Air-cathode microbial fuel cells (AC-MFC) use a gas-diffusionlayer (GDL) coating based on polytet... more Air-cathode microbial fuel cells (AC-MFC) use a gas-diffusionlayer (GDL) coating based on polytetrafluoroethylene applied to the cathode to prevent electrolyte leakage. However, this type of GDL can also lead to a decrease in MFC performance due to electron-transfer limitation, mass-transfer limitation or catalyst availability. This study provides a comprehensive understanding of the significance of the GDL coating, demonstrating the interaction between the number of GDL coatings and the external resistance (R ext) used. An experimental design in 28 mL AC-MFCs was prepared and conducted using two different R ext (10 and 249 Ω) and four different GDL coatings (1 to 4 layers). The coating effect was not significant when operating with a high R ext , where the electron transfer was the limiting process. However, when the R ext was low, the amount of polytetrafluoroethylene limited the cathode performance due to a significant decrease in the Pt availability on the catalytic surface. Thus, GDL-1 with 10 Ω as R ext reached 0.96 mA/cm 2 , 3-fold higher than that obtained with 249 Ω as R ext (ca. 0.30 mA/cm 2). Besides, the current density did not vary noticeably in the other cathodes with 249 Ω as R ext. Contrarily, the current density with 10 Ω as R ext decreased as the number of GDL increased (0.74, 0.57 and 0.37 for GDL-2, GDL-3 and GDL-4 respectively). These values agreed with those of the polarization curve. Furthermore, limitations were also observed in electrochemical impedance spectroscopy measurements: the charge resistance increased with the number of GDL, related to the ease of electron flow. These values were18 Ω, 22 Ω, 53 Ω and 58 Ω for GDL-1, GDL-2, GDL-3 and GDL-4, respectively, for both 10 and 249 Ω cathodes.
Nano-sized titanium dioxide particles (nTiO 2) are one of the most widely used nano-scale enginee... more Nano-sized titanium dioxide particles (nTiO 2) are one of the most widely used nano-scale engineered materials. Evidence of the presence of nTiO 2 in freshwater systems has been reported by recent ecotoxicological studies, which indicated the potential toxic effects of nTiO 2 to aquatic organisms. This study aimed at exploring lethal and sub-lethal endpoints of aqueous exposure of the aquatic insect Hydropsyche exocellata Dufour, 1841 (Trichoptera, Hydropsychidae) to nTiO 2 at different concentrations. Abdominal contractions significantly increased with nTiO 2 exposure. Levels of lipid peroxidation (LPO) increased with nTiO 2 dose, whereas the opposite was recorded for the antioxidant enzyme catalase activity (CAT). Moreover, the highest exposure (50.0 mg/L) resulted in the highest mortality (56% of mortality two weeks after pulse exposure to nTiO 2). Overall, our results show that nTiO 2 has potential toxic effects on H. exocellata at concentrations of 50.0 mg/L.
The incorporation of nanomaterials on (bio)sensors based on composite materials has led to import... more The incorporation of nanomaterials on (bio)sensors based on composite materials has led to important advances in analytical chemistry field due to the extraordinary properties that these materials offer. Nanodiamonds (NDs) are a novel type of material that has raised much attention, as they have the possibility of being produced on large scale by using relatively inexpensive synthetic methodologies. Moreover, NDs present some other interesting features as suitability for fluorescence due to surface functionalization and a proved biocompatibility, which makes them well suited for biomedical applications. In addition, NDs can be modified with metallic nanoparticles (NP), such as silver or gold, in order to combine the special features of both. The aim of this research work is the nanostructuration of novel sensing devices using NDs combined with silver (Ag@NDs) and gold (Au@NDs) nanoparticles. A complete morphological and electrochemical characterization as function of the prepared na...
