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Dec 2010

Volume 4, Issue 4, Articles (04xxxx)

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Biomicrofluidics 4, 043007 (2010); http://dx.doi.org/10.1063/1.3497934 (7 pages)

Xiaole Mao, Zackary I. Stratton, Ahmad Ahsan Nawaz, Sz-Chin Steven Lin, and Tony Jun Huang
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Electric field assisted manipulation of microdroplets on a superhydrophobic surface

L. T. Shi, C. G. Jiang, G. J. Ma, and C. W. Wu

Biomicrofluidics 4, 041101 (2010); http://dx.doi.org/10.1063/1.3523472 (7 pages) | Cited 1 time

Online Publication Date: 14 December 2010

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The efficient manipulation of low-volume droplets offers many potential applications in relation to chemical and biomedical tests and protocols. A novel approach to the manipulation of a microdroplet on a superhydrophobic surface is introduced in the present communication. The microdroplet was first picked up onto a hydrophilic needle, transported from one location to another, and finally released under the action of an electric field force. Three key parameters in this process, the radius of the droplet, the distance between the two electrodes, and the required voltage, were investigated. This study should be helpful for the design of microfluidic devices.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
47.55.D- Drops and bubbles
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
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A perspective on microfluidic biofuel cells

Jin wook Lee and Erik Kjeang

Biomicrofluidics 4, 041301 (2010); http://dx.doi.org/10.1063/1.3515523 (12 pages) | Cited 3 times

Online Publication Date: 10 November 2010

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This review article presents how microfluidic technologies and biological materials are paired to assist in the development of low cost, green energy fuel cell systems. Miniaturized biological fuel cells, employing enzymes or microorganisms as biocatalysts in an environmentally benign configuration, can become an attractive candidate for small-scale power source applications such as biological sensors, implantable medical devices, and portable electronics. State-of-the-art biofuel cell technologies are reviewed with emphasis on microfabrication compatibility and microfluidic fuel cell designs. Integrated microfluidic biofuel cell prototypes are examined with comparisons of their performance achievements and fabrication methods. The technical challenges for further developments and the potential research opportunities for practical cell designs are discussed.
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88.20.F- Renewable alternative fuels from biomass energy
87.14.ej Enzymes
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Preface to Special Topic: Optofluidics

Ai-Qun Liu

Biomicrofluidics 4, 042901 (2010); http://dx.doi.org/10.1063/1.3533774 (2 pages) | Cited 2 times

Online Publication Date: 30 December 2010

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This Special Topic section of Biomicrofluidics is on optofluidics or micro-optofluidic systems (MOFS), a burgeoning technology that aims to manipulate light and fluid at microscale and exploits their interaction to create highly versatile devices and integrated systems. This special issue puts together various contributed articles focusing on optofluidics or MOFS, which help inspire new research ideas and innovation in the microfluidics and nanofluidics community.
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01.30.-y Physics literature and publications
47.85.Np Fluidics
87.80.-y Biophysical techniques (research methods)

Review Article: Recent advancements in optofluidic flow cytometer

Sung Hwan Cho, Jessica M. Godin, Chun-Hao Chen, Wen Qiao, Hosuk Lee, and Yu-Hwa Lo

Biomicrofluidics 4, 043001 (2010); http://dx.doi.org/10.1063/1.3511706 (23 pages)

Online Publication Date: 30 December 2010

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There is an increasing need to develop optofluidic flow cytometers. Optofluidics, where optics and microfluidics work together to create novel functionalities on a small chip, holds great promise for lab-on-a-chip flow cytometry. The development of a low-cost, compact, handheld flow cytometer and microfluorescence-activated cell sorter system could have a significant impact on the field of point-of-care diagnostics, improving health care in, for example, underserved areas of Africa and Asia, that struggle with epidemics such as HIV/AIDS. In this paper, we review recent advancements in microfluidics, on-chip optics, novel detection architectures, and integrated sorting mechanisms.
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87.85.gf Fluid mechanics and rheology
87.80.Ek Mechanical and micromechanical techniques
47.85.-g Applied fluid mechanics

