Dual Photonic-Electrochemical Lab on a Chip for Online Simultaneous

Article pubs.acs.org/ac

Dual Photonic-Electrochemical Lab on a Chip for Online Simultaneous Absorbance and Amperometric Measurements Olga Ordeig,†,§ Pedro Ortiz,† Xavier Muñoz-Berbel,† Stefanie Demming,‡ Stephanus Büttgenbach,‡ César Fernández-Sánchez,*,† and Andreu Llobera*,† †

Instituto de Microelectrónica de Barcelona, IMB-CNM (CSIC), Campus UAB, 08193-Bellaterra, Barcelona, Spain Institut für Mikrotechnik, Technische Universität Braunschweig, Alte Salzdahlumer Straße 201, 38124 Braunschhweig, Germany

‡

S Supporting Information *

ABSTRACT: 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.

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formulations.11 In fact, when analyzed in depth, the information obtained using both transduction methods seems to be, in most of the cases, complementary. In the determination of carbaryl noted above, optical methods may allow for the measurement of low concentrations, whereas high concentrations are better determined amperometrically.11 Another example is the detection of suspended bacteria where low bacteria concentrations may be determined using impedance spectroscopy, whereas for high concentrations an optical method is recommended.12 Thus, the integration of optical and electrochemical transduction mechanisms in a single LOC is justified in order to increase the target analyte concentration range, but also it can provide a self-validating mechanism, which enhanced the robustness and reliability of the analytical system. This feature is of key importance in several application fields, as could be clinical diagnosis, where the number of false positive results has to be kept at a minimum level. Finally, this configuration also opens the possibility of multiparametric analysis, since optical and electrochemical

n recent years, the lab on a chip1 (LOC) concept has been the main driving force behind the efforts of many academic and industrial research groups to achieve integration of chemical and biological analysis into low-cost, fast, and reliable systems.2,3 Although important advances have already been attained, the implementation of robust detection methods in complex LOC structures is still quite challenging. In this sense, most of the reported LOCs that integrate detection approaches rely on either optical or electrochemical transduction modes.4−8 This may be associated with the fact that, in comparison with other methods of biochemical analysis, electrochemical and optical instrumentation are relatively easy to miniaturize and to produce in large scale. Both transduction mechanisms present advantages and disadvantages, and therefore it becomes difficult to compare, since their performance mainly depends on the protocols used and the specific application. For instance, in the analysis of different inorganic ions including cyanide, the amperometric detection was found to be much more selective and sensitive than the UV−vis absorbance detection method which, by contrast, presented a wider linear range, higher robustness, and simpler handling.9,10 By contrast, the opposite behavior was observed in the determination of carbaryl in natural water and commercial © 2012 American Chemical Society

Received: November 24, 2011 Accepted: March 19, 2012 Published: March 19, 2012 3546

