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This study reports the performance of simple low-cost synthesized bifunctional Cu/Cu2O nanoparticles (NPs) used as a catalyst for energy-harvesting applications through of a microfluidic fuel cell (µFC), and further, as cholesterol (Chol) sensor. TEM characterization of the NPs showed spheres between 4 and 10 nm, while XRD and XPS analysis confirmed the composition and preferential crystallographic plane of Cu/Cu2O. In addition, 25.26 m2 g−1 surface area was obtained, which is greater than those commercial materials. NPs showed high activity toward the cholesterol oxidation reaction when were used as a sensor, obtaining a linear interval between 0.5 and 1 mM and 850 µA mM−1 mg−1 of sensitivity and 8.9 µM limit of quantification LOQ. These values are comparable to results previously reported. Moreover, Cu/Cu2O NPs were used as anode in a µFC with 0.96 V of cell voltage and 6.5 mA cm−2 and 1.03 mW cm−2 of current and power density, respectively. This performance is the highest currently reported for cholesterol application as an alternative fuel, and the first one reported for a microfluidic fuel cell system as far as is known. Results showed that the obtained Cu-based NPs presented an excellent performance for the dual application both µFC and sensor, which has potential applications in biomedicine and as an alternative energy source.

This work reports on Fe2O3 and ZnO materials for lactate quantification. In the synthesis, the bi-phase γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO nanoparticles (NPs) were obtained for their application in a lactate colorimetric sensor. The crystalline phases of the NPs were analyzed by XRD and XPS techniques. S/TEM images showed spheres with an 18 nm average and a needle length from 125 to 330 nm and 18 nm in diameter. The γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO were used to evaluate the catalytic activity of peroxidase with the substrate 3,3,5,5-tetramethylbenzidine (TMB), obtaining a linear range of 50 to 1000 μM for both NPs, and a 4.3 μM and 9.4 μM limit of detection (LOD), respectively. Moreover, γ-/α-Fe2O3 and γ-/α-Fe2O3/ZnO/lactate oxidase with TMB assays in the presence of lactate showed a linear range of 50 to 1000 µM, and both NPs proved to be highly selective in the presence of interferents. Finally, a sample of human serum was also tested, and the results were compared with a commercial lactometer. The use of ZnO with Fe2O3 achieved a greater response toward lactate oxidation reaction, and has implementation in a lactate colorimetric sensor using materials that are economically accessible and easy to synthesize.

Ferrocene-based polymers as redox mediators are considered versatile and important in the study of glucose biosensors. Poly-L-lysine (PLL), as a cationic polymer, possesses good properties including biocompatibility, biodegradation and water solubility. In this work, PLL was modified with ferrocene carboxylate in a very simple way by activating the carboxyl group of Fc, which reacted with the amino groups of the polymer. The resulting product was analysed by FTIR. Performance as a redox mediator (Fc-PLL) with the enzyme glucose oxidase was tested by cyclic voltammetry and showed an increase in the oxidation current in the presence of glucose in PBS pH 7.4. Additionally, performance as a biosensor was evaluated by amperometry and gave a linear range of 0-10 mM, a limit of detection of 23 μM, a sensitivity of 6.55 μA/cm

A self-powered glucose biosensor (SPGB) was developed based on biofuel cells (BFCs)and a microfluidic system as a suitable technology for high potential application in clinical diagnosis. In this work, a bioanode and biocathode were assembled by glucose oxidase-based and laccase-based electrodes, respectively, which were incorporated into a microfluidic system (m-SPGB), while the anolyte and catholyte were phosphate buffered at different pH values of 7.4 and 5.6, respectively. The m-SPGB showed a linear dynamic interval of 0–10 mM (R2 = 0.9907), a low limit of detection of 0.48 mM and a response to interfering species. Subsequently, human blood was used in the anolyte to quantify glucose molecules in real samples, obtaining a low relative error percentage when compared with a commercial glucometer. The coupling of the m-SPGB with a wireless electronic device allowed the detection and processing of the signal in the quantification of glucose directly without using a potentiostat/galvanostat. The promising results of the m-SPGB connected to a Wi-Fi electronic device are well suited for clinical application.

