Electrochemical Approach for Detection of Extracellular Oxygen Released from Erythrocytes Based on Graphene Film Integrated with Laccase and 2,2-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Computational studies and biosensory applications of graphene-based nanomaterials: a state-of-the-art review

Graphene, graphene oxide (GO) and graphene quantum dots (GQDs) are expected to play a vital role in the diagnosis of severe ailments. Computer-based simulation approaches are helpful for understanding theoretical tools prior to experimental investigation. These theoretical tools still have a high computational requirement. Thus, more efficient algorithms are required to perform studies on even larger systems. The present review highlights the recent advancement in structural confinement using computer simulation approaches along with biosensory applications of graphene-based materials. The computer simulation approaches help to identify the interaction between interacting molecules and sensing elements like graphene sheets. The simulation approach reduces the wet-lab experiment time and helps to predict the interaction and interacting environment. The experimental investigation can be tuned at a molecular level easily to predict small changes in structural configuration. Here, the molecular simulation study could be useful as an alternative to actual wet experimental approaches. The sensing ability of graphene-based materials is a result of interactions like hydrogen bonding, base-base interaction, and base-to-pi interaction to name a few. These interactions help in designing and engineering a substrate for sensing of various biomolecules.

Nanostructured pencil graphite electrodes for application as high power biocathodes in miniaturized biofuel cells and bio-batteries

This work describes a simple method for the fabrication of an enzymatic electrode with high sensitivity to oxygen and good performance when applied as biocathode. Pencil graphite electrodes (PGE) were chosen as disposable transducers given their availability and good electrochemical response. After electrochemical characterization regarding hardness and surface pre-treatment suited modification with carbon-based nanostructures, namely with reduced graphene, MWCNT and carbon black for optimal performance was proceeded. The bioelectrode was finally assembled through immobilization of bilirubin oxidase (BOx) lashed on the modified surface of MWCNT via π-π stacking and amide bond functionalization. The high sensitivity towards dissolved oxygen of 648 ± 51 µA mM-1 cm-2, and a LOD of 1.7 µM, was achieved for the PGE with surface previously modified with reduced graphene (rGO), almost the double registered for direct anchorage on the bare PGE surface. Polarization curves resulted in an open circuit potential (OCP) of 1.68 V (vs Zn electrode) and generated a maximum current density of about 650 μA cm-2 in O2 saturated solution.

Purification, Biochemical Characterization, and Facile Immobilization of Laccase from Sphingobacterium ksn-11 and its Application in Transformation of Diclofenac

An extracellular laccase enzyme secreted from Sphingobacterium ksn-11 was purified to electrophoretic homogeneity, showing a molecular weight of 90 kDa. The purified enzyme was monomeric in nature confirmed by sodium dodecyl gel electrophoresis. The optimum temperature and pH were found to be 40 °C and 4.5 respectively. The enzyme showed highest substrate specificity for 2,2 azino-bis (ethylthiozoline-6-sulfonate) (ABTS), followed by syringaldazine. The K_m value for ABTS was 2.12 mM with a V_max value of 33.33 U/mg which was higher when compared with syringaldazine and guaiacol substrates. Sodium azide and EDTA inhibited the activity by 30%, whereas presence of Ca²⁺ and iron increased activity by 50%. The purified enzyme was immobilized in sodium alginate-silicon dioxide-polyvinyl alcohol beads and evaluated for diclofenac transformation studies. LC-MS analysis confirmed that immobilized laccase transformed diclofenac to 4-OH diclofenac after 4 h of incubation. 45 % of diclofenac was able to transform even at 3rd cycle of immobilized laccase use. Therefore, immobilized laccase can be used to transform or degrade several recalcitrant compounds from industrial effluents.

