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In this work, an alcohol dehydrogenase (ADH) enzyme was used for ethanol oxidation in an air-breathing type microfluidic fuel cell. A bioanode was prepared using a catalytic ink prepared by using a...

Fuel cell-based self-powered electrochemical sensors have attracted considerable attention because contrary to conventional electrochemical sensors, they do not need external power supplies and complex devices due to they operate through the use of electrical output as sensing signal provided by redox reactions in fuel cells. Creatinine has been considered as an indicator of renal function specifically after dialysis, thyroid malfunction and muscle damage. The development of a suitable catalytic material for creatinine sensing able to generate electrical energy from its oxidation is still a challenge. Creatinine can form complexes with different transition metals due to the number of binding sites that coordinate with the metal donor groups such as copper. However, Cu suffers fast oxidation under environmental conditions and thus, the development of Cu alloys is needed. In this work, we developed an electrode with a catalytic ink containing a CuAg bimetallic material as an electrocatalyst for creatinine oxidation. The electrode was evaluated in a fuel cell and creatinine sensing.

TiO 2 nanotube membranes (TNM) were synthesized, separated (by electrochemical anodization) and modified with Pt-Ru electrocatalyst to assess their photoelectrocatalytic activity towards methanol (MeOH) oxidation. The feasibility of use of these composite materials was evaluated in different supports to observe the development of the electrochemical responses as a function of the nature of the electrical collecting substrate. The results suggested that, while the Pt-Ru decorated TMN present photoelectrocatalytic activity, the electrical contact in the back might be the limiting step in current collection. Such findings were demonstrated by performing scanning electrochemical microscopy SECM over the surface of the TNMs, where methanol was oxidized in the microelectrode tip of the SECM. This approach corroborated the suitability of TNMs to be modified with an electrocatalyst and its application in current technology such as microfluidic fuel cells.

This work presents the integration of a paper-based microfluidic fuel cell inside a lateral flow assay-human immunodeficiency virus (HIV) test. To modify the HIV test, a bioanode that oxidizes the glucose present in a serum or blood sample and a cathode that reduces the oxygen delivered from air were stacked on the bottom and top, respectively, of a paper-strip test. A mixture of glucose oxidase enzyme, Nafion®, glutaraldehyde, deionized water and tetrabutylammonium bromide were deposited on a methylene blue electro-polymerized Toray® paper and used as the bioanode. Meanwhile, Pt/C (Vulcan XC-72) on Toray® paper was used as an air-breathing cathode. The GOx enzyme anchored on the carbon-based surface was examined by scanning electron microscopy. The electrochemical response of the bioanode array demonstrated the oxidation of 0.1 M glucose, leading to a current density increase due to FAD+/FADH reactions. The above procedure was corroborated through scanning electrochemical microscopy, which showed an increase in the current (400 pA) in the presence of glucose on the bioanode. The paper-based microfluidic fuel cell performance showed power densities of 0.16 and 0.12 mW cm−2 using human serum and blood samples, respectively. Furthermore, the stability of the device was measured in terms of the recovery after obtaining four polarization curves that lasted 30 min, after which the sample dried out. This work represents a great advancement in the integration of a paper-based microfluidic fuel cell towards autonomous lateral flow assays.

The purpose of this work is to evaluate single and double-cell membraneless microfluidic fuel cells (MMFCs) that operate in the presence of simulated body fluids SBF, human serum and blood enriched with ethanol as fuels. The study was performed using the alcohol dehydrogenase enzyme immobilised by covalent binding through an array composed of carbon Toray paper as support and a layer of poly(methylene blue)/tetrabutylammonium bromide/Nafion and glutaraldehyde (3D bioanode electrode). The single MMFC was tested in a hybrid microfluidic fuel cell using Pt/C as the cathode. A cell voltage of 1.035V and power density of 3.154mWcm-2 were observed, which is the highest performance reported to date. The stability and durability were tested through chronoamperometry and polarisation/performance curves obtained at different days, which demonstrated a slow decrease in the power density on day 10 (14%) and day 20 (26%). Additionally, the cell was tested for ethanol oxidation in simulated body fluid (SBF) with ionic composition similar to human blood plasma. Those tests resulted in 0.93V of cell voltage and a power density close to 1.237mWcm-2. The double cell MMFC (Stack) was tested using serum and human blood enriched with ethanol. The stack operated with blood in a serial connection showed an excellent cell performance (0.716mWcm-2), demonstrating the feasibility of employing human blood as energy source.