Journal of Chemical Technology & Biotechnology, 2020
BackgroundCyclic voltammetry (CV) has become a standard tool in the study of bioelectrochemical s... more BackgroundCyclic voltammetry (CV) has become a standard tool in the study of bioelectrochemical systems (BES) because it is a nondestructive technique that provides useful information on the electron transfer capacity of these systems. When applied to the large‐surface electrodes typically found in BES, the scan rate must be severely diminished or otherwise the capacitive current masks the faradaic current. Decreasing the scan rate results in an increase in the duration of the experiments, which can lead to a significant alteration of the initial system conditions.ResultsThe repeatability of low scan rate cyclic voltammetry (LSCV) in air cathode microbial fuel cells (AC‐MFCs) operating in batch mode was examined. Consecutive LSCVs at 0.1 mV s−1 were recorded with and without prior renewal of the culture medium. Significant deviations in CV replicates were observed when the medium was not replaced (as high as 40% of maximum intensity). These deviations decreased (<18%) when the me...
With a growing demand for the availability of inexpensive, simple and rapid prototyped devices, t... more With a growing demand for the availability of inexpensive, simple and rapid prototyped devices, the prospect of miniaturization of the reference electrodes using printing techniques becomes promising. A stable and reusable full inkjet-printed solid-state reference electrode (IPRE) was developed. The reference electrode was fully produced by consecutive inkjet printing of several layers. Ag ink was printed and chlorinated by NaClO printing forming a Ag/AgCl pseudo-reference electrode. Then, a surface protection by printing a Clsaturated polyvinyl butyral membrane finally gave a reference electrode that demonstrated an outstanding performance comparable to commercial ones. This full inkjet printing fabrication strategy will improve the viability of producing low-cost miniaturized reference electrodes with interest in many electrochemical sensor dependent areas.
Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nan... more Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nanohorns, carbon nanotubes, graphene, graphite and related with a wide range of (bio)modifiers have been extensively studied for their incorporation on different pure metal or carbon electrode surfaces via drop-casting. However, CNMs are also shown to be important functional additives for polymers, having great potential to produce rigid nanocomposite materials with a range of enhanced properties, including mechanical, optical, electrical, thermal and electrochemical. The high malleability derived from the host polymer allows alternative strategies that can be carried out in order to incorporate different types of (bio)modifiers in/on/into a polymeric nanocomposite electrode. Accordingly, this mini review overviews the main methodologies used for the bio-functionalization of electrochemical transducers based on nanocomposite carbon paste electrodes (NC-CPEs). Additionally, the most extensively (bio)modifiers used in electrochemical (bio)sensing, together with their various electrocatalytical performance are also discussed, fact that might serve as a general outlook for planning further research.
Nanocomposites with a tuned distribution of nanoparticles for water treatment and electrochemical... more Nanocomposites with a tuned distribution of nanoparticles for water treatment and electrochemical assays are prepared by the intermatrix synthesis technique.
Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functi... more Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with Quantum Dots
Abstract This work is focused on the application of advanced characterization techniques for the ... more Abstract This work is focused on the application of advanced characterization techniques for the development of optimized electrochemical sensors based on graphene–polymer nanocomposites. Reduced graphene oxide (rGO) was synthesized and used as conducting nanofiller material in nanocomposite electrodes based on epoxy resin. A series of rGO/epoxy nanocomposite electrodes were fabricated containing 8%–20% of nanofiller material. Composition ratios have been studied using percolation theory and characterized by different electrochemical techniques, demonstrating that an optimization of the rGO/epoxy composition ratio is mandatory to enhance electrochemical performance. The potential of this approach in terms of electroanalytical response has been demonstrated by means of the amperometric detection of ascorbic acid, which was used as a model analyte. Finally, different morphological experiments were also carried out in order to verify the electrochemical and electroanalytical enhancement obtained for the optimized-nanocomposite sensors.
We report the benefit of using an optimized composite electrode, based on a multiwall carbon nano... more We report the benefit of using an optimized composite electrode, based on a multiwall carbon nanotubes and epoxy resin, as working electrode in an automated flow system. The optimal composite electrode composition consists in a 10% carbon nanotubes and 90% epoxy resin. This composition provides lower limit of detection and increases the stability and reproducibility of the analytical signal compared to the 20% conventional composition electrodes. Moreover, the standard solutions are on-line prepared with an automated flow system. The integration of the developed carbon nanotube electrodes in the proposed flow system provides a highly sensitive analyzer for free chlorine determination in water down to the 20microgL(-1). The working range was found to be 0.02-4mgL(-1) with an analysis time of 60s. The system sensitivity was maintained into the control limits (+/-2sigma) for one month, with a mean value of -0.146 (+/-0.008) microALmg(-1). Validation of the analytical system has been pe...
