University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Journal of Micromechanics and Microengineering

  • Publisher: Institute of Physics (IOP)
  • FAD Code: JMMM
  • CODEN: JMMIEZ
  • ISSN: 0960-1317
  • Abbreviation: J. Micromech. Microeng.
  • DOI Prefix: 10.1088/0960-1317
  • Language: English
  • Comments: Fulltext from 1991 V1

Citations 16

"Integrated Microfluidic Systems For Cell Lysis, Mixing/pumping And DNA Amplification"
J. Micromech. Microeng. 2005 Volume 15, Issue 6 Pages 1215-1223
Chia-Yen Lee, Gwo-Bin Lee, Jr-Lung Lin, Fu-Chun Huang and Chia-Sheng Liao

Abstract: The present paper reports a fully automated microfluidic system for the DNA amplification process by integrating an electroosmotic pump, an active micromixer and an on-chip temperature control system. In this DNA amplification process, the cell lysis is initially performed in a µcell lysis reactor. Extracted DNA samples, primers and reagents are then driven electroosmotically into a mixing region where they are mixed by the active micromixer. The homogeneous mixture is then thermally cycled in a micro-PCR (polymerase chain reaction) chamber to perform DNA amplification. Experimental results show that the proposed device can successfully automate the sample pretreatment operation for DNA amplification, thereby delivering significant time and effort savings. The new microfluidic system, which facilitates cell lysis, sample driving/mixing and DNA amplification, could provide a significant contribution to ongoing efforts to miniaturize bio-analysis systems by utilizing a simple fabrication process and cheap materials.
Microfluidic Instrumentation

"Micromachine-based Multi-channel Flow Cytometers For Cell/particle Counting And Sorting"
J. Micromech. Microeng. 2005 Volume 15, Issue 3 Pages 447-454
Gwo-Bin Lee, Che-Hsin Lin and Shen-Chie Chang

Abstract: This paper reports a new micromachine-based flow cytometer capable of parallel processing of cell/particle counting and sorting using microfluidic technologies. Hydrodynamic focusing of multiple sample streams is first achieved by using a new layout of sheath flow channels coming from one single inlet port. Thus only one syringe pump is required during the operation. The flow rate of each sheath flow could be much more stable and uniform with this approach. The images of the focused multiple samples are then recorded downstream utilizing a high-speed digital CCD camera. The digital image processing technique is then used to count the number of the cells/particles. Theoretical models based on a 'flow-rate-ratio' method are used to predict the width of the multiple focused streams, which could be incorporated with a digital image processing system for cell/particle counting. Experimental data are found to be highly consistent with the theoretical results. Experimental data show that the developed device can successfully detect the number of cells/particles in two parallel sample streams and the velocities of the cells/particles in each cell line as well. Low counting error and high counting reliability are also verified by counting a mixture of polystyrene beads with different sizes. In addition, human red blood cells are used for the cell-counting test. Subsequently, cell/particle sorting could be achieved using dielectrophoretic (DEP) forces generated by built-in micro-electrodes downstream. Cell/particle sorting has been performed successfully using the DEP electrodes. The development of the multi-channel micro-flow cytometer could be crucial for the advancement of the cell-counting device.
Cells Microfluidic Instrumentation

"Micromixers—a Review"
J. Micromech. Microeng. 2005 Volume 15, Issue 2 Pages R1-R16
Nam-Trung Nguyen and Zhigang Wu

Abstract: This review reports the progress on the recent development of micromixers. The review first presents the different micromixer types and designs. Micromixers in this review are categorized as passive micromixers and active micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, passive micromixers will be the focus of this review. Next, the review discusses the operation points of the micromixers based on characteristic dimensionless numbers such as Reynolds number Re, Peclet number Pe, and in dynamic cases the Strouhal number St. The fabrication technologies for different mixer types are also analyzed. Quantification techniques for evaluation of the performance of micromixers are discussed. Finally, the review addresses typical applications of micromixers.
Mixing device Microfluidic Review

"Flow Control For Capillary-pumped Microfluidic Systems"
J. Micromech. Microeng. 2004 Volume 14, Issue 11 Pages 1503-1506
T Vestad, D W M Marr and J Oakey

