Amperometric Response Research Articles

Enhancement of Glucose Oxidase-Based Bioanode Performance by Comprising Spirulina platensis Microalgae Lysate

In this study, Spirulina platensis-based lysate was used as a biological redox mediator to design glucose oxidase (GOx) based biofuel cell bioanode. Chemically oxidized multi-walled carbon nanotubes (CNT) were deposited on carbon-electrode and were covered with eco-friendly algae cell-based lysate that facilitated the electron transfer and served as a biocompatible matrix for enzyme immobilization, which reduced the inactivation of GOx by CNT. The designed GC/PEI/CNT/S.p./GOx bioanode exhibited an open circuit potential (OCP) of −262 mV vs Ag/AgCl(3MKCl) in the presence of 12.5 mM of glucose. The maximum power output of the proposed bioanode was 21.8 times higher and reached 3.2 μW cm−2 at −51 mV vs Ag/AgCl(3MKCl) if the S. platensis cell lysate was used for bioanode design. The amperometric responses of GC/PEI/CNT/S.p./GOx bioelectrode towards the addition of glucose were linear at glucose concentrations ranging between 250 μM and 5 mM. These characteristics enable applying this bioanode as a part of biofuel cell and the electrode of an amperometric glucose biosensor, which response within 15 s, with a detection limit of 118 μM and a sensitivity of 15.09 μA mM−1 cm−2.

Ag doped Co/Ni bimetallic organic framework for determination of luteolin

Electrochemical determination of luteolin is vital to food industry owing to its bioactive properties such as anti-viral, anti-ulcer. However, bare electrode of traditional electrochemical sensors generally have narrow linear range and low sensitivity, which sets limit on their practical application. Accordingly, a new nano-architecture fabricated with Ag doped CoNi-bimetal metal–organic frameworks (Ag-CoNi-MOF) is developed as a material for electrochemical determination of luteolin. The introduction of Ag to three-dimensional (3D) flower-like hierarchical structure greatly increases specific surface area and electrical conductivity, which subsequently provides more excellent active sites for luteolin oxidation. Under optimal conditions, Ag-CoNi-MOF sensor presents a broader linear response to luteolin concentration of 0.002 – 1.0 μM with the detection limit as low as 0.4 nM (S/N = 3). Ag-CoNi-MOF has good anti-interference according to compared amperometric current response of luteolin within different organic analytes and metal ions. Finally, the sensor platform is implemented directly to determine luteolin in human urine for evaluation of its practical application. In general, Ag-CoNi-MOF sensors fabricated perform larger linear range with high sensitivity and anti-interference properties, which can be used as a potential material for electrochemical determination of luteolin.

Highly efficient Ag doped δ-MnO2 decorated graphene: Comparison and application in electrochemical detection of H2O2

Cytotoxic H2O2 is an inevitable part of our life, even during this contemporary pandemic COVID-19. Personal protective equipment of the front line fighter against coronavirus could be sterilized easily by H2O2 for reuse. In this study, Ag doped δ-MnO2 nanorods supported graphene nanocomposite (denoted as Ag@δ-MnO2/G) was synthesized as a nonenzymatic electrochemical sensor for the sensitive detection of H2O2. The ternary nanocomposite has overcome the poor electrical conductivity of δ-MnO2 and also the severe aggregation of Ag NPs. Furthermore, δ-MnO2/G provided a rougher surface and large numbers of functional groups for doping more numbers of Ag atoms, which effectively modulate the electronic properties of the nanocomposite. As a result, electroactive surface area and electrical conductivity of Ag@δ-MnO2/G increased remarkably as well as excellent catalytic activity observed towards H2O2 reduction. The modified glassy carbon electrode exhibited fast amperometric response time (<2 s) in H2O2 determination. The limit of detection was calculated as 68 nM in the broad linear range (0.005–90.64 mM) with high sensitivity of 104.43 µA mM−1 cm−2. No significant interference, long-term stability, excellent reproducibility, satisfactory repeatability, practical applicability towards food samples and wastewater proved the efficiency of the proposed sensor.