A microfluidic biofuel cell (µBFC) can be defined as a BFC where the delivery of fuel and removal of waste takes place via a microfluidic channel incorporating electrode structures. These devices typically do not require a physical barrier to separate the anodic and cathodic compartments. One type of µBFC is a flow-through device that consists of porous electrodes where the fuel and oxidant flow-through the electrodes. The implementation of flow-through µBFC technologies allow for higher enzyme loadings and high surface area to volume ratios to promote the surface-based electrochemical reactions catalyzed by the immobilized enzymes. Although µBFC have been evaluated for glucose and ethanol mainly, they have never evaluated the use of lactate as fuel. Lactate/O2 BFC can have high theoretical energy densities of up to 507 Wh/L using a sinlge enzyme and the complete oxidation of lactate could theoretically result in a maximum energy density of 3041 Wh/L. For this reason, lactate is an interesting fuel source for alternative energy generation. In this work, lactate oxidase (LOx) was coupled with a ferrocene-based redox polymer (dimethylferrocene-modified linear polyethylenimine, FcMe2-LPEI) as the bioanode and laccase (Lc) was compared connected to pyrene-anthracene and anthracene-modified carbon nanotubes (PyrAn-MWCNT and An-MWCNT) to facilitate the direct electron transfer at the biocathode and TBAB-modified Nafion was added and it was deposited onto a TCP electrode using a brush and allowed to dry for 2 h. Both electrodes were evaluated in two µBFC configurations using different concentrations of lactate, in the range found in sweat (0, 2, 10, 20 and 40 mM). The µBFC with an air-breathing cathode was fabricated using two plates made of PMMA [poly-(methyl methacrylate)] with a silicon elastomer film (Silastic®) compressed between the plates used to seal the device and define the channel pattern. In the top plate, an air-intake window was constructed with a dimension of 0.22 cm2 enabling oxygen delivery from the air. The FcMe2-LPEI/LOx bioanode was characterized by oxidation and reduction peak potentials of 0.28 and 0.16 V (vs. SCE). In the presence of 70 mM lactate, the limiting current density was 213 mA cm-2, corresponding to the mediated oxidation of lactate by LOx. The catalytic kinetics of the LOx bioanode were studied by amperometry similar current density of 204.1 mAcm-2 using 70 mM lactate and an apparent Michaelis constant of 8.9 ± 1.1 mM calculated by double-reciprocal evaluation of the Lineaweaver-Burk equation. On other hand, two different modifications of An-MWCNT and PyrAn-MWCNT were performed by cyclic voltammograms in 0.1 M PBS at pH 5.6 and. An-MWCNT/Lc electrodes resulted in a current density of 68 mA cm-2 without stirring, while PyrAn-MWCNT/Lc electrodes yielded a current density of 111.3 mA cm-2. Therefore, we utilized the PyrAn-MWCNT/Lc electrodes for µBFC experiments. The performance of the µBFC using 0.05 M PBS and a pH of 5.6 as anolyte and catholyte achievement a maximum OCP of 0.67 V using 20 and 40 mM of lactate, 1700 ± 77 mA cm-2 and 305 ± 20 mW cm-2 using 40 mM lactate, respectively. In order to take advantage of the µBFC design that allows the use of individual electrolyte inlets for the anode and cathode, the pH of the anolyte was changed to pH 7.4 (0.05 M), as appropriate for use in physiological conditions, and the pH of the catholytewas kept at 5.6 (0.05 M). With these change, the OCP increased to 0.73 V and remained constant at concentrations ranging from 2 to 40 mM of lactate, achieving maximum current and power densities of 2087 ± 84 mA cm-2 and 402 ± 23 mW cm-2 using 10 mM of lactate. This is a 19% and 24% enhancement in performance compared to employing the same pH. Also, the effect of flow rate was evaluated using a concentration of 10 mM lactate in 0.05 M at pH 7.4 for the anolyte and pH 5.6 for the catholyte. The OCP of the µBFC was 0.73 V. The results show that a flow rate of 3mL h-1 allowed the OCP to reach a maximum in less time, 6.9 min, compared to a flow rate of 9 mL h-1 which resulted in an improved current density of 1875 mA cm-2 although the average stabilization time was 11.2 min. Interestingly, the current density begins to decrease at a flow rate of 12 mL h-1, perhaps due to flow-induced mechanical instabilities in the CNT immobilization. This is the highest performing lactate/oxygen biofuel cell utilizing a single enzyme system. Future work will focus on incorporating multi-enzyme cascades to further improve performance.

