A

mciTm©

K

1

LalsipuptOswcnbeimfl

0d

Sensors and Actuators B 123 (2007) 628–635

A cost effective, re-configurable electrokinetic microfluidic chip platform

Colin Dalton, Karan V.I.S. Kaler ∗BioSystems Research and Applications Group, Department of Electrical and Computer Engineering, Schulich School of Engineering,

University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Received 27 March 2006; received in revised form 29 August 2006; accepted 30 August 2006Available online 6 October 2006

bstract

A reconfigurable microfluidic chip system is described which facilitates multiple electrode contacts to a PDMS micro-fluidic chip. The PDMSicro-channels are reversibly bonded on to the chip, and are readily removed for cleaning, changing analytes or to allow different micro-fluidic

hannel or electrode geometries to be used. Up to 60 independent electrical connections to the on-chip microelectrodes are provided by a zero

nsertion force connector (ZIF). As well as forming a reliable electrical connection, the ZIF socket allows the quick and easy changing of chips.he system is flexible and ideal for many different types of electrokinetic research. The system allows cost effective, rapid prototyping of bothicroelectrode designs and microfluidic systems using standard microfabrication techniques, available to most research groups.2006 Elsevier B.V. All rights reserved.

AS);

iepit

ipnfmct

ehemt

eywords: Dielectrophoresis; Electrorotation; Micro-total-analysis-system (�T

. Introduction

There has been considerable development and application ofab-on-a-Chip technology in recent years due to its inherentdvantages. These include the cost effective implementation ofaboratory sample preparation, rapid processing and analysis ofamples, particle detection and manipulation as well as non-nvasive techniques, such as dielectrophoresis, which allow therocessed samples to be used for further on or off-chip testssing other methods. Utilising Lab-on-a-Chip technology torocess very small volumes of analyte allows for very sensi-ive and rapid processing in a controlled and accurate manner.ne possible application is rapidly analysing a patient’s blood

ample. By combining the appropriate chemical and bio-sensorsith any required actuators, it is possible to obtain a range of

linically relevant measurements within seconds. The sensitiveon-invasive cell manipulation and cell separation capability cane utilized to affect or aid clinical diagnostics of blood borne dis-ases and cancers [1,2]. Discrimination of cell subpopulations

n cell suspensions has traditionally been accomplished by suchethods as affinity chromatography [3], centrifugation [4] oruorescence activated cell-sorting [5] for physiologically del-

∗ Corresponding author. Tel.: +1 403 220 5809; fax: +1 403 282 6855.E-mail address: kaler@ucalgary.ca (K.V.I.S. Kaler).

cpmtbvm

925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2006.08.036

Microfluidic; Re-configurable; PDMS

cate mammalian cells, all of which involve rather bulky andxpensive laboratory equipment. Such cell manipulation androcessing functions can be more compactly implemented byntegrating the domains of microfluidics and ac particle elec-rokinetics.

ac electrokinetic techniques can be readily implemented andntegrated to microfluidic channels by employing and housinglanar microelectrodes on to one or more sides of the microchan-el structures. ac electrokinetic techniques are particularly use-ully as they provide a variety of cellular and other bioparticleanipulations not possible using electrophoresis since biologi-

al particles in suspension have similar electrophoretic mobili-ies, thus making it difficult to distinguish between them.

The electrokinetic methods of dielectrophoresis (DEP), trav-lling wave dielectrophoresis (TWD) and electrorotation (ROT)ave been extensively studied, both from a theoretical and anxperimental perspective, and can be used for the controlledanipulation, isolation, concentration, separation and charac-

erization of electrically polarizable particles, such as intactells and even macromolecules. In biological studies, thesearticles have included proteins, viruses, bacteria, cells andicro-organisms [6–8]. Dielectrophoresis has also been used

o identify, separate, collect and manipulate biological and non-iological particles [9–15] and has been usefully applied in aariety of biotechnology and clinical applications requiring cellanipulation [16–24].

s and

bpnsotbt

vqttowtbemtnrap

LioieuPtnTasT

at

2

seats

2

stmei6sstbptaLecat

r

Ft

C. Dalton, K.V.I.S. Kaler / Sensor

DEP, TWD and ROT in Lab-on-a-Chip applications haveeen recently reviewed [20,25–29] and there have been severalapers published that combine two or more of the DEP tech-iques onto a single chip [10,30–32] The advantages of suchystems are to aid the manipulation or characterisation of cellsn chip, an important step in realising Lab-on-a-Chip and micro-otal-analysis (�TAS) devices, and as such several systems haveeen described that facilitate multiple DEP electrode configura-ions under external PC control [18,33–36].