Optofluidic microcavities: Dye-lasers and biosensors

Y. Chen, L. Lei, K. Zhang, J. Shi, L. Wang, H. Li, X. M. Zhang, Y. Wang, and H. L. W. Chan

Biomicrofluidics 4, 043002 (2010); http://dx.doi.org/10.1063/1.3499949 (14 pages)

Online Publication Date: 30 December 2010

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Optofluidic microcavities are integrated elements of microfluidics that can be explored for a large variety of applications. In this review, we first introduce the physics basis of optical microcavities and microflow control. Then, we describe four types of optofluidic dye lasers developed so far based on both simple and advanced device fabrication technologies. To illustrate the application potential of such devices, we present two types of laser intracavity measurements for chemical solution and single cell analyses. In addition, the possibility of single molecule detection is discussed. All these recent achievements demonstrated the great importance of the topics in biology and several other disciplines.
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47.85.Np Fluidics
47.61.-k Micro- and nano- scale flow phenomena
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.80.Ek Mechanical and micromechanical techniques
87.17.-d Cell processes
87.14.-g Biomolecules: types

Cell rotation using optoelectronic tweezers

Yuan-Li Liang, Yuan-Peng Huang, Yen-Sheng Lu, Max T. Hou, and J. Andrew Yeh

Biomicrofluidics 4, 043003 (2010); http://dx.doi.org/10.1063/1.3496357 (8 pages)

Online Publication Date: 30 December 2010

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A cell rotation method by using optoelectronic tweezers (OET) is reported. The binary image of a typical OET device, whose light and dark sides act as two sets of parallel plates with different ac voltages, was used to create a rotating electric field. Its feasibility for application to electrorotation of cells was demonstrated by rotating Ramos and yeast cells in their pitch axes. The electrorotation by using OET devices is dependent on the medium and cells’ electrical properties, the cells’ positions, and the OET device’s geometrical dimension, as well as the frequency of the electric field.
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87.80.Fe Micromanipulation of biological structures
87.17.-d Cell processes
85.60.-q Optoelectronic devices
87.50.ch Electrophoresis/dielectrophoresis and other mechanical effects

Optofluidic planar reactors for photocatalytic water treatment using solar energy

Lei Lei, Ning Wang, X. M. Zhang, Qidong Tai, Din Ping Tsai, and Helen L. W. Chan

Biomicrofluidics 4, 043004 (2010); http://dx.doi.org/10.1063/1.3491471 (12 pages)

Online Publication Date: 30 December 2010

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Optofluidics may hold the key to greater success of photocatalytic water treatment. This is evidenced by our findings in this paper that the planar microfluidic reactor can overcome the limitations of mass transfer and photon transfer in the previous photocatalytic reactors and improve the photoreaction efficiency by more than 100 times. The microreactor has a planar chamber (5 cm×1.8 cm×100 μm) enclosed by two TiO2-coated glass slides as the top cover and bottom substrate and a microstructured UV-cured NOA81 layer as the sealant and flow input/output. In experiment, the microreactor achieves 30% degradation of 3 ml 3×10−5M methylene blue within 5 min and shows a reaction rate constant two orders higher than the bulk reactor. Under optimized conditions, a reaction rate of 8% s−1 is achieved under solar irradiation. The average apparent quantum efficiency is found to be only 0.25%, but the effective apparent quantum efficiency reaches as high as 25%. Optofluidic reactors inherit the merits of microfluidics, such as large surface/volume ratio, easy flow control, and rapid fabrication and offer a promising prospect for large-volume photocatalytic water treatment.
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89.20.Kk Engineering
47.85.L- Flow control
89.60.-k Environmental studies
87.80.Ek Mechanical and micromechanical techniques
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.Hp Processes caused by visible and UV light

Characterization of a microflow cytometer with an integrated three-dimensional optofluidic lens system

M. Rosenauer and M. J. Vellekoop

Biomicrofluidics 4, 043005 (2010); http://dx.doi.org/10.1063/1.3502672 (12 pages)

