External Mediator Research Articles

A novel photoelectrochemical based water splitting and uric acid biosensing using PLD grown In2Se3 thin films

By altering the deposition pressure during the film growth process using the pulsed laser deposition (PLD) technology, indium selenide (In2Se3) thin films have been optimized to produce their distinct phases. The phase purity, optical and morphological studies were carried out using XRD, Raman spectroscopy, XPS, UV–visible spectroscopy, AFM and FESEM measurements. A high absorption in the visible region is observed for In2Se3 thin films with suitable band edges for hydrogen evolution. Photoelectrochemical (PEC) activity for In2Se3 photoelectrodes having various phases was analyzed based on CV and I-t response. A good charge transport characteristics were observed using the EIS measurements on PLD grown In2Se3 thin films. The Mott–Schottky analysis for the charge carrier density, flat band potential, and depletion layer width was performed for the deposition pressure dependent phase formation and high performance for PEC water splitting conversion efficiency of 0.48 %, 0.57 % and 0.98 % corresponding to α-In2Se3, β-In2Se3 and γ-In2Se3 were observed, respectively. The as prepared In2Se3 thin films were employed for the detection of Uric Acid (UA) using the cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry. The high sensitivity (0.38 mA/mM), selectivity and repeatability of the prepared biosensor demonstrates In2Se3 as potential candidate for the PEC based water splitting and biosensing application without the presence of an external mediator and can work in the self-powered mode.

Bacterial community issued from a Chlorophytum plant-microbial fuel cell for electricity generation

Some microorganisms, particularly bacteria, can adhere to conductive surfaces and grow as an electroactive biofilm, on which they communicate electrochemically and generate electricity. Here, a bacterial community isolated from anodic electroactive biofilms of a Microbial Fuel Cell planted with Chlorophytum comosom is studied. Seventeen different bacterial strains were isolated from electroactive biofilms and were identified using the 16S rRNA marker gene. The strains were affiliated to 8 bacteria families and 8 genera (Aeromonas, Enterobacter, Alcaligenes, Pseudomonas, Clostridium, Paraclostridium, Enterococcus and Kurthia spp.). After that, it was demonstrated using electrochemical methods, principally imposed potential chronoamperometry under +0.155 mV/SCE, that the consortium constituted of 17 strains was able to exchange electrons with conductive materials. A maximum current density of 345 µA/cm2 was revealed at 48h of the study, using acetate as the sole carbon source and without any additional external mediator.

Self-signal generating bioelectronic sensor surface using gadolinium hexacyanoferrate nanocomposite for oral cancer diagnosis

External redox reagents and chemical mediators in measuring solutions are extensively used to monitor the analytical signals in electrochemical immunosensors. These mediators add more steps and complications to the sensing procedures which are aggravated when testing the target molecule in real samples. Thus, it is important to resolve such issues by fabricating and engineering sensitive electroactive surfaces without the requirement of mediators in the solution phase. In this work, we report a self-reporting electrochemical biosensor for cyfra-21–1 detection in saliva samples without using any external mediator molecules in solution phase. To fabricate an electrochemically active surface, a redox active Gadolinium hexacyanoferrate (GdHCF) nanoparticles have been synthesized and deposited onto the electrode surface for label-free detection of cyfra-21–1 in combination with gold nanoparticles (AuNP) and graphene oxide (GO). The sensor probe was thoroughly characterized using X-ray diffraction (XRD), UV–vis spectroscopy, transmission electron microscopy (TEM), Raman Spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). An alternation in the protein biomarker concentrations led to a change in the current response of the electrode surface. differential pulse voltammetry (DPV) was used to establish the analytical performance of the fabricated biosensor. The sensor achieved a clinically relevant range as well as a wide linear dynamic range (LDR) of 2–50 ng/mL of cyfra-21–1 and a detection limit (DL) of 0.039 ( ± 0.01) ng/mL ((RSD < 4.12%, 95% confidence level, n = 3), with negligible interferences effect due to various co-existing molecules. This is the first-ever report where a redox-active surface has been fabricated comprising GdHCF for direct detection of cyfra-21–1 in human saliva samples without using any redox mediator in the solution phase.