Surface charge-controlled electron transfer and catalytic behavior of immobilized cytochrome P450 BM3 inside dendritic mesoporous silica nanoparticles

Understanding the influencing factors on the reaction kinetics of P450 BM3 within confined spaces is essential for developing efficient P450 BM3 bioreactors. Herein, two dendritic mesoporous silica nanoparticles (OH-DMSNs and NH₂-DMSNs) with similar pore size but opposite surface charge have been prepared and served as the vehicle to immobilize P450 BM3. With the help of the film-forming material of chitosan, P450 BM3/OH-DMSN and P450 BM3/NH₂-DMSN composites were immobilized on GC electrode and characterized with electrochemical measurements. Compared with P450 BM3/OH-DMSNs/GCE, P450 BM3/NH₂-DMSNs/GCE showed higher electron transfer efficiency with higher current charge and lower k_s value. Besides, the generated catalytic current towards testosterone on P450 BM3/NH₂-DMSNs/GCE was 1.81 times larger than P450 BM3/OH-DMSNs/GCE. Furthermore, P450 BM3 inside NH₂-DMSNs displayed higher affinity towards testosterone with the lower K_m^app value of 244.82 μM. These results are attributed to the positively charged internal walls of NH₂-DMSNs so that P450 BM3 adapts to an orientation favorable for electron exchange with electrodes and substrate binding with the active sites. The present study provides fundamentals for regulating the surface charge to optimize redox process and catalytic behavior in CYP bioreactors through electrostatic interactions.

Colorimetric Assay Using Mesoporous Fe-Doped Graphitic Carbon Nitride as a Peroxidase Mimetic for the Determination of Hydrogen Peroxide and Glucose

Iron can enter the electron-rich cavities of graphitic carbon nitride (g-C₃N₄). On account of this phenomenon, Fe-doped g-C₃N₄ (Fe-g-C₃N₄) was prepared as a peroxidase mimetic by using one-step pyrolysis of urea and FeCl₃·6H₂O. Compared to g-C₃N₄, Fe-g-C₃N₄ has a large specific surface area due to the presence of mesopores and cracks, a smaller band gap, and a high loading of Fe in its structure. Thus, Fe-g-C₃N₄ exhibits greater peroxidase activity with a more obvious color change when using 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate in the presence of hydrogen peroxide (H₂O₂). The color of a mixture of TMB and Fe-g-C₃N₄ gradually deepens with increasing concentrations of H₂O₂. Accordingly, a rapid, sensitive, and low-cost colorimetric assay for the detection of H₂O₂ was developed. After optimization, this method boasts a wide linear dynamic range for H₂O₂ detection from 0.005 to 400 μM (r² = 0.9971) with a detection limit of 0.005 μM. Because H₂O₂ is a main product of glucose oxidation by glucose oxidase (GOx), a colorimetric assay for glucose detection was also realized, with a linear dynamic range of 1-1000 μM (r² = 0.9996) and a detection limit of 0.5 μM. These assays were applied to the quantitative detection of H₂O₂ in milk and glucose in human serum, respectively.

Non-covalent assembled laccase-graphene composite: Property, stability and performance in beta-blocker removal

Immobilization of enzymes on carriers have been pursued to make the enzyme stable, reusable and obtaining even better enzyme activity. Due to the highly stable two-dimensional layer structure, large surface area and pore volume, graphene materials were seemed as ideal carrier for enzyme immobilization. In this paper, pristine few layer graphene (FLG) was applied to interact with laccase to synthesize laccase-graphene composite and the results of AFM, FT-IR and adsorption isotherm suggested that laccase was loaded on the FLG with a very high loading dosage (221.1 mg g^-1). Based on the measured interaction force and binding type between laccase and graphene, we proposed that the great enzyme loading on FLG is likely due to the non-covalent π-π stacking in addition to the large surface area of FLG. The composite has better stability to the variance of pH and storage temperature than free laccase. The synthesized composite can effectively transform beta-blocker labetalol with an enhanced efficiency, though the possible reaction pathways kept not changing. We further performed molecular simulation study on the crystal structure variation of laccase binding on FLG and proposed that catalytic activity enhancement may be attributed to the more exposure extent of the catalytic center of laccase. In addition, the laccase-graphene composite can be reused more than ten times in catalyzing the labetalol removal.