Online Publication Date: 30 December 2010

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Flow cytometry is a standard analytical method in cell biology and clinical diagnostics and is widely distributed for the experimental investigation of microparticle characteristics. In this work, the design, realization, and measurement results of a novel planar optofluidic flow cytometric device with an integrated three-dimensional (3D) adjustable optofluidic lens system for forward-scattering/extinction-based biochemical analysis fabricated by silicon micromachining are presented. To our knowledge, this is the first planar cytometric system with the ability to focus light three-dimensionally on cells/particles by the application of fluidic lenses. The single layer microfluidic platform enables versatile 3D hydrodynamic sample focusing to an arbitrary position in the channel and incorporates integrated fiber grooves for the insertion of glass fibers. To confirm the fluid dynamics and raytracing simulations and to characterize the sensor, different cell lines and sets of microparticles were investigated by detecting the extinction (axial light loss) signal, demonstrating the high sensitivity and sample discrimination capability of this analysis system. The unique features of this planar microdevice enable new biotechnological analysis techniques due to the highly increased sensitivity.
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87.16.-b Subcellular structure and processes
42.79.Bh Lenses, prisms and mirrors

Miniaturization of dielectric liquid microlens in package

Chih-Cheng Yang, C. Gary Tsai, and J. Andrew Yeh

Biomicrofluidics 4, 043006 (2010); http://dx.doi.org/10.1063/1.3494030 (9 pages)

Online Publication Date: 30 December 2010

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This study presents packaged microscale liquid lenses actuated with liquid droplets of 300–700 μm in diameter using the dielectric force manipulation. The liquid microlens demonstrated function focal length tunability in a plastic package. The focal length of the liquid lens with a lens droplet of 500 μm in diameter is shortened from 4.4 to 2.2 mm when voltages applied change from 0 to 79 Vrms. Dynamic responses that are analyzed using 2000 frames/s high speed motion cameras show that the advancing and receding times are measured to be 90 and 60 ms, respectively. The size effect of dielectric liquid microlens is characterized for a lens droplet of 300–700 μm in diameter in an aspect of focal length.
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42.79.Bh Lenses, prisms and mirrors

Optofluidic tunable microlens by manipulating the liquid meniscus using a flared microfluidic structure

Xiaole Mao, Zackary I. Stratton, Ahmad Ahsan Nawaz, Sz-Chin Steven Lin, and Tony Jun Huang

Biomicrofluidics 4, 043007 (2010); http://dx.doi.org/10.1063/1.3497934 (7 pages)

Online Publication Date: 30 December 2010

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We have designed, demonstrated, and characterized a simple, novel in-plane tunable optofluidic microlens. The microlens is realized by utilizing the interface properties between two different fluids: CaCl2 solution and air. A constant contact angle of ∼ 90° is the pivotal factor resulting in the outward bowing and convex shape of the CaCl2 solution-air interface. The contact angle at the CaCl2 solution-air interface is maintained by a flared structure in the polydimethylsiloxane channel. The resulting bowing interface, coupled with the refractive index difference between the two fluids, results in effective in-plane focusing. The versatility of such a design is confirmed by characterizing the intensity of a traced beam experimentally and comparing the observed focal points with those obtained via ray-tracing simulations. With the radius of curvature conveniently controlled via fluid injection, the resulting microlens has a readily tunable focal length. This ease of operation, outstandingly low fluid usage, large range tunable focal length, and in-plane focusing ability make this lens suitable for many potential lab-on-a-chip applications such as particle manipulation, flow cytometry, and in-plane optical trapping.
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87.80.Ek Mechanical and micromechanical techniques
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Bh Lenses, prisms and mirrors
87.80.Cc Optical trapping

Optofluidic refractometer using resonant optical tunneling effect

A. Q. Jian, X. M. Zhang, W. M. Zhu, and M. Yu

Biomicrofluidics 4, 043008 (2010); http://dx.doi.org/10.1063/1.3502671 (11 pages)

