Yegermal Tesfaw Atalay

University of Leuven, Louvain, Flanders, Belgium

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Publications (13)23.42 Total impact

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    ABSTRACT: In this work the design of a segmented flow microfluidic device is presented that allows droplet splitting ratios from 1:1 up to 20:1. This ratio can be dynamically changed on chip by altering an additional oil flow. The design was fabricated in PDMS chips using the standard SU-8 mold technique and does not require any valves, membranes, optics or electronics. To avoid a trial and error approach, fabricating and testing several designs, a computational fluid dynamics model was developed and validated for droplet formation and splitting. The model was used to choose between several variations of the splitting T-junction with the extra oil inlet, as well to predict the additional flow rate needed to split the droplets in various ratios. Experimental and simulated results were in line, suggesting the model’s suitability to optimize future designs and concepts. The resulting asymmetric droplet splitter design opens possibilities for controlled sampling and improved magnetic separation in bio-assay applications.
    Microfluidics and Nanofluidics 08/2013; 15(2). DOI:10.1007/s10404-013-1139-3 · 2.53 Impact Factor
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    ABSTRACT: Although several applications of electrowetting on dielectric digital lab-on-a-chips are reported in literature, there is still a lack of knowledge about the influence of operational and design parameters on the performance of an analytical assay. This paper investigates how droplet size variability, introduced by droplet dispensing and splitting, influences the assay performance with respect to repeatability and accuracy and presents a novel method to reduce this variability. Both a theoretical and experimental approach were followed. Monte Carlo simulations were applied to study the cumulative effect of the variability caused by different droplet manipulations on the final assay performance. It is shown that a highly controllable droplet generation and manipulation is achieved with respect to droplet size variability through an accurate control of actuation voltage, activation time, relaxation time, and electrode size. As a case study, it is illustrated that through optimization of these parameters a complete on-chip calibration curve is obtained for a d-glucose assay with an average CV-value of 2%. These new insights aim to bring the digital lab-on-a-chip technology closer to researchers in the field of diagnostics offering them a valuable and accessible alternative to standard analysis platforms. KeywordsDigital microfluidics–Electrowetting–Analytical performance–Enzymatic assay
    Microfluidics and Nanofluidics 07/2011; 11(1):25-34. DOI:10.1007/s10404-011-0769-6 · 2.53 Impact Factor
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    ABSTRACT: Assuring the safety and quality of food is vital in today’s world-wide integrated food supply chain. In this context, microfluidics is a technology that allows constructing small, fast and cheap microfluidic analytical systems. Microfluidic analytical systems are mainly used in biomedical applications. In this review, we survey some of the applications of microfluidic technology with respect to the development of high performance analytical devices for food analysis. We discuss the main challenges related to microfluidic applications and current trends towards building multi-purpose microfluidic platforms that integrate multiple unit operations for real food sample analysis.
    Trends in Food Science & Technology 07/2011; 22(7-7):386-404. DOI:10.1016/j.tifs.2011.05.001 · 4.65 Impact Factor
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    ABSTRACT: This paper presents the implementation of a multiple analyte enzyme assay, based on the sequential injection of the different enzyme solutions, in an electrokinetic driven microfluidic chip. The assay methodology for the simultaneous quantification of d-glucose and d-fructose was reported in previous publications but here the real integration of both enzyme assays was achieved. When assays were executed separately, good reproducibility was observed with average CV values of 5.2% and 4.5% for the d-glucose and d-fructose assay, respectively. Next, the assays for the quantification of d-glucose and d-fructose were integrated simultaneously on chip, where each assay was executed consecutively in the same microreactor by applying a specific sequence of potentials at the reservoirs. This article proves the integration of a sequential based quantification approach in continuous microfluidic chips with electrokinetic actuation.
    Microfluidics and Nanofluidics 03/2011; 12(5). DOI:10.1007/s10404-011-0920-4 · 2.53 Impact Factor
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    ABSTRACT: A model-based methodology was developed to optimize microfluidic chips for the simultaneous enzymatic quantification of sucrose, d-glucose and d-fructose in a single microfluidic channel with an integrated optical detection system. The assays were based on measuring the change in concentration of the reaction product NADH, which is stoichiometrically related to the concentration of those components via cascade of specific enzymatic reactions. A reduced order mathematical model that combines species transport, enzyme reaction, and electrokinetic bulk flow was developed to describe the operation of the microfluidic device. Using this model, the device was optimized to minimize sensor response time and maximize signal output by manipulating the process conditions such as sample and reagent volume and flow rate. According to this simulation study, all sugars were quantified within 2.5min in the optimized microchip. A parallel implementation of the assays can further improve the throughput. In addition, the amount of consumed reagents was drastically reduced compared to microplate format assays. The methodology is generic and can easily be adapted to other enzymatic microfluidic chips.
    Microfluidics and Nanofluidics 09/2009; 7(3):393-406. DOI:10.1007/s10404-008-0393-2 · 2.53 Impact Factor
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    ABSTRACT: An electrokinetic driven microfluidic lab-on-a-chip was developed for glucose quantification using double-enzyme assay. The enzymatic glucose assay involves the two-step oxidation of glucose, which was catalyzed by hexokinase and glucose-6-phosphate dehydrogenase, with the concomitant reduction of NADP(+) to NADPH. A fluorescence microscopy setup was used to monitor the different processes (fluid flow and enzymatic reaction) in the microfluidic chip. A two-dimensional finite element model was applied to understand the different aspects of design and to improve the performance of the device without extensive prototyping. To our knowledge this is the first work to exploit numerical simulation for understanding a multisubstrate double-enzyme on-chip assay. The assay is very complex to implement in electrokinetically driven continuous system due to the involvement of many species, which has different transport velocity. With the help of numerical simulation, the design parameters, flow rate, enzyme concentration, and reactor length, were optimized. The results from the simulation were in close agreement with the experimental results. A linear relation exists for glucose concentrations from 0.01 to 0.10 g l(-1). The reaction time and the amount of enzymes required were drastically reduced compared to off-chip microplate analysis.
    Biomicrofluidics 01/2009; 3(4):44103. DOI:10.1063/1.3250304 · 3.36 Impact Factor

