06327586

IEEE SENSORS JOURNAL, VOL. 13, NO. 2, FEBRUARY 2013 601

PDMS Microcantilever-Based Flow SensorIntegration for Lab-on-a-Chip

Amir Sanati Nezhad, Mahmood Ghanbari, Carlos G. Agudelo, Muthukumaran Packirisamy,Rama B. Bhat, and Anja Geitmann

Abstract— In this paper, a simple practical method is presentedto fabricate a high aspect ratio horizontal polydimethylsiloxane(PDMS) microcantilever-based flow sensor integrated into amicrofluidic device. A multilayer soft lithography process isdeveloped to fabricate a thin PDMS layer involving the PDMSmicrocantilever and the microfluidics network. A three-layer fab-rication technique is explored for the integration of the microflowmeter. The upper and lower PDMS layers are bonded to the thinlayer to release the microcantilever for free deflection. A 3-Dfinite element analysis is carried out to simulate fluid-structureinteraction and estimate cantilever deflection under various flowconditions. The dynamic range of flow rates that is detectableusing the flow sensor is assessed by both simulation and experi-mental methods and compared. Limited by the accuracy of the1.76-µm resolution of the image acquisition method, the presentsetup allows for flow rates as low as 35 µL/min to be detected.This is equal to 0.8-µN resolution in equivalent force at the tip.This flow meter can be integrated into any type of microfluidic-based lab-on-a-chip in which flow measurement is crucial, suchas flow cytometry and particle separation applications.

Index Terms— Flow sensor, lab-on-a-chip, multilayer softlithography, polydimethylsiloxane (PDMS) microcantilever.

I. INTRODUCTION

APPLICATION of microfluidic technology on lab-on-a-chip for biological and chemical processes has tremen-

dous potential. Chemical analysis, mixing, bio-sensing, andparticle separation are just a few examples of these applica-tions. Among those, particle sorting/separation [1] and cytom-etry [2] are extremely sensitive to the flow rate within themicrofluidic network. Therefore, flow meters integrated withina lab-on-a-chip to enable real time monitoring of the flow ratesignificantly improve the functionality of such a device.

Various flow meters have been reported in the literatureby employing micro-electro-mechanical systems (MEMS) to

Manuscript received May 8, 2012; revised August 19, 2012; acceptedOctober 1, 2012. Date of publication October 9, 2012; date of current versionJanuary 11, 2013. The associate editor coordinating the review of this paperand approving it for publication was Prof. Boris Stoeber.

A. S. Nezhad, M. Ghanbari, C. G. Agudelo, and M. Packirisamy are with theMechanical Engineering Department, Optical Bio-Microsystem Laboratory,Concordia University, Montreal, QC H3G 1M8, Canada (e-mail: [email protected]; [email protected]; [email protected]; [email protected]).

R. B. Bhat is with the Mechanical Engineering Department, Concordia Uni-versity, Montreal, QC H3G 1M8, Canada (e-mail: [email protected]).

A. Geitmann is with the Département de Sciences Biologiques, Institut deRecherche en Biologie Végétale, University of de Montreal, Montreal, QCH3T 1J4, Canada (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSEN.2012.2223667

miniaturize the flow sensor and to integrate it within themicrofluidic device in order to monitor locally the flow rate[3], [4]. Although these flow sensors have impressive per-formance, they usually involve complex fabrication includingmulti-step layer patterning which requires expensive facilities[5], [6]. Silicon or SU8 have mostly been used as a micro-mechanical element in the form of a microcantilever to sensethe flow drag force. Since these materials have high elasticmodulus, the deflection of the mechanical element is toosmall and has to be detected by employing advanced detectionmethods such as optical or electrical [7], [8]. Integration ofoptical or electrical components and their calibration is oftenelaborate and hence limits the application of these sensors forgeneral lab. In addition, living cells are sensitive to electricalfields and the use of electrical detection methods has thepotential to cause artifacts that make the interpretation ofstudies difficult [9]. Similarly, thermal flow sensors have thepotential to change the medium temperature [10]–[12] and aretherefore equally unsuitable for certain applications despitetheir simple readout system.