Influence of enzyme immobilization and skin-sensor interface on non-invasive glucose determination from interstitial fluid obtained by magnetohydrodynamic extraction

We integrated a magnetohydrodynamic fluid extractor with an amperometric glucose biosensor to develop a wearable device for non-invasive glucose monitoring. Reproducible fluid extraction through the skin and efficient transport of the extracted fluid to the biosensor surface are prerequisites for non-invasive glucose monitoring. We optimized the enzyme immobilization and the interface layer between the sensing device and the skin. The monitoring device was evaluated by extracting fluid through porcine skin followed by glucose detection at the biosensor. The biosensor featured a screen-printed layer of Prussian Blue that was coated with a layer containing glucose oxidase. Both physical entrapment of glucose oxidase in chitosan and tethering of glucose oxidase to electrospun nanofibers were evaluated. Binding of glucose oxidase to nanofibers under mild conditions provided a stable biosensor with analytical performance suitable for accurate detection of micromolar concentrations of glucose. Hydrogels of varying thickness (95–2000 μm) as well as a thin (30 μm) nanofibrous polycaprolactone mat were studied as an interface layer between the biosensor and the skin. The effect of mass transfer phenomena at the biosensor-skin interface on the analytical performance of the biosensor was evaluated. The sensing device detected glucose extracted through porcine skin with an apparent (overall) sensitivity of −0.8 mA/(M·cm2), compared to a sensitivity of −17 mA/(M·cm2) for measurement in solution. The amperometric response of the biosensor correlated with the glucose concentration in the fluid that had been extracted through porcine skin with the magnetohydrodynamic technique.

Theoretical and Numerical Analysis of Nonlinear Processes in Amperometric Enzyme Electrodes with Cyclic Substrate Conversion

A theoretical model of amperometric enzyme electrodes has been developed in which chemical amplification occurs in a single enzyme membrane via cyclic substrate conversion. The system is based on non-stationary diffusion equations with a nonlinear factor related to the Michaelis–Menten kinetics of the enzymatic reaction. By solving the nonlinear equations using the AGM technique, simple analytical expressions of concentration substrate, product, and amperometric current response are derived. Further, biosensor sensitivity, resistance, and gain are obtained from the current. MATLAB programming was used to carry out the digital simulation. The analytical results are validated with the numerical results. The effect of substrate concentration, maximum enzymatic rate, and membrane thickness on biosensor response was evaluated.

Electrochemical detection of glutamate by metal–organic frameworks-derived Ni@NC electrocatalysts

With the aim of developing an electrochemical sensor for the detection of glutamate, in the present study, Ni@NC nanoparticles were prepared by embedding Ni derived from Ni-based metal–organic frameworks in N-enriched carbon via a high-temperature calcination process. Further, the resulting material was investigated as an electrode modifier for sensor applications. Cyclic voltammetry measurements revealed that the Ni@NC nanoparticles prepared at 700 °C exhibited the most prominent activity for the electrocatalytic oxidation of glutamate, affording an amperometric response in a linear range of glutamate concentration of 5 × 10−3–500 μM with a low detection limit of 1.67 × 10−3 μM (S/N = 3), which was comparable with previously reported data. Furthermore, this electrochemical sensor demonstrated a high rate of recovery in real samples, providing a valuable method for the rapid detection of glutamate. As a potential candidate for glutamate sensing, the Ni@NC system can be expected to find application in many biomedical fields.

Organic β-cyclodextrin Nanoparticle: An Efficient Building Block Between Functionalized Poly(pyrrole) Electrodes and Enzymes.

Glyconanoparticles (GNPs) made by self-assembly of carbohydrate-based polystyrene-block-β-cyclodextrin copolymer are used as a building block for the design of nanostructured biomaterials of electrode. The firm immobilization of GNPs is carried out on electrochemically generated polymer, poly(pyrrole-adamantane), and copolymer, poly(pyrrole-adamantane)/poly(pyrrole-lactobionamide) via host-guest interactions between adamantane and β-cyclodextrin. The ability of GNPs for the specific anchoring of biological macromolecules is investigated using glucose oxidase enzyme modified by adamantane groups as a protein model (GOx-Ad). The immobilization of GOx-Ad is carried out by incubation of an aqueous enzyme solution on a coating of GNPs adsorbed on a platinum electrode. The presence of immobilized GOx-Ad is evaluated in aqueous glucose solution by potentiostating the underlying platinum electrode at 0.7V/SCE for the electro-oxidation of H2 O2 generated by the enzyme. The analytical performance of the bioelectrodes for the detection of glucose is compared to control electrodes prepared without GNPs or without electropolymerized films. The better permeability of copolymer compared to polymer and the possibility to elaborate two alternating layers of GNPs and GOx-Ad are clearly observed. The best amperometric response is recorded with a multilayered bioelectrode displaying a wide linear range linear range of the calibration curve: 68µmol L-1 to 0.1 molL-1 .

