Matrix For Enzyme Immobilization Research Articles

Passive fuel delivery and efficient anoxic condition in anode improve performance of methanol biofuel cell

The operational stability, power efficiency, and technical simplicity of enzymatic biofuel cells are the focus area of research for practical applications of this green energy-generating device. Here, we report some critical findings on these issues on a methanol-fuelled pure biofuel cell fabricated by using alcohol oxidase and bilirubin oxidase as anodic and cathodic catalysts, respectively. The cell was fabricated with a new design strategy comprising efficient anoxic condition in the anodic chamber, adequate airflow to the cathode for enhancing oxygen reduction reactions, and a passive fuel pumping facility to the anode. A magnetic nanoparticle-based bio-nanocomposite matrix on the carbon-cloth electrode offered as a biocompatible enzyme immobilization matrix for harvesting electrons in the cell through the direct electron transfer mechanism as validated by cyclic voltammetry. Six units of the cells, when connected in a series, the device's potential increased to 4.3-fold (3.1 V) and rested at a stable state under a load with a half-life of ∼ 372 days and a coulombic efficiency of 60%. This high operational stability has been attributed to the efficient anoxic setup in the anodic chamber that supported the stability of alcohol oxidase, the activity of which was intact even after 49 days of the operation. This work also demonstrated that the prolonged interaction of molecular oxygen with the oxidase drastically inactivates it without affecting the structural integrity of the enzyme protein. This enzymatic fuel cell with improved design and functions is a step forward for achieving practical application as a standalone power supply to small-scale devices.

Dual Valorization of Lignin as a Versatile and Renewable Matrix for Enzyme Immobilization and (Flow) Bioprocess Engineering.

Lignin has emerged as an attractive alternative in the search for more eco‐friendly and less costly materials for enzyme immobilization. In this work, the terephthalic aldehyde‐stabilization of lignin is carried out during its extraction to develop a series of functionalized lignins with a range of reactive groups (epoxy, amine, aldehyde, metal chelates). This expands the immobilization to a pool of enzymes (carboxylase, dehydrogenase, transaminase) by different binding chemistries, affording immobilization yields of 64–100 %. As a proof of concept, a ω‐transaminase reversibly immobilized on polyethyleneimine‐lignin is integrated in a packed‐bed reactor. The stability of the immobilized biocatalyst is tested in continuous‐flow deamination reactions and maintains the same conversion for 100 cycles. These results outperform previous stability tests carried out with the enzyme covalently immobilized on methacrylic resins, with the advantage that the reversibility of the immobilized enzyme allows recycling and reuse of lignin beyond the enzyme inactivation. Additionally, an in‐line system also based on lignin is added into the downstream process to separate the reaction products by catch‐and‐release. These results demonstrate a fully closed‐loop sustainable flow‐biocatalytic system based exclusively on lignin.

Enzymatic Cascade Reactions Mediated by Highly Efficient Biomimetic Quasi Metal-Organic Frameworks.

The integration of chemo- and enzymatic catalysis for effective multistep cascades has presented critical challenges for decades. In this work, the biomimetic quasi NH2-MIL-101 (qNM) with highly efficient peroxidase-like activity was synthesized via a palmitic acid-induced strategy followed by pyrolysis. The effects of the amount of palmitic acid and calcination temperature on the synthesis of qNM were optimized. It was found that qNM was an excellent catalyst for oxidations of various peroxidase substrates, and a possible mechanism was proposed, i.e., the presence of FeII species in qNM was responsible for its excellent activity, which facilitated the transition between FeII and FeIII species to produce more hydroxyl radicals by H2O2 decomposition. The qNM served as the potential matrix for enzyme immobilization through a cross-linking method, and kinetic studies revealed that the catalytic efficiency (kcat/Km) for the immobilized GOx (23.7 mM-1 s-1) is comparable to that of free GOx (26.9 mM-1 s-1). The immobilized GOx also showed improved stability against high temperatures and organic solvents compared to free GOx, and analysis of the secondary structure of GOx indicated that the improved stability resulted from enzyme rigidity by the intense covalent linkage with qNM. Furthermore, qNM contributed its biomimetic activity to cooperate with a single enzyme (GOx) or two enzymes (β-Gal and GOx) for the enzymatic cascade reactions. Compared with the mixture of each component in the solution, the combination of the single-enzyme system (GOx) or the two-enzyme system (β-Gal and GOx) in qNM achieved 2.67-fold and 1.83-fold enhancements in the activity of catalytic cascades, respectively. This study provides new insights into the construction of effective and synergistic cascade reactions by integrating biomimetic MOF with natural enzyme, which holds potential for applications in biotechnology and ecofriendly and biomimetic catalysis.