Besides conventional materials such as silicon or SU8 [13],Polydimethylsiloxane (PDMS) is a favorable alternative mater-ial due to its low elasticity modulus (ranging between 0.5 MPato 2 MPa depending upon the ratio of curing agent) [14]. Itsimplifies the detection system by measuring the deflection ofthe microcantilever’s tip using vision based optical microscopydue to its large deflection in the range of few micrometers [15].Other PDMS attributes such as good biocompatibility, opticaltransparency, low chemical reactivity and non-toxicity in amicrofluidic environment are also important factors in cellanalysis [16]. The fabrication of a PDMS chip is also costeffective, making it suitable for disposable uses in biologicalapplications.

Few vertical PDMS microcantilevers have been presentedin the literature to measure the force within microfluidicdevices. Sasoglu et al. [17] used vertical PDMS microbeamsto sense micro-scale cell forces. Liu et al [18] employeda visual algorithm for tracking the PDMS beam displace-ments to measure forces in the range of a few nanoNewton.Tan et al. [19] applied pillar structures while visually inspect-ing their deflection. Since fabrication limits the length ofvertical cantilevers, they typically have a low aspect ratiowhich limits the range of forces that can be measured accu-rately. A high aspect ratio PDMS microcantilever is promisingsince it may provide flow meters with higher sensitivity andimproved linear response for LOC applications.

1530–437X/$31.00 © 2012 IEEE

602 IEEE SENSORS JOURNAL, VOL. 13, NO. 2, FEBRUARY 2013

In order to deduce flow drag force from microcantileverdeflection, it is necessary to know the mechanical stiffnessof the beam. Several experiments have been carried out tomeasure the Young’s modulus of PDMS for bulk and thinPDMS layers. Depending upon the cantilever length, the smalldeflection beam theory for beam aspect ratios greater than10 [20] or large deflection beam theory [21] have been usedto determine beam stiffness. In addition, the Mooney–Rivlin(MR) constitutive model [22], the hyperelastic model [23] andfinite element analysis have been used in order to consider thenonlinear properties of PDMS [24].

In this paper, a high aspect ratio PDMS micro-cantilever-based flow sensor is presented. The micro-cantilever isintegrated into a microfluidic device and fabricated usingmultilayer soft lithography. The microcantilever and themicrochannels network are embedded into a thin PDMS layer.The flow sensor is made of PDMS material identical to thematerial of the microfluidic network in order to avoid anydifficulties in bonding non-similar multi-layers. A three layerfabrication technique is used for the integration of the microflow sensor. A thin middle layer is sandwiched between twoother PDMS layers in order to release the microcantileverand to seal the microfluidic device. The performance of theflow sensor is tested by introducing various flow rates intothe microfluidic device and measuring the deflection of thecantilever’s tip using an optical microscope. The elasticitymodulus of the cantilever is measured using a precisionbalance method developed in house to measure the sensitivityof the microcantilever to the flow drag force. Based on theelastic modulus of the cantilever and the deflection, the dragforce applied on the cantilever is determined.

3D finite element analysis (FEM) is carried out usingCOMSOL Multiphysics 3.5 to simulate the fluid-structureinteraction and to estimate the cantilever deflection undervarious fluid forces. The comparison of simulation and exper-imental results helps to identify the linear range of the can-tilever response and to find the dynamic range of flow ratesdetectable by the flow meter. Due to the high aspect ratioof the cantilever (>10), the calibration of the cantilever issimple and the effect of shear force on the deflection canbe ignored. In addition, since the cantilever deflection is inthe range of few micrometers, it can be measured effectivelyusing vision based optical microscopy and it does not requireadvanced detection methods such as AFM or integrated opticalor electrical systems. In spite of the off-line measuring method,the proposed flow sensor can be integrated into any kindof microfluidic-based LOC to accurately measure the localflow rate. As the sensor does not introduce any potentiallydisturbing signal, it is particularly useful for applications inwhich external electrical or thermal signals at the point ofcare should be avoided.