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

Electrically-transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high-performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure-property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

Controlling enzyme function through immobilisation on graphene, graphene derivatives and other two dimensional nanomaterials

Controlling enzyme function through immobilisation on graphene, graphene derivatives and other two dimensional nanomaterials.

A novel Laccase Biosensor based on Laccase immobilized Graphene-Cellulose Microfiber Composite modified Screen-Printed Carbon Electrode for Sensitive Determination of Catechol

In the present work, we demonstrate the fabrication of laccase biosensor to detect the catechol (CC) using laccase immobilized on graphene-cellulose microfibers (GR-CMF) composite modified screen printed carbon electrode (SPCE). The direct electrochemical behavior of laccase was investigated using laccase immobilized different modified SPCEs, such as GR/SPCE, CMF/SPCE and GR-CMF/SPCE. Compared with laccase immobilized GR and CMF modified SPCEs, a well-defined redox couple of Cu^I/Cu^II for laccase was observed at laccase immobilized GR-CMF composite modified SPCE. Cyclic voltammetry results show that the as-prepared biosensor has 7 folds higher catalytic activity with lower oxidation potential towards CC than SPCE modified with GR-CMF composite. Under optimized conditions, amperometric i-t method was used for the quantification of CC, and the amperometric response of the biosensor was linear over the concertation of CC ranging from 0.2 to 209.7 μM. The sensitivity, response time and the detection limit of the biosensor for CC is 0.932 μMμA⁻¹ cm⁻², 2 s and 0.085 μM, respectively. The biosensor has high selectivity towards CC in the presence of potentially active biomolecules and phenolic compounds. The biosensor also accessed for the detection of CC in different water samples and shows good practicality with an appropriate repea.

Graphene-based multiplexed disposable electrochemical biosensor for rapid on-farm monitoring of NEFA and βHBA dairy biomarkers

Label-free assay using electrodeposited antibody-conjugated graphene biointerface for dual detection of NEFA and βHBA from dairy cow blood samples.

Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism

The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 μg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS²⁺ which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination.

Cyclodextrin functionalized graphene-gold nanoparticle hybrids with strong supramolecular capability for electrochemical thrombin aptasensor

We demonstrate a facile one-pot synthetic strategy for controlled synthesis of thio-β-cyclodextrin functionalized graphene/gold nanoparticles (SH-β-CD-Gr/AuNPs) composites using SH-β-CD as both the dispersant and linker. The obtained SH-β-CD-Gr/AuNPs integrate the excellent electrical properties and large surface area of graphene and AuNPs with supramolecular recognition ability of CD, which show more effective electron transfer and higher enriched ability for the ferrocene probe via the host-guest interaction between CD and ferrocene than SH-β-CD-Gr. In the presence of target, the stronger interaction between aptamer and target makes the ferrocene move closer to the electrode surface, thus facilitating the electron transfer. Based on this sensing mechanism, a new and highly sensitive biosensing concept by the use of SH-β-CD-Gr/AuNPs as enhancing materials is demonstrated for "signal-on" detection of targets (thrombin as a model target). This biosensor exhibits a wide linear range for thrombin from 1.6×10(-17) M to 8.0×10(-15) M and a very low limit of detection 5.2×10(-18) M, which is two-order magnitude better than those of SH-β-CD-Gr (the detection linear range from 1.6×10(-15) M to 8.0×10(-13) M and detection limit of 1.0×10(-15) M). Our proposed electrochemical aptasensor based on SH-β-CD-Gr/AuNPs shows good selectivity against other proteins such as human serum albumin, lysozyme and insulin. To the best of our knowledge, the present SH-β-CD-Gr/AuNPs hybrids are the most efficient graphene-based electrochemical active probes ever reported for biosensors.

