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ABSTRACT: Biological sample processing involves purifying target analytes from various sample matrices and concentrating them to a small volume from a large volume of crude sample. This complex process is the major obstacle for developing a microfluidic diagnostic platform. In this study, we present a microfluidic device that can continuously separate and concentrate pathogenic bacterial cells from complex sample matrices such as cerebrospinal fluid and whole blood. Having overcome critical limitations of dielectrophoretic (DEP) operation in physiological media of high conductivity, we utilized target specific DEP techniques to incorporate cell separation, medium exchange, and target concentration into an integrated platform. The proposed microfluidic device can uptake mL volumes of crude biological sample and selectively concentrate target cells into a submicrolitre volume, providing ~10(4) fold of concentration. We designed the device based on the electrokinetic theory and electric field simulation, and tested the device performance with different sample types. The separation efficiency of the device was as high as 97.0% for a bead mixture in TAE buffer and 94.3% and 87.2% for E. coli in human cerebrospinal fluid and blood, respectively. A capture efficiency of 100% was achieved in the concentration chamber. With a relatively simple configuration, the proposed device provides a robust method of continuous sample processing, which can be readily integrated into a fully automated microfluidic diagnostic platform for pathogen detection and quantification.
Lab on a Chip 09/2011; 11(17):2893-900. · 5.67 Impact Factor
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ABSTRACT: Global burdens from existing or emerging infectious diseases emphasize the need for point-of-care (POC) diagnostics to enhance timely recognition and intervention. Molecular approaches based on PCR methods have made significant inroads by improving detection time and accuracy but are still largely hampered by resource-intensive processing in centralized laboratories, thereby precluding their routine bedside- or field-use. Microfluidic technologies have enabled miniaturization of PCR processes onto a chip device with potential benefits including speed, cost, portability, throughput, and automation. In this review, we provide an overview of recent advances in microfluidic PCR technologies and discuss practical issues and perspectives related to implementing them into infectious disease diagnostics.
Biotechnology advances 06/2011; 29(6):830-9. · 8.25 Impact Factor
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ABSTRACT: We have developed a microfluidic device capable of fully integrated sample preparation and gene analysis from crude biosamples such as whole blood. Our platform takes the advantage of the silica superparamagnetic particle based solid phase extraction to develop an all-in-one scheme that performs cell lysis, DNA binding, washing, elution and the PCR in the same reaction chamber. The device also employs a unique reagent loading scheme, allowing efficient preparation of multiple reactions via a single injection channel. In addition, PCR is performed in a droplet-in-oil manner, eliminating the need for chamber sealing. The combination of these design features greatly reduces the complexity in implementing fully integrated lab-on-a-chip systems for genetic detection, facilitating parallel analysis of multiple samples or genes on a single microchip. The capability of the device is demonstrated by performing DNA isolation from the human whole blood sample and analyzing the Rsf-1 gene using the TaqMan probe based gene specific PCR assays.
Biomedical Microdevices 12/2010; 12(6):1043-9. · 3.03 Impact Factor
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ABSTRACT: This paper reports a droplet microfluidic, sample-to-answer platform for the detection of disease biomarkers and infectious pathogens using crude biosamples. The platform exploited the dual functionality of silica superparamagnetic particles (SSP) for solid phase extraction of DNA and magnetic actuation. This enabled the integration of sample preparation and genetic analysis within discrete droplets, including the steps of cell lysis, DNA binding, washing, elution, amplification and detection. The microfluidic device was self contained, with all reagents stored in droplets, thereby eliminating the need for fluidic coupling to external reagent reservoirs. The device incorporated unique surface topographic features to assist droplet manipulation. Pairs of micro-elevations were created to form slits that facilitated efficient splitting of SSP from droplets. In addition, a compact sample handling stage, which integrated the magnet manipulator, the droplet microfluidic device and a Peltier thermal cycler, was built for convenient droplet manipulation and real-time detection. The feasibility of the platform was demonstrated by analysing ovarian cancer biomarker Rsf-1 and detecting Escherichia coli with real time polymerase chain reaction and real time helicase dependent amplification.
Lab on a Chip 11/2010; 11(3):398-406. · 5.67 Impact Factor
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ABSTRACT: A microfluidic device with planar square electrodes is developed for capturing particles from high conductivity media using negative dielectrophoresis (n-DEP). Specifically, Bacillus subtilis and Clostridium sporogenes spores, and polystyrene particles are tested in NaCl solution (0.05 and 0.225 S∕m), apple juice (0.225 S∕m), and milk (0.525 S∕m). Depending on the conductivity of the medium, the Joule heating produces electrothermal flow (ETF), which continuously circulates and transports the particles to the DEP capture sites. Combination of the ETF and n-DEP results in different particle capture efficiencies as a function of the conductivity. Utilizing 20 μm height DEP chambers, "almost complete" and rapid particle capture from lower conductivity (0.05 S∕m) medium is observed. Using DEP chambers above 150 μm in height, the onset of a global fluid motion for high conductivity media is observed. This motion enhances particle capture on the electrodes at the center of the DEP chamber. The n-DEP electrodes are designed to have well defined electric field minima, enabling sample concentration at 1000 distinct locations within the chip. The electrode design also facilitates integration of immunoassay and other surface sensors onto the particle capture sites for rapid detection of target micro-organisms in the future.