II. SENSOR DESIGN

The proposed flow sensor can be integrated with LOC intwo different ways to measure the flow rate such as monolithicintegration and hybrid integration. For microfluidic-based LOCdevices fabricated by multilayer PDMS fabrication technique

LOC Flow sensor

Inlet Outlet

(b)

LOC Inlet Outlet

Platform

Platform

flow sensor

(a)

Fig. 1. Two different setups for integrating the flow sensor in a LOC device.(a) Monolithic integration. (b) Hybrid integration.

such as multilayer micromixers, the flow sensor can be mono-lithically integrated into the design as shown in Fig. 1a.If the desired LOC is not a multilayer PDMS device, the flowsensor can be hybrid integrated as a stand-alone unit as shownin Fig. 1b.

The 3D schematic of the flow sensor is shown in Fig. 2a.The flow enters the device through the inlet, faces themicrocantilever and then exits towards the outlet. Since themicrocantilever is free, the flow induces the loading tothe microcantilever and deflects it. The flow induced loadingcauses the cantilever’s deflection (Fig. 2b). The high aspectratio PDMS microcantilever is suspended within the microflu-idic device and is sandwiched between the bottom and topthick PDMS layers (Fig. 2c). As the microcantilever deflectswithin the horizontal plane, the deflection is readily detectedusing vision based optical microscopy.

III. FABRICATION OF INTEGRATED PDMSMICROCANTILEVER WITHIN A MICROCHANNEL

The fabrication process of the integrated PDMS microcan-tilever within the microfluidic network is detailed in Fig. 3.A 4-inch silicon wafer is cleaned with acetone and DI water,the surface is blow-dried with pure nitrogen, followed bybaking for 5 min at 200 °C to dehydrate the surface (Fig. 3a).A SU8 mold is made using a standard photolithographictechnique. The negative photoresist SU8 (MicroChem Corp.)is spin coated at 1500 rpm for 1 min to reach the thicknessof 80 μm (Fig. 3b). The SU-8 is next soft-baked for 3 min at65 °C and for 7 min at 95 °C in a hotplate. The resist is thencooled down at room temperature and exposed to UV lightfor 30 s using a photo mask (Fig. 3c). Post-exposure bakestep (PEB) is then carried out, baking the resist for 3 min at65 °C and for 6 min at 95 °C in order to cross-link the SU-8.The SU-8 layer is then developed to obtain the SU8 mold(Fig. 3d).

In order to employ flexible microstructures for bio-sensing,a multi-layer technique is developed. The microfluidic deviceinvolves a middle thin layer and two more top and bottom

NEZHAD et al.: PDMS MICROCANTILEVER-BASED FLOW SENSOR INTEGRATION FOR LAB-ON-A-CHIP 603

Top layer

Bottom layer

Middle layer

Inlet

Outlet

PDMS microcantilever

(a)

A-A

Thin layer

Top layer

Bottom layer

Microcantilever Hollow feature

Outlet

Hollow feature

Inlet

A

A

PDMS microcantilever

(b) (c)

Fluid loading

Fig. 2. Schematic of the PDMS microcantilever-based flow sensor. (a) 3-D schematic of the design. (b) Top view. (c) Cross section.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig. 3. Fabrication process of a multilayer PDMS device. (a) Cleaning.(b) SU8 coating. (b) UV exposure. (c) SU8 exposure to light. (e) Thin-layerPDMS loading. (f) Thin layer peeled off. (g) Thin- and bottom-layer bonding.(h) Top-layer bonding.