Third-generation oxygen amperometric biosensor based on Trametes hirsuta laccase covalently bound to graphite electrode

The response of low-density graphite electrodes hosting Trametes hirsuta laccase in a direct electron transfer regime is presented for real-time analysis of O

Graphene as a signal amplifier for preparation of ultrasensitive electrochemical biosensors

Early diagnostics of diseases performed with minimal money and time consumption has become achievable due to recent advances in development of biosensors. These devices use biorecognition elements for selective interaction with an analyte and signal readout is obtained via different types of transducers. Operational characteristics of biosensors have been reported to improve substantially, when a diverse range of nanomaterials was employed. This review presents construction of electrochemical biosensors based on graphene, atomically thin 2D carbon crystals, which is currently intensively studied nanomaterial. The most attractive directions of graphene applications in biosensor preparation are discussed here including novel detection and amplification schemes exploiting graphene's unique electrochemical, physical and chemical properties. The future of graphene-based biosensors is most likely bright, but there is still a lot of work to do to fulfill high expectations.

Applications of graphene and related nanomaterials in analytical chemistry

Graphene and its related materials remain a very bright and exciting prospect in analytical chemistry.

Three-dimensional graphene networks as a new substrate for immobilization of laccase and dopamine and its application in glucose/O2 biofuel cell

We report here three-dimensional graphene networks (3D-GNs) as a novel substrate for the immobilization of laccase (Lac) and dopamine (DA) and its application in glucose/O2 biofuel cell. 3D-GNs were synthesized with an Ni(2+)-exchange/KOH activation combination method using a 732-type sulfonic acid ion-exchange resin as the carbon precursor. The 3D-GNs exhibited an interconnected network structure and a high specific surface area. DA was noncovalently functionalized on the surface of 3D-GNs with 3,4,9,10-perylene tetracarboxylic acid (PTCA) as a bridge and used as a novel immobilized mediating system for Lac-based bioelectrocatalytic reduction of oxygen. The 3D-GNs-PTCA-DA nanocomposite modified glassy carbon electrode (GCE) showed stable and well-defined redox current peaks for the catechol/o-quinone redox couple. Due to the mediated electron transfer by the 3D-GNs-PTCA-DA nanocomposite, the Nafion/Lac/3D-GNs-PTCA-DA/GCE exhibited high catalytic activity for oxygen reduction. The 3D-GNs are proven to be a better substrate for Lac and its mediator immobilization than 2D graphene nanosheets (2D-GNs) due to the interconnected network structure and high specific surface area of 3D-GNs. A glucose/O2 fuel cell using Nafion/Lac/3D-GNs-PTCA-DA/GCE as the cathode and Nafion/glucose oxidase/ferrocence/3D-GNs/GCE as the anode can output a maximum power density of 112 μW cm(-2) and a short-circuit current density of 0.96 mA cm(-2). This work may be helpful for exploiting the popular 3D-GNs as an efficient electrode material for many other biotechnology applications.

Ultrasensitive IL-6 electrochemical immunosensor based on Au nanoparticles-graphene-silica biointerface

An Interleukin-6 (IL-6) electrochemical immunosensor was fabricated based on the Au nanoparticles (AuNP)-graphene-silica sol-gel as immobilization biointerface and AuNP-polydopamine (PDA)@carbon nanotubes (CNT) as the label of HRP-bound antibodies. The AuNP-graphene-silica sol-gel film was prepared in situ and modified on the ITO electrode, providing a stable network for the immobilization of antibody and exhibiting a dynamic working range of 1-40 pg/mL with a low detection limit of 0.3 pg/mL IL-6 (at 3s). The results of serum samples with the sensor received an acceptable agreement with the ELISA method. Importantly, this method provided a promising ultrasensitive assay strategy for clinical applications.