Online Publication Date: 30 December 2010

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This paper presents the design and analysis of a liquid refractive index sensor that utilizes a unique physical mechanism of resonant optical tunneling effect (ROTE). The sensor consists of two hemicylindrical prisms, two air gaps, and a microfluidic channel. All parts can be microfabricated using an optical resin NOA81. Theoretical study shows that this ROTE sensor has extremely sharp transmission peak and achieves a sensitivity of 760 nm/refractive index unit (RIU) and a detectivity of 85 000 RIU−1. Although the sensitivity is smaller than that of a typical surface plasmon resonance (SPR) sensor (3200 nm/RIU) and is comparable to a 95% reflectivity Fabry–Pérot (FP) etalon (440 nm/RIU), the detectivity is 17 000 times larger than that of the SPR sensor and 85 times larger than that of the FP etalon. Such ROTE sensor could potentially achieve an ultrahigh sensitivity of 10−9 RIU, two orders higher than the best results of current methods.
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07.60.Hv Refractometers and reflectometers
42.79.Bh Lenses, prisms and mirrors
47.85.Np Fluidics
47.61.-k Micro- and nano- scale flow phenomena
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Release monitoring of single cells on a microfluidic device coupled with fluorescence microscopy and electrochemistry

Bao-Xian Shi, Yu Wang, Tin-Lun Lam, Wei-Hua Huang, Kai Zhang, Yun-Chung Leung, and Helen L. W. Chan

Biomicrofluidics 4, 043009 (2010); http://dx.doi.org/10.1063/1.3491470 (9 pages)

Online Publication Date: 30 December 2010

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A method for monitoring the biological exocytotic phenomena on a microfluidic system was proposed. A microfluidic device coupled with functionalities of fluorescence imaging and amperometric detection has been developed to enable the real-time monitoring of the exocytotic events. Exocytotic release of single SH-SY5Y neuroblastoma cells was studied. By staining the cells located on integrated microelectrodes with naphthalene-2,3-dicarboxaldehyde, punctuate fluorescence consistent with localization of neurotransmitters stored in vesicles was obtained. The stimulated exocytotic release was successfully observed at the surface of SH-SY5Y cells without refitting the commercial inverted fluorescence microscope. Spatially and temporally resolved exocytotic events from single cells on a microfluidic device were visualized in real time using fluorescence microscopy and were amperometrically recorded by the electrochemical system simultaneously. This coupled technique is simple and is hoped to provide new insights into the mechanisms responsible for the kinetics of exocytosis.
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87.80.Ek Mechanical and micromechanical techniques
87.17.-d Cell processes
87.15.R- Reactions and kinetics
82.80.Fk Electrochemical methods
87.80.Kc Electrochemical techniques
87.64.kv Fluorescence

Optical manipulation and binding of microrods with multiple traps enabled in an inclined dual-fiber system

Yuxiang Liu and Miao Yu

Biomicrofluidics 4, 043010 (2010); http://dx.doi.org/10.1063/1.3504716 (12 pages) | Cited 1 time

Online Publication Date: 30 December 2010

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We present experimental demonstrations of optical manipulation and optical binding of microscopic glass rods using the multiple traps created by a dual-fiber optical trapping system. Trapping, alignment, rotation, and stacking of glass rods were realized. To the best of our knowledge, this is the first time that cylindrical particles are optically trapped and bound by an optical fiber-based system. The optical manipulation of rods is also investigated through numerical simulations, which are used to quantitatively explain the experimental results. The ability of manipulating multiple particles of different shapes, as well as the integrable nature of the fiber-based setup, bestows the system the potential to be used in microfluidic systems for versatile particle manipulations.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.25.Ja Polarization

Transmittance tuning by particle chain polarization in electrowetting-driven droplets

Shih-Kang Fan, Cheng-Pu Chiu, and Po-Wen Huang

Biomicrofluidics 4, 043011 (2010); http://dx.doi.org/10.1063/1.3516656 (8 pages)

