Guanine/Ionic Liquid Derived Ordered Mesoporous Carbon Decorated with AuNPs as Efficient NADH Biosensor and Suitable Platform for Enzymes Immobilization and Biofuel Cell Design

Guanine‐ionic liquid derived ordered mesoporous carbon (GIOMC) decorated with gold nanoparticles was used as electrocatalyste for NADH oxidation and electrochemical platform for immobilization of glucose dehydrogenase (GDH) enzyme. The resulting GIOMC/AuNPs on the glassy carbon electrode can be used as novel redox‐mediator free for NADH sensing and this integrated system (GIOMC/AuNPs/GDH) shows excellent electrocatalytic activity toward glucose oxidation. Furthermore, the ionic liquid derived ordered mesoporous carbon derivate with Ph‐SO₃H (IOMC‐PhSO₃H) decorated with AuNPs has been developed to bilirubin oxidase enzyme (BOD) immobilization and the GC/IOMC‐PhSO₃H/BOD integrated system shows excellent bioelectrocatalytic activity toward oxygen reduction reaction. The proposed mesostructured platforms decorated by AuNPs have been developed to enhance mass transfer and charge transfer from biocatalyst to electrode, leading these bioanode and biocathode used for biofuel cell assembly. Integration designed bioanode and biocathode yielding a membrane‐less glucose/O₂ biofuel cell with power density of 33 (mW.cm⁻²) at 257 mV. The open circuit voltage of this biofuel cell and maximum produced current density were 508 mV and 0.252 (mA.cm⁻²) respectively.     

One-step construction of an electrode modified with electrodeposited Au/SiO2 nanoparticles, and its application to the determination of NADH and ethanol

A new electrode was developed by one-step potentiostatic electrodeposition (at ?2.0 V for 20 s) of Au/SiO₂ nanoparticles on a glassy carbon electrode. The resulting electrode (nano-Au/SiO₂/GCE) was characterized by scanning electronic microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) at the nano-Au/SiO₂/GCE were thoroughly investigated. Compared to the unmodified electrode, the overpotential decreased by about 300 mV, and the current response significantly increased. These changes indicated that the modified electrode showed excellent catalytic activity in the oxidation of NADH. A linear relationship was obtained in the NADH concentration range from 1.0?×?10^?6 to 1.0?×?10^?4 mol?L^?1. In addition, amperometric sensing of ethanol at the nano-Au/SiO₂/GCE in combination with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A wide linear response was also found for ethanol in the range from 5.0?×?10^?5 to 1.0?×?10^?3 mol?L^?1 and 1.0?×?10^?3 to 1.0?×?10^?2 mol?L^?1, respectively. The method was successfully applied to determine ethanol in beer and biological samples.     

Enhanced NADH Oxidation Using Polytyramine/Carbon Nanotube Modified Electrodes for Ethanol Biosensing

Polytyramine (PT) has been electro‐deposited onto multi‐walled carbon nanotube (MWCNT) modified glassy carbon (GC) electrodes via oxidation of tyramine in 0.1 M H₃PO₄ by cycling the potential over the range of −400 mV to 1300 mV (versus Ag/AgCl). The reactivity of the resulting chemically‐modified electrodes was characterized using cyclic voltammetry in the presence and absence of reduced nicotinamide adenine dinucleotide (NADH). The modified electrodes displayed electrochemical activity due to the formation of quinone species and were catalytically active towards NADH oxidation by lowering the oxidation peak potential by 170 mV compared to the value of the MWCNT modified electrode with a peak potential of 180±10 mV (versus Ag/AgCl). The MWCNT/PT surface was further characterized using SEM and XPS methods, which indicated that a thin polymeric film had been formed on the electrode surface. The present work demonstrates the advantage of using PT as a platform that combines both the immobilization of alcohol dehydrogenase (ADH) and the mediation of NADH oxidation at a low overpotential essential to the design of high performance ethanol biosensors, all within an easily electropolymerizable film. The resulting biosensor displayed an ethanol sensitivity of 4.28±0.06 μA mM⁻¹ cm⁻², a linear range between 0.1 mM and 0.5 mM and a detection limit of 10 μM.     