En el presente trabajo, se evaluaron tres formas diferentes de inmovilización de la enzima glucosa oxidasa (GOx) para su uso como bioánodo en una biocelda de combustible híbrida microfluídica (BCH-¿F) que utiliza glucosa como combustible. Los métodos de inmovilización probados fueron: adsorción física, por entrecruzamiento e inmovilización covalente de la GOx. La inmovilización física de la GOx se caracterizó por voltamperometría cíclica (VC) encontrándose un pico de oxidación en -0.44 V y otro de reducción a -0.49 V (vs Electrodo de Calomel Saturado ECS) pertenecientes al cofactor FAD/FADH2 (Flavín adenín dinucleótido) respectivamente. Por otro lado, los dos agentes entrecruzadores evaluados fueron glutaraldehído (GA), poli-L-lisina y una combinación de ambos, obteniendo con GA (4.5 %) una mayor cantidad de GOx inmovilizada con un recubrimiento de 2.6865 x 10-9 mol cm-2. Posteriormente, el depósito se optimizó con el uso de nanotubos de carbono de multipared (NTCMP) combinados con GOx y GA (1%), mejorando la transferencia directa de electrones (TDE), caracterizado por métodos electroquímicos y por FTIR (espectroscopia de infrarrojo con transformadas de Fourier). Mediante el modelo de Laviron se estimó el coeficiente de transferencia de electrones (¿) cuyo valor resultante fue de 0.5 y la constante de velocidad de la transferencia de electrones (Ks) fue de 1.01 s-1 para GOx/NTCMP-GA sobre grafito. Con el uso del bioánodo GOx/NTCMP-GA se obtuvo el mejor rendimiento dentro de una BCH-¿F utilizando Pt/C como cátodo en presencia de glucosa 5mM en BF, logrando un valor de potencial a circuito abierto de 0.72 V, 1.43 mA cm-2 de densidad de corriente y una potencia de 610 ¿W cm-2, valores mayores de los reportados en literatura para una BCH-¿F de TDE. Adicionalmente, la inmovilización de la GOx/NTCMP-GA se realizó sobre una estructura de oro electrodepositada sobre grafito logrando un valor de ¿=0.5 y Ks=2.1 s-1. Después se construyó un diseño de electrodo formado por el ácido 3-mercaptopropiónico anclado sobre la superficie de oro en presencia de EDC/NHS (1-etil-3-(3-dimetilaminopropil) carbodiimida)/N-hidroxisuccinamida) para favorecer la inmovilización covalente de la GOx. In this work, three different glucose oxidase (GOx) immobilization methods were evaluated to be used as a bioanode inside hybrid microfluidic biofuel cell (BCH-¿F) using glucose as fuel. The GOx immobilization methods were: physical adsorption, cross-linking and covalent. The physical immobilization of GOx was characterized by cyclic voltammetry (CV); a -0.44 V oxidation peak and a -0.49 V reduction peak (vs Saturated Electrode Calomel) belonging to the FAD/FADH2 (Flavin adenine dinucleotide) cofactor respectively, were found. On other hand, the two cross-linking agents evaluated were glutaraldehyde (GA), poly-L-lysine (PLL) and a combination of both. The highest GOx immobilization, with a 2.6865 x 10-9 mol cm-2 cover, was obtained through GA (4.5 %). Afterwards, the deposit was optimized with multiwall carbon nanotubes (MWCNT) combined with GOx and GA (1 %), which improved direct electron transfer (DET), characterized by electrochemical methods and FTIR (Fourier transform infrared spectroscopy). The coefficient electron transfer (¿) was estimated at 0.5 and the constant rate of electron transfer (Ks) was estimated at 1.01 s-1 via Laviron¿s model for GOx/MWCNT-GA on a graphite electrode. The best performance of BCH-¿F with the GOx/MWCNT-GA bioanode using Pt/C as a cathode in 5 mM of glucose in BF was obtained, resulting in an open circuit potential (OCP) of 0.72 V, current density at 1.43 mA cm-2 and power density at 610 ¿W cm-2; these results are the highest reported for DET GOx/MWCNT-GA. Additionally, GOx/MWCNT-GA was immobilization on architecture of golden electrodeposited on graphite carbon obtaining values of ¿=0.5 y Ks=2.1 s-1. Afterwards, 3-mercaptopropionic acid electrode was adsorbed on gold surface and modified by a mixture of EDC/NHS (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/ N-hidroxisuccinamide) to promote covalent immobilization of GOx.