A novel microelectrode array (DO-MEA) sensor was designed and fabricated using microelectromechan... more A novel microelectrode array (DO-MEA) sensor was designed and fabricated using microelectromechanical systems technology on a needle for real time measurement of dissolved oxygen (DO). The sensor consisted of eleven gold disk microelectrodes and a rectangular auxiliary electrode along them. The sensor can also be operated with an external reference system. Three different sensor designs were fabricated, and their responses were fully characterized and evaluated under different environmental conditions. The DO-MEA sensor presented a linear response in the 0-8 mg DO•l-1concentration range in water, displaying high sensitivity and repeatability, and low detection and quantification limits, below 0.11mg DO•l-1 and 0.38 mg DO•l-1 respectively. Knowledge of bacterial activity inside biofilms is key to the optimization of applied biotechnologies. The developed sensor was validated against a commercial Clark-type microelectrode overcoming its drawbacks, by profiling a heterotrophic biofilm cultivated in a flat-plate bioreactor. The DO-MEA sensor provided a multipoint, simultaneous dissolved oxygen snapshot profile inside a biofilm with high spatial resolution due to its micrometric dimensions, thus becoming a powerful tool for the research of many similar biological-based processes and applications.
In this paper we report the development and assessment of a biomimetic pump based on soft polymer... more In this paper we report the development and assessment of a biomimetic pump based on soft polymeric actuators, i.e. polyurethane tubes (950 m internal diameter) with polypyrrole, which expands and contracts during redox cycling and provides the driving force for liquid movement. This pump can be integrated in the microfluidic channels, functioning in a similar manner similar to blood vessels. In principle, these biomimetic pumps and low power detectors could be integrated into a fully functional and totally integrated microanalytical platform. It was also low power (of the order of 100 mJ/L to obtain a flow rate of 0.08 L/s), operating using voltages of up to ±1 V, and requiring currents of less than 100 mA. The flow rates achieved are comparable to miniaturised commercial pumps, with the benefit of considerably reduced power consumption (a conventional miniaturised peristaltic pump consumes ca. 3.6 J/L to obtain the same flow rates as the pump integrated in this system). The microchip was constructed using polydimethylsiloxane (PDMS) and designed to provide the appropriate mixing of reagents in order to obtain optimum response from the sensors. The chip incorporated an optical detection system constructed using miniaturised light emitting diodes (LED) for both the light source and the detector. This low-cost and low-power detector was surprisingly sensitive due to its integrating mode of operation, and exhibited very low limits of detection. In the present system, conventional LEDs were employed as proof of concept. However, surface mount LEDs will be employed which will allow for a much more compact and compatible format for use in microfluidic manifolds than conventional LEDs. The low-power biomimetic pump, and the low power detector system were assessed as components that could be integrated into a futuristic integrated microanalytical platform.
Multiwall carbon nanotubes and resin epoxy have been used to fabricate a composite electrode for ... more Multiwall carbon nanotubes and resin epoxy have been used to fabricate a composite electrode for electroanalytical purposes. The optimum composite proportions for high electrode sensitivity, low limit of detection and fast response were investigated. Compositions were characterized by percolation theory, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, atomic force microscopy and chronoamperometry. We found that around the optimum composite proportion, the electrode performance is less affected by small variations in the composition of the composite. These composite electrodes provide easy surface renewal, low background current, an efficient mass transport and are suitable for chemical modification. The potentiality of this approach in terms of electroanalytical response is demonstrated by means of the amperometric detection of ascorbic acid in water solution.