All of the above devices required complex (and sometimesery expensive) fabrication methods, could not be easily oruickly redesigned and had limited operational lifetimes dueo electrode degradation or microfluidic channel blockage byhe particles under test. Recently an attempt to overcome somef these constraints was presented by Rajaraman et al. [37],ho investigated four different rapid, low cost microfabrication

echnologies for the production of a micro-fluidic layer toe placed over a photo-lithographically fabricated glass DEPlectrode chip. Although Rajaraman et al showed that theicrofluidic layer could be designed quickly and at low cost,

heir fabrication methods all resulted in devices that were perma-ently sealed to the DEP electrode layer. The bonding methodseported were epoxies and thermo-compression bonding, andll electrical connections were manually wire bonded intolace.

In this paper we present a simple, modular and low costab-on-a-Chip platform that allows rapid design iterations to be

mplemented without the need for re-wiring or re-positioningf a chip. Up to 60 metal (chrome–gold) electrodes can bendependently addressed in the present system, thus enablingxperimentation with multiple electrokinetic electrode config-rations, such as DEP, ROT and TWD, on the same chip. TheDMS layer housing the microfluidic channels can be removed

o aid cleaning of the electrode layer or for the installation of aew PDMS microfluidic layer onto the existing electrode chip.

his feature prolongs the operational lifetime of the electrodesnd cuts costs and time by not having to fabricate a new electrodeet each time the fluidic layer needs to be replaced or modified.he test system was assembled using off the shelf components

1cpe

ig. 1. Four inputs linked to the electrodes via jumper pin system. In the image, inphe ground return). From pin nine onwards, the configuration is for TWD or ROT, i.e

Actuators B 123 (2007) 628–635 629

nd standard processes, thus making it cost effective and simpleo fabricate, and highly suitable for the research community.

. Materials and methods

The implementation of the system consists of three separateections. A printed circuit board (PCB) section that provides thelectrical connections and physical base for the test assembly,glass chip section that houses the photolithographically pat-

erned planar metal electrodes and the PDMS microfludic layerection attached on top of the glass section.

.1. PCB design

A standard two layer PCB was designed to fit into the viewingtage of an optical microscope (Olympus BX-51). The PCB sec-ion also housed the electrical interconnects that facilitated the

ultiplexing of the four input signal lines (A–D) to 60 on-chiplectrodes. A jumper pin connection system was used to facil-tate flexible configuration of the four input connections to the0 electrodes. A schematic and picture of the actual jumper pinystem is shown in Fig. 1. The physical limitation of the micro-cope stage viewing slot dictated the size of the PCB and hencehe jumper pin layout. However, smaller pitch jumper pins cane used, although this would make the set up of the 60 jumperins a more delicate and tedious task. Another viable option iso employ solid state relays. Ultimately the system can be fullyutomated using an FPGA system linked to a computer runningabView, which could also control the four input signals. In thexample chip described in this paper, the on chip electrodes areonfigured to allow DEP, ROT and TWD operation. However,ny desired electrode configuration can be implemented withinhe size limitations given.

A standard ZIF socket (Meritec, Canada) was modified byemoving the physical alignment block between pins 11 and

2. This allowed the 1mm thick patterned gold/chrome glasships to be inserted. The glass chips were patterned by standardhotolithography to have a compatible set of standard ZIFlectrode contacts. These contacts allow the on-chip electrodes

ut A is supplying a DEP signal to the first eight electrodes (B is being used as. supplying four inputs alternatively to the electrode array.

6 s and

tut

DwP∼

2

imtea3tc

ospwmfhfoosbe

2

ttvsZucsAG5

Ugdttt(

pastUltm

ei15itotanbd

2

mmtrueoitaavc2[e1acPtnta

Ds#

30 C. Dalton, K.V.I.S. Kaler / Sensor

o be accessed individually. This connection system is of partic-lar advantage for TWD operation, as it is far less complicatedo fabricate than those previously reported [10,38–40].

All of the components were ‘off the shelf’ and bought fromigiKey Corporation, Canada, bar the ZIF socket. The PCBas fabricated by AP Circuits, Alberta, Canada. The completeCB unit, including connectors, pins, ZIF socket and cables costUS$250.

.2. Electrical connection

The ZIF socket allows the glass chips to be quickly and easilynserted and removed from the system. ZIF sockets are further-

ore designed for repeatable and reliable contact alignment, andhe physical PCI based locator (glass chip length) works repeat-dly, with no misalignment. This necessitates that the glass chipsre cut to size accurately and reliably using a dicing saw (DAD21, Disco Hi-Tec America). The ZIF system also means thathere is less damage to electrode contacts, allowing repeatedhip usage and prolonging chip lifetime.

By reducing the area taken by the jumper pins, 60 electrodesn the underside of the PCB could be accessed via the ZIFocket, allowing up to 120 on chip electrodes to be addressed (60er side). However, the PCB layout would get complicated; asould the glass chip fabrication since double sided mask align-ent would be required. For some instances, accessing only a

ew underside electrodes could be advantageous, for example byaving a flip chip bonded sensor beneath a microfluidic channelor cell counting [41]. Another possible variant would be a sec-nd ZIF socket mounted on a ribbon cable that attached to thepposite side of the fixed ZIF socket, allowing a further 60 topide electrodes to be potentially addressed. Again, this woulde a more complicated PCB design, and would also reduce thelectrode active region.