An Air‐breathing Carbon Cloth‐based Screen‐printed Electrode for Applications in Enzymatic Biofuel Cells

We report a prototype air‐breathing carbon cloth‐based electrode that was fabricated starting from a commercially available screen‐printed electrode equipped with a transparent ITO working electrode (DropSens, ref. ITO10). The fabrication of the air‐breathing electrodes is straightforward, shows satisfactory reproducibility and a good electrochemical response as evaluated by means of [Fe(CN)₆]^3?/4? voltammetry. The gas‐diffusion electrodes were successfully modified with the O₂ reducing enzyme bilirubin oxidase from Myrothecium verrucaria in a direct electron transfer regime. The enzyme modified electrodes showed a remarkable high current density for O₂ reduction in passive air‐breathing mode of up to 5 mA cm^?2. Moreover, the enzyme modified electrodes were applied as O₂ reducing biocathodes in a glucose/air enzymatic biofuel cell in combination with a high current density glucose oxidase/redox polymer bioanode. The biofuel cell provides a high maximum power density of (0.34±0.02) mW cm^?2 at 0.25 V. The straightforward design, low cost and the high reproducibility of these electrodes are considered as basis for standardized measurements under gas‐breathing conditions and for high throughput screening of gas converting (bio‐)catalysts.     

Silver‐Palladium Nanoalloys Modified Carbon Ionic Liquid Electrode with Enhanced Electrocatalytic Activity Towards Formaldehyde Oxidation

Electrocatalysis of the oxidation of formaldehyde on silver‐palladium‐modified carbon ionic liquid electrode (AgPd/CILE) was investigated in 0.1 M NaOH. The electrochemical performance of the AgPd/CILE was compared with those of Pd/CILE and Ag/CILE. Ag plays an important role in the catalytic performance of AgPd nanocatalyst and yields an excellent antifouling effect. Amperometric measurements showed that AgPd/CILE is a promising sensor for the detection of formaldehyde in the range of 10.0 µM–70.0 mM with a sensitivity of 240.6 µA mM^?1 cm^?2 and a detection limit of 2 µM. The method is free from interference of methanol, ethanol and formic acid.     

Biofuel Cell Operating in Vivo in Rat

Biocatalytic electrodes made of buckypaper were modified with PQQ‐dependent glucose dehydrogenase on the anode and with laccase on the cathode. The enzyme modified electrodes were assembled in a biofuel cell which was first characterized in human serum solution and then the electrodes were placed onto exposed rat cremaster tissue. Glucose and oxygen dissolved in blood were used as the fuel and oxidizer, respectively, for the implanted biofuel cell operation. The steady‐state open circuitry voltage of 140±30 mV and short circuitry current of 10±3 µA (current density ca. 5 µA cm^?2 based on the geometrical electrode area of 2 cm²) were achieved in the in vivo operating biofuel cell. Future applications of implanted biofuel cells for powering of biomedical and sensor devices are discussed.     

An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles

An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe₃O₄@Au NPs) is presented. ADH was immobilized on Fe₃O₄@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO₂. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD⁺); working electrode: carbon paste with magnetically attached Fe₃O₄@Au NPs (0.012 mg ? cm^?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm² of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r²=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM^?1 ? cm^?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %.     

Electrochemical and Photoelectrochemical Sensing of NADH and Ethanol Based on Immobilization of Electrogenerated Chlorpromazine Sulfoxide onto Graphene‐CdS Quantum Dot/Ionic Liquid Nanocomposite

Here, a simple one‐step solvothermal procedure was employed to synthesize a nanocomposite containing graphene‐nanosheets and CdS quantum dots (GNs‐CdS QDs). The electrochemical oxidation of chlorpromazine (CPZ) to chlorpromazine‐sulfoxide (CPZ‐SO) onto a GNs‐CdS QDs/ionic liquid (IL) nanocomposite modified glassy carbon (GC) electrode give rise to redox‐active products which showed excellent electrocatalytic and photoelectrocatalytic activity toward NADH oxidation at reduced overpotential. A linear response up to 200 µM was obtained for photoamperometric determination of NADH with detection limit 1 µM. Immobilizing alcohol dehydrogenase(ADH) onto the modified electrode via a simple cross linking procedure, the photoelectrochemical capability of the proposed system toward ethanol biosensing was clearly shown.     

The NADH Electrochemical Detection Performed at Carbon Nanofibers Modified Glassy Carbon Electrode

In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10^?5 to 2.1×10^?3 mol L^?1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm²), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors.     