The demand for hydrophobic polymer-based protective coatings to impart high corrosion resistance has increased recently. The increase of the hydrophobicity in a hybrid coating is a new challenge, for that reason and in order to protect a metallic surface of oxidant agents, a poly (methyl methacrylate) (PMMA) coating with the addition of a different amount of silicon dioxide (SiO2) was developed. The hybrid coating was applied on a sample of stainless steel AISI 304 by the dip-coating method. The characterization of the coatings was determined by electrochemical impedance spectroscopy and with a scanning electrochemical microscopy. The best coatings were PMMA and PMMA + SiO2 0.01% that exhibits a real impedance in the Nyquist diagram of 760 and 427,800 M&Omega, &sdot, cm2, respectively, and the modulus of the real impedance in the Bode diagram present values of 2.2 &times, 108 and 3.3 &times, 108 &Omega, cm2. Moreover, the phase angle presents constant values around 75&deg, to 85&deg, and 85&deg, for the PMMA and PMMA + SiO2 0.01%, respectively. Moreover, the values of the real resistance for the PMMA + SiO2 0.01% coating present values in the order of Mega-ohms despite the coating exhibits an artificial defect in their surface. The contact angle test showed that the hydrophobicity of the hybrid PMMA + SiO2 0.01% coating is higher than that of the pure PMMA coatings. The hybrid PMMA + SiO2 coatings developed in this work are a very interesting and promising area of study in order to develop efficient products to protect metallic surfaces from corrosion phenomenon.

Ethanol co-laminar flow fuel cells operating at room temperature have rarely been reported, primarily due to problems associated with the kinetics of ethanol oxidation. In this work, we present a study of the effect of ethanol concentration, pH of anodic and cathodic streams, and nature of the oxidant on the performances of an acrylic cell and a paper-based, membraneless co-laminar flow fuel cell (LFFC), with total cell volumes of 14.29 cm3 and 0.62 cm3, respectively. Additionally, this work reports the synthesis of a Pd-NiO anodic nanocatalyst by a simple, fast, and environmentally friendly method in order to match the clean, easy-to-use, and simple fabrication methods of these ethanol co-laminar flow fuel cells. The synthesized Pd-NiO exhibited a crystallite size of 8.1 nm and an average particle size of 8.7 nm for Pd-NiO/C. The highest performances were obtained by combining an alkaline anodic stream with an acidic cathodic stream, increasing the cell voltage, and decreasing cathodic limitations caused by the simultaneous occurrence of oxygen reduction as well as hydrogen reduction reactions. With these improvements, power densities of 108 and 85.5 mW cm−2 were obtained for the acrylic and the paper-based co-laminar flow fuel cell, respectively, which are the highest values reported to date for ethanol LFFCs at room temperature.

Alcohol dehydrogenase enzyme (ADH) has been used for the development of bioanodes for the ethanol oxidation reaction. In this work, the immobilization of this enzyme was carried out using titanium dioxide nanotubes for the development of photoelectrodes for an air-breathing microfluidic device. TiO2 nanotubes (TNT) have excellent properties such as pH resistance, superior mechanical strength, good biocompatibility making them great candidates for the process of immobilization of ADH. TNT were fabricated by electrochemical anodic oxidation on Ti foils. Then enzyme alcohol dehydrogenase was immobilized and the electrode was evaluated in the microfluidic fuel cell using an inorganic cathode based on commercial Pt / C, obtaining a good performance when was exposed under ultraviolet light.

The growth of the world population and the lack of energy supply have led to the development of technologies to obtain alternative energy that has a minimal environmental impact, as is the case of fuel cells. In this work, the development of electrodes using glucose oxidase enzyme immobilized with functionalized carbon nanofibers on graphite rods is proposed for its application in a fuel cell implanted in living plants, specifically in cacti. The purpose is to convert solar energy to chemical and then, to electric energy, carrying out the glucose oxidation contained in these plants. The use of a living plant as a fuel cell comes from the idea of taking advantage of more efficiently the conversion of chemical energy, which comes from the plant’s photosynthesis until is converted into electrical energy.

In this research two electrodes were developed, a bioanode where the enzyme oxidase was immobilized on Sigracet GDL 39 by means of the covalent binding method and a biocathode with laccase enzyme immobilized on Toray carbon paper by the adsorption method. The evaluation of these electrodes was carried out in a microfluidic fuel cell using cholesterol as fuel and oxygen as oxidant. The electrical conductivity of the electrodes was measured by the kelvin method. Microfluidic fuel cell (mFFC) was constructed using Poly-(methyl methacrylate) (PMMA) for the fuel and oxidant channels; the cathode electrode was incorporated as a wall to obtain the major O2 quantity for the reduction reaction. The evaluation of the microfluidic cell was carried out using different solutions of cholesterol all in phosphate buffer solutions at pH 7.5, where it was possible to obtain 1.38 mW/cm2 of maximum power density and 0.75V of open circuit potential using 500mg/dL of cholesterol.

In this work, an enzymatic glucose oxidase (GOx) electrode immobilized on double layered hydroxides of NiAl (NiAl-LDHs) was developed for the detection of serotonin neurotransmitters that may be present in human blood samples and carry out the glucose oxidation present in this fluid for energy conversion, and can be applied as self-feeding electrodes in Lab-on-a-Chip devices. The self-feeding electrodes based on fuel cells have a very promising future in lab-on-a-chip devices because they do not occupy an external power source, their manufacturing processes are relatively simple and low cost, and can be developed for different applications such as the determination of biomolecules for diagnosis of various diseases.