Online Publication Date: 30 December 2010

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A tiny droplet containing nano/microparticles commonly handled in digital microfluidic lab-on-a-chip is regarded as a micro-optical component with tunable transmittance at programmable positions for the application of micro-opto-fluidic-systems. Cross-scale electric manipulations of droplets on a millimeter scale as well as suspended particles on a micrometer scale are demonstrated by electrowetting-on-dielectric (EWOD) and particle chain polarization, respectively. By applying electric fields at proper frequency ranges, EWOD and polarization can be selectively achieved in designed and fabricated parallel plate devices. At low frequencies, the applied signal generates EWOD to pump suspension droplets. The evenly dispersed particles reflect and/or absorb the incident light to exhibit a reflective or dark droplet. When sufficiently high frequencies are used on to the nonsegmented parallel electrodes, a uniform electric field is established across the liquid to polarize the dispersed neutral particles. The induced dipole moments attract the particles each other to form particle chains and increase the transmittance of the suspension, demonstrating a transmissive or bright droplet. In addition, the reflectance of the droplet is measured at various frequencies with different amplitudes.
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87.80.Ek Mechanical and micromechanical techniques
47.85.Np Fluidics
47.55.D- Drops and bubbles
82.70.Kj Emulsions and suspensions
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Optofluidic tweezer on a chip

K. Ono, S. Kaneda, T. Shiraishi, and T. Fujii

Biomicrofluidics 4, 043012 (2010); http://dx.doi.org/10.1063/1.3509436 (6 pages)

Online Publication Date: 30 December 2010

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A novel method to realize an optical tweezer involving optofluidic operation in a microchannel is proposed. To manipulate the optical tweezer, light from an optical fiber is passed through both PDMS (polydimethylsiloxane)-air surface lenses and an optofluidic region, which is located in a control channel. Two liquids with different refractive indices (RIs) are introduced into the control channel to form two different flow patterns (i.e., laminar and segmented flows), depending on the liquid compositions, the channel geometry, and the flow rates. By altering the shapes of the interface of the two liquids in the optofluidic region, we can continuously or intermittently control the optical paths of the light. To demonstrate the functionality of the proposed method, optical tweezer operations on a chip are performed. Changing the flow pattern of two liquids with different RIs in the optofluidic region results in successful trapping of a 25 μm diameter microsphere and its displacement by 15 μm.
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87.80.Cc Optical trapping
87.80.Ek Mechanical and micromechanical techniques
42.50.Wk Mechanical effects of light on material media, microstructures and particles
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
47.54.Fj Chemical and biological applications

Tunable visual color filter using microfluidic grating

Z. G. Li, Y. Yang, X. M. Zhang, A. Q. Liu, J. B. Zhang, L. Cheng, and Z. H. Li

Biomicrofluidics 4, 043013 (2010); http://dx.doi.org/10.1063/1.3491469 (7 pages)

Online Publication Date: 30 December 2010

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This paper reports a tunable visual color filter based on a microfluidic transmission grating. The grating lines are formed by the microflows in an array of evenly spaced straight microchannels. In experimental study, the transmission of white light measures a shift of visual color from red to blue in the zeroth order diffraction in response to a change of the refractive index from 1.3290 to 1.3782 in the microflows. The merit of large tunability of transmission peak (Δλ = 408 nm) makes this grating potential for various applications in biological and chemical measurements, such as space- and time-resolving micropattern spectrophotometers and separation of the fluorescence from the excitation.
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42.79.Ci Filters, zone plates, and polarizers
42.25.Bs Wave propagation, transmission and absorption
42.79.Dj Gratings

Optofluidic in situ maskless lithography of charge selective nanoporous hydrogel for DNA preconcentration

Hyoki Kim, Junhoi Kim, Eun-Geun Kim, Austen James Heinz, Sunghoon Kwon, and Honggu Chun

Biomicrofluidics 4, 043014 (2010); http://dx.doi.org/10.1063/1.3516037 (9 pages)