Electrochemical Benzylic C(sp3)–H Amidation via Ritter-Type Reaction in the Absence of External Mediator and Oxidant

AbstractA straightforward method involving electrochemical Ritter-type amidation of alkylarenes in the absence of external mediator and oxidant is described. This direct benzylic C(sp3)–H amidation utilizes cheap CH3CN or other nitriles as the nitrogen source and trace amount of H2O in the solvent as the oxygen and hydrogen source. A wide range of alkylarenes were found to be compatible, providing a variety of N-benzyl-substituted amides in moderate to good yields.

Perspectives on restorative practices and online-mediated harm in schools: implementation challenges

ABSTRACT While many schools have gravitated away from an emphasis on ‘zero tolerance’ discipline, embracing a range of ‘restorative practices’ (RP), only a handful of empirical studies have examined how RP have been received by educators. Moreover, frameworks which embrace RP in the classroom often neglect newer forms of online-mediated conflict and harm (e.g., cyberbullying, ‘sexting’). The current study, drawing on 77 qualitative interviews with Canadian pre-service and practicing educators, examines their responses regarding the effectiveness of RP in response to online conflict and harm. Challenges include educator emotional burnout, pressures on popular teachers to run RP, and the need for resources and administrative support in RP or an external mediator. These challenges, we argue, are difficult to overcome without a whole school framework that helps to instill cultural commitments attending to the wider goal of repairing harm situated at the level of a school’s community.

Performance of Methylococcus capsulatus based microbial and enzymatic proton exchange membrane fuel cells

Activation of methane in low-temperature fuel cells has been a challenge due to its thermodynamic stability. In this study, we demonstrate the feasibility of using a pure culture of Methylococcus capsulatus microbial fuel cell in a proton exchange membrane (PEM) fuel cell in whole-cell and crude enzymatic modes. The impact of time and mediators of the microbial fuel cells (MFCs) was studied. Additionally, a mathematical model was used to predict and explain the fuel cell's electrochemical performance and mechanic details. The fuel cell generated an open-circuit voltage of 378.91 mV and a power density of 438.57 μW/m2 in the whole-cell mode, whereas an OCV of 125.62 mV and a power density of 117.94 μW/m2 in the enzymatic mode without the use of an external mediator. Although the cell was stable throughout the test duration of ten days in the whole-cell mode, the stability declined within minutes in the enzymatic mode. This work demonstrates the feasibility of generating electricity via a proton exchange membrane (PEM) fuel cell in microbial and enzymatic modes using methane as the only carbon source at room temperature with a pure culture of M. capsulatus as a direct electron-transporting biocatalyst.

Measurements of working parameters of external mediators for biodetectors based on the polydopamine@magnetite nanoparticles

This paper describes the role of various external redox mediators in biodetector systems using bioinspired nanomaterials based on magnetite@polydopamine (Fe3O4@PDA), and their influence on the working parameters of the designed systems. The investigated mediators were hydroxy(methylferrocene, 1,4-benzoquinone, methylene blue, hydroquinone, and [Fe(CN)6]3-/4- redox couple. The amperometric glucose biosensor was fabricated by immobilizing glucose oxidase from Aspergillus niger (GOx) onto the Fe3O4@PDA nanomaterial, with the addition of a strictly defined amount of a specific external mediator. Among all tested mediators, the most favorable results were obtained for hydroxymethyl(ferrocene) with the integrated GC/Fe3O4@PDA-GOx system. The mediator exhibited ahigh linear amperometric response in a glucose concentration range from 1 to 20 mM, with a relatively high sensitivity of 139.71 μAmM−1 cm−2 and a limit of detection of 1.54 μM. Moreover, the system showed good stability over time, reproducibility, and resistance to interference.

Development of a universal conductive platform for anchoring photo- and electroactive proteins using organometallic terpyridine molecular wires.