Successful stabilization of functionalized hybrid graphene for high-performance antimicrobial activity

We have prepared an antimicrobial nanocomposite composed of reduced graphene oxide (rGO) using antimicrobial agents and catechol derivative conjugated to polyethylene glycol-grafted poly(dimethylaminoethyl methacrylate) (PEG-g-PDMA). Graphene oxide (GO) has been simultaneously reduced by 2-chloro-3',4'-dihydroxyacetophenone (CCDP) in Tris buffer at pH 8.5 following catechol chemistry. Both CCDP and antimicrobial agent 1-bromododecane (C12) were quaternized to PEG-g-PDMA (CCDP-C12)-q-(PEG-g-PDMA). This synthesized polymer functionalized rGO as an antimicrobial nanocomposite, rGO/(CCDP-C12)-q-(PEG-g-PDMA). To increase antimicrobial activity, silver nanoparticles (Ag NPs) were deposited onto the high surface area of rGO/(CCDP-C12)-q-(PEG-g-PDMA). The prepared antimicrobial nanocomposite shows significant stability in aqueous media due to the hydrophilic behaviour of PEG. X-ray photoelectron spectroscopy investigation clearly shows the quaternization of C-12 and deposition of Ag NPs onto rGO surfaces. Ag NP-deposited rGO/(CCDP-C12)-q-(PEG-g-PDMA) shows better antimicrobial activity both against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria at lower concentration compared to without applying Ag NPs. Investigation of the cytotoxicity demonstrates outstanding non-toxic properties of both the prepared nanocomposite as well as the synthesized polymer.

Activity of laccase immobilized on TiO2-montmorillonite complexes

The TiO₂-montmorillonite (TiO₂-MMT) complex was prepared by blending TiO₂ sol and MMT with certain ratio, and its properties as an enzyme immobilization support were investigated. The pristine MMT and TiO₂-MMT calcined at 800 °C (TiO₂-MMT800) were used for comparison to better understand the immobilization mechanism. The structures of the pristine MMT, TiO₂-MMT, and TiO₂-MMT800 were examined by HR-TEM, XRD and BET. SEM was employed to study different morphologies before and after laccase immobilization. Activity and kinetic parameters of the immobilized laccase were also determined. It was found that the TiO₂ nanoparticles were successfully introduced into the MMT layer structure, and this intercalation enlarged the “d value” of two adjacent MMT layers and increased the surface area, while the calcination process led to a complete collapse of the MMT layers. SEM results showed that the clays were well coated with adsorbed enzymes. The study of laccase activity revealed that the optimum pH and temperature were pH = 3 and 60 °C, respectively. In addition, the storage stability for the immobilized laccase was satisfactory. The kinetic properties indicated that laccase immobilized on TiO₂-MMT complexes had a good affinity to the substrate. It has been proved that TiO₂-MMT complex is a good candidate for enzyme immobilization.

Graphene oxide-induced conformation changes of glucose oxidase studied by infrared spectroscopy

The adsorption of proteins on the surface of nanomaterials can induce changes in the structure and biological activity of the proteins. Although there have been a number of studies aimed at developing an understanding of the interactions of proteins with surfaces of nanomaterials, a detailed description of the actual state of the adsorbed proteins or the functional consequences of protein adsorption onto nanomaterials has yet to be reported. In this study, the conformation changes of glucose oxidase (GOx) induced by adsorption on graphene oxide (GO) sheets were investigated by quantitative second-derivative infrared analysis and two-dimensional infrared correlation spectroscopy (2D IR). The adsorption of GOx on GO sheets resulted in the conversion of α-helix to β-sheet structures and therefore led to substantial conformation changes of GOx, even the unfolding of the protein. These alterations in the conformation of GOx caused a significant decrease in the catalytic activity of the enzyme for glucose oxidation. This study demonstrates that nanomaterials can strongly influence the conformation and activity of adsorbed proteins. In addition to the importance of this effect in cases of the direct adsorption of proteins on nanomaterials, the results have implications for proteins adsorbed on materials with nanometer-scale surface roughness.