Online Publication Date: 30 December 2010

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An optofluidic maskless photopolymerization process was developed for in situ negatively charged nanoporous hydrogel [poly-AMPS (2-acrylamido-2-methyl-1-propanesulfonic acid)] fabrication. The optofluidic maskless lithography system, which combines a high power UV source and digital mirror device, enables fast polymerization of arbitrary shaped hydrogels in a microfluidic device. The poly-AMPS hydrogel structures were positioned near the intersections of two microchannels, and were used as a cation-selective filter for biological sample preconcentration. Preconcentration dynamics as well as the fabricated polymer shape were analyzed in three-dimensions using fluorescein sample and a confocal microscope. Finally, single-stranded DNA preconcentration was demonstrated for polymerase chain reaction-free signal enhancement.
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82.35.Pq Biopolymers, biopolymerization
82.50.-m Photochemistry
82.70.Gg Gels and sols
81.16.Nd Micro- and nanolithography
87.14.gk DNA
87.80.Ek Mechanical and micromechanical techniques
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Integrated electrical concentration and lysis of cells in a microfluidic chip

Christopher Church, Junjie Zhu, Guohui Huang, Tzuen-Rong Tzeng, and Xiangchun Xuan

Biomicrofluidics 4, 044101 (2010); http://dx.doi.org/10.1063/1.3496358 (10 pages) | Cited 3 times

Online Publication Date: 1 October 2010

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Lysing cells is an important step in the analysis of intracellular contents. Concentrating cells is often required in order to acquire adequate cells for lysis. This work presents an integrated concentration and lysis of mammalian cells in a constriction microchannel using dc-biased ac electric fields. By adjusting the dc component, the electrokinetic cell motion can be precisely controlled, leading to an easy switch between concentration and lysis of red blood cells in the channel constriction. These two operations are also used in conjunction to demonstrate a continuous concentration and separation of leukemia cells from red blood cells in the same microchannel. The observed cell behaviors agree reasonably with the simulation results.
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87.17.Jj Cell locomotion, chemotaxis
87.17.Aa Modeling, computer simulation of cell processes
87.16.Uv Active transport processes
82.45.Jn Surface structure, reactivity and catalysis
87.80.Ek Mechanical and micromechanical techniques

Thermal mixing of two miscible fluids in a T-shaped microchannel

Bin Xu, Teck Neng Wong, Nam-Trung Nguyen, Zhizhao Che, and John Chee Kiong Chai

Biomicrofluidics 4, 044102 (2010); http://dx.doi.org/10.1063/1.3496359 (13 pages) | Cited 1 time

Online Publication Date: 1 October 2010

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In this paper, thermal mixing characteristics of two miscible fluids in a T-shaped microchannel are investigated theoretically, experimentally, and numerically. Thermal mixing processes in a T-shaped microchannel are divided into two zones, consisting of a T-junction and a mixing channel. An analytical two-dimensional model was first built to describe the heat transfer processes in the mixing channel. In the experiments, de-ionized water was employed as the working fluid. Laser induced fluorescence method was used to measure the fluid temperature field in the microchannel. Different combinations of flow rate ratios were studied to investigate the thermal mixing characteristics in the microchannel. At the T-junction, thermal diffusion is found to be dominant in this area due to the striation in the temperature contours. In the mixing channel, heat transfer processes are found to be controlled by thermal diffusion and convection. Measured temperature profiles at the T-junction and mixing channel are compared with analytical model and numerical simulation, respectively.
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87.80.Ek Mechanical and micromechanical techniques
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
07.10.Cm Micromechanical devices and systems
47.27.te Turbulent convective heat transfer

Observation of hydrophobic-like behavior in geometrically patterned hydrophilic microchannels

G. O. F. Parikesit, E. X. Vrouwe, M. T. Blom, and J. Westerweel

Biomicrofluidics 4, 044103 (2010); http://dx.doi.org/10.1063/1.3499416 (7 pages) | Cited 4 times

Online Publication Date: 8 October 2010

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We present our observation of meta-hydrophobicity, where geometrically patterned surfaces make hydrophilic microchannels exhibit hydrophobic-like behaviors. We analyze the wetting-induced energy decrease that results from the surface geometries and experimentally demonstrate how those geometries can modulate the dynamics of capillary-driven wetting and evaporation-driven drying of microfluidic systems. Our results also show that the modulated wetting dynamics can be employed to generate regulated patterns of microbubbles.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels
68.08.Bc Wetting
47.55.nb Capillary and thermocapillary flows
47.55.D- Drops and bubbles