PDMS layers sealing the middle layer. The thickness of themiddle layer is critical as it determines the thickness andhence the stiffness of the microcantilever. To fabricate thethin middle layer, a mixture of PDMS prepolymer (Sylgard

184 Dow Corning) with a curing agent at a volume ratio of10:1 is poured onto the SU8 mold and placed in a vacuumchamber for degasification. A plastic film is then carefullyplaced on the PDMS to avoid introducing any bubble under-neath. It is then loaded with a clamp to remove the extraPDMS (Fig. 3e). By applying pressure, the plastic film comesinto physical contact with the mold features and the PDMSis removed from the contact area. Next, the whole setup iskept in an oven to cure the PDMS for 2 hours at 60 °C. Aftercuring, the thin layer is peeled off from the mold (Fig. 3f).Similarly, top and bottom PDMS layers are fabricated bypouring PDMS onto the mold, curing in the oven, and thenpeeling off from the mold. The resulting thin middle layerand bottom layer are then subjected to plasma treatment andbonded using microscope alignment (Fig. 3g). Last, the plasticlayer is separated from the package and the top PDMS layer isplaced on top (Fig. 3h). The alignment is done manually underthe microscope, achieving an accuracy of less than 10 μm.

The PDMS squeezed between the plastic film and the moldtends to cover the mold features with a very thin blocking filmin the range of a few micrometers, leaving a residual PDMSlayer (Fig. 4a and b).

Various methods have been presented to remove this resid-ual PDMS layer such as squeezing the thin layer [25], blowingthe PDMS residue away [26] and rupturing the residue bya sharp needle [27]. Although the sharp needle or blowingmethod might be useful for fabrication of conventional thinPDMS layers, when a high aspect ratio microcantilever isembedded within the thin PDMS layer, these methods will leadto rupture of the microcantilever. The squeezing method seemsmore applicable for an integrated PDMS microcantilever and


SU8Si

SU8 PDMS

Blocking

SU8 Si

SU8 PDMS

(a) (b)

Clamping force

50 µm

10 µm

(c) (d) (e)

PDMS

Fig. 4. Blocking PDMS film as challenge in fabricating thin PDMS layer. (a) Squeezing the thin layer. (b) Blocking PDMS film. (c) PDMS microcantilever.(d) Cross section of PDMS microcantilever with blocking layer. (e) Cross section of fully released PDMS microcantilever without blocking layer.

has been used in this report to remove the blocking PDMSlayer using the clamp method. Fig. 4c shows the top viewimage of the fabricated PDMS microcantilever. The crosssection of the cantilever with blocking PDMS layer attached isseen in Fig. 4d. By applying sufficient clamping force on thethin PDMS layer, the blocking layer is removed and only twosmall residues are left at the bottom edge of the cantileverwhich does not have significant effect on its performance(Fig. 4e).

IV. MECHANICAL CHARACTERIZATION OF THE

PDMS MICROCANTILEVER

To be able to use the microcantilever in quantitative manner,the exact stiffness needs to be determined to allow for cali-bration. A precision balance method is employed to measurethe force on the tip and hence the stiffness of PDMS micro-cantilever (700 μm length, 70 μm width, 80 μm thickness)(Fig. 5). In order to provide free space around the cantilevertip, the thin PDMS layer is bonded to a support PDMS layerin such a way that the cantilever could freely face the balance(Denver instrument S1-114, sensitivity of 0.1 mg (1 μN)).Fig. 5a illustrates the schematic of the calibration setup. Inthis technique, a thin PDMS layer is bonded to a 2 mm thickPDMS substrate such that the cantilever has a free tip to touchthe balance. It is then mounted on a positioner (ULTRAlign™Metric Linear 3 Axis Stag, resolution of 1 μm) and is movedtoward the balance at a distance of 250 μm from its clampedend. The positioner is gradually moved down to force the glassplate. The glass plate is positioned on the balance to serve asa rigid body. The force is directly transferred to the balance(Fig. 5 b and c). Based on the displacement of the positioner(δ) and the recorded force (F) from the precision balance, thevariation of force against deflection is obtained. The deflection

of the glass placed on the balance due to the cantilever forcecan be neglected. In order to consider the effect of out of centererror in the precision balance, a sample mass is positionedon the center and out of center on the glass. A deviationof 2 μN was detected due to the out of center error for asample mass of 500 mg (5 mN). Since the maximum forcedetected for the cantilever deflection is 80 μN (60 times lessthan the force of sample mass), the out of center error would benegligible.