Environmentally Friendly Preparation of Magnetic Composites Featuring Proteolytic Properties

The enzyme-containing magnetic composites are presented. The magnetic matrix for enzyme immobilization is obtained by sequential application of an amine-containing polysaccharide—chitosan and a synthetic polymer—poly(ethylene-alt-maleic acid) to the magnetite microparticles to form the interpolyelectrolyte complex shell. Then, the enzyme (trypsin) is immobilized by covalent or noncovalent binding. Thus, the suggested composites can be readily obtained in the environmentally friendly manner. The enzyme capacity of the resulting composites reaches 28.0–32.6 mg/g. The maximum hydrolysis rates of the H-Val-Leu-Lys-pNA substrate provided by these composites range within 0.60·10–7–0.77·10–7 M/min.

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.

Glucose Microsensor with Covalently Immobilized Glucose Oxidase for Probing Bacterial Glucose Uptake by Scanning Electrochemical Microscopy

We have developed a new dual-tip glucose sensing scanning electrochemical microcopy (SECM) probe by covalently immobilizing the glucose oxidase (GOD) enzyme onto an ultramicro electrode (UME) to measure the local glucose consumption of Streptococcus mutans (S. mutans) biofilms. GOD was immobilized on a novel enzyme immobilization matrix of functionalized multiwalled carbon nanotubes (f-MWCNTs) and 1-butyl-4-methylpyridinium hexafluorophosphate (ionic liquid/IL) packed into the etched Pt UME. The highly selective GOD-based SECM tip showed a high current density of 94.44 (±18.55) μA·mM-1·cm-2 from 0.10 to 1.0 mM at 37 °C as a result of the synergetic effects of f-MWCNTs and ionic liquid. The detection limit of the new 25 μm diameter glucose sensor is 10.0 μM with a linear range up to 4.0 mM. The sensor was successfully used to quantify the rate of glucose consumption of S. mutans biofilms in the presence of sucrose. S. mutans catabolizes both glucose and sucrose, producing lactic acid, reducing the local pH, and causing dental caries. With sucrose, S. mutans produces exopolysaccharides to enhance bacterial adhesion on the tooth surface; subsequent lactic acid production reduces the local pH, resulting in dental caries. Because of the high selectivity of the sensor, we were able to quantify glucose consumption in the presence of sucrose. S. mutans preferentially consumed sucrose in a mixed diet of both sucrose and glucose. Furthermore, using this unique fast-response (∼2 s) glucose sensor, we were for the first time able to map the distribution of the glucose consumption profile in the local environment of S. mutans biofilm. These findings provide insight into how the fast-growing S. mutans creates nutrient-depleted regions that affect the survival and metabolic behavior of other bacterial species within oral biofilm.

Oxidized bacterial cellulose membrane as support for enzyme immobilization: properties and morphological features

Bacterial cellulose (BC) membrane can be architected to covalently immobilize biomolecules, generating materials with new functionality. The processes of purification (via alkaline treatment) and chemical modification (via NaIO4) to the wet BC membrane is the innovation of this work. This wet oxidized BC (OxBC) membrane could act as a support matrix for covalent immobilization of enzymes. BC produced over 5 days of static fermentation, followed by purification with K2CO3 (BC-5d-K2CO3) was selected for our study due to high porosity and surface area, which are properties that favor its chemical modification. This wet BC membrane proven suitable for NaIO4 oxidation. Time and temperature conditions were evaluated in the oxidation reaction, with oxidation BC (OxBC) performed at 1% (w/v) NaIO4 for 6 h at 55 °C under most advantageous conditions, as it provided 50% oxidation degree and preserved its morphological structure. BC and OxBC were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Scanning electron microscopy, mechanical test, and thermal analysis. The oxidation reaction decreased BC crystallinity, tensile strength, and thermal stability and compacted the cellulose layers. BC and OxBC showed non-cytotoxicity. Fourier transform infrared confirmed that OxBC can covalently immobilize papain and that after immobilization the enzyme showed a recovered enzymatic activity of 93.1%. In addition, the oxidized membrane presented greater amount of immobilized papain in its study than BC, proving to be a more efficient support for enzymatic immobilization.