Hybrid membraneless fuel cells HMFC are devices that use an abiotic catalysts and an enzymatic material, in the anode or cathode, with the main target of provide stability and higher performance. HMFC was evaluated using Glucose oxidase enzyme supported in Multiwalled carbon nanotubes and glutaraldehyde mixtures (GOx/MWCNT-GA) and Pt/C as anode and cathode respectively under ideal conditions. The anode electrode based on GOx/MWCNT-GA was characterized by electrochemical techniques showing a successful direct electron transfer (DET) between GOx and MWCNT to electrode surface. The performance of ideal HMFC delivers a higher OCP of 1.2 V and a maximum power density of 200 µW cm-2 in the presence of 10 mM glucose as fuel in phosphate buffer (PB) pH 7 as anolyte and oxygen-saturated 0.3M KOH as catholyte. These results show a highest performance reported to HMFC that implement DET in the anode electrode, with potential application in implantable devices inside living organisms.

The enzyme immobilization on conductive materials is a topic research for the development of biosensors and biofuel cells. The most common anchoring methods (covalent binding, cross-linking or inclusion in gels and membranes), often interfere with enzymatic catalysis due to active sites occlusion, enzyme denaturation or substrate diffusion problems. The use of Quantum dots (QD) as support matrix for the enzyme immobilization, has been reported as a viable alternative for the macromolecules anchoring, diminishing to a great extent the most well-known problems. In this work, a comparison between Graphene QD´s (GSH-CQD) and CdTe QD´s (GSH-CdTeQD) coated with glutathione is presented for the immobilization of the enzyme Glucose oxidase (GOx) as well as enzymes Lacasse (Lc), Glucose dehydrogenase (GDH) and β-galactosidase (Gal). The surfaces of graphite electrodes, carbon nanofoam and Toray paper was modified, with 5,10,15,20-Tetrakis (1-methyl-4-pyridinium) Porphyrin, a layer of QD was deposited to finally anchor GOx. The modified electrodes were evaluated by various electrochemical and physicochemical techniques. The results obtained show that QD´s modified electrodes have a greater immobilization capacity than graphite electrode and electrodes modified with GSH-CdTeQD are more sensitive to glucose. This suggests that the Porphyrin/GSH-CdTeQD/GOx system is suitable to be implemented in the development of a biofuel cell. La inmovilización de enzimas sobre materiales conductores, es un tema de investigación ampliamente estudiado para el desarrollo de biosensores y bioceldas de combustible. Los métodos más comunes para el anclaje de estas moléculas (enlace covalente, cross-linking, o inclusión en geles y membranas) a menudo interfieren con la catálisis enzimática debido a la oclusión de sitios activos, desnaturalización de la enzima o problemas de difusión del sustrato. El uso de Quantum dots como matriz de soporte para la inmovilización enzimática ha sido reportada como una alternativa viable para el anclaje de macromoléculas, disminuyendo en gran medida los problemas antes mencionados. En este trabajo se presenta una comparación entre Quantum dots de carbono (GSH-CQD) y de CdTe (GSH-CdTeQD) ambos recubiertos con glutatión (GSH), para la inmovilización de la enzima Glucosa oxidasa (GOx) así como de las enzimas Lacasa (Lc) Glucosa deshidrogenasa (GDH) y β-Galactosidasa (Gal). La superficie de electrodos de grafito, nanoesponja y papel de fibra de carbono (Toray) fue modificada con 5,10,15,20-Tetrakis (1-metil-4-piridinio) Porfirina, luego se depositó una capa de Quantum dots (GSH-CQD o GSH-CdTeQD) para finalmente anclar la GOx. Los electrodos modificados fueron evaluados por diversas técnicas tanto electroquímicas como fisicoquímicas. Los resultados obtenidos muestran que los GSH-CQD y GSH-CdTeQD tienen una mayor capacidad de inmovilización que el electrodo de grafito sin modificaciones sin embargo los electrodos modificados con GSH-CdTeQD son más sensibles a la glucosa. Esto sugiere que el sistema Porfirina/GSH-CdTeQD/GOx es adecuado para implementarse en el desarrollo de una biocelda de combustible.