Abstract: Advantages of performing analytical and diagnostic tasks in microfluidic-based systems include small sample volume requirements, rapid transport times and the promise of compact, portable instrumentation. The application of such systems in home and point-of-care situations has been limited, however, because these devices typically require significant associated hardware to initiate and control fluid flow. Capillary-based pumping can address many of these deficiencies by taking advantage of surface tension to pull fluid through devices. The development of practical instrumentation however will rely upon the development of precision control schemes to complement capillary pumping. Here, we introduce a straightforward, robust approach that allows for reconfigurable fluid guidance through otherwise fixed capillary networks. This technique is based on the opening and closing of microfluidic channels cast in a flexible elastomer via automated or even manual mechanical actuation. This straightforward approach can completely and precisely control flows such as samples of complex fluids, including whole blood, at very high resolutions according to real-time user feedback. These results demonstrate the suitability of this technique for portable, microfluidic instruments in laboratory, field or clinical diagnostic applications.
Microfluidic Pump Instrumentation

"Electrokinetically Driven Active Micro-mixers Utilizing Zeta Potential Variation Induced By Field Effect"
J. Micromech. Microeng. 2004 Volume 14, Issue 10 Pages 1390-1398
Chia-Yen Lee, Gwo-Bin Lee, Lung-Ming Fu, Kuo-Hoong Lee and Ruey-Jen Yang

Abstract: This paper presents a new electrokinetically driven active micro-mixer which uses localized capacitance effects to induce zeta potential variations along the surface of silica-based microchannels. The mixer is fabricated by etching bulk flow and shielding electrode channels into glass substrates and then depositing Au/Cr thin films within the latter to form capacitor electrodes, which establish localized zeta potential variations near the electrical double layer (EDL) region of the electroosmotic flow (EOF) within the microchannels. The potential variations induce flow velocity changes within a homogeneous fluid and a rapid mixing effect if an alternating electric field is provided. The current experimental data confirm that the fluid velocity can be actively controlled by using the capacitance effect of the buried shielding electrodes to vary the zeta potential along the channel walls. While compared with commonly used planar electrodes across the microchannels, the buried shielding electrodes prevent current leakage caused by bad bonding and allow direct optical observation during operation. It also shows that the buried shielding electrodes can significantly induce the field effect, resulting in higher variations of zeta potential. Computational fluid dynamic simulations are also used to study the fluid characteristics of the developed active mixers. The numerical and experimental results demonstrate that the developed microfluidic device permits a high degree of control over the fluid flow and an efficient mixing effect. Moreover, the developed device could be used as a pumping device as well. The development of the active electrokinetically driven micro-mixer could be crucial for micro-total-analysis-systems.
Microfluidic Mixing

"Serial Dilution Microchip For Cytotoxicity Test"
J. Micromech. Microeng. 2004 Volume 14, Issue 8 Pages 1165-1170
Hyunwoo Bang, Sun Hee Lim, Young Kyung Lee, Seok Chung, Chanil Chung, Dong-Chul Han and Jun Keun Chang

Abstract: Today's pharmaceutical industry is facing challenges resulting from the vast increases in sample numbers produced by high-throughput screening (HTS). In addition, the bottlenecks created by increased demand for cytotoxicity testing (required to assess compound safety) are becoming a serious problem. We have developed a polymer PDMS (polydimethylsiloxane) based microfluidic device that can perform a cytotoxicity test in a rapid and reproducible manner. The concept that the device includes is well adjustable to automated robots in huge HTS systems, so we can think of it as a potential dilution and delivery module. Cytotoxicity testing is all about the dilution and dispensing of a drug sample. Previously, we made a PDMS based microfluidic device which automatically and precisely diluted drugs with a buffer solution with serially increasing concentrations. This time, the serially diluted drug solution was directly delivered to 96 well plates for cytotoxicity testing. Cytotoxic paclitaxel solution with 2% RPMI 1640 has been used while carrying out cancerous cell based cytotoxicity tests. We believe that this rapid and robust use of the PDMS microchip will overcome the growing problem in cytotoxicity testing for HTS.
Microfluidic Dilution

"A Review Of Micropumps"
J. Micromech. Microeng. 2004 Volume 14, Issue 6 Pages R35-R64
D J Laser and J G Santiago

Abstract: We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.
Microfluidic Pump Instrumentation Review

"Double-L Injection Technique For High Performance Capillary Electrophoresis Detection In Microfluidic Chips"
J. Micromech. Microeng. 2004 Volume 14, Issue 4 Pages 639-646
Che-Hsin Lin, Ruey-Jen Yang, Chang-Hsien Tai, Chia-Yen Lee and Lung-Ming Fu

