2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, 2011
An integrated lab on a chip that enables simultaneous optical and electrochemical analysis workin... more An integrated lab on a chip that enables simultaneous optical and electrochemical analysis working in continuous flow mode is presented. Both transducers are integrated into a single detection cell and operated simultaneously with no evidences of cross-talk and in agreement with theoretical predictions by Levich equation (electrochemical ) and by Lambert-Beer law (absorbance). Their performance is demonstrated by continuous detection of lactate via a double enzymatic reaction with lactate oxidase (LOX) and horseradish peroxidase (HRP). The consumption of the enzymatic reaction mediator (ferrocyanide, (Fe(CN)6 t) is recorded by amperometry, while the product (ferricyanide, (Fe(CN)6 t) is quantified by absorbance. The ability to quantifY reagent and product simultaneously increases the robustness of the system by making it self-verifying, in addition to the inherent advantages of micro fluidic devices.
Arrays of microdisc electrodes have found widespread use in electroanalysis. These are commonly p... more Arrays of microdisc electrodes have found widespread use in electroanalysis. These are commonly produced lithographically and practical arrays may contain up to hundreds of individual disc electrodes (e.g. of gold, platinum, indium,...) to maximise sensitivity and minimise limits of detection. Typically, however, the lithographic fabrication process is imperfect resulting in a significant fraction (often tens of percent) of electrochemically inactive electrodes. We demonstrate that a 2-dimensional simulation based on the diffusion domain approximation in conjugation with simple experiments on the ferrocyanide redox couple in aqueous solutions can be used to rigorously 'count' the number of active electrodes in a non-destructive fashion. The agreement with an independent count in which active electrodes are identified via electro-plating with copper followed by ex situ microscopic examination is quantitatively excellent.
Regular arrays of ca. micron sized droplets on a gold electrode surface can block diffusion to th... more Regular arrays of ca. micron sized droplets on a gold electrode surface can block diffusion to the electrode surface of one metal ion (which binds with the material in the droplet) whilst having no significant effect on another (which does not), so allowing interference effects in electroanalysis to be eliminated.
This work presents the first true solid-state microrespirometer. It consists on a naturally devel... more This work presents the first true solid-state microrespirometer. It consists on a naturally developed biofilm of Pseudomonas aeruginosa over a Nafion modified array of gold microdisc electrodes. Such a device can be used to monitor acute toxicity in water streams ...
... Chem. 585 (2005) 63) two dimensional simulation method for the linear sweep response of array... more ... Chem. 585 (2005) 63) two dimensional simulation method for the linear sweep response of arrays of randomly distributed microdisc electrodes is applied to 'RAM electrodes' (S. Fletcher, MD Horne, Electrochem. Commun. ... In a typical RAM ca. ...
Porous liquid crystalline lipid-based nanoparticles are shown here to enable protein analysis in ... more Porous liquid crystalline lipid-based nanoparticles are shown here to enable protein analysis in microchip electroseparation by reducing sample adsorption. Additionally, higher stability and reproducibility of the separations were observed. The method was tested by separating green fluorescent protein (GFP) in hot embossed cyclic olefin polymer microchips with integrated fiber grooves for LIF detection. The sample adsorption was indirectly quantified by measuring the height, width and asymmetry of the separation peaks for various concentrations of nanoparticles in the sample and background electrolyte. Without nanoparticles, electropherograms displayed typical signs of extensive adsorption to the channel walls, with low, broad tailing peaks. Higher, narrower more symmetric peaks were generated when 0.5-10% nanoparticles were added, showing a dramatic reduction of sample adsorption. The current through the separation channel decreased with nanoparticle concentration, reducing to half its value when the nanoparticle concentration was increased from 0.5 to 4%. Addition of nanoparticles enabled separations that were otherwise hindered by extensive adsorption, e.g. separation of GFP mutants differing by only one amino acid. It was also observed that increasing the nanoparticle concentration increased the number of impurities that could be resolved in a GFP sample. This indicates that the adsorption is further reduced, and/or that the nanoparticles provide an interacting pseudostationary phase for electrochromatography.