Fabrication of Acid Violet 34/Nickel Hydroxide Ultrathin Film and Its Electrocatalytic Performance for Glucose

This article reports the fabrication of Acid Violet 34 (AV34)/nickel hydroxide nanosheets ultrathin film on the glassy carbon electrode (GCE) via the electrostatic layer‐by‐layer (LBL) technique, and its electrocatalytic oxidation for glucose was demonstrated. UV‐vis absorption and electrochemical impedance spectra indicate the uniform deposition of the LBL film, with a continuous and smooth film surface observed by SEM and AFM. The electrochemical performance of the ultrathin film was studied by cyclic voltammetry and chronoamperometry. The (AV34/Ni(OH)₂)₅ ultrathin film modified electrode displays a fast direct electron transfer attributed to the Ni²⁺/Ni³⁺ redox couple as well as remarkable electrocatalytic activity towards the oxidation of glucose. The linear response was obtained in the range 0.5–13.5 mM (R=0.9994) with a low detection limit (14 µM), high sensitivity (25.9 µA mM^?1 cm^?2), rapid response (less than 1 s) and excellent anti‐interference properties to the species including ascorbic acid (AA), uric acid (UA), acetamidophenol (AP) and structurally related sugars. Therefore, the AV34/Ni(OH)₂ ultrathin film can be potentially used as a feasible electrochemical sensor for the determination of glucose.     

Redox‐Polymer‐Based High‐Current‐Density Gas‐Diffusion H2‐Oxidation Bioanode Using [FeFe] Hydrogenase from Desulfovibrio desulfuricans in a Membrane‐free Biofuel Cell

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual‐gas diffusion electrode H₂/O₂ biofuel cell equipped with a [FeFe] hydrogenase/redox polymer‐based high‐current‐density H₂‐oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm^?2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer‐based biofuel cell with outstanding power densities of 5.4 mW cm^?2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O₂.     

Electrochemical Oxidation of Ibuprofen and Its Voltammetric Determination at a Boron‐Doped Diamond Electrode

The electrochemical oxidation of ibuprofen at a boron‐doped diamond electrode (BDDE) and its voltammetric determination is reported for the first time. A well‐defined oxidation peak was observed at around 1.6 V in 0.1 mol L^?1 H₂SO₄ solution with 10 % (v/v) ethanol at the BDDE surface activated by either cathodic or anodic pretreatments. A differential‐pulse voltammetric method for the determination of ibuprofen in pharmaceutical formulations was optimized with a detection limit of 5 µmol L^?1 and compared with the British Pharmacopeia method.     

A biofuel cell based on pyrroloquinoline quinone and microperoxidase-11 monolayer-functionalized electrodes

A pyrroloquinoline quinone (PQQ) monolayer-functionalized-Au-electrode and a microperoxidase-11 (MP-11)-modified Au-electrode are used as catalytic anode and cathode in a biofuel cell element, respectively. The cathodic oxidizer is H₂O₂ whereas the anodic fuel-substrate is 1,4-dihydronicotinamide adenine dinucleotide, NADH. The PQQ-monolayer electrode catalyzes the oxidation of NADH in the presence of Ca²⁺ ions. The MP-11-functionalized electrode catalyzes the reduction of H₂O₂. The biofuel cell generates an open-circuit voltage, V_oc, of ca. 320 mV and a short-circuit current density, I_sc, of ca. 30 μA·cm⁻². The maximum electrical power, W_max, extracted from the cell is 8 μW at an external load of 3 kΩ. The fill factor of the biofuel cell, f=W_max·I_sc⁻¹·V_oc⁻¹, is ca. 25%.     

Nonenzymatic Hydrogen Peroxide Electrochemical Sensor Based on Au‐HS/SO3H‐PMO (Et) Nanocomposite

A newly nonenzymatic sensor for hydrogen peroxide (H₂O₂) based on the (Au‐HS/SO₃H‐PMO (Et)) nanocomposite is demonstrated. The electrochemical properties of the as‐prepared nanocomposite were studied. It displayed an excellent performance towards H₂O₂ sensing in the linear response range from 0.20 µM to 4.30 mM (R=0.9999) with a sensitivity of 6.35×10² µA µM^?1 cm^?2 and a low detection limit of 0.0499 µM. Furthermore, it was not affected by electroactive interference species. These features proved that the modified electrode was suitable for determination of H₂O₂.     