An integrated microfluidic cell array for apoptosis and proliferation analysis induction of breast cancer cells

Huixue Song, Tan Chen, Baoyue Zhang, Yifan Ma, and Zhanhui Wang

Biomicrofluidics 4, 044104 (2010); http://dx.doi.org/10.1063/1.3497376 (10 pages) | Cited 4 times

Online Publication Date: 8 October 2010

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In vitro sensitivity testing of tumor cells could rationalize and improve the choice of chemotherapy and hormone therapy. In this report, a microfluidic device made from poly(dimethylsiloxane) and glass was developed for an assay of drug induced cytotoxicity. We evaluated the apoptotic and proliferation-inhibitory effects of anticancer drugs mitomycin C (MMC) and tamoxifen (TAM) using MCF-7 breast cancer cells. MMC and TAM both induced apoptosis and inhibited proliferation of MCF-7 cells in a concentration-dependent manner. MMC caused the expression of antiapoptotic protein Bcl-2 a dose-dependent reduction in MCF-7 cells. The expression of Bcl-2 did not change significantly in MCF-7 cells treated by TAM. The results in the microfluidic device were correlated well with the data obtained from the parallel experiments carried out in the conventional culture plates. The developed microfluidic device could be a potential useful tool for high content screening and high throughput screening research.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
87.80.Ek Mechanical and micromechanical techniques
87.17.-d Cell processes

A microfluidic platform for generation of sharp gradients in open-access culture

David M. Cate, Christopher G. Sip, and Albert Folch

Biomicrofluidics 4, 044105 (2010); http://dx.doi.org/10.1063/1.3490784 (10 pages) | Cited 2 times

Online Publication Date: 2 November 2010

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Control of the 3D microenvironment for cultured cells is essential for understanding the complex relationships that biomolecular concentration gradients have on cellular growth, regeneration, and differentiation. This paper reports a microfluidic device for delivering gradients of soluble molecules to cells in an open reservoir without exposing the cells to flow. The cells are cultured on a polyester membrane that shields them from the flow that delivers the gradient. A novel “lid” design is implemented which prevents leakage from around the membrane without requiring sealing agents or adhesives. Once layers are molded, device fabrication can be performed within minutes while at room temperature. Surface gradients were characterized with epifluorescence microscopy; image analysis verified that sharp gradients ( ∼ 33 μm wide) can be reproducibly generated. We show that heterogeneous laminar flow patterns of Orange and Green Cell Tracker (CT) applied beneath the membrane can be localized to cells cultured on the other side; concentration profile scans show the extent of CT diffusion parallel to the membrane’s surface to be 10–20 μm. Our device is ideal for conventional cell culture because the cell culture surface is readily accessible to physical manipulation (e.g., micropipette access), the cell culture medium is in direct contact with the incubator atmosphere (i.e., no special protocols for ensuring proper equilibration of gas concentrations are required), and the cells are not subjected to flow-induced shear forces, which are advantageous attributes not commonly found in closed-channel microfluidic designs.
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87.80.Ek Mechanical and micromechanical techniques
87.17.-d Cell processes
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.63.-b Biological fluid dynamics
87.85.gf Fluid mechanics and rheology

Specific binding and magnetic concentration of CD8+ T-lymphocytes on electrowetting-on-dielectric platform

Gaurav J. Shah, Jeffrey L. Veale, Yael Korin, Elaine F. Reed, H. Albin Gritsch, and Chang-Jin “CJ” Kim

Biomicrofluidics 4, 044106 (2010); http://dx.doi.org/10.1063/1.3509457 (12 pages)