In order to determine the stiffness, the force (F) is measuredfor the deflections (δ) of 50 μm, 100 μm, 150 μm, 200 μm ofthe microcantilever. As the sensitivity of the balance setup isnot high enough to find the stiffness of a long microcantileverwith 700 μm length, this microcantilever meets the balance at250 μm away from the cantilever’s support (Fig. 5a). Due tolarge deflections, slight non-linearity is found in the stiffness.As shown in Fig. 6, linear regression is used to estimate thebeam stiffness using the equation of F = Kδ. This test wasrepeated three times and the average stiffness of 0.46 N/mis estimated for the cantilever. The elastic modulus is thencalculated from the deflection equation of the beam K =(

3E IL3

)as E = 802 kPa.

The force-deflection response of the microcantilever con-firms the linear behavior of the PDMS microcantilever evenfor large deflection. The value of the Young’s modulus is closeto that reported in the range of 400–1000 kPa for thin PDMSlayer [28]. The authors reasoned that the Young’s modulusof PDMS is dependent on the thickness of the layer andthe fabrication process. They reported that thin layer PDMSfabricated by spin coating has greater mechanical strengththan the layer created in soft lithography by pouring thePDMS mixture on the mold due to the difference in thecross-linking.


F

Support

Microcantilever

250 μm

700 μm

δ

(a)

(b) (c)

L

500 µm

Fig. 5. Characterization of the PDMS microcantilever using a precision balance. (a) Schematic of the balance setup. (b) Experimental setup. (c) Contactbetween the PDMS microcantilever and glass plate.

y = 0.46x

0102030405060708090

100

0 50 100 150 200 250

Forc

e (µ

N)

Deflection (µm)

Fig. 6. Microcantilever characterization force against deflection.

V. FLOW SENSOR TESTING

To assess the performance of the PDMS micro-cantileversuspended within the microfluidic channel, it was subjectedto fluid flow. It was observed that the microcantilever oftenstuck to the microchannel floor or ceiling during fabricationin plasma bonding, most likely due to the large area of thestructure (700 μm length by 70 μm width). In order toovercome stiction, the size of the microcantilever was modifiedto reduce its surface area. The new microcantilever has a lengthof 510 μm and a width of 40 μm. The thickness is maintainedat 80 μm in order to avoid any change on the elastic modulusdue to thickness alteration. By keeping the microcantilever’swidth less than its height, the bending of the structure towardsthe top or bottom is minimized whereas the bending in the

horizontal plane along the actual flow direction is promoted.Fig. 7a shows the schematic of experimental testing of flowsensor. Water with a density of ρ = 1000 kg/m3 and dynamicviscosity η = 0.001 Pa·s is injected into the microdevicethrough the inlet using a syringe pump with various flowrates while the cantilever deflection is monitored throughthe optical microscope (Fig. 7b). The PDMS microdevicefabricated with PDMS multilayer technique consists of a thinPDMS layer with integrated microcantilever and microfluidicsnetwork sealed by two other top and bottom PDMS layers asshown in Fig. 7c. The flow introduced into the chip throughthe inlet, induces the loading force on the microcantileverto bend it and is transferred out toward the outlet. Theinlet microchannel has a width of 840 μm and a depthof 80 μm which is equal to the thickness of thin PDMSlayer. The microfluidic chip has a depth of 240 μm at thelocation of the flow sensor since there are hollow featuresabove and below the microcantilever in order for it to befree. The deflection of the modified micro-cantilever is shownin Fig. 7d.