Serotonin is a potential biomarker for diverse neuropsychiatric and neurodevelopmental disorders. In this study a novel biocomposite based on the enzyme monoamine oxidase-A (MAO-A) immobilized by covalent binding on multi-walled carbon nanotubes (MWCNT) has been developed for detection of serotonin. Immobilized MAO-A (MWCNT/MAO-A) retained 94.3% of its catalytic activity, showing good thermal and pH stability at temperatures from 35 to 40 °C and pH from 7–8.5. A decrease of the apparent Michaelis-Menten constant was observed compared to free MAO-A indicating an improvement of its affinity towards its substrate. Evaluation of MWCNT/MAO-A by scanning electrochemical microscopy (SECM) demonstrated that the immobilized enzyme maintains its activity. The biocomposite was employed for successfull detection of serotonin through quantification of the enzymatically produced hydrogen peroxide (H2O2). A MWCNT/MAOA modified glassy carbon electrode (GCE) was characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Electrochemical measurements were performed in simulated body fluid (SBF), obtaining a linear response of 5.67 × 10-7 M - 2.26 × 10-6 M, with a low detection limit of 2 × 10-7 M (35.6 ng mL-1;S/N = 3) and a quantification limit of 6.73 × 10-7 M (118.7 ng mL-1;S/N = 3); values that are in range with serotonin levels found in different neurological disorders. The biocomposite have the potential to be employed in future development of biosensing devices for serotonin detection.

In this work, an enzymatic bioanode was developed using functionalized carbon nanofibers for the immobilization of alcohol dehydrogenase enzyme, using Nafion, tetrabutylammonium bromide and glutaraldehyde onto Toray carbon paper. Two alcoholic fuels, methanol (MeOH) and ethanol (EtOH) were used to demonstrate the oxidation versatility of the electrode created as well as being able to convert energy from these fuels using an air-breathing microfluidic device. Commercial Pt/C (30% E-TEK) onto carbon nanofoam (Marketech Inc) was using as inorganic cathode. Carbon nanofibers were previously treated with nitric acid to produce oxygen-containing functional groups in order to facilitate the enzyme immobilization. A phosphates buffer solution pH 8.86 was used as electrolyte. The use of ethanol as fuel shows a better performance obtaining 8.643mAcm−2 and 0.847 V as current density and open circuit voltage respectively, compared to that use methanol as fuel (2.655 mAcm−2 and 0.567V).

A novel stacked microfluidic fuel cell design comprising re-utilization of the anodic and cathodic solutions on the secondary cell is presented. This membraneless microfluidic fuel cell employs porous flow-through electrodes in a "V"-shape cell architecture. Enzymatic bioanodic arrays based on glucose oxidase were prepared by immobilizing the enzyme onto Toray carbon paper electrodes using tetrabutylammonium bromide, Nafion and glutaraldehyde. These electrodes were characterized through the scanning electrochemical microscope technique, evidencing a good electrochemical response due to the electronic transference observed with the presence of glucose over the entire of the electrode. Moreover, the evaluation of this microfluidic fuel cell with an air-breathing system in a double-cell mode showed a performance of 0.8951 mWcm-2 in a series connection (2.2822mAcm-2, 1.3607V), and 0.8427 mWcm-2 in a parallel connection (3.5786mAcm-2, 0.8164V).

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AldH) enzymes were immobilized by covalent binding and used as the anode in a bi-enzymatic membraneless ethanol hybrid microfluidic fuel cell. The purpose of using both enzymes was to optimize the ethanol electro-oxidation reaction (EOR) by using ADH toward its direct oxidation and AldH for the oxidation of aldehydes as by-products of the EOR. For this reason, three enzymatic bioanode configurations were evaluated according with the location of enzymes: combined, vertical and horizontally separated. In the combined configuration, a current density of 16.3 mA cm-2, a voltage of 1.14 V and a power density of 7.02 mW cm-2 were obtained. When enzymes were separately placed in a horizontal and vertical position the ocp drops to 0.94 V and to 0.68 V, respectively. The current density also falls to values of 13.63 and 5.05 mA cm-2. The decrease of cell performance of bioanodes with separated enzymes compared with the combined bioanode was of 31.7% and 86.87% for the horizontal and the vertical array.

In this work, a nanofluidic fuel cell (NFC) in which streams flow through electrodes was used to investigate the role of pH in the cell performance using ethanol as fuel and two Pd nanoparticles as electrocatalysts: one commercially available (Pd/C from ETEK) and other synthesized using ionic liquids (Pd/C IL). The cell performances for both electrocatalysts in acid/acid (anodic/cathodic) streams were of 18.05 and 9.55 mW cm-2 for Pd/C ETEK and Pd/C IL. In alkaline/alkaline streams, decrease to 15.94 mW cm-2 for Pd/C ETEK and increase to 15.37 mW cm-2 for Pd/C IL. In alkaline/acidic streams both electrocatalysts showed similar cell voltages (up to 1 V); meanwhile power densities were of 87.6 and 99.4 mW cm-2 for Pd/C ETEK and Pd/C IL. The raise in cell performance can be related to a decrease in activation losses, the combined used of alkaline and acidic streams and these high values compared with flow-over fuel cells can be related to the enhancement of the cathodic mass transport by using three dimensional porous electrodes and two sources of oxygen: from air and from a saturated solution.