The construction of an efficient conductive interface between electrodes and electroactive proteins is a major challenge in the biosensor and bioelectrochemistry fields to achieve the desired nanodevice performance. Concomitantly, metallo-organic terpyridine wires have been extensively studied for their great ability to mediate electron transfer over a long-range distance. In this study, we report a novel stepwise bottom-up approach for assembling bioelectrodes based on a genetically modified model electroactive protein, cytochrome c553 (cyt c553) and an organometallic terpyridine (TPY) molecular wire self-assembled monolayer (SAM). Efficient anchoring of the TPY derivative (TPY-PO(OH)2) onto the ITO surface was achieved by optimising solvent composition. Uniform surface coverage with the electroactive protein was achieved by binding the cyt c553 molecules via the C-terminal His6-tag to the modified TPY macromolecules containing Earth abundant metallic redox centres. Photoelectrochemical characterisation demonstrates the crucial importance of the metal redox centre for the determination of the desired electron transfer properties between cyt and the ITO electrode. Even without the cyt protein, the ITO-TPY nanosystem reported here generates photocurrents whose densities are 2-fold higher that those reported earlier for ITO electrodes functionalised with the photoactive proteins such as photosystem I in the presence of an external mediator, and 30-fold higher than that of the pristine ITO. The universal chemical platform for anchoring and nanostructuring of (photo)electroactive proteins reported in this study provides a major advancement for the construction of efficient (bio)molecular systems requiring a high degree of precise supramolecular organisation as well as efficient charge transfer between (photo)redox-active molecular components and various types of electrode materials.

From Nile Basin Initiatives (NBI) to External mediator: Challenges of the Ethiopia's Renaissance Dam Negotiations

From Nile Basin Initiatives (NBI) to External mediator: Challenges of the Ethiopia's Renaissance Dam Negotiations

From Nile Basin Initiatives (NBI) to External mediator: Challenges of the Ethiopia's Renaissance Dam Negotiations

The riparian countries, especially Egypt, Sudan and Ethiopia, have had intricated relations since the building of the Great Ethiopian Renaissance Dam (GERD). There have been many mediations but none of Egypt's historical, Sudan's development and Ethiopia's natural rights have ever been settled satisfactorily. Egypt and Sudan continue to state their dissatisfaction with the status quo as they rejected Ethiopia's proposal. The mediator also departed, peripheral actors apart from the Nile basin and the African Union. The US efforts to mediate in all three countries have also failed. Thus, from the Nile riparian states to external mediation, the Renaissance dam negotiations were not

A double auction mechanism for coordinating lot-sizing in supply chains

This paper presents an auction mechanism for the coordination of dynamic, uncapacitated lot-sizing problems in two-party supply chains where parties’ local data are private information and no external mediator is involved. In the first stage of the mechanism, the buyer generates supply proposals which potentially lead to system-wide improvements, and communicates them to the supplier. Then both parties evaluate the cost impact of the different proposals for their local planning domains. In the second stage, buyer and supplier submit sealed bids on each proposal. Then the bids are opened and the proposal with the greatest surplus is implemented. The procedure for proposal generation is efficient and scalable. It identifies the system-wide optimum in special cases, finds close-to-optimal solutions for general settings in computational tests, while the number of needed proposals increases linearly with the number of time periods and items supplied. Further analytical and numerical analyses indicate that the auction in the second stage is highly efficient.

A 3rd generation Biosensor Towards the Continuous Long-Term Glucose Monitoring without Ag/AgCl Reference Electrode

