[show abstract][hide abstract] ABSTRACT: We present a novel, simple and highly efficient protocol for the extraction of magnetic particles out of individual droplets on a digital lab-on-chip in the presence of a spatially fixed magnet with a permanent magnetic field. In this approach, the particles were extracted from the droplet by the interplay of capillary, magnetic and electrowetting forces, thereby avoiding the use of mechanical components that would be needed for removing the magnet when particle resuspension is required. This droplet manipulation allowed the execution of very efficient and fast washing protocols on the digital microfluidic (DMF) platform. To demonstrate the effectiveness of this particle extraction protocol, an IgG immunoassay was implemented on the DMF platform. Our improved protocol reduced the overall assay variability to 3% coefficient of variation (CV) while all incubation and washing steps were automatically performed on-chip. In addition, the suspended magnetic particles allowed the introduction of a very efficient mixing strategy by using the magnetic particles as magnetic stirrers, resulting in an improvement of 90% in detection limit compared to a passive mixing strategy, solely based on diffusion.
Sensors and Actuators B Chemical 01/2014; 196:282–291. · 3.54 Impact Factor
[show abstract][hide abstract] ABSTRACT: The first microfluidic method for accurately depositing monodisperse single MOF crystals is presented, enabling unprecedented high-throughput, yet flexible single-crystal printing. Individual droplets of MOF precursor solutions are actuated over a matrix of hydrophilic-in-hydrophobic micropatterns for the controlled generation of femtoliter droplets. As such, thousands of monodisperse single MOF crystals are printed per second in a desired pattern, without the use of impractically expensive equipment.
[show abstract][hide abstract] ABSTRACT: In this paper we report on the controlled biofunctionalization of the hydrophobic layer of electrowetting-on-dielectric (EWOD) based microfluidic chips with the aim to execute (adherent) cell-based assays. The biofunctionalization technique involves a dry lift-off method with an easy to remove Parylene-C mask and allows the creation of spatially controlled micropatches of biomolecules in the Teflon-AF(®) layer of the chip. Compared to conventional methods, this method (i) is fully biocompatible; and (ii) leaves the hydrophobicity of the chip surface unaffected by the fabrication process, which is a crucial feature for digital microfluidic chips. In addition, full control of the geometry and the dimensions of the micropatches is achieved, allowing cells to be arrayed as cell clusters or as single cells on the digital microfluidic chip surface. The dry Parylene-C lift-off technique proves to have great potential for precise biofunctionalization of digital microfluidic chips, and can enhance their use for heterogeneous bio-assays that are of interest in various biomedical applications.
Lab on a Chip 07/2011; 11(16):2790-4. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: Electrowetting-on-dielectric (EWOD) lab-on-a-chip systems have already proven their potential within a broad range of bio-assays. Nevertheless, research on the analytical performance of those systems is limited, yet crucial for a further breakthrough in the diagnostic field. Therefore, this paper presents the intrinsic possibilities of an EWOD lab-on-a-chip as a versatile platform for homogeneous and heterogeneous bio-assays with high analytical performance. Both droplet dispensing and splitting cause variations in droplet size, thereby directly influencing the assay's performance. The extent to which they influence the performance is assessed by a theoretical sensitivity analysis, which allows the definition of a basic framework for the reduction of droplet size variability. Taking advantage of the optimized droplet manipulations, both homogeneous and heterogeneous bio-assays are implemented in the EWOD lab-on-a-chip to demonstrate the analytical capabilities and versatility of the device. A fully on-chip enzymatic assay is realized with high analytical performance. It demonstrates the promising capabilities of an EWOD lab-on-a-chip in food-related and medical applications, such as nutritional and blood analyses. Further, a magnetic bio-assay for IgE detection using superparamagnetic nanoparticles is presented whereby the nanoparticles are used as solid carriers during the bio-assay. Crucial elements are the precise manipulation of the superparamagnetic nanoparticles with respect to dispensing and separation. Although the principle of using nano-carriers is demonstrated for protein detection, it can be easily extended to a broader range of bio-related applications like DNA sensing. In heterogeneous bio-assays the chip surface is actively involved during the execution of the bio-assay. Through immobilization of specific biological compounds like DNA, proteins and cells a reactive chip surface is realized, which enhances the bio-assay performance. To demonstrate this potential, on-chip adhesion islands are fabricated to immobilize MCF-7 human breast cancer cells. Viability studies are performed to assess the functionalization efficiency.
Journal of Micromechanics and Microengineering 04/2011; 21(5):054026. · 1.79 Impact Factor
[show abstract][hide abstract] 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 01/2011; 11(1):25-34. · 3.22 Impact Factor
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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 12(5). · 3.22 Impact Factor
[show abstract][hide abstract] 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 5(6):837-849. · 3.22 Impact Factor
[show abstract][hide abstract] 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 7(3):393-406. · 3.22 Impact Factor