dx.doi.org/10.1021/ac203106x | Anal. Chem. 2012, 84, 3546−3553

Analytical Chemistry

Article

chemical reagent in ultrapure deionized water (DI). Lactate oxidase (LOX, EC 1.13.12.4, Sigma, Germany) and peroxidase (HRP, EC 1.11.1.7, Sigma, Germany) were dissolved in 0.015 M phosphate buffered saline (PBS) pH 7.4 [composition (1 L): 8.0 g of NaCl, 0.2 g of KH2PO4, 1.1 g of Na2HPO4, and 0.2 g of KCl]. All chemicals were of analytical reagent grade and were used as received without any further purification. Instrumentation. A set of neMESYS syringe pumps (Cetoni GmbH, Germany) independently controlled by neMESYS user interface software (version 2.5) was used to obtain a flow of solution through the microfluidic channel. Cyclic voltammetric and amperometric experiments were carried out with a portable μSTAT2000 bipotentiostat (DropSens, Spain) interfaced to a PC using the Dropview (version 1.3) software. A halogen lamp (HL-2000-FHSA, Ocean Optics) was used as a light source for the absorbance measurements, and a spectrometer (QE65000, Ocean Optics) controlled via SpectraSuite software. A Thermo Electron Multiskan EX plate reader (VWR International, Pennsylvania) was used for the optimization of the bienzymatic reaction conditions. Fabrication. The fluidic platform consists of a disposable glass-PDMS DLOC and a PMMA manifold. This platform was designed to be a plug and play, world-to-chip interface. The DLOC consists of a PDMS top part, including the microfluidic channels as well as the required photonic elements, all of them fabricated by soft lithography in a single step, following the protocol reported in ref 18. A multiple internal reflection (MIR) system formed by a 225 μm high, 11.245 mm long zigzagging channel (light path) was defined together with two concave air mirrors located at the channel vertices as well as optical fiber insertion/alignment channels and PDMS-defined biconvex microlenses to correct the numerical aperture of the fiber. The bottom glass die contains a set of microband gold electrodes, electrical contact pads, as well as alignment features. The electrode configuration consists of (in the following order when looking in the downstream direction) an 80 μm wide reference electrode, two 60 μm wide working electrodes, and a 200 μm wide counter electrode. These were fabricated by sputtering a 20 nm thick adhesion layer of Cr and a 200 nm thick Au layer on the glass substrate. Then a photolithographic step was carried out to define the electrode layout followed by an Au and Cr wet chemical etching. It should be noted that the electrodes have a length of 2400 μm as they span diagonally across the detection channel, which at this point has a width of 987 μm. The layout of the microdevice can be found in Figure 1a. In a final step, the PDMS and glass dies were exposed to oxygen plasma (using a TePla plasma processor), brought into contact, aligned, and finally cured at 80 °C overnight to form a permanent bond. It should be noted that alignment of the gold and PDMS features is aided by adding several drops of ethanol to the PDMS surface, after plasma treatment, allowing for the PDMS die to be moved while in contact with the glass. The overall thickness of the disposable DLOC is roughly 1.8 mm. The two-part manifold that includes mixer and DLOC housing modules was fabricated by PMMA micromilling (Step Four, basi540) and solvent assisted bonding. High-pressure fittings (Upchurch Scientific) were used as fluidic interconnects and PEEK tubing (Upchurch Scientific) was used to establish the connection between modules. The mixer module consists of a T-junction and a 66.6 cm long, 0.8 mm high, 0.2 mm wide meandering channel. The diffusivity values of the tested analytes were taken into account for the design of this module.

transducers can operate independently. In this context, Lapos et al.13 implemented both transduction mechanisms in a single electrophoresis chip for the simultaneous detection of dopamine, catechol, arginine, phenylalanine, and glutamic acid from cerebral spinal fluid of multiple sclerosis patients. Dopamine and catechol were directly detected on-chip by amperometry, whereas the other analytes were fluorescently labeled and measured externally by laser-induced fluorescence with a confocal fluorescence microscope. Although the integration of both transduction mechanisms was not complete (no photonic elements were found on the chip), this approach allowed the authors to carry out multiplexed measurements in complex samples without evidence of cross-talk. In the same line, Chang et al.14 and Pereira-Rodrigues et al.15 presented a dual amperometric/fluorescence detection system for the simultaneous determination of intra- and extracellular superoxide and nitric oxide produced by glioblastoma cells in culture wells, respectively. As in the previous case, although the electrochemical transducer was integrated in the well plate system, the optical measurements were performed externally using a customized fluorescence microscope, with no photonic elements being integrated in the device structure. A step forward, in terms of integration, was taken by Grabowska et al.16 They presented a poly(dimethylsiloxane) (PDMS) microfluidic system that appears to incorporate electrochemical and optical transduction elements in separate areas of a single chip for the measurement of creatinine or urea. However, the report fails to address several critical questions related to the fabrication, characterization, and performance of the system. In this paper, we present a disposable glass-PDMS dual photonic-electrochemical LOC (DLOC) that integrates (i) microfluidics, (ii) an electrochemical cell, and (iii) photonic elements, including microlenses, air mirrors,17 and selfalignment channels for fiber optics positioning. This configuration enables the online dual absorbance-amperometic detection of target analytes, conferring the DLOC a selfverifying capability highly appreciated in clinical analysis applications. The here proposed DLOC based system was fabricated using a combination of compatible photolithographic and rapid prototyping methods, which allowed easy integration of the elements in a unique compact structure thus reducing the consumption of reagents and dilution issues. The DLOC performance in the continuous flow regime was evaluated by using ferrocyanide/ferricyanide model target analytes and comparing the experimental absorbance and amperometric data with theoretical values obtained by using the Beer− Lambert law and the Levich equation, respectively. Additionally, the possible cross-talk between transduction mechanisms when operating simultaneously was also assessed. The DLOC based system proposed here as a simple and robust analytical tool for the online dual detection of target analytes was investigated by the indirect determination of L-lactate via a bienzymatic reaction using ferrocyanide as a mediator.