.3. Glass chip fabrication

The glass chips, housing the microelectrodes, were 1 mmhick and 80 mm by 36 mm in size. The ZIF socket dictatedhe length of the glass chip, and the width was dictated by theiewing area of the microscope. Electrodes were patterned bytandard photolithography. Discounting the contact pads for theIF socket, any pattern of electrodes can be fabricated in thesable area of the chip, which is 25 mm × 80 mm. The chromehip mask was designed by mask layout software (L-Edit Ver-ion 7, Tanner) and fabricated at the NanoFab (University oflberta, Edmonton) using a Heidelberg DWL-200 Laser Patternenerator. The chip size allows for two designs on a standardin.2 chrome mask.

A Borofloat glass wafer (Silicon Valley Microsystems, CA,SA) was cleaned in piranha solution (1:3 by volume of hydro-en peroxide and sulphuric acid) rinsed in deionized water andried in an inert atmosphere. The glass substrate was then sput-

ered with a layer of chrome of thickness 20 nm and gold ofhickness ∼180 nm (KJLC-CMS-18HV, Kurt J Lesker, Clari-on, USA). The metalized glass substrate was then spin-coatedmodel # 5110-CD, Solitec Spinner, CA, USA) with positive

uaPp

Actuators B 123 (2007) 628–635

hotoresist HPR 504 (Microchem Co.) to a thickness of 1.3 �mnd then soft-baked in an oven at 110 ◦C for 30 min. UV expo-ure (8 s, 356 nm) of the spin-coated substrate was performedhrough the chrome mask using a mask aligner (ABM Inc., CA,SA). The substrate was then developed (Developer 354, Ship-

ey Microelectronics, MA, USA) for approximately 24 s, withhe end time determined by visible inspection under an optical

icroscope.To demonstrate the versatility of the system, several differ-

nt electrode geometries were fabricated onto one chip. Thesencluded three basic rotation chambers of inter electrode gaps00, 200 and 500 �m; two sets of 20 TWD electrodes, with 4 and�m electrode widths and four DEP structures, 50 and 100 �m

nter-digitated electrodes and 50 and 100 �m castellated elec-rodes. Fig. 2 shows the fabricated chip and magnified imagesf some of the electrode structures. An advantage of having allhe electrodes on the same chip is that various dielectrophoreticreas of the chip can all be coated with exactly the same thick-ess of dielectric material if required, prior to the PDMS layereing attached, thus allowing for truly comparative experimentalata to be obtained utilizing the different structures.

.4. PDMS fluidic layer

Poly(dimethylsiloxane) (PDMS), in many regards, is theaterial of choice for researchers for readily creatingicrostructures and micro-channels [42–45]. PDMS is one of

he most actively developed polymers for microfluidics, as iteduces the time, complexity and cost of prototyping and man-facturing [46,47]. This is due to several factors, including itsase of handling, good sealing properties at low temperatures,ptical transparency (wavelength down to 230 nm), chemicalnertness, flexibility, low surface charge, low electrical conduc-ivity and low cost. Traditional materials, such as glass, siliconnd quartz, are expensive and time consuming to use, as theyll require chemical etching of sacrificial layers through con-entional photolithographically produced masks. PDMS micro-hannels, however, can be fabricated by soft lithography within4 h and do not require specialized laboratories and equipment48,49]. Thus rapid prototyping of micro-channel designs canasily be achieved [45]. Replica moulds with feature sizes of0 nm can be achieved through the use of suitable masters. Andditional advantage is that once a design has been tested andompleted, the final functional device can also be fabricated fromDMS. PDMS is also bio-compatible due to it being permeable

o gases, non-permeable to water at moderate temperatures andon-toxic to cells [50,51]. The solvent compatibility and elec-rokinetic properties of PDMS have also been characterized andre well understood [52,53].