In Vitro Evaluation of Miniaturized Amperometric Enzyme Sensor Based on the Direct Electron Transfer Principle for Continuous Glucose Monitoring.

The bacterial derived flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (FADGDH) is the most promising enzyme for the third-generation principle-based enzyme sensor for continuous glucose monitoring (CGM). Due to the ability of the enzyme to transfer electrons directly to the electrode, recognized as direct electron transfer (DET)-type FADGDH, although no investigation has been reported about DET-type FADGDH employed on a miniaturized integrated electrode. The miniaturized integrated electrode was formed by sputtering gold (Au) onto a flexible film with 0.1 mm in thickness and divided into 3 parts. After an insulation layer was laminated, 3 openings for a working electrode, a counter electrode and a reference electrode were formed by dry etching. A reagent mix containing 1.2 × 10-4 Unit of DET-type FADGDH and carbon particles was deposited. The long-term stability of sensor was evaluated by continuous operation, and its performance was also evaluated in the presence of acetaminophen and the change in oxygen partial pressure (pO2) level. The amperometric response of the sensor showed a linear response to glucose concentration up to 500 mg/dL without significant change of the response over an 11-day continuous measurement. Moreover, the effect of acetaminophen and pO2 on the response were negligible. These results indicate the superb potential of the DET-type FADGDH-based sensor with the combination of a miniaturized integrated electrode. Thus, the described miniaturized DET-type glucose sensor for CGM will be a promising tool for effective glycemic control. This will be further investigated using an in vivo study.

A novel construct of an electrochemical acetylcholinesterase biosensor for the investigation of malathion sensitivity to three different insect species using a NiCr2O4/g-C3N4 composite integrated pencil graphite electrode.

Herein, an electrochemical biosensor has been prepared to assess the sensitivity of an organophosphate insecticide, malathion, to acetylcholinesterase (AChE) enzyme of three insects including Apis mellifera (honeybee), Tribolium castaneum (red flour beetle), and Zootermopsis nevadensis (dampwood termite). A composite of nickel chromite (NiCr2O4) and graphitic carbon nitride (g-C3N4) was prepared and characterized for its morphological, chemical and electrical properties. The NiCr2O4/g-C3N4 composite integrated pencil graphite electrodes were used to covalently immobilize insect AChE enzymes and amperometric response of bioelectrodes was determined through cyclic voltammetry. The prepared bioelectrodes exhibited high enzyme immobilization efficiency and electro-catalytic performance. The integrated bioelectrodes could efficiently detect malathion induced inhibition of insects' AChEs. The linear ranges for malathion were found to be 0.1–1.6 μM, 1–40 nM and 2–100 nM, and LODs were 2 nM, 0.86 nM and 2.3 nM for A. mellifera, T. castaneum, and Z. nevadensis, respectively. Additionally, the biosensing platform developed using A. mellifera AChE was found highly sensitive and effective for malathion recoveries from spiked wheat flour samples with high recovery rates. Moreover, the proposed method was adequately reproducible and selective. The results revealed that A. mellifera AChE is less sensitive to inhibition by malathion as compared to T. castaneum, and Z. nevadensis AChE. The experimental results were validated through computational docking of malathion with insect AChEs and the results were in correspondence to experimental outcomes. The proposed method can be a plausible alternate to conventional analytical methods to assess the pesticide sensitivity and toxicity of various compounds against insect enzymes.

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid.