The performance of the flow meter was tested within thetypical range of fluid flows in microfluidic devices. The deflec-tion of the microcantilever was measured for various flow ratesbetween 0.2–1.3 ml/min using image processing techniquesand the results are shown in Fig. 8. Images were taken witha 4× objective (calibrated pixel size: 1.76 μm × 1.76 μm)during the flow experiment for a duration of 40 sec with aninterval of 100 ms. The start and stop point indicate the instantwhen the water pumping is turned on and off and correspondto 1 s and 30 s, respectively.


CCD Microscope

Lens

Inlet Outlet

Image processing

Flow sensor

Microcantilever

Syring pump

(a) (b)

100 µm

Inlet Outlet

Bottom layer Top layer

Thin layer

(c) (d)

Fig. 7. (a) Schematic of experimental setup for the fluid flow test of the PDMS microcantilever. (b) Experimental setup. (c) Fabricated microdevice.(d) Deflected cantilever under fluid flow.

0

20

40

60

80

100

0 10 20 30 40 50

Can

tilev

er d

efle

ctio

n (µ

m)

Time (s)

0.2 ml/min

0.5 ml/min

0.7 ml/min

1.0 ml/min

1.3 ml/min

Stop Start

Fig. 8. Deflection of the cantilever tip for different flow rates.

VI. SIMULATION

3D numerical analysis is performed to estimate the deflec-tion of microcantilever under various flow rates. The proposedmodel consists of the main microchannel with one inlet,one outlet and the microcantilever suspended within themicrochannel (Fig. 9a). Water with density of ρ = 1000 kg/m3

and dynamic viscosity η = 0.001 Pa·s is used as the mediumto test the cantilever performance.

The sequential coupled method is used to numerically solvethe interactions between the fluid and the solid structure.The flow is assumed to be laminar Newtonian, viscous and

incompressible. The fluid domain is governed by the incom-pressible Navier-Stokes equations and the continuity equations[29] as follows

ρ∂u∂ t

− ∇ · (−pI + η(∇u + (∇u)T) + ρ(u · ∇) · u) = F (1)

−∇ · u = 0 (2)

where I is the unit diagonal matrix, u = (u, v) is the velocityfield, p is the fluid pressure and F is the volume forceaffecting the fluid. Since the gravitation and other volumeforces affecting on the fluid are negligible, so F = 0.

For each flow rate, the fluid velocity at the entrance of themicrochannel is provided as the boundary condition for theinlet. The pressure at the outlet is set to atmospheric pressure.At all other boundaries, no-slip condition and defined as u = 0.

The fluid flow loading acting on the microcantilever isdefined as the force per area, similar to [30]:

FT = −n · (−p I + η(∇u + (∇u)T)) (3)

where n is the normal unit vector of the boundary, u is thevelocity field on the cantilever surface pointing out from fluid.FT is the fluid loading consists of pressure and viscous forces.The first term in equation (3) is the pressure gradient extractedfrom the fluidic simulation results. The second term is the vis-cous component of the force depending on the velocity and thedynamic viscosity of the fluid. For the structural deformation,


500 µm

Microcantilever

Inlet

Outlet

Microchannel

(a) (b)

Fig. 9. 3-D numerical result of fluid structure interaction for a water flow rate of 0.2 mL/min. (a) CAD model. (b) Deflected condition of microcantilever.

the end point of microcantilever is considered as fixed bound-ary condition. The fluid loading is applied on the cantileversurface. The PDMS microcantilever is considered isotropicwith Young’s modulus of estimated K value of 802 KPa(Fig. 6) and Poisson’s ratio of 0.45. The microchannel’s crosssection has 840 μm width and 240 μm depth.