Prepolymer of PDMS and the curing agent (Sylgard 184,ow Corning, NC, USA) were mixed in proportions of 1:10,

tirred mechanically and degassed in a vacuum chamber (model1415M, Shelldon Lab, OR, USA) at 67 kPa for 20 min prior to

se. The mix was then poured into a polished CNC milled castluminium mold (Fig. 3) and cured at 60 ◦C for 1 h [54]. TheDMS replica was then carefully peeled from the mould andlaced onto the glass/electrode chip under manual pressure,

C. Dalton, K.V.I.S. Kaler / Sensors and Actuators B 123 (2007) 628–635 631

Fig. 2. Image of whole chip showing the gold/chrome TWD/DEP/ROT electrodes, ZIF alignment gap and 60 ZIF contact electrodes. 10× bright field imagess �m ce phoreo

fdghaFlq

ala

hown of 50 �m inter-digitated dielectrophoresis electrodes (bottom right); 50lectrorotation electrodes (top left) and 25 and 24 �m travelling wave dielectrof the TWD electrodes.

orming a weak but reversible seal. For experimentationescribed in this investigation, a strong seal between thelass and PDMS was not required. Strong reversible seals canowever be formed if required as detailed in [55]. We adopted

simpler method using a clear lacquer (Del Laboratories, Inc.,armingdale, NY) to form a seal around the edges of the PDMS

ayer. The lacquer adheres to both PDMS and glass, driesuickly and uniformly and is easily dissolved in acetone, thus

TaDc

astellated dielectrophoresis electrodes (top right); 200 �m inter electrode gapsis electrodes (bottom left). The top set of electrodes are for impedance testing

llowing quick and easy removal or replacement of the PDMSayer. As has been previously reported [56], acetone doesn’tdversely affect cured PDMS.

An overall view of the PDMS glass chip is shown in Fig. 4.

he meniscus formed around the posts during curing is visibleround the fluidic inlets and outlet. The inset shows the 100 �mEP castellated electrodes clearly visible through the PDMS

hamber.

632 C. Dalton, K.V.I.S. Kaler / Sensors and Actuators B 123 (2007) 628–635

Fbp

2

giphro

u2Pcafttpt

FtiP

Fig. 5. Complete system, showing signal generator, syringe pump, oscilloscope,isl

atacS

2

mfirtsfioimar

ig. 3. CNC milled cast aluminium mold (A) for fabricating microfluidic cham-ers and channels in PDMS (B) by replica molding. The smooth finish from theolished mold allows PDMS to seal to glass under no external pressure (bottom).

.5. Re-useable fluidic connection method

Fluidic connections between the macro and micro world areenerally problematic. A recent paper proposed re-usable multi-nlet PDMS micro fluidic connectors [57]. In that paper, lowressure connectors were fabricated by inserting tubing intooles in 3 or 6 mm thick cast PDMS layers. The connectorseportedly withstood flow rates of 0.05–5 �l/min, and a pressuref ∼8 kPa. For high pressure systems the authors used a jig.

In this paper we use a similar style of system, in that wese a compression fit method whereby tubing of outer diameter.25 mm is inserted into 2 mm diameter holes in the ∼2 mm thickDMS fluidic layer. As PDMS is elastomeric and self sealing, aompression seal is formed as the PDMS deforms (reversibly) toccommodate the slightly larger diameter tubing. The meniscusormed during curing of the PDMS layer (Fig. 4) aids struc-

ural support of the tubing. Extra structural support, so that theubing does not apply tangential stress to the PDMS layer, isrovided by a clear lacquer that is applied around the edges ofhe PDMS section. The lacquer is readily removed by acetone,

ig. 4. PDMS microfluidic layer on the glass chip. The meniscus formed aroundhe posts during curing is clearly visible around the fluidic inlets and outlet. Thenset shows the 100 �m DEP castellated electrodes clearly visible through theDMS chamber.

3

spttcttT

(cnnr

mage capture PC and camera fitted to an Olympus BX-51 microscope. The insethows a magnified image of the unit in place in the microscope stage, fitted withong working distance objectives.

llowing for easy removal of the PDMS layer. An advantage ofhe system presented here is that the PDMS layer is formed frommilled aluminium mould, which is simpler, quicker and more

ost effective to fabricate than the etched silicon route taken byaarela et al. [57].

.6. Complete system

Fig. 5 shows the complete unit secured in place on a motorisedicroscope stage. The jumper pins are set up for DEP to therst eight electrodes and TWD/ROT to the rest. The chip can beemoved simply by lowering the microscope stage and releasinghe ZIF socket—thus allowing for a chip to be cleaned or a newample to be loaded without disrupting the X–Y positioning oror the PDMS layer to be replaced entirely. If a sealed microflu-dic unit is required to operate at higher chamber pressuresr different materials are required to address bio-compatibilityssues with samples, an alternate approach reported by Rajara-

an et al. [37] can be used to fabricate the microfluidic section,nd utilized in the fabrication and fixturing of the glass chipeported in this work.

. Results

The PCB unit was mounted on the microscope stage andecured in place using screws, which provided a stable viewinglatform for electrokinetic experiments. Some minor changeso the PCB layout were performed to provide better access tohe four co-axial connecting ports, which enabled easier dis-onnection and re-connection of the input signal wires. Set-ing the jumper pin connectors was achieved in quicker timehan expected, taking only ∼3 min to configure the DEP andWD/ROT setup described.