. This paper describes the development of a new flow system by substituting the injection valve ... more . This paper describes the development of a new flow system by substituting the injection valve of a FIA system with an automatic microburette controlled by a PC via an RS-232 interface to introduce flexibility into the system. Initially, the response of the system was characterized without a chemical reaction by using a reference system (6-port valve) and a modified system
Air-cathode microbial fuel cells (AC-MFC) use a gas-diffusionlayer (GDL) coating based on polytet... more Air-cathode microbial fuel cells (AC-MFC) use a gas-diffusionlayer (GDL) coating based on polytetrafluoroethylene applied to the cathode to prevent electrolyte leakage. However, this type of GDL can also lead to a decrease in MFC performance due to electron-transfer limitation, mass-transfer limitation or catalyst availability. This study provides a comprehensive understanding of the significance of the GDL coating, demonstrating the interaction between the number of GDL coatings and the external resistance (R ext) used. An experimental design in 28 mL AC-MFCs was prepared and conducted using two different R ext (10 and 249 Ω) and four different GDL coatings (1 to 4 layers). The coating effect was not significant when operating with a high R ext , where the electron transfer was the limiting process. However, when the R ext was low, the amount of polytetrafluoroethylene limited the cathode performance due to a significant decrease in the Pt availability on the catalytic surface. Thus, GDL-1 with 10 Ω as R ext reached 0.96 mA/cm 2 , 3-fold higher than that obtained with 249 Ω as R ext (ca. 0.30 mA/cm 2). Besides, the current density did not vary noticeably in the other cathodes with 249 Ω as R ext. Contrarily, the current density with 10 Ω as R ext decreased as the number of GDL increased (0.74, 0.57 and 0.37 for GDL-2, GDL-3 and GDL-4 respectively). These values agreed with those of the polarization curve. Furthermore, limitations were also observed in electrochemical impedance spectroscopy measurements: the charge resistance increased with the number of GDL, related to the ease of electron flow. These values were18 Ω, 22 Ω, 53 Ω and 58 Ω for GDL-1, GDL-2, GDL-3 and GDL-4, respectively, for both 10 and 249 Ω cathodes.
Nano-sized titanium dioxide particles (nTiO 2) are one of the most widely used nano-scale enginee... more Nano-sized titanium dioxide particles (nTiO 2) are one of the most widely used nano-scale engineered materials. Evidence of the presence of nTiO 2 in freshwater systems has been reported by recent ecotoxicological studies, which indicated the potential toxic effects of nTiO 2 to aquatic organisms. This study aimed at exploring lethal and sub-lethal endpoints of aqueous exposure of the aquatic insect Hydropsyche exocellata Dufour, 1841 (Trichoptera, Hydropsychidae) to nTiO 2 at different concentrations. Abdominal contractions significantly increased with nTiO 2 exposure. Levels of lipid peroxidation (LPO) increased with nTiO 2 dose, whereas the opposite was recorded for the antioxidant enzyme catalase activity (CAT). Moreover, the highest exposure (50.0 mg/L) resulted in the highest mortality (56% of mortality two weeks after pulse exposure to nTiO 2). Overall, our results show that nTiO 2 has potential toxic effects on H. exocellata at concentrations of 50.0 mg/L.
The incorporation of nanomaterials on (bio)sensors based on composite materials has led to import... more The incorporation of nanomaterials on (bio)sensors based on composite materials has led to important advances in analytical chemistry field due to the extraordinary properties that these materials offer. Nanodiamonds (NDs) are a novel type of material that has raised much attention, as they have the possibility of being produced on large scale by using relatively inexpensive synthetic methodologies. Moreover, NDs present some other interesting features as suitability for fluorescence due to surface functionalization and a proved biocompatibility, which makes them well suited for biomedical applications. In addition, NDs can be modified with metallic nanoparticles (NP), such as silver or gold, in order to combine the special features of both. The aim of this research work is the nanostructuration of novel sensing devices using NDs combined with silver (Ag@NDs) and gold (Au@NDs) nanoparticles. A complete morphological and electrochemical characterization as function of the prepared na...