Online Publication Date: 10 November 2010

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In the quest to create a low-power portable lab-on-a-chip system, we demonstrate the specific binding and concentration of human CD8+ T-lymphocytes on an electrowetting-on-dielectric (EWOD)-based digital microfluidic platform using antibody-conjugated magnetic beads (MB-Abs). By using a small quantity of nonionic surfactant, we enable the human cell-based assays with selective magnetic binding on the EWOD device in an air environment. High binding efficiency ( ∼ 92%) of specific cells on MB-Abs is achieved due to the intimate contact between the cells and the magnetic beads (MBs) produced by the circulating flow within the small droplet. MBs have been used and cells manipulated in the droplets actuated by EWOD before; reported here is a cell assay of a clinical protocol on the EWOD device in air environment. The present technique can be further extended to capture other types of cells by suitable surface modification on the MBs.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
47.85.-g Applied fluid mechanics
87.17.-d Cell processes
87.19.U- Hemodynamics
87.85.gf Fluid mechanics and rheology

Thermomodulated cell culture/harvest in polydimethylsiloxane microchannels with poly(N-isopropylacrylamide)-grafted surface

Dan Ma, Hengwu Chen, Zhiming Li, and Qiaohong He

Biomicrofluidics 4, 044107 (2010); http://dx.doi.org/10.1063/1.3516038 (8 pages) | Cited 3 times

Online Publication Date: 19 November 2010

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Cell culture and harvest are the most upstream operation for a completely integrated cell assay chip. In our previous work, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was successfully grafted onto polydimethylsiloxane (PDMS) surface via benzophenone-initiated photopolymerization. In the present work, the PNIPAAm-grafted-PDMS (PNIPAAm-g-PDMS) surface was explored for thermomodulated cell culture and noninvasive harvest in microfluidic channels. Using COS 7 fibroblast from African green monkey kidney as the model cells, the thermomodulated adhering and detaching behaviors of the cells on the PNIPAAm-g-PDMS surfaces were optimized with respect to PNIPAAm-grafting yields and gelatin modification. The viability of the cells cultured on and harvested from the PNIPAAm-g-PDMS surface with the thermomodulated noninvasive protocol was estimated against the traditional cell culture/harvest method involving trypsin digestion. The configuration of the microchannel on the PNIPAAm-g-PDMS chip was evaluated for static cell culture. Using a pipette-shaped PNIPAAm-g-PDMS microchannel, long-term cell culture could be achieved at 37 °C with periodic change of the culture medium every 12 h. After moving the microchip from the incubator set at 37 °C to the room temperature, the proliferated cells could be spontaneously detached from the PNIPAAm-g-PDMS surface of the upstream chamber and transferred by a gentle fluid flow to the downstream chamber, wherein the transferred cells could be subcultured. The thermomodulated cell culture, harvest, and passage operations on the PNIPAAm-g-PDMS microfluidic channels were demonstrated.
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87.17.Rt Cell adhesion and cell mechanics
87.16.-b Subcellular structure and processes
87.18.-h Biological complexity
87.80.Ek Mechanical and micromechanical techniques

A novel micropump droplet generator for aerosol drug delivery: Design simulations

Guoguang Su, P. Worth Longest, and Ramana M. Pidaparti

Biomicrofluidics 4, 044108 (2010); http://dx.doi.org/10.1063/1.3517231 (18 pages) | Cited 2 times

Online Publication Date: 19 November 2010

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One challenge of generating a liquid aerosol is finding an efficient way to break up bulk amounts of the compound into micron-sized droplets. Traditional methods of aerosol generation focus on the principle of creating the liquid droplets by blowing air at high speed over or through a liquid. In this study, a novel micropump droplet generator (MDG) is proposed based on a microfluidics device to produce monodisperse droplets on demand (DoD). The micropump design was employed to both pump the fluid into the air and to encourage droplet breakup and aerosol formation. Computational simulation modeling of the new MDG was developed and validated with comparisons to experimental data for current generators. The device was found to produce an aerosol similar to a vibrating orifice DoD device. Most importantly, the input power required by the newly proposed device (MDG) was several orders of magnitude below existing DoD generators for a similar droplet output. Based on the simulation results obtained in comparison with current DoD generators, the MDG device performed effectively at higher frequencies, smaller nozzle diameters, and regardless of the liquid viscosity of the solution.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
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