Repeated insertion of the glass chip into the ZIF socketover 500 times) resulted in only minor scratches to the on-chip

hrome–gold electrode contact points, as expected, but this didot compromise the electrical connectivity. The electrical con-ection scheme provided by the ZIF socket to the chip showedeliable operation, with no degradation to the applied signal over

s and

asrespZtc

qHraqbrla

eoTetrBfltgtrFppit

teal2tadaa

4

ccval

rt

fmacDh∼siwi

siah5blsatr

A

NAtafAUF

R

C. Dalton, K.V.I.S. Kaler / Sensor

wide frequency range (1 Hz to 4 MHz). The physical alignmentystem worked repeatedly, with no incorrect alignments occur-ing. Having a precisely cut to size glass chip facilitated this. Tonsure that the glass chip was held level during experimentation,o that the viewing area was in the same focal plane, a small sup-ort bar under the edge of the chip that was not inserted into theIF socket was required. Alternatively, the viewing hole cut in

he PCB could be reduced and the PCB edge used to provide thehip support.

Removal of the PDMS layer by dissolving the adhesive lac-uer was simple to accomplish using acetone from a wash bottle.owever, once the PDMS microfluidic layer was removed, it was

equired that the glass chip be immersed in acetone and gentlygitated for about 20 min, to fully remove the remaining lac-uer. After this, the chip was placed in an ultrasonic cleaningath filled with DI water and agitated for ∼5 min to remove anyesidual acetone and ensure a clean surface for future PDMSayer attachment. The chip was dried under a stream of pure dryir.

The compression seal system for fluidic interconnects workedxtremely well, and was simple and easy to implement, requiringnly minor manual force to insert the tubing into the PDMS port.he tubing was removed and re-inserted several times duringxperimentation with no loss of seal. Using a Harvard Appara-us model 33 syringe pump, flow rates of up to 50 �l/min wereepeatedly passed through the entire system without leakage.y placing 15 �m latex beads (Duke Scientific, USA) into theuid, the equivalent particle velocity for these flow rates within

he DEP chamber was measured as 400 �m/s. For the channeleometries used, these flow rates equated to a nominal opera-ional pressure of 5 psi. The lacquer seal system failed at a flowate of 1 ml/min, which was equivalent to a pressure of 100 psi.or different channel geometries, the maximum fluid flow andressure will obviously be different. For higher flow rates andressures a support jig may be utilised to provide physical clamp-ng and also to distribute the tangential pressure of the tubing inhe PDMS ports.

The DEP, TWD and ROT sections of the chip, as described inhis paper, were tested with biological particles and functioned asxpected. Over 2500 mammalian cells were successfully trappednd concentrated from a flow of 50 �l/min over the 50 �m castel-ated array by positive DEP provided by an applied field ofMHz, 10 Vpp. The cells were subsequently released and levi-

ated above the array by negative DEP for removal under flow byn applied field of 10 kHz, 10 Vpp. The full DEP experimentalata obtained will be the subject of a forthcoming publication,s this paper is focussed on the system design, implementationnd operation.

. Conclusions

A test system that facilitates quick, reliable and repeatedhanges of electrokinetic microfluidic chip prototypes, with no

omplicated connectors, permanent soldering or mass of indi-idual physical connectors, has been presented. The system useszero insertion force electrical connector, increasing electrode

ifetime, facilitating easier chip changes and eliminating the

Actuators B 123 (2007) 628–635 633

equirement for via holes and/or multiple layer fabrication inhe case of TWD.

The availability of photolithography enables new chips to beabricated in-house, typically in less than a week (mask design,ask generation and chip fabrication). This allows researchersfast turnaround for fairly complex designs for a reasonable

ost. This group has previously implemented an integratedEP/ROT/TWD chip using 0.18 CMOS technology [10], whichad a turnaround time of ∼5 months and a far higher cost at$1200 US. This shows the flexibility and potential of this

ystem for researchers in a wide range of areas. Re-usable multi-nlet PDMS fluidic connectors have recently been reported thatould greatly aid the elution of samples on this device and

mprove its flexibility [57].Furthermore, the potential benefits of the PCB/ZIF base test

ystem as described here can be significant in terms of facilitat-ng the practical utility of fluidic microsystems. Commerciallyvailable Digital Data Synthesisers with back end analogueigh voltage gain stages can be configured to give four-phase,0 MHz, 10 Vpp outputs, ideal for DEP applications, and cane easily incorporated onto the PCB board footprint. Furtherevels of system integration, with microcontrollers, custom sen-ors and high voltage fluidic actuator CMOS chips can be eitherttached to the glass/electrode chip via flip chip bonding [41] oro the main PCB unit are anticipated and a current focus of ouresearch laboratory.

cknowledgements

The authors acknowledge the financial support provided bySERC under the Strategic Project Grant program, and thelberta Cancer Diagnostic Consortium (ACDC) to facilitate

his work. We thank Ranjit Prakash and Thiru Kanagasabap-thi in fabricating the glass chips. Part of the device micro-abrication work was performed at the University of Calgarydvanced Microsystems Integration Facility (AMIF) and theniversity of Alberta Micromachining and Nanofabricationacility (NanoFab).

eferences

[1] I.K. Glasgow, H.C. Zeringue, D.J. Beebe, S.-J. Choi, J.T. Lyman, N.G.Chan, M.B. Wheeler, Handling individual mammalian embryos usingmicrofluidics, IEEE Trans. Biomed. Eng. 48 (2001) 570–578.