Enhanced electrochemical sensing performance by insitu electrocopolymerization of pyrrole and thiophene-grafted chitosan

Nowadays, there is increasing number of electrochemical biosensors which utilize chitosan (Ch); as an enzyme immobilization matrix, and conductive nanomaterials; as electron carriers improving sensitivity of the biosensor. However, the challenge these sensors face is the lack of uniform dispersion of nanomaterials throughout the Ch film, which can negatively affect analytical performance of the biosensor. In this study, we report the development of an enzyme immobilization matrix that displays enhanced electrochemical performance thanks to a novel conductive thin film prepared via in situ electrocopolymerization of pyrrole (Py) and thiophene-grafted chitosan (Th-Ch). This is a simple thin film preparation method that can help overcome aforementioned challenges by providing a uniformly distributed conductive layer on the electrode. We are also for the first time reporting the synthesis and characterization of Th-Ch, where grafted Th plays an essential role as a linking group between Ch and Py. The resulting conductive Ch-based thin film was modified with glucose oxidase (GOx) which served as a model enzyme. In situ electrocopolymerization of Py with Th-Ch resulted in a highly conductive thin film enabling approximately 40% higher sensitivity when compared to a Py-Ch composite. This new type of composite thin film is promising in biosensor technology due to its biocompatibility, the chemically and physically modifiable structure, as well as its electrical conductivity.

A Hydrogen Peroxide Biosensor from Horseradish peroxidase Immobilization onto Acrylic Microspheres

The sensitive and rapid detection of hydrogen peroxide is very important in the areas of clinical and environmental analyses. A sensitive and selective Horseradish peroxidase (HRP)-hydrogen peroxide (H2O2) biosensor was developed based on acrylic microspheres. Hydrophobic poly(n-butyl acrylate-N-acryloxysuccinimide) [poly(nBA-NAS)] microspheres were synthesized using photopolymerization in an emulsion to form an enzyme immobilization matrix. The HRP enzyme was covalently immobilized onto the acrylic microspheres via the succinimide functionality. Field emission scanning electron microscope (FESEM) has been utilized to characterize the screen-printed carbon paste electrode (SPE) constructed from enzyme conjugated acrylic microspheres and gold nanoparticles (AuNPs) composite (HRP/nBA-NAS/AuNPs/SPE). Differential pulse voltammetry was used to assess the biosensor performance. The linear response range of the hydrogen peroxide biosensor obtained was from 1.0 × 10-2 to 1.0 × 10-10 M (R2 = 0.99) with the limit of detection (LOD) approximately at 1.0 × 10-10 M. This is an improvement over many hydrogen peroxide biosensors reported so far. Such improvement may be attributed to the large surface area provided by the acrylic microspheres as a matrix for immobilization of the HRP enzyme.

Investigation of dopant effect on the electrochemical performance of 1-D polypyrrole nanofibers based glucose biosensor

Glucose plays an imperative role in human metabolism and any imbalance in glucose concentration can cause chronic disease like diabetes mellitus. With the drastic increase in the number of diabetic patients around the world, demand for point of care testing device for continuous monitoring of blood glucose level has been accelerated. In this respect, electrochemical glucose biosensors play a vital role for measurement of glucose concentration in human blood. In this work, for the first time, we demonstrate a systematic study of the effect of two different types of dopants viz. lithium perchlorate (LiClO4) and para-toluenesulfonic acid (p-TSA) on the performance of polypyrrole (PPy) based enzymatic glucose biosensor. Both the dopants (LiClO4 and p-TSA) were utilized with the aim of improving the charge transfer capability of PPy films. The PPy nanofibers were synthesized over a Platinum coated glass substrate by electrochemical method. The morphological and electrochemical properties of electrosynthesized PPy nanofibers utilizing template-free method have been tailored by dopant variation (LiClO4 and pTSA) during electropolymerization. The as-prepared PPy nanofibers were used as a support matrix for enzyme immobilization. The as-fabricated enzymatic biosensors were later examined for the detection of glucose. Both the morphological and electrochemical properties of PPy electrode have been observed to improve with p-TSA (PPy–pTSA), as compared to LiClO4 (PPy–LiClO4). The as-fabricated PPy–pTSA/GOx based glucose biosensor has exhibited the highest sensitivity of 6.12 mA cm−2 M−1 with a linear range of 0.1–7.5 mM, which is better as compared to PPy-LiClO4/GOx biosensor. Additionally, the as-prepared PPy–pTSA/GOx biosensor has presented noteworthy stability, selectivity, and reproducibility that validates the importance of the dopant effect in electrosynthesized PPy based biosensing applications.