This work presents for the first time the systematic preparation of a novel carbon nanotube-MCM-41 hybrid employing the mesoporous material MCM-41 as a successful dispersant for multiwall carbon nanotubes (MWCNTs). Relevant dispersion variables such as the amount of MWCNTs, MCM-41 concentration, and sonication time were optimized through a central composite design (CDD)/response surface methodology (RSM). Several solvents were evaluated and N,N-dimethylformamide (DMF) was selected because it allowed reaching stable dispersions with very good electrochemical response. The electrochemical performance of glassy carbon electrodes (GCE) modified with different hybrids was evaluated by cyclic voltammetry (CV) using ascorbic acid (AA) as redox marker, while their surface morphology was characterized by SEM microscopy. The optimal MWCNT-MCM-41 dispersion condition was 0.75 mg mL-1 MWCNTs, 0.25 mg mL-1 MCM-41, and 30 min sonication. Both, electrochemical results and SEM images correlate with a percolation behavior from MWCNT-MCM-41 hybrid. Electrooxidation of AA at GCE modified with the optimal hybrid occurred under diffusion control and exhibited an enhanced current response (65 μA) and a lower overvoltage (-0.005 V) compared to bare GCE (ip = 22 μA, Ep = 0.255 V). The amperometric response of AA at GCE/MWCNT-MCM-41 exhibited remarkable figures of merit, including an ultralow detection limit (1.5 nM), high sensitivity (45.4 × 103 μA M-1), excellent short- and long-term stability, and very good anti-interference ability for AA detection. The analytical applicability of the developed electrochemical sensor was evaluated by sensing AA in several real samples, showing excellent correlation with the values reported by manufacturers in both pharmaceutical and food samples.

3D nanoporous core-shell ZnO@Co3O4 electrode materials for high-performance supercapacitors and nonenzymatic glucose sensors

• A three-dimensional nanoporous core shell ZnO/Co 3 O 4 heterojunction structure was applied in electrochemical sensing and high-performance supercapacitor. • Desirable detection limit of glucose and sensitivity were achieved to be 0.0426 μM, and 4082.1 µA µM −1 cm −2 , respectively. Transition metal oxides have excellent electrochemical activity and properties because of the various valence states, high electrical conductivity, and ample active sites. In this study, a composite electrode comprising Co 3 O 4 nanowire arrays and ultrathin and porous ZnO nanoflake films is formed by a simple hydrothermal method and pulsed electrodeposition. In this unique three-dimensional (3D) nanoporous core – shell ZnO@Co 3 O 4 heterojunction, the Co 3 O 4 nanowire arrays in the core with good electrical conductivity and porous ZnO nanosheets in the shell synergistically increase the active sites, expedite mass transfer, and improve the structural stability. The ZnO@Co 3 O 4 sensor detects glucose selectively as manifested by a short amperometric response time of 3 s while delivering excellent performance such as a wide dynamic linear range (0.001–18.917 mM), low detection limit (0.0426 µM), and high sensitivity (4082.1 µA µM −1 cm −2 ). The ZnO@Co 3 O 4 structure is also suitable for supercapacitors as it shows a high specific capacitance of 1618.26 F g −1 at a current density of 10 A g −1 , excellent rate performance (retention of 97.1 % up to 10 A g −1 ), and long cycling stability (91.23% retention for 5,000 cycles). These remarkable properties confirm the feasibility of the materials design and the ZnO@Co 3 O 4 structure has large potential as multi-functional materials in electrochemical sensing and energy storage.

Nanoporous naphthalene diimide surface enhances humidity and ammonia sensing at room temperature

We report fabrication and characterisation of humidity and ammonia sensors based on a nanoporous naphthalene diimide (NDI) thin layer, the active material coded as NDI-1, operating at room temperature. A thin layer of NDI-1 as an organic semiconducting sensing material was deposited onto the interdigitated electrodes using the spin-coating technique. Surface morphology investigations of the thin film using atomic force microscopy and scanning electronic microscopy revealed a uniform nanoporous surface. Structural and thermal behaviour studies of the NDI-1 using X-ray diffraction and thermogravimetric analyses confirmed the crystallinity and thermal stability, respectively. The capacitive type NDI-1 humidity sensor displayed a sensitivity of 10.13 pF/%RH, quick response and recovery (20.1/6.28 s), low hysteresis (0.72%), long-term stability and more importantly, a wide working range of relative humidity (10–95%) at 250 Hz. Interestingly, the developed sensor was sensitive enough to monitor respiration rate and demonstrated an excellent non-contact skin humidity sensing performance. The amperometric response of the sensor towards ammonia was also investigated. An increase in the sensor current was recorded when exposed to different ammonia concentrations (25, 37.5 and 50 ppm). The sensor showed high selectivity and good sensitivity (27.7%) towards 50 ppm ammonia with 200 s and 350 s response and recovery times, respectively.

