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grown to sub-confluence were washed with phosphate-buffered saline (PBS, Biochrome, pH 7.4) and harvested by a 5-min treatment with 0.25% Trypsin and 0.02% EDTA (Sigma, US). The cells for the experiments were then suspended in a sucrose solution with an 8.62 wt% and a measured conductivity of 1.76×10 -3 S/m. For the dielectrophoresis of cells, the sucrose solution was employed to raise the osmolarity to the normal physiological level. IV. RESULTS AND DISCUSSION Numerical simulations of the electric field were performed using commercial software CFDRC-ACE + (ESI Group, France). The effect of the presence of particles on the electric field was not considered in the simulation for the sake of simplification. After applying 16 volts from the outer microelectrode pair to the central pair of microelectrodes subsequently, the simulated square of the electric field (E 2 ) was revealed, as shown in Fig. 4. The numerical results indicate that the high-electric-field region moved to where the electric field was applied, and its area decreased according to the pattern of the microelectrodes. Therefore, HeLa cells with positive dielectrophoretic response were conveyed in the direction of the stepping electric field, which is toward the center of the microchamber and concentrated at the central pair of electrodes, demonstrating the realization of the concept of the present design. The preliminary experiment for cellular enrichment was investigated herein, as depicted in Fig. 5. The HeLa cells, with a concentration of 5×10 5 cells/mL, were introduced into the microchamber using a pipette. About 50 cells were in the microchamber. The peak-to-peak voltage of 16 volts and a frequency of 600 kHz were applied to the electrodes. The electric field at the peripheral pair of electrodes was turned on to aggregate the cells. The electric field was held for about 20 seconds and then switched to the next adjacent pair of electrodes. The duration of cellular concentration from the outermost to the central pair of microelectrodes was about 160 seconds. The experimental results indicate that the enrichment of HeLa cells were successfully exhibited at the center pair of microelectrodes. Furthermore, the experimental results indicate that the HeLa cells were successfully concentrated at the center pair of microelectrodes with an approximate efficiency of 75%. V. CONCLUSIONS A handheld device providing the stepping electric fields and a dielectrophoretic microchip with circular microelectrode for cellular enrichment was proposed and demonstrated in the present study. The positive dielectrophoretic cells were conveyed due to the movement 11-13 May 2011, Aix-en-Provence, France of the high-electric-field region. Furthermore, the cells were concentrated at the center pair of microelectrodes due to the fact that the area of the high-electric-field between the adjacent electrodes was gradually decreased from the peripheral to the center pair of microelectrodes. The preliminary experiment for cellular enrichment also indicated that the HeLa cells were successfully concentrated at the center pair of microelectrodes with an approximate efficiency of 75% when the time interval of relay switching was set at 20 s. The operational method of the cellular enrichment herein could enhance the sensitivity of further CTC detections. Besides, the handheld device presented in this work can be applied in point-of-care applications. ACKNOWLEDGMENT The authors would like to thank the National Science Council of the Republic of China for its financial support of this research under contract Nos. NSC-99-2923-E-194-001-MY3 and NSC-99-2221-E-194-014. In addition, the National Center for High-Performance Computing for the use of computer time and its facilities is also acknowledged. REFERENCES [1] Mostert B., Sleijfer S., Foekens J.A., Gratama J.W.: “Circulating tumor cells (CTCs): Detection methods and their clinical relevance in breast cancer,” Cancer Treat. Rev., 2009, 35, pp. 463-474 [2] Cheng X., Gupta A., Chen C., Tompkins R.G., Rodriguez W. and Toner M.: “Enhancing the performance of a point-of-care CD4+ T-cell counting microchip through monocyte depletion for HIV/AIDS diagnostics,” Lab Chip, 2009, 9, pp. 1357-1364 [3] Paterlini-Brechot P.and Benali N.L.: “Circulating tumor cells (CTC) detection: Clinical impact and future directions,” Cancer Lett., 2007, 253, pp. 180-204. [4] Grodzinski P., Yang J., Liu R.H. and Ward M.D.: “A modular microfluidic system for cell pre-concentration and genetic sample preparation,” Biomed. Microdevices, 2003, 5, pp. 303-310 [5] Dharmasiri U., Witek M.A., Adams A.A., and Soper S. A.: “Microsystems for the capture of low-abundance cells,” Ann. Rev. Anal. Chem., 2010, 3, pp. 409-431. [6] Pohl H.A.: Dielectrophoresis, Cambridge University Press, New York, 1978. [7] Jones T.B. and Kraybill J.P.: “Active feedback-controlled dielectrophoretic levitation,” J. Appl. Phys., 1986, 60, pp. 1247-1252. [8] Ramos A., Morgan H., Green G.N. and Castellanos A.: “AC Electrokinetics: A review of forces in microelectrode structure,” J. Phys. D: Appl. Phys., 1998, 31, pp. 2338-2353. [9] Voldman J.: “Electrical forces for microscale cell manipulation,” Annu. Rev. Biomed. Eng., 2006, 8, pp. 425-454. [10] Jones T.B.: Electromechanics of particles, Cambridge University Press, New York, 1995. [11] Jen C.P. and Chen T.W.: “Selective trapping of live and dead mammalian cells using insulator-based dielectrophoresis within open-top microstructures,” Biomed. Microdevices, 2009, 11, pp. 597-607. 354