COMSOL Multiphysics 3.5 software is used to model thefluid flow within the channel and to solve the governingequations of fluid structure interaction. The iterative couplingwith individual systems of equations is solved for the fluidand the structure. Coupling is achieved through the transfer offluid structure interaction between the fluid and the structurewithin a nonlinear iteration loop. Since the microcantileverhas a large deformation and the fluid flow domain alsochanges considerably, the moving mesh application mode isused to model the fluidic domain deformation along with themechanical structure. The deflection of microcantilever underthe flow rate of 0.2 ml/min is shown in Fig. 9b.

The numerical results for the microcantilever response tovarious flow rates are compared with the experimental datain Fig. 10. The comparison of simulation and experimentalresults confirm the reasonable accuracy of the model presentedfor the PDMS microcantilever for the range of flow ratesconsidered. For more linear response, one could use the linearrange of the response (0–0.6 ml/min).

Since the accuracy of the measurement is limited by the1.76 μm resolution of the image taken by optical microscopy,the minimum flow rate that can be detected in the presentcombination of flow meter and optical camera is 35 μl/min asestimated by FE simulation. This corresponds to a 0.8 μNresolution in equivalent force at the tip. By employing athinner top PDMS layer, higher resolution optical objectivescan be used to increase the quality of the image taken by themicroscope and improve the minimum detectable flow rate.Additionally, the sensitivity of the cantilever can be increasedby modifying the geometry of the cantilever. The presentflow sensor has special application in environments with noelectric field hence, integration of electrical elements such aspiezoresistive or piezoelectric elements to the sensing elementshould be avoided. However, this flow sensor can be integratedwith optical waveguides within the PDMS microcantilever in

Fig. 10. Comparison of simulation and experiment results for the deflectionof the PDMS microcantilever for different flow rates.

order to provide an electrical readout for online monitoring ofthe flow rate [31]. The performance of the flow sensor wastested by a syringe pump. However, for practical use in lowflow rates, it has to be calibrated with a more accurate flowinstrument.

VII. CONCLUSION

A high aspect ratio PDMS microcantilever-based flow sen-sor has been fabricated using a multilayer PDMS fabricationprocess. The stiffness of the cantilever has been found by aprecision balance setup and the elastic modulus is estimatedby linear beam theory. The performance of the flow sensorhas been tested by introducing different flow rates into themicrofluidic device and monitoring the cantilever response tothe fluid force using optical microscopy method. The practicalflow range of 0-600 μl/min was achieved for operation withwater. The minimum flow rate of 35 μl/min was estimatedusing finite element simulation. The sensitivity of the proposedflow sensor can be increased either by modifying the dimen-sion of the microcantilever or by employing higher resolutionoptical objectives.


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Amir Sanati Nezhad received the B.Sc. degree inmechanical engineering from the Isfahan Universityof Technology, Isfahan, Iran, and the M.Sc. degreein mechanical engineering and mechatronics fromthe Amirkabir University of Technology (TehranPolytechnic), Tehran, Iran. He is currently pursuingthe Ph.D. degree at the Optical Bio-MicrosystemsLaboratory, Mechanical and Industrial EngineeringDepartment, Concordia University, Montreal, QC,Canada.

His current research interests include optical bio-MEMS, lab-on-a-chip, and single-cell analysis within integrated microfluidicchips.

Mahmood Ghanbari received the B.Sc. degreefrom the Isfahan University of Technology, Isfa-han, Iran, and the M.Sc. degree from TarbiatModares University, Tehran, Iran, in 2006 and 2009,respectively, both in mechanical engineering. He iscurrently pursuing the Ph.D. degree at the Opti-cal Bio Microsystems Laboratory, Mechanical andIndustrial Engineering Department, Concordia Uni-versity, Montreal, QC, Canada.

His current research interests include integratedmicrosystems for biological applications, lab-on-a-

chip, single-cell analysis, microfluidics, biophotonics, and micro-sensors andactuators.