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EXPERIMENTAL SECTION Chemicals. Potassium hexacyanoferrate (II) ([Fe(CN)6]4−, ferrocyanide, Sigma-Aldrich, Germany), potassium hexacyanoferrate (III) ([Fe(CN)6]3−, ferricyanide, Panreac, Spain), potassium nitrate (Sigma-Adrich, Germany), sodium chloride (Fluka, Germany), potassium chloride (Fluka, Germany), potassium dihydrogen phosphate (Panreac, Spain), and disodium hydrogen phosphate (Panreac, Spain) solutions were prepared by dissolving the suitable amount of each 3547



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a fluidic point of view, three syringe pumps, independently controlled, were connected to the PMMA serpentine mixer placed upstream from the DLOC. These syringes were used for the automatic preparation of the samples at different concentrations by mixing at the correct flow ratio a concentrated sample solution with buffer, keeping the total flow rate through the microfluidic channel constant at 200 μL min−1. The serpentine mixer was designed to ensure the perfect mixture of the solutions. Furthermore, the minimum and maximum flow rates that ensured stable flow of all reagents was determined empirically to be 60 and 140 μL min−1 , respectively. Absorbance measurements were carried out using a halogen lamp as a light source, which was coupled to the DLOC by means of a 200 μm diameter optical fiber (FG200LCC, Thorlabs, Germany) inserted in the integrated fiber optic selfalignment component. Transmitted light was collected at the opposite end of the DLOC using another optical fiber and recorded using a spectrometer with a spectral resolution of 2 nm. The integration time for all the experiments was fixed to 80 ms. The electrochemical experiments were carried out with the electrochemical cell described in the previous section but shortcircuiting the two working electrodes. The reference electrode was located upstream from the working and the counter electrodes in order to avoid interferences that could affect its stability. The potential of the quasi-reference electrode was found to be −147 ± 8 mV vs SCE in 0.5 M KNO3. This potential remained stable during the experiments provided that the measurements were carried out in solutions containing 0.5 M KNO3, thus keeping the ionic concentration constant. A spring-loaded connector was used to contact the electrochemical cell to the potentiostat used for recording amperometric data. In general, the experimental protocol was as follows. First the DLOC and the serpentine mixer were rinsed with DI water and buffer for 5 min, respectively. After the rinsing step, the first sample concentration was injected for 4 min and the electrochemical and/or absorbance measurements were started. Between sample injections, the DLOC and the serpentine mixer were always rinsed with buffer to recover the baseline. ELISA-Plate Experiments. Optimization of experimental conditions of the bienzymatic reaction was performed off-chip. Polystyrene 96-well ELISA plates (Corning Incorporated, NY) and a Thermo Electron Multiskan EX plate reader were used for sample preparation and recording absorbance data, respectively. Samples were prepared in independent wells by combining the suitable concentration of enzymes, ferrocyanide, and L-lactate in 0.015 M PBS, pH 7.4, to a final volume of 100 μL. Absorbance values were recorded at a wavelength of 420 nm every 15 s for the duration of the experiment.

Figure 1. (a) Layout of the disposable DLOC. (b) 3D drawing of the DLOC interface assembly and a picture of the actual microdevice. Photonic elements, electrodes, and channels can be observed.