A Novel Amperometric Aptamer–Antibody Sandwich Assay for the Detection of Tuberculosis With Diazonium Electrografted Enhanced Modified Electrode

In this study, a sensitive aptamer-antibody-based sandwich biosensor utilizing chronoamperometry for early detection of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Mycobacterium tuberculosis</i> CFP10 antigen is reported. An anti-CFP10 aminated aptamer was covalently immobilized onto the disposable screen-printed carbon electrode via carbodiimide chemistry with the electrografted 4-carboxyphenyl diazonium salt. The CFP10 aptamer recognized and captured the target protein through affinity binding. The quantification of CFP10 antigen was based on amperometric responses from the electrocatalytic reaction between horseradish peroxidase (HRP) and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , with hydroquinone as an electron transfer mediator. The developed aptasensor displayed an excellent analytical performance with a linear range of 5 to 500 ng mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and a detection limit of 1.22 ng mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> in buffer solution. The diazonium-based sensor was also successfully applied on spiked human serum sample and exhibited a detection limit of 1.05 ng mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Furthermore, the fabricated aptasensor demonstrated high sensitivity to CFP10 antigen over other proteins. The proposed aptamer-based sensor is rapid, sensitive, and disposable, thus suitable for point-of-care tuberculosis detection. This work also highlights the use of CFP10 aptamer as a less expensive and stable alternative reagent to antibodies for the development of a better diagnosis of tuberculosis.

Hydrogen Peroxide Detection Using Prussian Blue‐modified 3D Pyrolytic Carbon Microelectrodes

AbstractA highly sensitive amperometric Prussian blue‐based hydrogen peroxide sensor was developed using 3D pyrolytic carbon microelectrodes. A 3D printed multielectrode electrochemical cell enabled simultaneous highly reproducible Prussian blue modification on multiple carbon electrodes. The effect of oxygen plasma pre‐treatment and deposition time on Prussian blue electrodeposition was studied. The amperometric response of 2D and 3D sensors to the addition of hydrogen peroxide in μM and sub‐μM concentrations in phosphate buffer was investigated. A high sensitivity comparable to flow injection systems and a detection limit of 0.16 μM was demonstrated with 3D pyrolytic carbon microelectrodes at stirred batch condition

Nanobody-Based Immunosensor Detection Enhanced by Photocatalytic-Electrochemical Redox Cycling.

Detection of antigenic biomarkers present in trace amounts is of crucial importance for medical diagnosis. A parasitic disease, human toxocariasis, lacks an adequate diagnostic method despite its worldwide occurrence. The currently used serology tests may stay positive even years after a possibly unnoticed infection, whereas the direct detection of a re-infection or a still active infection remains a diagnostic challenge due to the low concentration of circulating parasitic antigens. We report a time-efficient sandwich immunosensor using small recombinant single-domain antibodies (nanobodies) derived from camelid heavy-chain antibodies specific to Toxocara canis antigens. An enhanced sensitivity to pg/mL levels is achieved by using a redox cycle consisting of a photocatalytic oxidation and electrochemical reduction steps. The photocatalytic oxidation is achieved by a photosensitizer generating singlet oxygen (1O2) that, in turn, readily reacts with p-nitrophenol enzymatically produced under alkaline conditions. The photooxidation produces benzoquinone that is electrochemically reduced to hydroquinone, generating an amperometric response. The light-driven process could be easily separated from the background, thus making amperometric detection more reliable. The proposed method for detection of the toxocariasis antigen marker shows superior performances compared to other detection schemes with the same nanobodies and outperforms by at least two orders of magnitude the assays based on regular antibodies, thus suggesting new opportunities for electrochemical immunoassays of challenging low levels of antigens.