Enzyme immobilization on ZIF-67/MWCNT composite engenders high sensitivity electrochemical sensing

Metal-organic frameworks (MOFs) as a type of potential matrix for enzyme immobilization have attracted much interest. However, the sensitivity of most MOF-enzymatic electrochemical biosensors has not been satisfactory so far due to the poor conductivity and low apparent affinity of MOFs. In this work, new strategies have been presented: (i) using MOFs that themselves possess catalytic properties for substrates, so the synergistic catalysis by combining the MOFs and immobilized enzymes can be reinforced; (ii) introducing hydrophilic carbon nanomaterials and preparing MOF/carbon composites, not only the conductivity of the matrix but also the apparent affinity of immobilized enzyme for hydrophilic substrate can be remarkably enhanced. Horseradish peroxidase (HRP) and zeolite imidazolate framework-67(Co)/multi-walled carbon nanotube composite (ZIF-67(Co)/MWCNT) were adopted as the model enzyme and the immobilized matrix to illustrate and examine the proposed strategies. Compared with single component (ZIF-67(Co) or MWCNTs) based HRP electrochemical biosensors, the composite electrochemical biosensor displayed increased apparent substrate affinity (Michaelis constant Km reduced by ~75%) and 1.3-fold increased sensitivity in the detection of H2O2. The sensitivity (315μAmM−1cm−2) was also much larger than that of most previously reported MOF-HRP electrochemical biosensors. The proposed strategies are envisaged to be useful for other MOF-enzymes systems, which will be beneficial to the development of biocatalysis and biosensing.

Immobilization of Cholesterol Oxidase: An Overview

Background:Cholesterol oxidases are bacterial oxidases widely used commercially for their application in the detection of cholesterol in blood serum, clinical or food samples. Additionally, these enzymes find potential applications as an insecticide, synthesis of anti-fungal antibiotics and a biocatalyst to transform a number of sterol and non-sterol compounds. However, the soluble form of cholesterol oxidases are found to be less stable when applied at higher temperatures, broader pH range, and incur higher costs. These disadvantages can be overcome by immobilization on carrier matrices.Methods:This review focuses on the immobilization of cholesterol oxidases on various macro/micro matrices as well as nanoparticles and their potential applications. Selection of appropriate support matrix in enzyme immobilization is of extreme importance. Recently, nanomaterials have been used as a matrix for immobilization of enzyme due to their large surface area and small size. The bio-compatible length scales and surface chemistry of nanoparticles provide reusability, stability and enhanced performance characteristics for the enzyme-nanoconjugates.Conclusion:In this review, immobilization of cholesterol oxidase on nanomaterials and other matrices are discussed. Immobilization on nanomatrices has been observed to increase the stability and activity of enzymes. This enhances the applicability of cholesterol oxidases for various industrial and clinical applications such as in biosensors.

Rational Design of Mimic Multienzyme Systems in Hierarchically Porous Biomimetic Metal-Organic Frameworks.

A facile approach was reported to establish mimic multienzyme systems with hierarchically porous (HP) biomimetic metal-organic frameworks (MOFs) and natural enzymes for tandem catalysis. The hierarchically porous MOF HP-PCN-224(Fe) with peroxidase-like activity and tunable hierarchical porosity was synthesized via a modulator-induced strategy. HP-PCN-224(Fe) not only acts as the enzyme-immobilization matrix but also as an effective enzyme mimic, which could cooperate with the immobilized natural enzyme to catalyze the cascade reactions. The mimic multienzyme systems were used for the efficient colorimetric detection of a series of biomolecules, including glucose and uric acid. This work displays the great potential to construct highly functional biocatalysts by integrating the merits of both natural enzymes and MOF mimics, which are promising for applications in biosensing and biomimetic catalysis.

Immobilization of horseradish peroxidase on amino-functionalized carbon dots for the sensitive detection of hydrogen peroxide.