Olga Ordeig,a Javier del Campo,b* Francesc Xavier Munoz,a Craig E. Banks,c Richard G. Comptond a... more Olga Ordeig,a Javier del Campo,b* Francesc Xavier Munoz,a Craig E. Banks,c Richard G. Comptond a Centro Nacional de Microelectrónica, IMB-CNM. CSIC, Campus de la Universidad Autónoma de Barcelona, Bellaterra 08193, Spain b Institut de Biotecnologia i Biomedicina and ...
Abstract This article describes the direct detection of Bromate, but also of chlorate and iodate,... more Abstract This article describes the direct detection of Bromate, but also of chlorate and iodate, using modified arrays of platinum ultramicroelectrodes. The detection limits for these ions are IO equation image= 0.76 μM; BrO equation image= 2.34 μM and ClO equation ...
Abstract The electroanalytical detection of trace mercury(II) at gold ultra-microelectrode arrays... more Abstract The electroanalytical detection of trace mercury(II) at gold ultra-microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in ...
We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally sp... more We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 mum, are used to support liquid 5-nonyl-salicylaldoxime (Acorga-P50) droplets on the surface. By voltametrically monitoring the transport-controlled reduction rate of Cu(II) (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of Cu(II) at the droplet-aqueous solution interface as the droplet "fills up" with Cu(II). Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic-droplet phase and of diffusion coefficients within the droplet. The partition coefficient for Cu(II) between water and 5-nonyl-salicylaldoxime was found to be 200 at 25 degrees C and the diffusion coefficient of Cu(II) inside the organic phase was determined to be 5 x 10(-11) cm2 s(-1).
Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide i... more Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array.
A dual lab on a chip (DLOC) approach that enables simultaneous optical and electrochemical detect... more A dual lab on a chip (DLOC) approach that enables simultaneous optical and electrochemical detection working in a continuous flow regime is presented. Both detection modes are integrated for the first time into a single detection volume and operate simultaneously with no evidence of cross-talk. The electrochemical cell was characterized amperometrically by measuring the current in ferrocyanide solutions at +0.4 V vs gold pseudoreference electrode, at a flow rate of 200 μL min(-1). The experimental results for ferrocyanide concentrations ranging from 0.005 to 2 mM were in good agreement with the values predicted by the Levich equation for a microelectrode inside a rectangular channel, with a sensitivity of 2.059 ± 0.004 μA mM(-1) and a limit of detection (LoD) of (2.303 ± 0.004) × 10(-3) mM. Besides, optical detection was evaluated by measuring the absorbance of ferricyanide solutions at 420 nm. The results obtained therein coincide with those predicted by the Beer-Lambert law for a range of ferricyanide concentrations from 0.005 to 0.3 mM and showed an estimated LoD of (0.553 ± 0.001) × 10(-3) mM. The DLOC was finally applied to the analysis of L-lactate via a bienzymatic reaction involving lactate oxidase (LOX) and horseradish peroxidase (HRP). Here, the consumption of the reagent of the reaction (ferrocyanide) was continuously monitored by amperometry whereas the product of the reaction (ferricyanide) was recorded by absorbance. The DLOC presented good performance in terms of sensitivity and limit of detection, comparable to other fluidic systems found in the literature. Additionally, the ability to simultaneously quantify enzymatic reagent consumption and product generation confers the DLOC a self-verifying capability which in turn enhances its robustness and reliability.
Chlorine is probably the most widely used disinfecting agent [1]. In water, it is generally used ... more Chlorine is probably the most widely used disinfecting agent [1]. In water, it is generally used to ensure pathogen control, but at too high levels it also becomes noxious for humans. Its detection and control is therefore of vital importance. The most usual detection methods rely on the ...