The housing module (see Figure 1b) was composed of a base piece and a lid, which in turn comprised three PMMA layers. The bottom layer of the lid includes a groove (2 mm deep) corresponding to the footprint of the DLOC and round relief features used for input/output water-tight seal. Also, a channel was machined on the intermediate layer of the lid for fluid transport between the DLOC and the fluidic connects. The fittinǵs threads were machined on the top layer of the lid. An observation window, screw holes, alignment pin holes, and a specific cavity for inserting a customized spring-loaded connector (8PD Series, Preci-Dip, Switzerland), used to contact the electrochemical cell, were also included in the lid. The base piece included a machined DLOC footprint, guiding grooves for the fiber optics, and screw threads. The top and base parts were fastened together using M3 screws, once the DLOC was in place and the fiber optics inserted (an assembly process animation can be found in the Supporting Information). For the bonding, the machined pieces were initially cleaned in an ultrasonic bath with DI water for 10 min, blow dried, aligned (using alignment pins), and immersed in an ethanol ultrasonic bath for another 10 min. The piece was then removed from the solvent solution and pressed together with a piston force of 2 kN at 80 °C for 2 h. A PW 10 hydraulic press (P/O/Weber) was used for this purpose. Experimental Setup. A picture of the experimental setup can be found in Figure S1 of the Supporting Information. From

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RESULTS AND DISCUSSION

In a previous work reported by our group, the applicability of MIR systems to detect several target analytes by absorbance or fluorescence measurements was demonstrated, under quiescent fluid conditions (absence of flow).19 A significant step forward has been taken in the present work where (i) photonic and electrochemical transducers were implemented in a single DLOC and (ii) simultaneous dual absorbance/amperometric measurements in the continuous flow regime were performed. The successful integration of both transduction modes required 3548



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the entire width of the channel was considered, resulting in a microband electrode 291 μm wide and 987 μm long. Figure 2a shows the amperometric response of the system at +0.4 V (vs gold pseudoreference electrode) for ferrocyanide

a full understanding of flow rate related effects as well as ensuring that there was no cross-talk between them. Influence of Flow Rate. Optical analyses are volumedependent and they should not be influenced by the flow rate. In our case, a 5.5% increase in the absorbance signal, measured at 420 nm, for a 5 mM ferricyanide solution was recorded when the flow rate increased from 0 to 300 μL min−1. This small variation may be associated with the mechanical properties of the PDMS. When high flow rates were applied, high pressures inside the microfluidic channel could be generated, which in turn would expand the PDMS and thus increase the optical path and/or modify the shape of the microoptical elements. On the other hand, it is well-known that the electrochemical sensors are dependent on the mass transfer (and thus on the flow rate). Since the flow in a microchannel is laminar, under mass transfer control the diffusion layer thickness should be stable, reproducible, and steady state voltammograms should be observed.20,21 In order to choose a flow rate that ensured working under mass transfer control, cyclic voltammograms were recorded from −0.5 to +0.5 V (vs gold pseudoreference electrode) in a 5 mM ferro/ferricyanide solution at different flow rates ranging from 50 to 350 μL min−1. As steady state voltammograms were not fully developed for flow rates lower than 150 μL min−1, a working flow rate of 200 μL min−1 was chosen for all the experiments presented below. Characterization of the DLOC Performance. When two different transduction mechanisms are simultaneously operated in a single volume, it is of key importance to evaluate the level of cross-talk between them. For this reason, the system was characterized in single (the transduction mechanisms operating individually) and dual mode (both transduction mechanisms operating simultaneously). Electrochemical Transducer in Single Mode. Prior to commencing each experiment, the working electrode was electrochemically activated by cycling the potential from −1.5 V to +1.3 V (vs gold pseudoreference electrode) in a 0.5 M KNO3 solution. In order to guarantee the reproducibility of the electrochemical cell performance, an estimation of the electrochemical active area was always carried out at the beginning and at the end of each experiment by recording a cyclic voltammogram in a 2 mM ferro/ferricyanide in 0.5 M KNO3 solution. A detailed description is included in the Supporting Information (Figure S2). The performance of the electrochemical transducer under flow conditions was evaluated by amperometry, measuring different concentrations of ferrocyanide in a range between 0.005 mM and 2 mM in 0.5 M KNO3, and comparing the results with Levich’s prediction for a microband electrode inside a channel with a rectangular cross-section:20,22 ⎛ U ⎞1/3 I = 0.925nFcw(xeD)2/3 ⎜ 2 ⎟ ⎝h d⎠