The authors describe the preparation of amino-functionalized carbon dots (NH2-CDs) via a one-step hydrothermal process using silver nitrate and chitosan as the precursors. The NH2-CDs have a fairly consistent size distribution with an average size of 2.8 ± 0.5nm. This is attributed to the introduction of Ag(I) both as acatalyst and a precipitant. The NH2-CDs are highly crystalline. Their surface carries amino groups and carboxy groups which is confirmed by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Horseradish peroxidase (HRP) was immobilized in the NH2-CDs and then placed on a glassy carbon electrode (GCE). Spectroscopic and electrochemical analyses evidenced the stability and good bioactivity of the immobilized HRP. This reveals that NH2-CD is a desirable matrix for enzyme immobilization. The modified GCE exhibits enhanced electro-catalytic activity towards hydrogen peroxide (H2O2) reduction as compared to that of plainCDs. The effects of pH value and loading on the performances of the modified GCEs were studied. Under optimized conditions, the biosensor has a linear response in the 5 to 590nM H2O2 concentration range, with a 1.8nM defection limit (at an S/N ratio of 3). The sensor is stable, reproducible and selective. Finally, the sensor was applied to determine H2O2 in real samples, and satisfactory recoveries were achieved. Graphical abstract Amino-functionalized carbon dots (NH2-CDs) can provide more active sites and a friendly microenvironment for horseradish peroxidase (HRP) immobilization. Thus, a novel sensitive H2O2 biosensor has been developed.

Influence of LiClO4 Concentration on 1-D Polypyrrole Nanofibers for Enhanced Performance of Glucose Biosensor

In the present work, a template-free single-step fabrication of Lithium perchlorate (LiClO4) doped 1-D Polypyrrole nanofibers network (PNN) (without using electrospinning) toward glucose biosensing application has been reported. The PNN with different concentrations of LiClO4 was grown over the Platinum coated glass substrate by electropolymerization method and utilized as a support matrix for immobilization of enzyme. The effect of LiClO4 concentration on glucose biosensor performance has been demonstrated for the first time. The modification in morphology and reduction in charge transfer resistance of PNNs by varying LiClO4 concentration were found to play a significant role in the improved figure of merits of the biosensor. Among all the types of as-fabricated PNN electrodes (prepared by using different concentrations of LiClO4 viz. 1, 10, 50, and 70 mM) the best response was obtained corresponding to highest LiClO4 concentration. The enzyme loading and charge transfer resistance were drastically improved by approximately three folds owing to the higher surface area and improved conductivity of PNN electrodes thereby resulting in ten-fold increment in sensitivity. The as-prepared biosensor showed the highest sensitivity of 4.34 mA-cm−2-M−1 and a linear range of 0.1–4.6 mM with good stability and high selectivity for glucose detection.

SnO2 hollow nanotubes: a novel and efficient support matrix for enzyme immobilization

A major challenge in the industrial use of enzymes is maintaining their stability at elevated temperatures and in harsh organic solvents. In order to address this issue, we investigated the use of nanotubes as a support material for the immobilization and stabilization of enzymes in this work. SnO2 hollow nanotubes with a high surface area were synthesized by electrospinning the SnCl2 precursor and polyvinylpyrrolidone (dissolved in dimethyl formamide and ethanol). The electrospun product was used for the covalent immobilization of enzymes such as lipase, horseradish peroxidase, and glucose oxidase. The use of SnO2 hollow nanotubes as a support was promising for all immobilized enzymes, with lipase having the highest protein loading value of 217 mg/g, immobilization yield of 93%, and immobilization efficiency of 89%. The immobilized enzymes were fully characterized by various analytical methods. The covalently bonded lipase showed a half-life value of 4.5 h at 70 °C and retained ~91% of its original activity even after 10 repetitive cycles of use. Thus, the SnO2 hollow nanotubes with their high surface area are promising as a support material for the immobilization of enzymes, leading to improved thermal stability and a higher residual activity of the immobilized enzyme under harsh solvent conditions, as compared to the free enzyme.