2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, 2011
An integrated lab on a chip that enables simultaneous optical and electrochemical analysis workin... more An integrated lab on a chip that enables simultaneous optical and electrochemical analysis working in continuous flow mode is presented. Both transducers are integrated into a single detection cell and operated simultaneously with no evidences of cross-talk and in agreement with theoretical predictions by Levich equation (electrochemical ) and by Lambert-Beer law (absorbance). Their performance is demonstrated by continuous detection of lactate via a double enzymatic reaction with lactate oxidase (LOX) and horseradish peroxidase (HRP). The consumption of the enzymatic reaction mediator (ferrocyanide, (Fe(CN)6 t) is recorded by amperometry, while the product (ferricyanide, (Fe(CN)6 t) is quantified by absorbance. The ability to quantifY reagent and product simultaneously increases the robustness of the system by making it self-verifying, in addition to the inherent advantages of micro fluidic devices.
Arrays of microdisc electrodes have found widespread use in electroanalysis. These are commonly p... more Arrays of microdisc electrodes have found widespread use in electroanalysis. These are commonly produced lithographically and practical arrays may contain up to hundreds of individual disc electrodes (e.g. of gold, platinum, indium,...) to maximise sensitivity and minimise limits of detection. Typically, however, the lithographic fabrication process is imperfect resulting in a significant fraction (often tens of percent) of electrochemically inactive electrodes. We demonstrate that a 2-dimensional simulation based on the diffusion domain approximation in conjugation with simple experiments on the ferrocyanide redox couple in aqueous solutions can be used to rigorously 'count' the number of active electrodes in a non-destructive fashion. The agreement with an independent count in which active electrodes are identified via electro-plating with copper followed by ex situ microscopic examination is quantitatively excellent.
Regular arrays of ca. micron sized droplets on a gold electrode surface can block diffusion to th... more Regular arrays of ca. micron sized droplets on a gold electrode surface can block diffusion to the electrode surface of one metal ion (which binds with the material in the droplet) whilst having no significant effect on another (which does not), so allowing interference effects in electroanalysis to be eliminated.
This work presents the first true solid-state microrespirometer. It consists on a naturally devel... more This work presents the first true solid-state microrespirometer. It consists on a naturally developed biofilm of Pseudomonas aeruginosa over a Nafion modified array of gold microdisc electrodes. Such a device can be used to monitor acute toxicity in water streams ...
... Chem. 585 (2005) 63) two dimensional simulation method for the linear sweep response of array... more ... Chem. 585 (2005) 63) two dimensional simulation method for the linear sweep response of arrays of randomly distributed microdisc electrodes is applied to 'RAM electrodes' (S. Fletcher, MD Horne, Electrochem. Commun. ... In a typical RAM ca. ...
Porous liquid crystalline lipid-based nanoparticles are shown here to enable protein analysis in ... more Porous liquid crystalline lipid-based nanoparticles are shown here to enable protein analysis in microchip electroseparation by reducing sample adsorption. Additionally, higher stability and reproducibility of the separations were observed. The method was tested by separating green fluorescent protein (GFP) in hot embossed cyclic olefin polymer microchips with integrated fiber grooves for LIF detection. The sample adsorption was indirectly quantified by measuring the height, width and asymmetry of the separation peaks for various concentrations of nanoparticles in the sample and background electrolyte. Without nanoparticles, electropherograms displayed typical signs of extensive adsorption to the channel walls, with low, broad tailing peaks. Higher, narrower more symmetric peaks were generated when 0.5-10% nanoparticles were added, showing a dramatic reduction of sample adsorption. The current through the separation channel decreased with nanoparticle concentration, reducing to half its value when the nanoparticle concentration was increased from 0.5 to 4%. Addition of nanoparticles enabled separations that were otherwise hindered by extensive adsorption, e.g. separation of GFP mutants differing by only one amino acid. It was also observed that increasing the nanoparticle concentration increased the number of impurities that could be resolved in a GFP sample. This indicates that the adsorption is further reduced, and/or that the nanoparticles provide an interacting pseudostationary phase for electrochromatography.