Journal of Chemical Technology & Biotechnology, 2020
BackgroundCyclic voltammetry (CV) has become a standard tool in the study of bioelectrochemical s... more BackgroundCyclic voltammetry (CV) has become a standard tool in the study of bioelectrochemical systems (BES) because it is a nondestructive technique that provides useful information on the electron transfer capacity of these systems. When applied to the large‐surface electrodes typically found in BES, the scan rate must be severely diminished or otherwise the capacitive current masks the faradaic current. Decreasing the scan rate results in an increase in the duration of the experiments, which can lead to a significant alteration of the initial system conditions.ResultsThe repeatability of low scan rate cyclic voltammetry (LSCV) in air cathode microbial fuel cells (AC‐MFCs) operating in batch mode was examined. Consecutive LSCVs at 0.1 mV s−1 were recorded with and without prior renewal of the culture medium. Significant deviations in CV replicates were observed when the medium was not replaced (as high as 40% of maximum intensity). These deviations decreased (<18%) when the me...
With a growing demand for the availability of inexpensive, simple and rapid prototyped devices, t... more With a growing demand for the availability of inexpensive, simple and rapid prototyped devices, the prospect of miniaturization of the reference electrodes using printing techniques becomes promising. A stable and reusable full inkjet-printed solid-state reference electrode (IPRE) was developed. The reference electrode was fully produced by consecutive inkjet printing of several layers. Ag ink was printed and chlorinated by NaClO printing forming a Ag/AgCl pseudo-reference electrode. Then, a surface protection by printing a Clsaturated polyvinyl butyral membrane finally gave a reference electrode that demonstrated an outstanding performance comparable to commercial ones. This full inkjet printing fabrication strategy will improve the viability of producing low-cost miniaturized reference electrodes with interest in many electrochemical sensor dependent areas.
Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nan... more Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nanohorns, carbon nanotubes, graphene, graphite and related with a wide range of (bio)modifiers have been extensively studied for their incorporation on different pure metal or carbon electrode surfaces via drop-casting. However, CNMs are also shown to be important functional additives for polymers, having great potential to produce rigid nanocomposite materials with a range of enhanced properties, including mechanical, optical, electrical, thermal and electrochemical. The high malleability derived from the host polymer allows alternative strategies that can be carried out in order to incorporate different types of (bio)modifiers in/on/into a polymeric nanocomposite electrode. Accordingly, this mini review overviews the main methodologies used for the bio-functionalization of electrochemical transducers based on nanocomposite carbon paste electrodes (NC-CPEs). Additionally, the most extensively (bio)modifiers used in electrochemical (bio)sensing, together with their various electrocatalytical performance are also discussed, fact that might serve as a general outlook for planning further research.
Nanocomposites with a tuned distribution of nanoparticles for water treatment and electrochemical... more Nanocomposites with a tuned distribution of nanoparticles for water treatment and electrochemical assays are prepared by the intermatrix synthesis technique.
Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functi... more Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with Quantum Dots
Abstract This work is focused on the application of advanced characterization techniques for the ... more Abstract This work is focused on the application of advanced characterization techniques for the development of optimized electrochemical sensors based on graphene–polymer nanocomposites. Reduced graphene oxide (rGO) was synthesized and used as conducting nanofiller material in nanocomposite electrodes based on epoxy resin. A series of rGO/epoxy nanocomposite electrodes were fabricated containing 8%–20% of nanofiller material. Composition ratios have been studied using percolation theory and characterized by different electrochemical techniques, demonstrating that an optimization of the rGO/epoxy composition ratio is mandatory to enhance electrochemical performance. The potential of this approach in terms of electroanalytical response has been demonstrated by means of the amperometric detection of ascorbic acid, which was used as a model analyte. Finally, different morphological experiments were also carried out in order to verify the electrochemical and electroanalytical enhancement obtained for the optimized-nanocomposite sensors.
We report the benefit of using an optimized composite electrode, based on a multiwall carbon nano... more We report the benefit of using an optimized composite electrode, based on a multiwall carbon nanotubes and epoxy resin, as working electrode in an automated flow system. The optimal composite electrode composition consists in a 10% carbon nanotubes and 90% epoxy resin. This composition provides lower limit of detection and increases the stability and reproducibility of the analytical signal compared to the 20% conventional composition electrodes. Moreover, the standard solutions are on-line prepared with an automated flow system. The integration of the developed carbon nanotube electrodes in the proposed flow system provides a highly sensitive analyzer for free chlorine determination in water down to the 20microgL(-1). The working range was found to be 0.02-4mgL(-1) with an analysis time of 60s. The system sensitivity was maintained into the control limits (+/-2sigma) for one month, with a mean value of -0.146 (+/-0.008) microALmg(-1). Validation of the analytical system has been pe...