  • Acta horticulturae 12/2008; DOI:10.17660/ActaHortic.2008.802.4
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    ABSTRACT: Microfluidic systems are increasingly popular for rapid and cheap determinations of enzyme assays and other biochemical analysis. In this study reduced order models (ROM) were developed for the optimization of enzymatic assays performed in a microchip. The model enzyme assay used was β-galactosidase (β-Gal) that catalyzes the conversion of Resorufin β-d-galactopyranoside (RBG) to a fluorescent product as previously reported by Hadd et al. (Anal Chem 69(17): 3407–3412, 1997). The assay was implemented in a microfluidic device as a continuous flow system controlled electrokinetically and with a fluorescence detection device. The results from ROM agreed well with both computational fluid dynamic (CFD) simulations and experimental values. While the CFD model allowed for assessment of local transport phenomena, the CPU time was significantly reduced by the ROM approach. The operational parameters of the assay were optimized using the validated ROM to significantly reduce the amount of reagents consumed and the total biochip assay time. After optimization the analysis time would be reduced from 20 to 5.25min which would also resulted in 50% reduction in reagent consumption.
    Microfluidics and Nanofluidics 12/2008; 5(6):837-849. DOI:10.1007/s10404-008-0291-7 · 2.53 Impact Factor
  • Y.T. Atalay · P. Verboven · S. Vermeir · B.M. Nicolai · J. Lammertyn ·
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    ABSTRACT: Multiple enzyme assays were systematically performed for simultaneous quantification of sucrose, D-glucose and D-fructose in a single microchannel reactor. The assay was based on optical detection of the reaction product, NADH, formed through a cascade of enzymatic reactions. For design optimization of the system, a model was developed for the microfluidic flow, enzyme kinetics and mass transfer of the different species involved in the analysis. The performance of the device was then optimized using the reduced form of these models in terms of process conditions (reagents volume and flow rate) thereby facilitating biosensor development. The proposed multiplexed device increases throughput and improves user-friendliness compared to equivalent microtiter plate assays. All sugars were quantified within 2.5 min in the optimized microchip based continuous system whereas it took at least two hours in standard microtiter plate analysis. Parallelization can further improve the throughput. In addition, the amount of reagents consumed reduced drastically. For example, the amount of Hexokinase used to detect glucose in 96 well microtiter plates with a total volume of 200 muL was 21.7 ng whereas in the designed microfluidic chip it only required 4.1 ng.
    Sensors, 2008 IEEE; 11/2008
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    ABSTRACT: A direct model, using the explicit geometry of stacked products in boxes, was developed and used to study the local and average airflow through stacks of horticultural products. The discrete element method was employed to generate a random stacking of spherical products in the box. A computational fluid dynamics model was then applied to study explicitly the airflow through the air gaps in the box and in the voids between the stacks of different random fillings. The flow resistance was affected by the confinement ratio, product size, porosity, box vent hole ratio, and much less by the random filling. The predicted pressure drop over stacks agreed with experimental correlations for porous media. Air velocity profiles inside the boxes compared well to measurements. The methodology was used to obtain more accurate pressure drop correlation for stacks of vented boxes that can now be used in large scale simulations of cool rooms.
    Journal of Food Engineering 11/2008; 89(1-89):33-41. DOI:10.1016/j.jfoodeng.2008.03.026 · 2.77 Impact Factor
  • Yegermal Atalay · Pieter Verboven · Steven Vermeir · Jeroen Lammertyn ·

    Nondestructive Testing of Food Quality, 04/2008: pages 283 - 319; , ISBN: 9780470388310
  • Y T Atalay · P Verboven · N Vergauwe · S Vermeir · B Nicolaï · J Lammertyn ·

    Communications in agricultural and applied biological sciences 02/2007; 72(1):93-7.
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    ABSTRACT: This paper presents the optimization of a flow injection analysis (FIA) biosensor with respect to its design and operational parameters such as flow cell geometry, microfluidic channel dimensions, and flow rate. Since it is time consuming and costly to investigate the effect of each factor on the biosensor performance by building it, computational fluid dynamics (CFD) theory is presented as a great tool for finding optimal parameter values. This modeling approach has a high potential in the design of high accuracy FIA-biosensors, regardless of the chosen enzyme substrate system. As an example the optimal design for a glucose/glucose oxidase FIA biosensor is calculated with the CFD theory
    Sensors, 2005 IEEE; 01/2005