Olga Ordeig,a Javier del Campo,b* Francesc Xavier Munoz,a Craig E. Banks,c Richard G. Comptond a... more Olga Ordeig,a Javier del Campo,b* Francesc Xavier Munoz,a Craig E. Banks,c Richard G. Comptond a Centro Nacional de Microelectrónica, IMB-CNM. CSIC, Campus de la Universidad Autónoma de Barcelona, Bellaterra 08193, Spain b Institut de Biotecnologia i Biomedicina and ...
Abstract This article describes the direct detection of Bromate, but also of chlorate and iodate,... more Abstract This article describes the direct detection of Bromate, but also of chlorate and iodate, using modified arrays of platinum ultramicroelectrodes. The detection limits for these ions are IO equation image= 0.76 μM; BrO equation image= 2.34 μM and ClO equation ...
Abstract The electroanalytical detection of trace mercury(II) at gold ultra-microelectrode arrays... more Abstract The electroanalytical detection of trace mercury(II) at gold ultra-microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in ...
We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally sp... more We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 mum, are used to support liquid 5-nonyl-salicylaldoxime (Acorga-P50) droplets on the surface. By voltametrically monitoring the transport-controlled reduction rate of Cu(II) (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of Cu(II) at the droplet-aqueous solution interface as the droplet "fills up" with Cu(II). Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic-droplet phase and of diffusion coefficients within the droplet. The partition coefficient for Cu(II) between water and 5-nonyl-salicylaldoxime was found to be 200 at 25 degrees C and the diffusion coefficient of Cu(II) inside the organic phase was determined to be 5 x 10(-11) cm2 s(-1).
Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide i... more Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array.
A dual lab on a chip (DLOC) approach that enables simultaneous optical and electrochemical detect... more A dual lab on a chip (DLOC) approach that enables simultaneous optical and electrochemical detection working in a continuous flow regime is presented. Both detection modes are integrated for the first time into a single detection volume and operate simultaneously with no evidence of cross-talk. The electrochemical cell was characterized amperometrically by measuring the current in ferrocyanide solutions at +0.4 V vs gold pseudoreference electrode, at a flow rate of 200 μL min(-1). The experimental results for ferrocyanide concentrations ranging from 0.005 to 2 mM were in good agreement with the values predicted by the Levich equation for a microelectrode inside a rectangular channel, with a sensitivity of 2.059 ± 0.004 μA mM(-1) and a limit of detection (LoD) of (2.303 ± 0.004) × 10(-3) mM. Besides, optical detection was evaluated by measuring the absorbance of ferricyanide solutions at 420 nm. The results obtained therein coincide with those predicted by the Beer-Lambert law for a range of ferricyanide concentrations from 0.005 to 0.3 mM and showed an estimated LoD of (0.553 ± 0.001) × 10(-3) mM. The DLOC was finally applied to the analysis of L-lactate via a bienzymatic reaction involving lactate oxidase (LOX) and horseradish peroxidase (HRP). Here, the consumption of the reagent of the reaction (ferrocyanide) was continuously monitored by amperometry whereas the product of the reaction (ferricyanide) was recorded by absorbance. The DLOC presented good performance in terms of sensitivity and limit of detection, comparable to other fluidic systems found in the literature. Additionally, the ability to simultaneously quantify enzymatic reagent consumption and product generation confers the DLOC a self-verifying capability which in turn enhances its robustness and reliability.
Chlorine is probably the most widely used disinfecting agent [1]. In water, it is generally used ... more Chlorine is probably the most widely used disinfecting agent [1]. In water, it is generally used to ensure pathogen control, but at too high levels it also becomes noxious for humans. Its detection and control is therefore of vital importance. The most usual detection methods rely on the ...
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