11-13 May 2011, Aix-en-Provence, France Figure 1: Operation concept of the cellular enrichment by dielectrophoresis in the stepping electric field. Figure 4: Simulated results of square of the electric field (E 2 ) while the electric field was applied from the peripheral to the center pair of microelectrodes. The voltage applied to the electrode pair is 16 volts. (a) (b) Figure 2: (a) Schematic diagram of the cellular microchip using dielectrophoresis and (b) the dimensions of the circular microelectrodes. (a) (b) Figure 5: Experimental results of enrichment for HeLa cells. The peak-to-peak voltage and frequency applied was 16 volts and 600 kHz, respectively. The time interval of relay switching was 20 seconds. The duration from (a) to (i) was about 160s. (c) Figure 3: The images of: (a) the fabricated chip for cellular enrichment, (b) circular microelectrodes and (c) the complete handheld microchip with the electric module providing the stepping electric field. ISBN:978-2-35500-013-3 355
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COLLECTION OF PAPERS PRESENTED AT T
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III
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V
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Table of Contents Wednesday 11 May
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PANEL DISCUSSION TEXTILE MICROSYSTE
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Friday 13 May SESSION C4: APPLICATI
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SPECIAL SESSION OF BIO-MEMS/NEMS a
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suspended membrane can be pulled to
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most likely due to not yet consider
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that detectors may measure the diff
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2) Cavity width effect To verify th
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Fig.9. Capacitive sensor output, Va
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The anode and cathode are connected
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! TABLE 3 SUMMARY OF SELECTIVITIES
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The fabrication of optical Cap-Wafe
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the glass is polished down in a cos
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Fig. 14. Time history of the envelo
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Y X Fig. 1. Scanning electron mic
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10 3 11-13 May 2011, Aix-en-Proven
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Intenstiy (counts/second) Fig. 1. X
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etween x 2 to L (remember that x 2
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piezoelectric displacement transduc
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Figure 7 Displacement conditions of
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A. Continuous domain Starting from
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Fig. 8. Central finite difference m
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700 11-13 May 2011, Aix-en-Provenc
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o o o o o o o o Check applicability
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C. Identification Results The ident
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The proposed solution for this prob
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teen wire segments of a coil, as in
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As the metallization is too reflect
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B. Implemented die overview A die c
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IN CLK OUT Fig. 16. Probe setup for
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adhesive material with 30μm thickn
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B. Dynamics of Energy Flows For a l
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fibers which define the electric co
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Figure 15. Key board input system.
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ρ = h 2∆α∆T + + E 1h 3 1 +E 2
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inches silicon wafers which have th
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samples tested in different vacuum
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l c 11-13 May 2011, Aix-en-Provence
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Vp (V) 3,5 3,0 2,5 2,0 1,5 1,0 0,5
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II. MATHEMATICAL MODEL AND NUMERICA
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fluids travel along a curved channe
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measured mixing indices are depicte
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length, which enables them to focus
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however, a rotation for coincidence
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value of every active channel. Ther
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electrocardiogram. • The heart be
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coefficient compatible with the mic
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Variable Description Value Crab-leg
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REFERENCES [1] G. Mehta, J. Lee, W.
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followed by titanium (Ti) which sho
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exposure dose, post exposure bake t
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B. Energy Applications Society is f
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Presently, the microfabrication pro
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