Continuous glucose monitoring (CGM) is highly important, especially, for the diagnostics and control of Type I diabetes. [1] In recent years, automatic insulin pumps (artificial pancreas) are being applied and CGM is necessary for their operation. The insulin pump should deliver a correct dose of insulin based on real-time data about glucose levels in blood. Therefore, CGM sensors should be very selective and accurate, as well as reliable and stable. For this reason, CGM sensors are developed using selective enzymes – glucose oxidase or and FAD-dependent glucose dehydrogenase. [2] They usually operate by measuring either glucose oxidation current (amperometric biosensors) or potential (potentiometric biosensors). Historically, those biosensors are divided into three generations according to the electron acceptor: O2 dependent (1st), mediator depended (2nd) and direct electron transfer (3rd). The 3rd generation biosensors are the most attractive since they are most accurate, sensitive, operate at low potential and their response does not depend on the concentration of external mediator (either O2 or synthetic). However, to this date there are multiple unresolved problems which still hold the development of 3rd generation glucose biosensors for the CGM. Some of those problems include low stability (typically from a few hours to a few days) and miniaturization difficulties due to the usage of bulk reference electrodes for the control of the potential (Ag/AgCl, Hg/Hg2Cl2, etc.). Moreover, typical reference electrodes are poorly suited for long-time operation because they leak electrolyte and ions to the media. [3] A prolonged leakage of electrolyte solution changes the potential of reference electrode and may cause health risk if CGM biosensor in directly implanted in the patient. In this work, we present an open circuit potential (OCP) type 3rd generation glucose biosensor, which addresses the mentioned issues and operates in an electrolyte solution (pH 7.4) which mimics the composition of human serum. Our biosensor is composed of two electrodes: gold nanoparticle-glucose dehydrogenase (AuNPs-GDH) based bioanode and gold nanoparticles-laccase (AuNPs-LAC) based biocathode (Figure A). We have used AuNPs-LAC biocathode, which we have reported earlier [4], as a counter/reference electrode since its potential depends on oxygen reduction reaction. In the majority of solutions, O2 concentration is constant, thus it has a very stable OCP which is independent on glucose concentration and holds a constant value of 0.48 V vs.Ag/AgCl (Sat.) in an electrolyte solution. We have used AuNPs-GDH electrode as a working electrode since its OCP is dependent on glucose concentration raging from 10-6 M to 0.05 M. The OCP difference between two electrodes was -0.374 V and decreased depending on the concentration of glucose (10-6 M – 0.05 M) according to Nernst model (Figure B and C). The biosensor was calibrated in glucose range of 0.001 M to 0.01 M (typical glucose concentrations present in human blood) and a high correlation calibration curve was obtained (Figure D). Moreover, biosensor had showed an excellent stability and was able to operate at least for two weeks without a significant change in OCP. In conclusion, we have developed a promising biosensor for a constant long-term glucose monitoring which operates in an electrolyte solution, mimicking human serum conditions. A future challenge is to apply and optimize our biosensor to operate in serum and blood.

Investigation in Mediated Heterogeneous Oxygen Reduction of Immobilized Laccase

Dynamics of heterogeneous catalysis on oxygen reduction for Lac based electrode capped with a layer of Chitosan-multi-wall carbon nano-tubes complex in the presence of dissolved mediator, was investigated on the basis of precondition that the detainment of substrate and mediator could be neglected. Rates of steps involved in the whole catalytic cycle were determined by the means of UV–Vis spectroscopy, atomic adsorption spectroscopy, linear sweeping voltammetry and cyclic voltammetry in combination with rotating disk electrode technique. These kinetic parameters were normalized under the same dimension. Thus rate determining step was verified to be the diffusion of external mediator. Results also revealed the fact from analysis in changes of morphology and electric conductivity after protein incorporation into nano-composite that random adsorption of enzyme molecules on the conductive support resulted in the decrease in conductive area of nano-composite and hindered the direct electron transfer between active sites in enzyme molecules and conductive matrix. Non-oriented arrangement of protein molecules on the matrix also crippled the mechanical stability of nano-complex with enzyme resulting from weak interaction between incorporated protein molecules and carrier. Catalytic effect on dissolved oxygen reduction reaction for electrode which was over-coated by a layer of nano-complex with immobilized Laccase consisting of Chitosan and multi wall carbon nano-tubes, were found to be restrained by diffusion of electron relay.