Biomicrofluidics 01/2010; 4(3). · 3.37 Impact Factor
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ABSTRACT: Electrokinetic transport of particles through an L-shaped microchannel under DC electric fields is theoretically and experimentally investigated. The emphasis is placed on the direct current (DC) dielectrophoretic (DEP) effect arising from the interactions between the induced spatially nonuniform electric field around the corner and the dielectric particles. A transient multiphysics model is developed in an arbitrary Lagrangian-Eulerian (ALE) framework, which comprises the Navier-Stokes equations for the fluid flow and the Laplace equation for the electrical potential. The predictions of the DEP-induced particle trajectory shift in the L-shaped microchannel are in quantitative agreement with the obtained experimental results. Numerical studies also show that the DEP effect can alter the angular velocity and even the direction of the particle's rotation. Further parametric studies suggest that the L-shaped microfluidic channel may be utilized to focus and separate particles by size via the induced DEP effect.
Langmuir 10/2009; 26(4):2937-44. · 4.19 Impact Factor
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ABSTRACT: We demonstrate negative dielectrophoresis (DEP) trapping of particles from high-conductivity media using a novel planar microelectrode that allows electrothermal enhancement of DEP traps. DEP force and electrothermal flow motion are investigated using a scaling analysis, numerical simulations, and experiments. Results show that the DEP trapping is enhanced by lateral transport of particles toward the capture zones due to electrothermal flow, whereas DEP trapping occurred only in limited spatial ranges without the flow motion. The electrothermally enhanced DEP will broaden the limit of electrokinetic manipulations in high-conductivity media. By providing patterned trapping zones that can act as target-specific attachment/detection sites, the presented device allows development of biosensor applications for rapid detection of pathogens and other microorganisms within a practical range of buffer conductivity.
Analytical Chemistry 03/2009; 81(6):2303-10. · 5.86 Impact Factor
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ABSTRACT: Alternating current (ac) electrokinetic motion of colloidal particles suspended in an aqueous medium and subjected to a spatially nonuniform ac electric field are examined using a simple theoretical model that considers the relative magnitudes of dielectrophoresis, electrophoresis, ac-electroosmosis, and Brownian motion. Dominant electrokinetic forces are explained as a function of the electric field frequency, amplitude, and conductivity of the suspending medium for given material properties and geometry. Parametric experimental validations of the model are conducted utilizing interdigitated microelectrodes with polystyrene and gold particles and Clostridium sporogenes bacterial spores. The theoretical model provides quantitative descriptions of ac electrokinetic transport for the given target species in a wide spectrum of electric field amplitude and frequency and medium conductivity. The presented model can be used as an effective framework for design and optimization of ac electrokinetic devices.
Analytical Chemistry 05/2008; 80(8):2832-41. · 5.86 Impact Factor
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Seungkyung Park
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ABSTRACT: Recent advances in microfluidic technologies have enabled integration of the functional units for biological and chemical analysis onto miniaturized chips, called Labon- a-Chip (LOC). However, the effective manipulation and control of colloidal particles suspended in fluids are still challenging tasks due to the lack of clear characterization of particle control mechanisms. The aim of this dissertation is to develop microfluidic techniques and devices for manipulating colloids and biological particles with the utilization of alternating current (AC) electric fields and acoustic waves. The dissertation presents a simple theoretical tool for predicting the motion of colloidal particles in the presence of AC electric field. Dominant electrokinetic forces are explained as a function of the electric field conditions and material properties, and parametric experimental validations of the model are conducted with particles and biological species. Using the theoretical tool as an effective framework for designing electrokinetic systems, a dielectrophoresis (DEP) based microfluidic device for trapping bacterial spores from high conductivity media is developed. With a simple planar electrode having well defined electric field minima that can act as the targetattachment/ detection sites for integration of biosensors, negative DEP trapping of spores on patterned surfaces is successfully demonstrated. A further investigation of DEP colloidal manipulation under the effects of electrothermal flow induced by Joule heating of the applied electric field is conducted. A periodic structure of the electrothermal flow that enhances DEP trapping is numerically simulated and experimentally validated. An acoustic method is investigated for continuous sample concentration in a microscale device. Fast formation of particle streams focused at the pressure nodes is demonstrated by using the long-range forces of the ultrasonic standing waves (USW). High frequency actuation suitable for miniaturization of devices is successfully applied and the device performance and key parameters are explained. Further extension and integration of the technologies presented in this dissertation will enable a chip scale platform for various chemical and biological applications such as drug delivery, chemical analyses, point-of-care clinical diagnosis, biowarfare and biochemical agent detection/screening, and water quality control.