Figure 2. (a) Continuous amperometric detection of different ferrocyanide concentrations (0.06, 0.09, 0.13, 0.16, 0.19, and 0.25 mM) in 0.5 M KNO3. (b) The experimental limiting currents (●) and the corresponding predicted currents according to the Levich equation (−) as a function of the ferrocyanide concentration. The inset shows a close view of the experimental limiting current values recorded for the lower concentration range. The experimental results were obtained using a three-electrode configuration at +0.4 V vs gold pseudoreference electrode under a constant flow rate of 200 μL min−1. Each current value corresponds to the average of at least three different experimental values, the error bars being the corresponding standard deviation.

concentrations ranging from 0.06 to 0.25 mM with time. Figure S3 in the Supporting Information shows the corresponding amperometric response for the lower ferrocyanide concentration range between 0.005 and 0.02 mM. A response time of around 4 min was found for all the sample injections, and a stable baseline was always recovered after the rinsing steps were carried out in between measurements. The limiting currents obtained from the experiment described above were plotted as a function of ferrocyanide concentration (Figure 2b). As it can be seen, the electrochemical transducer exhibited a linear response range from 0.005 to 2 mM, with good linearity (R2 = 0.9998) and a limit of detection (LoD) (based on the 3σ criterion) of (2.303 ± 0.004) × 10−3 mM. In Figure 2b are also represented the theoretical limiting current values for our system predicted by

(1)

where n is the number of exchanged electrons, F is the Faraday constant (96 485 C mol−1), c and D are the concentration and the diffusion coefficient of the electroactive species, respectively, d is the channel width, h is half the height of the channel, xe and w are the length and the width of the microband electrodes, respectively, and U is the flow rate. In the particular geometry used in this work, the microband electrode crossed the microchannel diagonally instead of perpendicularly. In order to apply the Levich equation, a microband electrode of the same area perpendicular to the flow direction that covered 3549



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further improved by increasing the flow rate (what would imply an increase of reagents consumption) or by reducing the dead volume of the flow system (which is related to the tubing and fluidic connections). The absorbance calibration curve for ferricyanide was carried out in a concentration range from 0.005 to 2 mM (Figure 3b). A linear relationship was obtained for ferricyanide concentrations up to 0.3 mM, above which the absorbance vs concentration does no longer fulfill the Beer−Lambert law:25

the Levich equation (eq 1). The value used for the diffusion coefficient of ferrocyanide was D = 6.5 × 10−10 m2 s−1,23 the microband electrode dimensions were set to be w = 987 μm, xe = 291 μm, and the channel dimensions to be d = 987 μm and 2h = 225 μm. Notice that the response of our system is in good agreement with the Levich prediction. The small differences (5 mM).

Figure 4. (a) Amperometric detection of ferrocyanide at +0.4 V vs gold pseudoreference electrode and (b) absorbance detection of ferricyanide at 420 nm as a function of time; when the transducers worked in single mode (red) and in dual mode (black). For all sets of experiments, the ferrocyanide and ferricyanide concentrations were 0.06, 0.09, 0.16, 0.19, and 0.25 mM and the flow rate was fixed at 200 μL min−1.

quantified by absorbance at a wavelength of 420 nm. The consumption/production of both species was used to indirectly determine the L-lactate concentration. The fact of being able to measure both processes simultaneously made the system selfverifying and improved its robustness significantly. Enzymes are extremely sensitive to environmental factors (e.g., temperature, pH, etc.) and the concentration of the different substrates involved in their corresponding reactions. Consequently, previously to proceed to the L-lactate detection, the optimization of the enzymatic reaction in terms of concentration of LOX and HRP, enzyme ratio, and buffer conductivity in the flow had to be addressed. A detailed description of the studies carried out to optimize these parameters can be found in the Supporting Information (including Figures S5b,c and S6). The LOX and HRP were

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CONCLUSIONS A dual optical-electrochemical detection system based on a LOC containing fluidic, optical, and electrochemical elements all integrated into a single detection volume has been presented. Both absorbance and amperometric transduction mechanisms showed an excellent performance either working

Table 1. Comparison of the Linear Detection Ranges in Terms of Slope, Regression Coefficient, and Limit of Detection for the Electrochemical and Optical Transducers Operating in Single and Dual Modes technique

mode

linear range

electrochemistry

single dual single dual

0.01−2 mM 0.01−2 mM 0.01−0.3 mM 0.01−0.3 mM

absorbance

sensitivity 2.059 2.013 1.026 0.996 3551

± ± ± ±

0.004 μA/mM 0.002 μA/mM 0.002 AU/mM 0.003 AU/mM

R2 0.9998 0.99994 0.9998 0.9997

LoD (3σ)/mM (2.303 (1.384 (0.553 (0.909

± ± ± ±

0.004) 0.001) 0.001) 0.003)