A novel low-powered uric acid biosensor based on arrayed p-n junction heterostructures of ZnO thin film and CuO microclusters

An array of p–n junction heterostructures is fabricated by loading the surface of n-type semiconducting ZnO thin film with p-type CuO microclusters (μCs) for realization of uric acid biosensor without any external mediator. Uricase is immobilized onto the prepared CuO/ZnO arrayed heterostructure in order to prepare the sensing electrode. The electrochemical performance of the prepared p-n junction based biosensor is investigated by means of cyclic voltammetry. A stable and well-defined peak corresponding to oxidation of uric acid is observed at a very low potential of 0.03V in a mediator free solution. The largely decreased sensing potential may be attributed to the substantial enhancement of surface reaction kinetics in the formed p-n junction heterostructure due to built-in electric field which facilitate charge transport. A linear sensing response is observed over a range of 0.05–1.0mM uric acid concentration with a high sensitivity of 1.74mA/mM. Moreover, the prepared biosensor has good affinity towards uric acid (Km∼ 0.05mM) and possesses long shelf life ( >20 weeks). The low operating potential (0.03V) of CuO/ZnO arrayed p-n heterojunction reduces the energy consumption of developed biosensor and efficiently minimizes interference from common oxidizable interferents, thereby, making the biosensor highly selective. Thus, CuO μCs/ZnO thin film based p-n junction heterostructure with internal electric field is a novel matrix for developing low powered biosensors to meet future energy demands.

PH-Responsive Coassembly of Oligo(ethylene glycol)-Coated Gold Nanoparticles with External Anionic Polymers via Hydrogen Bonding.

Stimuli-responsive assembly of gold nanoparticles (AuNPs) with precise control of the plasmonic properties, assembly size, and stimuli responsivity has shown potential benefits with regard to biosensing devices and drug-delivery systems. Here we present a new pH-responsive coassembly system of oligo(ethylene glycol) (OEG)-coated AuNPs with anionic polymers as an external mediator via hydrogen bonding in water. Hydrogen-bond-driven coassemblies of OEG-AuNPs with poly(acrylic acid) (PAA) were confirmed by the monitoring of plasmonic peaks and hydrodynamic diameters. In this system, the protonation of anionic polymers on change in pH triggered the formation of hydrogen bond between the OEG-AuNPs and polymers, providing sensitive pH responsivity. The plasmonic properties and assembly size are affected by both the ratio of PAA to AuNPs and the molecular weight of PAAs. In addition, the attachment of hydrophobic groups to the surface ligand or anionic polymer changed the responsive pH range. These results demonstrated that the coassembly with an external mediator via hydrogen bonding provides a stimuli-responsive assembly system with tunable plasmonic properties, assembly size, and stimuli responsivity.

Made in Havana: How Colombia and the FARC Decided to End the War

On November 24, 2016, the government of Colombia and the biggest guerrilla group in the country, the Fuerzas Armadas Revolucionarias de Colombia–Ejercito del Pueblo (FARC-EP), signed a final peace agreement. This accord put an end to the longest armed conflict in the Western Hemisphere and to long and convoluted peace talks. What elements of the process contributed to its success? While it may be too early to properly speak of “lessons learned,” IPI’s latest paper highlights the key elements that seemed to have worked and those that made progress difficult. Over the course of the process, several factors emerged as central, both to its successful resolution and to the problems likely to arise during implementation: - A limited agenda: Previous talks with the FARC-EP had been burdened by an extremely long agenda that included many issues the public believed should not be settled in a negotiation with an insurgent group. Reflecting this experience, the agreed final agenda addressed just six issues. - A peace process removed from Colombia: Cuba’s hosting of the negotiations buffered the talks from the daily occurrences of war and politics in Colombia and provided a controlled environment. While this proved to be essential for the parties to come to an agreement, it left many Colombians feeling removed from the process and limited their sense of ownership. - A strategic use of the international community: The dialogue was guided by a central premise: this would be a process “for Colombians, by Colombians.” This meant that the government tightly controlled the process and excluded the possibility of an external mediator. Nonetheless, the Colombian government reached out to and mobilized the international community. Although the involvement of these actors was essential to the successful outcome of the talks, it did not translate into wider legitimacy inside Colombia.

