Bioelectrochemistry (v.95, #C)

Bioelectrocatalytic reduction of oxygen at gold nanoparticles modified with laccase by Vida Krikstolaityte; Alejandro Barrantes; Arunas Ramanavicius; Thomas Arnebrant; Sergey Shleev; Tautgirdas Ruzgas (1-6).
To characterise bioelectrocatalytic oxygen reduction at gold nanoparticles (AuNPs) modified with Trametes hirsuta laccase (ThLc) combined electrochemical and quartz crystal microbalance measurements have been used. The electrodes with different degrees of AuNP-monolayer coverage, θ, have been studied. In every case of θ close to theoretically possible 44 ThLc molecules adsorbed at 22 nm diameter AuNP. The bioelectrocatalytic current was recalculated down to the current at a single AuNP. Unexpectedly, the current at a single AuNP was higher when θ was higher. The maximum current reached at a single AuNP was 31·10− 18  A which corresponds to the enzyme turnover (kcat ) 13 s− 1. This rate is lower than the homogeneous ThLc turnover (190 s− 1) suggesting partial denaturation of ThLc upon adsorption or that some ThLc are not in DET contact with the electrode surface.Display Omitted
Keywords: Bioelectrocatalytic oxygen reduction; Gold nanoparticle; Laccase; Direct electron transfer;

Simple laccase-based biosensor for formetanate hydrochloride quantification in fruits by Francisco Wirley Paulino Ribeiro; Maria Fátima Barroso; Simone Morais; Subramanian Viswanathan; Pedro de Lima-Neto; Adriana N. Correia; Maria Beatriz Prior Pinto Oliveira; Cristina Delerue-Matos (7-14).
This work describes the development of an electrochemical enzymatic biosensor for quantification of the pesticide formetanate hydrochloride (FMT). It is based on a gold electrode modified with electrodeposited gold nanoparticles and laccase. The principle behind its development relies on FMT's capacity to inhibit the laccase catalytic reaction that occurs in the presence of phenolic substrates. The optimum values for the relevant experimental variables such as gold nanoparticles electrochemical deposition (at − 0.2 V for 100 s), laccase immobilization (via glutaraldehyde cross-linking), laccase concentration (12.4 mg/mL), substrate selection and concentration (5.83 × 10− 5  M of aminophenol), pH (5.0), buffer (Britton–Robinson), and square-wave voltammetric parameters were determined. The developed biosensor was successfully applied to FMT determination in mango and grapes. The attained limit of detection was 9.5 × 10− 8  ± 9.5 × 10− 10  M (0.02 ± 2.6 × 10− 4  mg/kg on a fresh fruit weight basis). Recoveries for the five tested spiking levels ranged from 95.5 ± 2.9 (grapes) to 108.6 ± 2.5% (mango). The results indicated that the proposed device presents suitable characteristics in terms of sensitivity (20.58 ± 0.49 A/μM), linearity (9.43 × 10− 7 to 1.13 × 10− 5  M), accuracy, repeatability (RSD of 1.4%), reproducibility (RSD of 1.8%) and stability (19 days) for testing of compliance with established maximum residue limits of FMT in fruits and vegetables.
Keywords: Enzymatic biosensor; Gold nanoparticles; Laccase; Formetanate hydrochloride; Fruits;

Direct electrochemistry and intramolecular electron transfer of ascorbate oxidase confined on l-cysteine self-assembled gold electrode by Bhushan Patil; Yoshiki Kobayashi; Shigenori Fujikawa; Takeyoshi Okajima; Lanqun Mao; Takeo Ohsaka (15-22).
A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry.A well-defined redox wave centered at 166 ± 3 mV (vs. Ag│AgCl│KCl(sat.)) was observed in 5.0 mM phosphate buffer solution (pH 7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE.Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41 × 10− 11  mol cm− 2 with the apparent adsorption coefficient of 1.63 × 106  L mol− 1. The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function.
Keywords: Ascorbate oxidase; Self-assembled monolayer; Cysteine; Direct electron transfer; Intramolecular electron transfer;

Porous nitrogen-doped carbon nanosheet on graphene (PNCN) was used as an alternative cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Here we report a novel, low-cost, scalable, synthetic method for preparation of PNCN via the carbonization of graphite oxide–polyaniline hybrid (GO–PANI), subsequently followed by KOH activation treatment. Due to its high concentration of nitrogen and high specific surface area, PNCN exhibited an excellent catalytic activity for ORR. As a result, the maximum power density of 1159.34 mW m− 2 obtained with PNCN catalyst was higher than that of Pt/C catalyst (858.49 mW m− 2) in a MFC. Therefore, porous nitrogen-doped carbon nanosheet could be a good alternative to Pt catalyst in MFCs.
Keywords: Microbial fuel cells; Nitrogen-doped carbon; Oxygen reduction reaction;

The baicalin and baicalein are the major flavonoids found in Radix Scutellariae, an essential herb in traditional Chinese medicine for thousands of years. The interactions of the baicalin and baicalein with lipid bilayer membranes were studied using cyclic voltammetry and UV–Vis spectroscopy. The thickness d of supported bilayer lipid membranes was calculated as d = 4.59(± 0.36) nm using AC impedance spectroscopy. The baicalein interacted with egg PC bilayer membranes in a dose-dependent manner. The responses of K3Fe(CN)6 on lipid bilayer membrane modified Pt electrode linearly increased in a concentration range of baicalein from 6.25 μM to 25 μM with a detection limit of 0.1 μM and current-concentration sensitivity of 0.11(± 0.01) μA/μM, and then reached a plateau from 25 μM to 50 μM. However the baicalin showed much weaker interactions with egg PC bilayer membranes. UV–Vis spectroscopy also confirmed that the baicalein could interact with egg PC membranes noticeably, but the interaction of baicalin with membranes was hard to be detected. The results provide useful information on understanding the mechanism of action of Radix Scutellariae in vivo.Display Omitted
Keywords: Baicalin; Baicalein; Lipid bilayer membrane; Cyclic voltammetry; UV–Vis spectroscopy;

Corrigendum to “Solid-core and hollow magnetic nanostructures: Synthesis, surface modifications and biological applications” [Bioelectrochemistry 93 (2013) 2–14] by Dorota Nieciecka; Krzysztof Nawara; Krystyna Kijewska; Anna M. Nowicka; Maciej Mazur; Pawel Krysinski (34).