× × × ×

10−3 10−3 10−3 10−3



Article

Table 2. Comparison of the Performance of Some On-Line Lactate Sensors with the LOC Presented in This Work technique

method

linear range

LoD

ref

electrochemistry

bienzymatic reaction on-flow: LOX/HRP/ferrocyanide enzyme modified electrode: cellulose/LOX/ferricyanide LOX/Os-gel-HRP LOX/ferricyanide/TGA-SAM bienzymatic reaction with LOX/HRP: ferricyanide detection at 420 nm enzymatic reaction with LOX: chromogen detection at 540 nm enzymatic reaction with LDH: NADH detection at 340 nm

0.05−0.15 mM 1−50 mM 0.005−5 mM (1 × 10−7)−1 mM 0.05−0.15 mM 1−5 mM 0.05−1 mM

0.05 mM 1 mM 0.002 mM 3 × 10−7 mM 0.05 mM 0.5 mM

this work Sato et al.28 Kurita et al.29 Rahman et al.30 this work Wu et al.31 Schulz et al.32

absorbance

mikroPART FOR 856 (Microsystems for Particulate LifeScience Products).

individually (single mode) or simultaneously (dual mode). No evidence of cross-talk was recorded. Besides, the experimental results were in agreement with the theoretical predictions (Levich approximation and Beer−Lambert law for the electrochemical and absorbance modes, respectively). Finally, the dual detection was assessed for the analysis of L-lactate in a continuous flow regime via a bienzymatic reaction using ferrocyanide as the mediator. The DLOC showed a good response to the L-lactate concentration with a LoD below 0.05 mM, comparable to other fluidic systems found in the literature. However, the dual electrochemical and optical detection of L-lactate via the ferrocyanide enzyme mediator and corresponding ferricyanide product, respectively, enhanced the reliability of the DLOC by making it self-verifying. This feature is of special interest in clinical analysis where the sensitivity and specificity of the results must be strictly controlled and thus accurately measured. Future work is currently underway to implement the mixer together with the DLOC in a single substrate, in order to decrease the required sample volumes and thus improve the response time of the overall system. Also, a protocol to immobilize the enzymes on the mixer walls is being developed, with the aim of drastically reducing the reagents consumption.