Modified Tin Oxide Based Bioelectrode for Reagentless Detection of Uric Acid

A reagentless uric acid biosensor has been realized using Copper implanted tin oxide thin film (Cu:SnO2) based matrix. The biosensing characteristics of implanted matrix have been studied using the electrochemical impedance spectroscopy and cyclic voltammetry. The prepared matrix (Cu:SnO2), because of the presence of Cu, possess redox properties so that the electron transfer from enzyme to the electrode could be accomplished without using any external mediator in the electrolyte. The developed uric acid biosensor exhibits a high sensitivity of about 0.93 mA/ mM and a linear variation in current response over a concentration range from 0.05 to 1.0 mM of uric acid besides high shelf life (~20 weeks). The Michaelis-Menten kinetic parameter (Km) is found to be relatively very low (0.12 mM), which indicates the high affinity of the fabricated bioelectrode towards the uric acid (analyte). The results highlight the importance of implanted Cu:SnO2 thin film as an attractive matrix for the realization of reagentless biosensors towards uric acid.

Recovery Rhenium from roasted dust through super Para-magnetic Nano-particles

Rhenium, a valuable and rare metal, is a byproduct of Molybdenum. It is usually produced through the dust and smoke of roasting Molybdenum concentration. Heat roasting is the traditional method of producing Molybdenum from sulphuric resources (Molybdenum), which not only creates environmental problems but also wastes some of the existing Rhenium.To produce Rhenium, in this research, a Nano-technology-based solution is presented which is modern, fast, and economical. Rhenium, classified among the external mediator elements, is in group 7 of the periodic table. Regarding the arrangement of Rhenium's electron layer capacity, i.e. 5d5, its d orbital is completely sub-saturated and therefore, equipped with magnetic characteristic. As such, Rhenium can also be considered as a Para-magnetic metal. In this research, after providing metal ions solution, the absorption of Rhenium ions is examined under different operational conditions through the super Para-magnetic Nano-particles of Fe3O4, which helped to determine the best conditions for absorption to occur. Washing the Nano-absorbent after recovering Rhenium ions from Nano-particles makes it prepared for further operations.

Co-immobilization of laccase and mediator through a self-initiated one-pot process for enhanced conversion of malachite green

Laccase is a green biocatalyst. It works with molecular oxygen and produces water as the only by-product. However, its practical application is far less than satisfactory due to the low stability/poor reusability of free laccase and the potential secondary pollution caused by dissolved mediators. To address those bottlenecks in laccase-based catalysis, a novel biocatalyst (Immo-LMS) was fabricated by simultaneously immobilizing both laccase and a mediator (acetylacetone, abbreviated as AA) into a hydrogel through the laccase-AA initiated polymerization. This self-initiated immobilization process avoided the forced conformational change of laccase in the passive embedding to pre-existing carriers. Resulting from the effective cooperation of laccase and AA, the Immo-LMS had the highest substrate conversion quantity to malachite green, followed by the sole immobilized laccase and the immobilized laccase with an external mediator. Besides the improved activity, the Immo-LMS showed enhanced stability. The good performance of the Immo-LMS suggests that the co-immobilization of laccase and mediator through the self-initiated one-pot process was a promising strategy for the immobilization of laccase, which is expected to be helpful to cut down the running cost as well as the potential toxicity that come from mediators in the practical application of laccase.

ZnO-CuO composite matrix based reagentless biosensor for detection of total cholesterol.

An efficient reagentless biosensor for determination of free cholesterol and total cholesterol has been realized using a ZnO-CuO composite matrix grown onto ITO coated corning glass substrates by pulsed laser deposition (PLD) technique. The inclusion of CuO in ZnO matrix successfully introduces redox property and provides enhanced electron communication features. The optimized ZnO-CuO composite matrix has been used for development of ChOx/(ZnO-CuO)/ITO/glass and (ChEt-ChOx)/(ZnO-CuO)/ITO/glass bioelectrodes used for selective detection of free and total cholesterol respectively in the range of 0.12-12.93 mM and 0.5-12 mM without using any external mediator. The fabricated biosensors exhibit high sensitivity of about 680 µA mM(-1) cm(-2) and 760 µA mM(-1) cm(-2) towards free cholesterol and total cholesterol respectively with response time of 5 s, along with high shelf life. The results are encouraging and show the promising application of the ZnO-CuO composite matrix for the realization of reagentless integrated implantable biosensor.