A novel microelectrode array (DO-MEA) sensor was designed and fabricated using microelectromechan... more A novel microelectrode array (DO-MEA) sensor was designed and fabricated using microelectromechanical systems technology on a needle for real time measurement of dissolved oxygen (DO). The sensor consisted of eleven gold disk microelectrodes and a rectangular auxiliary electrode along them. The sensor can also be operated with an external reference system. Three different sensor designs were fabricated, and their responses were fully characterized and evaluated under different environmental conditions. The DO-MEA sensor presented a linear response in the 0-8 mg DO•l-1concentration range in water, displaying high sensitivity and repeatability, and low detection and quantification limits, below 0.11mg DO•l-1 and 0.38 mg DO•l-1 respectively. Knowledge of bacterial activity inside biofilms is key to the optimization of applied biotechnologies. The developed sensor was validated against a commercial Clark-type microelectrode overcoming its drawbacks, by profiling a heterotrophic biofilm cultivated in a flat-plate bioreactor. The DO-MEA sensor provided a multipoint, simultaneous dissolved oxygen snapshot profile inside a biofilm with high spatial resolution due to its micrometric dimensions, thus becoming a powerful tool for the research of many similar biological-based processes and applications.
In this paper we report the development and assessment of a biomimetic pump based on soft polymer... more In this paper we report the development and assessment of a biomimetic pump based on soft polymeric actuators, i.e. polyurethane tubes (950 m internal diameter) with polypyrrole, which expands and contracts during redox cycling and provides the driving force for liquid movement. This pump can be integrated in the microfluidic channels, functioning in a similar manner similar to blood vessels. In principle, these biomimetic pumps and low power detectors could be integrated into a fully functional and totally integrated microanalytical platform. It was also low power (of the order of 100 mJ/L to obtain a flow rate of 0.08 L/s), operating using voltages of up to ±1 V, and requiring currents of less than 100 mA. The flow rates achieved are comparable to miniaturised commercial pumps, with the benefit of considerably reduced power consumption (a conventional miniaturised peristaltic pump consumes ca. 3.6 J/L to obtain the same flow rates as the pump integrated in this system). The microchip was constructed using polydimethylsiloxane (PDMS) and designed to provide the appropriate mixing of reagents in order to obtain optimum response from the sensors. The chip incorporated an optical detection system constructed using miniaturised light emitting diodes (LED) for both the light source and the detector. This low-cost and low-power detector was surprisingly sensitive due to its integrating mode of operation, and exhibited very low limits of detection. In the present system, conventional LEDs were employed as proof of concept. However, surface mount LEDs will be employed which will allow for a much more compact and compatible format for use in microfluidic manifolds than conventional LEDs. The low-power biomimetic pump, and the low power detector system were assessed as components that could be integrated into a futuristic integrated microanalytical platform.
Multiwall carbon nanotubes and resin epoxy have been used to fabricate a composite electrode for ... more Multiwall carbon nanotubes and resin epoxy have been used to fabricate a composite electrode for electroanalytical purposes. The optimum composite proportions for high electrode sensitivity, low limit of detection and fast response were investigated. Compositions were characterized by percolation theory, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, atomic force microscopy and chronoamperometry. We found that around the optimum composite proportion, the electrode performance is less affected by small variations in the composition of the composite. These composite electrodes provide easy surface renewal, low background current, an efficient mass transport and are suitable for chemical modification. The potentiality of this approach in terms of electroanalytical response is demonstrated by means of the amperometric detection of ascorbic acid in water solution.
. This paper describes the development of a new flow system by substituting the injection valve ... more . This paper describes the development of a new flow system by substituting the injection valve of a FIA system with an automatic microburette controlled by a PC via an RS-232 interface to introduce flexibility into the system. Initially, the response of the system was characterized without a chemical reaction by using a reference system (6-port valve) and a modified system
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