[2] J. Yang, Y. Huang, X.B. Wang, F.F. Becker, P.R.C. Gascoyne, Cell sepa-ration on microfabricated electrodes using dielectrophoretic/gravitationalfield flow fractionation, Anal. Chem. 71 (1999) 911–918.

[3] R.E. Nordon, B.K. Milthorpe, K. Schindhelm, P.R. Slowiaczek, An exper-imental model of affinity cell separation, Cytometry 16 (1994) 25–33.

[4] H. Makinoshima, A. Nishimura, A. Ishihama, Fractionation of EscherichiaColi cell populations at different stages during growth transition to station-ary phase, Molec. Microbiol. 43 (2002) 269–279.

[5] I.H.Y. Yuk, S. Wildt, M. Jolicoeur, D.I.C. Wang, G. Stephanopoulos,A GFP-based screen for growth-arrested, recombinant protein-producing

cells, Biotechnol. Bioeng. 79 (2002) 74–82.

[6] C. Dalton, A.D. Goater, R. Pethig, H.V. Smith, Viability of Giardia intesti-nalis cysts and viability and sporulation state of Cyclospora cayetanensisoocysts determined by electrorotation, Appl. Environ. Microbiol. 67 (2001)586–590.

6 s and

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

34 C. Dalton, K.V.I.S. Kaler / Sensor

[7] P.R.C. Gascoyne, J.V. Vykoukal, J.A. Scwartz, T.J. Anderson, D.M. Vyk-oukal, K.W. Current, C. McConaghy, F.F. Becker, C. Andrews, Dielec-trophoresis based programmable fluidic processors, Lab Chip. (2004)299–309.

[8] R. Pethig, M.S. Talary, R.S. Lee, Enhancing travelling wave dielectrophore-sis with signal superposition, IEEE Eng. Med. Biol. Mag. (2003) 43–50.

[9] Y. Li, C. Dalton, H. Said, K.V.I.S. Kaler, An integrated microfluidic dielec-trophoretic (DEP) cell fractionation system, in: Proc. ICMM, 2005.

10] E.G. Cen, C. Dalton, Y. Li, S. Adamia, L.M. Pilarski, K.V.I.S. Kaler, Acombined dielectrophoresis, traveling wave dielectrophoresis and electro-rotation microchip for the manipulation and characterization of leukemiacells, J. Microbiol. Meth. 58 (2004) 387–401.

11] H. Morgan, N.G. Green, ac Electrokinetics: Colloids and Nanoparticles,Research Studies Press Ltd., Baldock, UK, 2003.

12] T.B. Jones, Electrostatics and the Lab-on a Chip, IOP Confer. Ser. 178(2004) 1–10.

13] J. Voldman, R.A. Braff, M. Toner, M.L. Gray, M.A. Schmidt, Holdingforces of single-particle dielectrophoretic traps, Biophys. J. 80 (2001)531–541.

14] F.F. Becker, X.B. Wang, Y. Huang, R. Pethig, J. Vykoukal, P.R.C. Gas-coyne, Separation of human breast-cancer cells from blood by differentialdielectric affinity, Proc. Natl. Acad. Sci. U.S.A. 92 (1995) 860–864.

15] R. Pethig, in: I. Karube (Ed.), Automation in Biotechnology, Elsevier, Ams-terdam, 1991, pp. 159–185.

16] J. Park, B. Kim, S.K. Choi, S. Hong, S.H. Lee, K.-L. Lee, An Efficientcell separation system using 3D-asymmetric microelectrodes, Lab. Chip 5(2005) 1264–1270.

17] C. Yu, J. Vykoukal, D.M. Vykoukal, J.A. Schwarz, L. Shi, P.R.C. Gascoyne,A three-dimensional dielectrophoretic particle focussing channel for micro-cytomety applications, J. Microelectromech. Sys. 14 (2005) 480–487.

18] P.R.C. Gascoyne, J.V. Vykoukal, J.A. Schwartz, T.J. Anderson, D.M.Vykoukal, K.W. Current, C. McConaghy, F.F. Becker, C. Andrews,Dielectrophoresis-based programmable fluidic processors, Lab. Chip 4(2004) 299–309.

19] E. Cummings, Streaming dielectrophoresis for continuous-flow microflu-idic devices, IEEE Eng. Med. Biol. Mag. (2003) 75–84.