Covalent Immobilisation of a Nanoporous Platinum Film onto a Gold Screen-Printed Electrode for Highly Stable and Selective Non-Enzymatic Glucose Sensing

Progress in the development of commercially available non-enzymatic glucose sensors continues to be problematic due to issues regarding selectivity, reproducibility and stability. Overcoming these issues is a research challenge of significant importance. This study reports a novel fabrication process using a double-layer self-assembly of (3 mercaptopropyl)trimethoxysilane (MPTS) on a gold substrate and co-deposition of a platinum–copper alloy. The subsequent electrochemical dealloying of the less noble copper resulted in a nanoporous platinum structure on the uppermost exposed thiol groups. Amperometric responses at 0.4 V vs. Ag/AgCl found the modification to be highly selective towards glucose in the presence of known interferants. The sensor propagated a rapid response time &lt;5 s and exhibited a wide linear range from 1 mM to 18 mM. Additionally, extremely robust stability was attributed to enhanced attachment due to the strong chemisorption between the gold substrate and the exposed thiol of MPTS. Incorporation of metallic nanomaterials using the self-assembly approach was demonstrated to provide a more reproducible and controlled molecular architecture for sensor fabrication. The successful application of the sensor in real blood serum samples displayed a strong correlation with clinically obtained glucose levels.

Effects of electroactive group and enzyme crosslinkers numbers on analytical performance for conductive polymer-based sensor platforms

This manuscript describes an amperometric sensor application of a new class of triazine-centered monomers functionalized with different numbers of carbazole and hydrazine. In the sensor system, carbazole and hydrazine are designed as transducer and enzyme crosslinker groups, respectively. The monomers (TECA and CTDA) containing different numbers of carbazole and hydrazine were electrochemically polymerized on a graphite (GR) electrode. A new sensor platforms for glucose determination have been obtained by immobilizing glucose oxidase (GOx) on the polymer film surfaces. The pTECA/GOx and pCTDA/GOx-based electrodes were investigated for an evaluation of electron transfer between the enzyme and electrode at bioelectrochemically relevant potentials via pTECA and pCTDA layer. The results show that amperometric response values were greater for the polymer containing more hydrazine ends than the polymer containing more carbazole groups. This is due to the that as the hydrazine ends increased, the more enzyme crosslinker groups at the same surface size. The evaluation of two different configurations (pTECA/GOx and pCTDA/GOx) of working electrodes suggested that the pTECA/GOx configuration, which was composed of more hydrazine ends and enzyme, is the more suitable candidate for biosensor applications. Moreover, it was determined that the pTECA/GOx and pCTDA/GOx-based electrodes are reliable for the establishment of advanced electron transfer between enzyme and electrode for the application in amperometric biosensors because of the observed high amperometric response values, and low LOD values.

The Kinetic and Analytical Aspects of Enzyme Competitive Inhibition: Sensing of Tyrosinase Inhibitors.

An amperometric biosensor based on tyrosinase, immobilized onto a carbon black paste electrode using glutaraldehyde and BSA was constructed to detect competitive inhibitors. Three inhibitors were used in this study: benzoic acid, sodium azide, and kojic acid, and the obtained values for fifty percent of inhibition (IC50) were 119 µM, 1480 µM, and 30 µM, respectively. The type of inhibition can also be determined from the curve of the degree of inhibition by considering the shift of the inhibition curves. Amperometric experiments were performed with a biosensor polarized at the potential −0.15 V vs. Ag/AgCl and using 0.1 M phosphate buffer (pH 6.8) as an electrolyte. Under optimized conditions, the proposed biosensor showed a linear amperometric response toward catechol detection from 0.5 µM to 38 µM with a detection limit of 0.35 µM (S/N = 3), and its sensitivity was 66.5 mA M−1 cm−2. Moreover, the biosensor exhibited a good storage stability. Conversely, a novel graphical plot for the determination of reversible competitive inhibition was represented for free tyrosinase. The graph consisted of plotting the half-time reaction (t1/2) as a function of the inhibitor concentration at various substrate concentrations. This innovative method relevance was demonstrated in the case of kojic acid using a colorimetric bioassay relying on tyrosinase inhibition. The results showed that the t1/2 provides an extended linear range of tyrosinase inhibitors.