Carlos G. Agudelo received the B.Sc. degree inelectrical engineering from the Universidad Nacionalde Colombia, Cundinamarca, Colombia, and theM.S. degree in electrical engineering from the ÉcolePolytechnique de Montréal, Montréal, QC, Canada,in 2001 and 2008, respectively. He is currentlypursuing the Ph.D. degree at the Department ofMechanical and Industrial Engineering, ConcordiaUniversity, Montreal.

He was a Graduate Research Assistant with AndesUniversity, Bogotá, Colombia, from 2000 to 2002.

From 2003 to 2004, he was a Research Fellow with the Technological Univer-sity of Cartagena, Cartagena, Colombia. In 2008, he was a Software Developerwith CAE, Montreal. His current research interests include BioMEMS, controlsystems, and software development.

Muthukumaran Packirisamy received the B.S.degree from the University of Madras, Chennai,India, the M.S. degree from the Indian Institute ofTechnology, Chennai, and the Ph.D. degree fromConcordia University, Montreal, QC, Canada.

He is currently a Professor and the Concor-dia Research Chair of optical bioMEMS with theDepartment of Mechanical and Industrial Engineer-ing, Concordia University. He has experience withmany microelectromechanical systems industries inCanada. He is currently involved in the development

of bioMEMS devices in collaboration with industry. He has authored or co-authored more than 225 articles published in journals and conference pro-ceedings. He holds nine patents. His current research interests include opticalbio-MEMS, integration of microsystems, and micro- and nanointegration.

Prof. Packirisamy was a recipient of the I. W. Smith Award from the Cana-dian Society for Mechanical Engineers, the Concordia University ResearchFellowship, the Petro Canada Young Innovator Award, and the ENCS YoungResearch Achievement Award. He is a fellow of the Canadian Society forMechanical Engineers.

Rama Bhat received the Bachelors degree in engi-neering from Karnataka Regional Engineering Col-lege, Srinivasanagar, India, (National Institute ofTechnology, Karnataka) in 1966, and the M.Tech.and Ph.D. degrees in mechanical engineering fromIIT Madras, Chennai, India, in 1968 and 1972,respectively.

He is a Professor of Mechanical and IndustrialEngineering with Concordia University, Montreal,QC, Canada. He has trained many Ph.D. studentsin these areas since he joined the Department of

Mechanical and Industrial Engineering in 1979. His current research interestsinclude mechanical vibrations, vehicle dynamics, structural acoustics, rotordynamics, dynamics of micro-electro-mechanical systems.

Dr. Bhat is a fellow of the Canadian Society for Mechanical Engineering,the Engineering Institute of Canada, the American Society of MechanicalEngineers, and the Indian Institution of Engineers. He served as the Presidentof the Canadian Society for Mechanical Engineering from 2004 to 2006. Hereceived the prestigious NASA Award for Technical Innovation for his contri-bution in developing "PROSSS—Programming Structured Synthesis System."He proposed the use of Boundary Characteristic Orthogonal Polynomials foruse in the Rayleigh Ritz Method in 1985.

Anja Geitmann received the B.Sc. degree inexchange studies from Oregon State University, Cor-vallis, and Stockholm University, Stockholm, Swe-den, the M.Sc. degree in biology from the Universityof Konstanz, Konstanz, Germany, the Ph.D. degreefrom the University of Siena, Siena, Italy, in 1997.

She was a Post-Doctoral Fellow with Laval Uni-versity, Quebec City, QC, Canada, and Wagenin-gen University, Wageningen, The Netherlands. Shejoined the Institut de Recherche en Biologie Végétaleand the Department of Biological Sciences, Univer-

sity of Montreal, Montreal, QC, in 2001, where she supervises a team ofbiologists and engineers. Her current research interests include mechanicalaspects of plant cell growth and morphogenesis.

Dr. Geitmann is the Vice-President of the Microscopical Society of Canadaand an Executive Member of the Canadian Society of Plant Biologists. Herpublications and outreach activities can be accessed at www.geitmannlab.org.

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