Abstract: This paper reports low-leakage injection techniques to deliver sample plugs within double-T-form electrophoresis microchips. Experimental and numerical investigations are used to predict and evaluate the leakage behavior during electrokinetic driving of the sample plugs. The principal material transport mechanisms including traditional cross-form, electro-floating, diffusion sampling injection techniques are discussed in this study. A simple and precise double-L injection technique that employs electrokinetic manipulations to avoid sample leakage within the microchip is also reported. The method needs only one electrical control point during injection and separation, so the control system can be smaller and cheaper. Experimental and numerical results show the proposed injection technique is able to reduce sample leakage significantly. No leakage happens after 16 sample injections using the double-L injection method while leakage usually happens using the traditional cross-form injection technique. The double-L injection technique proposed in this study has a great potential for use in high-precision analysis applications utilizing chip-based capillary electrophoresis.
Electrophoresis Microfluidic Injection technique

"Thermal Effects On Electro-osmotic Pumping Of Liquids In Microchannels"
J. Micromech. Microeng. 2002 Volume 12, Issue 6 Pages 962-970
T S Zhao and Q Liao

Abstract: In this paper we present a mathematical model predicting combined electro-osmotic- and pressure-driven flow behavior in a straight microchannel for the case when the system is under a non-isothermal condition. The distribution of the charge density is governed by a nonlinear, two-dimensional Poisson-Boltzmann equation, and a body force caused by the interaction between the charge density and the applied electrical potential field is included in the full Navier-Stokes equations. Under non-isothermal conditions, arising from heat sources (Joule heating) within the system and/or a temperature difference between the system and the ambient, the equation of energy conservation describing temperature distribution has to be considered as well. The governing equations, interlinked via temperature, are solved numerically using a finite difference method. The numerical results indicate that for a given cross-sectional mean velocity, there exists an optimal dimensionless parameter (kappah), which is the inverse Debye length multiplied by the channel size, which gives the highest hydraulic head generated by the electro-osmotic force. It has also been demonstrated that the pumping performance predicted by the isothermal model deviates substantially from that predicted by the non-isothermal model when Joule heating is significant.
Temperature

"Design And Simulation Of Bi-directional Microfluid Driving Systems"
J. Micromech. Microeng. 2002 Volume 12, Issue 2 Pages 115-121
Chun-Ping Jen and Yu-Cheng Lin

Abstract: Micro total analysis systems (µTAS) have been developed to perform a number of analytical processes involving chemical reactions, separation and sensing on a single chip. In medical and biomedical applications, µTAS must be designed considering special transport mechanisms to move samples and reagents through the microchannels in the system. For conventional micropumps, however, complicated relationships exist between the pumping mechanisms, the conditions under which the devices operate and the behavior of the multi-component fluids transported in these channels. A bi-directional microfluid driving system has been developed in this paper. This pneumatic system is an on-chip planar structure with no moving parts and does not require microfabricated heaters or electrodes. The pumping actuation is introduced to the microchannel fabricated in the chip by blowing an airflow through this device. The bi-directional driving module combines two individual components for suction and exclusion. The driving system provides a stable and flexible bi-directional microfluid driving control. The tunable parameters for adjusting the exclusion/suction ratios, such as the location of the inlet channel and the velocities of the airflow, have been observed in the numerical study. The optimal exclusion/suction ratio for the specific purpose of the driving system can be selected by changing the location of the microchannel to the reaction area for the sample/reagent. The velocity at the microchannel can be adjusted by varying the inlet velocities for the suction and exclusion components. For the presented design, no air conduit was employed to connect the servo-system to the driving system; therefore the packaging difficulty and leakage problem, which may arise in conventional systems, can be eliminated. The final airflow outlet was fixed in one direction so that it can prevent cross-contamination between the servo-system and the chip. The driving system is therefore particularly suited to microdevices for biochemical analysis.
Microfluidic Pump

"Characterization Method For A New Diffusion Mixer Applicable In Micro Flow Injection Analysis Systems"
J. Micromech. Microeng. 1999 Volume 9, Issue 2 Pages 199-202
T Veenstra, T S J Lammerink, M C Elwenspoek and A van den Berg

Abstract: A new mixer is designed for mixing a phenolic solution into water. The mixer design is such that it can be easily adjusted for the controlled mixing of a specific compound within a certain time. This paper describes the working principle of the mixer as well as a suitable characterization method for the mixer. Measurement results are presented which show the correct working of the mixer. A quantitative measure is introduced to express the extent of mixing performed by the mixer. The characterization method allows the measurement of the flow rate, pressure drop and extent of mixing.
Microfluidic Mixing Instrumentation