Enzyme-free monitoring of glucose utilization in stimulated macrophages using carbon nanotube-decorated electrochemical sensor

Carbon nanotubes (CNTs) have been extensively explored for a diverse range of applications due to their unique electrical and mechanical properties. CNT-incorporated electrochemical sensors have exhibited enhanced sensitivity towards the analyte molecule due to the excellent electron transfer properties of CNTs. In addition, CNTs possess a large surface area-to-volume ratio that favours the adhesion of analyte molecules as well as enhances the electroactive area. Most of the electrochemical sensors have employed CNTs as a nano-interface to promote electron transfer and as an immobilization matrix for enzymes. The present work explores the potential of CNTs to serve as a catalytic interface for the enzymeless quantification of glucose. The figure of merits for the enzymeless sensor was comparable to the performance of several enzyme-based sensors reported in literature. The developed sensor was successfully employed to determine the glucose utilization of unstimulated and stimulated macrophages. The significant difference in the glucose utilization levels in activated macrophages and quiescent cells observed in the present investigation opens up the possibilities of new avenues for effective medical diagnosis of inflammatory disorders.

A novel polyurethane/nano ZnO matrix for immobilization of chitinolytic enzymes and optical sensing of chitin

Purified chitinase from Vigna mungo and N-acetyl β glucosaminidase (NAGase) from Canavalia ensiformis were immobilized on to the novel polyurethane (PU)/zinc oxide nanoparticles (nano ZnO) composite matrix with a conjugation yield of 0.785±0.01mg/cm2 and 96.19±0.85% retention of specific activity. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) also confirmed the presence of nano ZnO and enzymes on the PU support. Thus synthesized PU/nano ZnO/chitinase/NAGase conjugates were optimized with respect to pH, temperature and substrate concentration and successfully employed for development of an absorbance based optical biosensor for chitin determination in stored wheat grains. The limit of detection was 0.01mM with linearity from 0.1 to 10.0mM. The% recoveries of added chitin (0.1 and 0.2mM) were >95.0% and >96.5% respectively and within-day and between-day coefficients of variations were 1.03% and 1.78% respectively. The method showed good correlation (R2=0.996) with the popular 3,5-dinitrosalicylic acid method. PU/nano ZnO bound chitinase/NAGase showed good thermal and storage stabilities and could be reused 10 times without any appreciable loss of activity.

Organic-inorganic hybrid matrix for electrochemical biosensing of tyrosine

The manuscript presents synthesis and application of organic-inorganic hybrid matrix, consisting of polypyrrole (PPy) and gold nanoparticles (AuNPs). The polypyrrole acts as conducting matrix and gold nanostructures play role of electro-catalysts. The composite of PPy-AuNPs was electrochemically synthesized on screen printed electrodes in single step and was characterized thoroughly using analytical techniques. The composite was used as matrix for immobilization of tyrosinase enzyme for tyrosine and catechin biosensing. The electrochemical measurements were performed using cyclic voltammetry (CV) and amperometry. For tyrosine, the composite based biosensor showed dynamic linearity from 10 to 100nM, having sensitivity of 1.0×10−2μAcm−2/nM, and LOD of 0.3nM. For catechin, the dynamic linearity range was from 1 to 20nM. The study showed that the biosensor exhibited more sensitivity towards tyrosine estimation as compared to catechin, which can be due to their structural difference. The biosensor was also used for sensing tyrosine and catechin in real samples and the study showed motivating results.

A Partially Graphitic Mesoporous Carbon Membrane with Three-Dimensionally Networked Nanotunnels for Ultrasensitive Electrochemical Detection

A hierarchically porous partially graphitic carbon (HPGC) membrane with three-dimensionally networked nanotunnels is prepared and applied as a monolithic matrix for electrochemical (bio)sensing. The walls of the nanotunnels (∼40–80 nm in diameter) are composed of partially graphitic carbon with ordered mesopores (∼6.5 nm in diameter). After modification with polydopamine, the HPGC membrane can be decorated with nanoparticles (i.e., Au NPs) and subsequently functions as a three-dimensional matrix for enzyme (i.e., glucose oxidase) immobilization. The Au NPs can accelerate electron transfer between the membrane electrode and enzyme and synergistically work with the enzyme in catalyzing glucose oxidation, thus considerably enhancing the sensitivity of the sensor. The signal intensity of the HPGC monolithic membrane electrode is ∼700 times higher than that obtained from mesoporous carbon/Nafion paste electrode counterparts. The limit of detection of the biosensor is 0.48 × 10–11 M toward glucose detection, 4 ...