of ZnO nanostructures and thin films and their applications in biosensor technology.

ZnO/Cu nanocomposite: a platform for direct electrochemistry of enzymes and biosensing applications

Unique structured nanomaterials can facilitate the direct electron transfer between redox proteins and the electrodes. Here, in situ directed growth on an electrode of a ZnO/Cu nanocomposite was prepared by a simple corrosion approach, which enables robust mechanical adhesion and electrical contact between the nanostructured ZnO and the electrodes. This is great help to realize the direct electron transfer between the electrode surface and the redox protein. SEM images demonstrate that the morphology of the ZnO/Cu nanocomposite has a large specific surface area, which is favorable to immobilize the biomolecules and construct biosensors. Using glucose oxidase (GOx) as a model, this ZnO/Cu nanocomposite is employed for immobilization of GOx and the construction of the glucose biosensor. Direct electron transfer of GOx is achieved at ZnO/Cu nanocomposite with a high heterogeneous electron transfer rate constant of 0.67 ± 0.06 s(-1). Such ZnO/Cu nanocomposite provides a good matrix for direct electrochemistry of enzymes and mediator-free enzymatic biosensors.