Synthesis of nanocubic shape controlled Gold-Prussian blue nanocomposite for enhanced electrocatalytic hydrazine oxidation

• A facile wet chemical method used for the synthesis of nano cubic shape controlled Au-PB-NCs. • Au-PB-NC/GCE shows 13 times higher catalytic current density of hydrazine than pristine PB-NCs. • The sensitivity of Au-PB-NCs/GCE is 111 μA.cm −2 μM −1 with LOD of 0.709 µM for sensing of hydrazine. Herein, we report for the first time, facile chemical synthesis of gold nanoparticles embedded in nano-cubic shaped prussian blue (Au-PB-NCs). To understand the role of gold nanoparticles (AuNPs) present in the Au-PB-NCs, the same chemical method is used without involving gold precursor solution for pristine prussian blue nanocubes (PB-NCs). For the proof-of-concept experiment, both Au-PB-NCs and PB-NCs are modified on glassy carbon electrodes (it is called as Au-PB-NCs/GCE and PB-NCs/GCE respectively) to study the electrocatalytic activity of hydrazine molecules as a model system. The exact size of the PB-NCs and the nature of the distribution of AuNPs into the Au-PB-NCs matrix are confirmed by high-resolution transmission electron microscopy (HR-TEM) and high-angle annular dark-field scanning transmission electron microscopic (HAADF-STEM) analysis. X-ray diffraction (XRD) and X-ray photon electron microscopy (XPS) results reveal that the PB-NCs has high crystalline and the oxidation state of Au is Au 0 and Au + in Au-PB-NCs. Compared with PB-NCs/GCE, the Au-PB-NCs/GCE showed higher redox current density and improved charge transfer kinetics in electrochemical measurements. Remarkably, it exhibits higher electrocatalytic oxidation current and excellent amperometric response with the linear range of 0–40 µM for hydrazine molecule when compared with PB-NCs/GCE. The calculated low detection limit and sensitivity value of Au-PB-NCs/GCE is 0.709 µM and 111 µA. cm −2 . µM −1 , respectively, which are comparable with reported literature. The selectivity and stability of electrooxidation of hydrazine molecule on fabricated Au-PB-NCs/GCE platform is investigated by amperometric method. The obtained results clearly indicate that Au-PB-NCs/GCE has excellent stability and selectivity towards hydrazine sensing without the impact of other interference. Also, the developed Au-PB-NCs/GCE sensor platform is applied to the real water samples analysis and showed the results of good recovery, reproducibility and repeatability, which implies its feasibility for realistic application in hydrazine estimation.

Design and Fabrication of Glucose Biosensors Based on Immobilization of Glucose Oxidase on Titanium Oxide Nanotube Arrays.

An electrochemical biosensor for the detection of glucose is realized by immobilizing glucose oxidase (GOx) enzyme onto titanium dioxide nanotube arrays by a coupling encapsulation process. We present details of a robust fabrication technique that results in a durable and reproducible sensor characteristics. The TiO₂ nanotube arrays are grown directly on a titanium substrate by a potentiostatic anodization process in a water and ethylene-glycol mixture solution, which contains ammonium fluoride. An electropolymerization process was also performed to enhance interfacial adhesion between GOx and TiO₂ nanotubes. Detection of glucose concentrations was achieved with a linear response in the range of 0.01 to 0.2 mM. Investigation of enhanced sensitivity by increasing the count, the length, and the cross-section of the nanotubes was also carried out. Surface morphologies of Ti substrate were examined by scanning electron microscopy to optimize the anodization process and thus the TiO₂/Ti nanotube dimensions. We utilized a time-based amperometric response for the quantitative determination of hydrogen peroxide concentration through electro-reduction reaction with a bare TiO₂/Ti nanotube-array electrodes, thus providing a reference for the determination of glucose levels with a GOx-coated TiO₂/Ti nanotube array electrodes. Detection levels down to 5.2 μM were recorded.