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(1) Manz, A. J. Pharm. Pharmacol. 1998, 50, 42. (2) Erickson, D.; Li, D. Anal. Chim. Acta 2004, 507, 11−26. (3) Figeys, D.; Pinto, D. Anal. Chem. 2000, 72, 330A−335A. (4) Hunt, H. C.; Wilkinson, J. S. Microfluid. Nanofluid. 2008, 4, 53− 79. (5) Kuswandi, B.; Nuriman, D.; Huskens, J.; Verboom, W. Anal. Chim. Acta 2007, 601, 141−155. (6) Nyholm, L. Analyst 2005, 130, 599−605. (7) Suárez, G.; Jin, Y. H.; Auerswald, J.; Berchtold, S.; Knapp, H. F.; Diserens, J.-M.; Leterrier, Y.; Manson, J.-A. E.; Voirin, G. Lab Chip 2009, 9, 1625−1630. (8) Yi, C.; Zhang, Q.; Li, C.-W.; Yang, J.; Zhao, J.; Yang, M. Anal. Bioanal. Chem. 2006, 384, 1259−1268. (9) Buchberger, W. W. TrAC, Trends Anal. Chem. 2001, 20, 296− 303. (10) Ma, J.; Dasgupta, P. K.; Blackledge, W.; Boss, G. R. Anal. Chem. 2010, 82, 6244−6250. (11) Portela, D. C.; Pereira, I. M. F.; Paíga, P.; Delerue-Matos, C.; Vaz, M. C. V. F. Anal. Bioanal. Chem. 2003, 377, 356−361. (12) Muñoz-Berbel, X.; Vigués, N.; Jenkins, A. T. A.; Mas, J.; Muñoz, F. J. Biosens. Bioelectron. 2008, 23, 1540−1546. (13) Lapos, J. A.; Manica, D. P.; Ewing, A. G. Anal. Chem. 2002, 74, 3348−3353. (14) Chang, S.-C.; Rodrigues, N. P.; Zurgil, N.; Henderson, J. R.; Bedioui, F.; McNeil, C. J.; Deutsch, M. Biochem. Biophys. Res. Commun. 2005, 327, 979−984. (15) Pereira-Rodrigues, N.; Zurgil, N.; Chang, S. C.; Henderson, J. R.; Bedioui, F.; McNeil, C. J.; Deutsch, M. Anal. Chem. 2005, 77, 2733−2738. (16) Grabowska, I.; Sajnoga, M.; Juchniewicz, M.; Chudy, M.; Dybko, A.; Brzozka, Z. Microelectron. Eng. 2007, 84, 1741−1743. (17) Llobera, A.; Wilke, R.; Büttgenbach, S. Talanta 2008, 75, 473− 479. (18) Llobera, A.; Demming, S.; Wilke, R.; Büttgenbach, S. Lab Chip 2007, 7, 1560−1566. (19) Ibarlucea, B.; Fernandez-Rosas, E.; Vila-Planas, J.; Demming, S.; Nogues, C.; Plaza, J. A.; Büttgenbach, S.; Llobera, A. Anal. Chem. 2010, 82, 4246−4251. (20) Compton, R. G.; Fisher, A. C.; Wellington, R. G.; Dobson, P. J.; Leigh, P. A. J. Phys. Chem. 1993, 97, 10410−10415. (21) Compton, R. G.; Unwin, P. R. J. Electroanal. Chem. 1986, 206, 57−67. (22) Levich, V. G. Physicochemical Hydrodynamics; Prentice Hall: Englewood Cliffs, NJ, 1962. (23) Bard, A. J.; Faulkner, L. R. Electrochemical Methods, 2nd ed.; Wiley: New York, 2001. (24) Alden, J. A.; Compton, R. G. J. Electroanal. Chem. 1996, 404, 27−35. (25) Göpel, W.; Hesse, J.; Zemel, J. N.; Wagner, E.; Dändliker, R.; Spenner, K. Sensors: A Comprehensive Survey; VCH: Weinheim, Germany, 1991. (26) Appleby, C. A.; Morton, R. K. Biochem. J. 1959, 71, 492−499.

ASSOCIATED CONTENT

S Supporting Information *

Details about the experimental setup, the estimation of the electrode active area, the amperometric response of the system in ferrocyanide solutions, the cross-talk, and optimization of the enzymatic reaction. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Phone: +34 93 594 77 00. Fax: +34 93 580 14 96. E-mail: [email protected] (A.L.); [email protected] (C.F-S.). Present Address §

New Jersey Institute of Technology (NJIT), Newark, NJ 07102, United States. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The research leading to these results has received funding from the European Research Council under the European Community’s Seventh Framework Programme (Grant FP7/ 2007-2013)/ERC Grant Agreement No. 209243. The authors would like to acknowledge the JAE-Doc Program and the German Research Foundation (DFG) for supporting this work in the framework of the Collaborative Research Group 3552



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(27) Mazurenka, M.; Wilkins, L.; Macpherson, J. V.; Unwin, P. R.; Mackenzie, S. R. Anal. Chem. 2006, 78, 6833−6839. (28) Sato, N.; Okuma, H. Anal. Chim. Acta 2006, 565, 250−254. (29) Kurita, R.; Hayashi, K.; Fan, X.; Yamamoto, K.; Kato, T.; Niwa, O. Sens. Actuators, B: Chem. 2002, 87, 296−303. (30) Rahman, M. M. Int. J. Biol. Med. Res. 2010, 1, 09−14. (31) Wu, M. H.; Wang, J.; Taha, T.; Cui, Z.; Urban, J. P. G Biomed. Microdevices 2007, 9, 167−174. (32) Schulz, C. M.; Scampavia, L.; Ruzicka, J. Analyst 2002, 127, 1583−1588.

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Dual Photonic-Electrochemical Lab on a Chip for Online Simultaneous

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