20] R. Gambari, M. Borgatti, L. Altomare, N. Manaresi, G. Medoro, A. Romani,M. Tartagni, R. Guerrieri, Applications to cancer research of “Lab-on-a-Chip” devices based on dielectrophoresis (DEP), Technol. Cancer Res.Treat. 2 (2003) 31–39.

21] G. Medoro, N. Manaresi, A. Leonardi, L. Altomare, M. Tartagni, R. Guer-rieri, A Lab-on-a-Chip for cell detection and manipulation, IEEE Sens. J.3 (2003) 317–325.

22] Y. Li, K.V.I.S. Kaler, Dielectrophoretic fluidic cell fractionation system,Anal. Chim. Acta 507 (2004) 151–161.

23] M.P. Hughes, Strategies for dielectrophoretic separation in laboratory-on-a-chip systems, Electrophoresis 23 (2002) 2569–2582.

24] J. Cheng, E.L. Sheldon, L. Wu, M.J. Heller, J.P. O’Connell, Isolation ofcultured cervical carcinoma cells mixed with peripheral blood cells on abioelectronic chip, Anal. Chem. 70 (1998) 2321–2326.

25] C.F. Gonzalez, V.T. Remcho, Harnessing dielecric forces for separationsof cells, fine particles and macromolecules, J. Chromatogr. A 1079 (2005)59–68.

26] R. Pethig, R.S. Lee, M.S. Talary, Cell physiometry tools based on dielec-trophoresis, JALA (2004) 324–330.

27] C. Dalton, A.D. Goater, J.P.H. Burt, H.V. Smith, Analysis of parasites byelectrorotation, J. Appl. Microbiol. 96 (2004) 24–32.

28] P.K. Wong, T.-H. Wang, J.H. Deval, C.-M. Ho, Electrokinetics in microde-vices for biotechnology applications, IEEE/ASME Trans. Mechatron.(2004) 366–376.

29] C.-F. Chou, F. Zenhausern, Electrodeless dielectrophoresis for micro totalanalysis systems, IEEE Eng. Med. Biol. Mag. (2003) 62–67.

30] G. Medoro, N. Manaresi, A. Leonardi, L. Altomare, M. Tartagni, R. Guer-

rieri, A Lab-on-a-Chip for cell detection and manipulation, IEEE Sens.Conf. (2002) 472–477.

31] R. Pethig, Development of dielectrophoresis and related ac electrokineticeffects for biotechnological and clinical applications, Abstr. Papers Am.Chem. Soc. 219 (2000) 465–470.

[

Actuators B 123 (2007) 628–635

32] A.D. Goater, J.P.H. Burt, R. Pethig, A combined travelling wave dielec-trophoresis and electrorotation device: applied to the concentration andviability determination of Cryptosporidium, J. Phys. D Appl. Phys. 30(1997) L65–L69.

33] P.R.C. Gascoyne, J.V. Vykoukal, Dielectrophoresis based sample handlingin general purpose programmable diagnostic instruments, Proc. IEEE. 92(2004) 22–42.

34] N. Manaresi, A. Roman, G. Medero, L. Altomare, A. Leonardi, M. Tartagni,R. Guerrieri, A CMOS chip for individual cell manipulation and detection,IEEE J. Solid State Circuits 38 (2003) 2297–2305.

35] L. Altomare, M. Borgatti, G. Medoro, N. Manaresi, M. Tartagni, R. Guer-rieri, R. Gambari, Levitation and movement of human tumor cells using aprinted circuit board device based on software-controlled dielectrophoresis,Biotechnol. Bioeng. 82 (2003) 474–479.

36] R. Holzel, Single particle characterization and manipulation by oppositefield dielectrophoresis, J. Electrostat. 56 (2002) 435–447.

37] S. Rajaraman, H. Noh, P.J. Hesketh, D.S. Gottfried, Rapid, low cost micro-fabrication technologies towards realization of devices for dielectrophoreticmanipulation of particles and nanowires, Sens. Actuators B: Chem 114(2006) 293–401.

38] S. Archer, T.T. Li, A.T. Evans, S.T. Britland, H. Morgan, Cell reactionsto dielectrophoretic manipulation, Biochem. Biophys. Res. Comm. 257(1999) 687–698.

39] K.V.I.S. Kaler, J.P. Xie, T.B. Jones, R. Paul, Dual frequency dielec-trophoretic levitation, Biophys. J. 63 (1992) 58–69.

40] L. Cui, H. Morgan, Design and fabrication of travelling wave dielec-trophoresis structures, J. Micromech. Microeng. 10 (2000) 72–79.

41] L.F. Hartley, K.V.I.S. Kaler, O. Yadid-Pecht, Hybrid integration of an activepixel sensor and microfluidics for cytometry on a chip, IEEE Trans. CircuitsSyst.: Smart Sens., in press (special issue).