Employing Methylene Green Coated Carbon Nanotube Electrodes to Enhance NADH Electrocatalysis for Use in an Ethanol Biofuel Cell

We prepared and characterized electrocatalysts based on multiwalled carbon nanotubes (MWCNTs) coated with methylene green (MG). These electrocatalysts can regenerate nicotinamide adenine dinucleotide (NAD⁺), so they are potentially applicable in the field of bioelectronics. NADH oxidation occurs between 0.14±0.002 and 0.16±0.002 V vs. Ag/AgCl. The most efficient bioanode furnishes 88±7 µW cm^?2 and 500 µA cm^?2 and an open circuit voltage of 590±22 mV. In conclusion, we obtained a reliable and easy‐to‐prepare electrocatalyst that can regenerate NAD⁺ and may be applicable in biosensors and bioelectronic devices that use a wide range of NAD⁺‐dependent enzymes.     

Electrochemical Activation of Graphite Nanosheets Decorated with Palladium Nanoparticles for High Performance Amperometric Hydrazine Sensor

Herein, we have demonstrated a preparation of palladium nanoparticles on electroactivated graphite nanosheets modified screen printed carbon electrode (PdNPs‐EGNS/SPCE) by a simple electrochemical method. The well‐prepared electrocatalyst was potentially applied to the high performance electrocatalytic oxidation of hydrazine in neutral medium. The PdNPs‐EGNS novel composite was characterized by scanning electron microscope (SEM) and the average diameter and thickness of PdNPs and EGNS were found to be ～38 nm and 85 nm, respectively. The high performance electrocatalytic determination of hydrazine was performed by the amperometric i‐t method. The fabricated sensor displayed irreversible electrocatalytic oxidation of hydrazine with diffusion‐controlled electrode process. The oxidation of hydrazine at PdNPs‐EGNS/SPCE showed wider linear range 0.05–1415 µM and high sensitivity 4.382 µA µM^?1 cm^?2. The as‐prepared electrocatalyst achieved quick response towards hydrazine with a lower detection limit 4 nM.     

Wireless Information Transmission System Powered by an Abiotic Biofuel Cell Implanted in an Orange

An “abiotic” biofuel cell composed of catalytic electrodes modified with inorganic nanoparticles (NPs) deposited on carbon black (CB) was used to activate a wireless information transmission system. The cathode and anode were made of carbon paper modified with Pt‐NPs/CB and buckypaper modified with Au₈₀Pt₂₀‐NPs/CB, respectively. The cathode/anode pair was implanted in orange pulp extracting power from its content (glucose and fructose in the juice). The open circuit voltage, V_oc, short circuit current density, j_sc, and maximum power produced by the biofuel cell, P_max, were found as 0.36 V, 1.3 mA cm^?2 and 182 µW, respectively. The voltage produced by the biofuel cell was amplified with an energy harvesting circuit and applied to a wireless transmitter. The present study continues the research line where different implantable biofuel cells are used for activation of electronic devices.     

High‐Performance Amperometric Sensors Using Catalytic Platinum Nanoparticles‐Thionine‐Multiwalled Carbon Nanotubes Nanocomposite

Thionine (TH) adsorbed on multiwalled carbon nanotubes (MWCNTs) increases the load and dispersion of platinum nanoparticles (PtNPs) generated by chemical reduction of H₂PtCl₆ with NaBH₄. Under the optimum conditions, the PtNPs‐TH‐MWCNTs/Au electrode electrocatalyzed the reduction and oxidation of H₂O₂ with high sensitivity, and after glucose oxidase (GOx) adsorption it responded to glucose concentration with a sensitivity of 0.14 A M^?1 cm^?2. The cyclic voltammetric cathodic peak current for NO₂^? reduction on PtNPs‐TH‐MWCNTs/Au responded linearly to NO₂^? concentration from 0.5 to 150 µM, with a sensitivity of 5.52 A M^?1 cm^?2 and a detection limit of 0.2 µM.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

A Simple and Effective Way to Integrate Nile Blue Covalently onto Functionalized SWCNTs Modified GC Electrodes for Sensitive and Selective Electroanalysis of NADH

A simple and new way to assemble Nile blue (NB) covalently onto the surface of functionalized single‐walled carbon nanotubes (f‐SWCNTs) modified glassy carbon (GC) electrode (NB/f‐SWCNTs/GC electrode) was described. The NB/f‐SWCNTs/GC electrode catalyzes effectively the oxidation of NADH with a remarkably decreased overpotential (ca. 700 mV) compared with that at the bare GC. The reaction was found to obey a so‐called Michaelis–Menten kinetics and the related kinetic parameters were determined. This modified electrode possesses promising characteristics as NADH sensor; a wide linear dynamic range of 0.2 to 200 µM, low detection limit of 0.18 µM, fast response time (1–2 s), high sensitivity (24 µA cm⁻² mM⁻¹), anti‐interference ability and anti‐fouling.