"Integrated Bio/chemical Microsystems Employing Optical Detection: The Clip-on"
J. Micromech. Microeng. 1998 Volume 8, Issue 2 Pages 143-150
Otto Leistiko and Peter Friis Jensen

Abstract: The fabrication and test of a new integrated optical detection circuit, which can be coupled to external microcapillary analysis systems, is presented. Simple optical waveguide and photodiode circuits, as well as the system for coupling light through the external microcapillary chemical transport system, are included on the same silicon, `clip-on', chip. A chemical reaction taking place in the external microcapillary system, which gives rise to a change in absorbance or luminescence, is detected as the reaction front moves past the optical detection circuit. Mesa photodiode structures are butt coupled to multilayer glass optical waveguides and have responsivities of about 0.5 plus a broad spectral response. The buried optical waveguide structures, which are formed in low loss (0.5 dB ) germanium doped core glass, couple very effectively to the mesa diodes. Light is coupled to the waveguides via optical fibers which are fastened to the chip by means of simple connectors etched into the silicon. Fluids are transported to and from the chip by means of quartz microcapillary, similarly fastened to the chip by means of an integrated connector.

"Three-dimensional Micro Flow Manifolds For Miniaturized Chemical Analysis Systems"
J. Micromech. Microeng. 1994 Volume 4, Issue 4 Pages 246-256
Verpoorte, E. M. J.; Van Der Schoot, B. H.; Jeanneret, S.; Manz, A.; Widmer, H. M.; De Rooij, N. F.

Abstract: A three-dimensional (3D) stack concept for the assembly of photolithographically fabricated microfluidic components is presented and discussed. The system uses silicon-based micropumps and simple planar structures which mimic standard elements of conventional flow systems. Detection is provided either by solid state electrochemical sensors or small volume optical detection. The general advantages of using micromachined flow manifolds for microchemical analysis are addressed. The particular benefits to be derived from this an approach compared with other assembly methods are also examined.

"Towards Integrated Microliquid Handling Systems"
J. Micromech. Microeng. 1994 Volume 4, Issue 4 Pages 227-245
M Elwenspoek, T S J Lammerink, R Miyake and J H J Fluitman

Abstract: In this paper we describe components for integrated microliquid handling systems such as fluid injection analysis, and first results of planar integration of components. The components discussed are channels, passive and active valves, actuators for micropumps, micromixers, microflow sensors, optical detectors, pumps and dosage systems. The dosage system described comprises a flow sensor and a pump micromachined on a single silicon wafer sandwiched between Pyrex wafers. The liquid pump is of the reciprocating type with a thermo-pneumatic actuator. The microliquid flow sensor is based on the thermal anemometer type. Both pump and flow sensor are realized in a 3 inch (100)- Si wafer using a KOH bulk etch from both sides of the wafer. The dosing system allows accurate dosing of liquid in the µl regime and can easily be integrated with components as mixers and detectors to microliquid handling systems. A new concept for micromixing of liquids is introduced and its feasibility is demonstrated. The mixer allows fast mixing of small amounts of two liquids and it is applicable to microliquid handling systems. The mixer has a channel for the liquid, an inlet port for the reagent, and a mixing area, the bottom of which has 400 micronozzles (15 µm*15 µm). Through these nozzles, a reagent is injected into the sample liquid, making many microplumes. These plumes speed up mixing by diffusion over a short distance.

"Microflow Devices And Systems"
J. Micromech. Microeng. 1994 Volume 4, Issue 4 Pages 157-171
S Shoji and M Esashi

Abstract: Microflow devices including microvalves, micropumps and microflow sensors fabricated by micromachining are reviewed from the point of view of the actuating principle and structures. Integration of microflow control devices and microflow sensors allowed very precise control of small flow. High performance liquid dosing microsystems and sophisticated chemical analyzing microsystems were demonstrated by the combination of microflow devices and microsensors. Applications of microflow devices and systems are also introduced.

"Microfluidics-a Review"
J. Micromech. Microeng. 1993 Volume 3, Issue 4 Pages 168-182
Gravesen, P.; Branebjerg, J.; Jensen. O. S.

Abstract: An overview is given of research activities in the field of fluid components or systems built with microfabrication technologies. This review focuses on the fluidic behavior of the various devices, such as valves, pumps and flow sensors as well as the possibilities and pitfalls related to the modelling of these devices using simple flow theory. Finally, a number of microfluidic systems are described and comments on future trends are given.