42] Y. Berdichevsky, J. Khandurina, A. Guttman, Y.H. Lo, UV/ozone modi-fication of poly(dimethylsiloxane) microfluidic channels, Sens. ActuatorsB: Chem. 97 (2004) 402–408.

43] W.M. Choi, O.O. Park, A soft-imprint technique for submicron structurefabrication via in situ polymerization, Nanotechnology 15 (2004) 135–138.

44] H. Makamba, J.H. Kim, K. Lim, N. Park, J.H. Hahn, Surface modifica-tion of poly(dimethylsiloxane) microchannels, Electrophoresis 24 (2003)3607–3619.

45] S.K. Sia, G.M. Whitesides, Microfluidic devices fabricated inpoly(dimethylsiloxane) for biological studies, Electrophoresis 24(2003) 3563–3576.

46] Y. Xia, G.M. Whitesides, Soft lithography, Angew. Chem. Int. Ed. English37 (1998) 551–575.

47] Y. Xia, G.M. Whitesides, Soft lithography, Ann. Rev. Mater. Sci. 28 (1998)153–184.

48] T. Thorsen, S.J. Maerkl, S.R. Quake, Microfluidic large-scale integration,Science 298 (2002) 580–584.

49] A.Y. Fu, H-P.M. Chou, C. Spence, F.H. Arnold, S.R. Quake, An integratedmicrofabricated cell sorter, Anal. Chem. 74 (2002) 2451–2457.

50] S.K. Sia, G.M. Whitesides, Microfluidic devices fabricated inpoly(dimethylsiloxane) for biological studies, Electrophoresis 24(21) (2003) 3563–3576.

51] M.T. Khorasani, H. Mirzadeh, In vitro blood compatibility of modifiedPDMS surfaces as superhydrophobic and superhydrophilic materials, J.Appl. Poly. Sci. 91 (2004) 2042–2047.

52] J.M. Lee, C. Park, G.M. Whitesides, Solvent compatibility ofpoly(dimethylsiloxane)-based microfluidic devices, Anal. Chem. 75 (2003)6544–6554.

53] A.-M. Spehar, S. Koster, V. Linder, S. Kulmala, N.F. deRooij, E.Verpoorte, H. Sigrist, W. Thormann, Electrokinetic characterizationof poly(dimethylsiloxane) microchannels, Electrophoresis 24 (2003)3674–3678.

54] J.C. McDonald, D.C. Duffy, J.R. Anderson, D.T. Chiu, H.W. Olivier,

J.A. Schuller, G.M. Whitesides, Fabrication of microfluidic systems inpoly(dimethylsiloxane), Electrophoresis 27 (2000) 27–40.

55] T.T. Kanagasabapathi, C. Dalton, K.V.I.S. Kaler, Design, developmentand experimental analysis of dielectrophoresis (DEP) in low cost PDMSmicrofluidic devices, in: Proceedings of ICMM, 2005.

s and

[

[

B

D1fga

aitt

D1fas

C. Dalton, K.V.I.S. Kaler / Sensor

56] J.M. Lee, C. Park, G.M. Whitesides, Solvent compatibility of poly(dime-thylsiloxane)-based microfluidic devices, Anal. Chem. 75 (2003)6544–6554.

57] V. Saarela, S. Franssila, S. Tuomokoski, S. Marttila, P. Ostman, T. Sikanen,T. Kotiaho, R. Kostiainen, Re-usable multi-inlet PDMS fluidic connector,Sens. Actuators B: Chem. 114 (2006) 552–557.

iographies

r. Colin Dalton received his electronic engineering BSc (Hons) degree in994 and his electronic materials MSc degree in 1998. He received his PhDrom the University of Wales, Bangor (UK) in 2002, working with the Pethigroup. He has since worked for the UK Lab-on-a-Chip Consortium and forScottish start up company. He is currently with the Biosystems Research

IacSd

Actuators B 123 (2007) 628–635 635

nd Applications Group at the University of Calgary and his research interestsnclude DEP, microfluidics, microfabrication and Lab-on-a-chip systems. Heeaches a graduate course in Microsystems Technologies and is a member ofhe IOP, IEE, IEEE and Mancef.

r. Karan V.I.S. Kaler was born in Ludhiana, Punjab (India) on 16 October951. He received BSc (Hons.) and PhD in 1974 and 1981 respectively, bothrom the University of Wales (UK). He is currently a Professor of Electricalnd Computer Engineering at the University of Calgary and a registered Profes-ional Engineer (PENG) in the Province of Alberta, Canada and a member of the

EEE. He has over 25 years of research experience in the field of Bioelectricsnd Biomedical Engineering. He heads the BioSystems Research and Appli-ations Group, which focuses on the development and integration of MEMS,ensors and Lab-on-a-chip technologies for bioanalysis, disease detection andiagnostics.