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Circulating tumor cells (CTCs) in peripheral blood has clinical significance in highlighting disease status for cancer patients. Thus analyzing blood samples, a commonly extracted body fluids in any health test, can be very helpful in prognosis. Here, we present a microdevice that permits separation of CTCs and blood constituents via their distinctively different biorheology. No functional modifications of the device were required and viable CTCs were obtained. Further studies on viable CTCs might give insights into the nature of the metastatic process. In our microfluidic device, the efficiency for isolating MCF-7 cells (breast adenocarcinoma) was 83%. Comparing with normal cultures, reseeded MCF-7 cells from isolation show no difference in proliferation rate highlighting these cells remain viable. Preliminary results show great promise to efficiently isolate and enumerate viable CTCs from peripheral blood with unique biomechanical characteristics. The microfluidic device presents an effective means for CTC studies and monitoring of cancer.

Microfluidic devices have shown remarkable success in generating emulsions with precise control over their size. Yet, highly sensitive nature of generation mechanism to surface wettability requires such devices to be built out of specific materials showing homogenous wettability that favors the continuous phase rather than the dispersed phase. Moreover, the need to switch the continuous phase and the dispersed phase requires switching the device wettability by applying a suitable surface treatment. Here, we demonstrate a microfluidic device that can generate water-in-oil and oil-in-water emulsions without the necessity of surface treatment. The device features a suspended glass micronozzle integrated inside a flow-focusing geometry formed by silicon and poly(dimethylsiloxane) channels where drops of the dispersed phase can be sheared off at the micronozzle tip without touching channel walls in a coflow of the continuous phase. The micronozzle structure is a partially released segment of a self-enclosed capillary entirely built in phosphosilicate glass and with a cylindrical lumen ∼1.5 μm in diameter. Owing to high fluidic resistance of such fine capillary, emulsion generation in the device takes place in a dripping process and no noticeable jet formation of the dispersed phase has been observed throughout the tested flow rates. The effect of the flow rates on the diameter of the emulsions and their rate of generation has been experimentally investigated and found to show a similar trend to that of a simple physical model based on the critical Capillary number.

Sensing biomolecules at minute quantities demands laborious and skill-laden laboratory protocols for sample preparation and amplification in order to improve signal-to-noise ratio. Nucleic-acid-based detection of viral particles in whole blood requires separation of viral particles from blood cells followed by extraction, amplification, and detection of viral nucleic acids. Here, three microfluidic chips have been independently shown to be capable of performing each critical step. Separation of viral particles involves a flow-through, shear-type microfilter chip that can handle large volume of blood. The remaining chips, although developed for genomic DNA, have been adopted for extraction and amplification of viral RNA. In the extraction chip, protein coatings around viral particles are chemically broken to liberate viral RNA which can reversibly bind to the chip surface under high-salt conditions. Viral RNA can be eluted out with a low-salt buffer after removal of unwanted debris. In the amplification chip, viral RNA is first transcribed into cDNA and then multiplied exponentially in copies by a continuous, isothermal, enzyme-based technique known as Nucleic Acid Sequence-Based Amplification (NASBA). The amplicons are detected on the same chip using DNA probes conjugated with horse radish peroxide (HRP) for colorimetry

The authors used thermally induced surface tension gradients to manipulate aqueous droplets in microchannels. Control of the droplet breakup process was demonstrated. Droplet sorting can be achieved with temperatures above a critical value. Numerical simulation using a two-dimensional model agrees qualitatively well with the experimental results. The used control temperature of less than 55 °C shows that this active control concept is suitable for biochemical applications. Thermal control promises to be a simple and effective manipulation method for droplet-based lab on a chip. Published version

Fluid velocity fields and particle motions were experimentally studied for the application of microfluidics in chip-based cell assays. muPIV measurements were conducted on diverging microchannels and a microfluidic cell trapping device to characterize the respective fluid flow fields. A highspeed camera was then used to capture and characterize the motion of particles released into the corresponding flows. The distributions of the particle pathlines when undergoing divergence were shown to have negligible inertial effects. Whereas deviations of pathlines within the cell trapping device and were attributed to the design of the macro-micro interfaces in the packaging.

A disposable polydimethylsioxane package is developed for ‘Bio-Microfluidic System’. Disposable Bio-Microfluidic system avoids the contamination of the system after each use and this requires the use of low cost materials. Polydimethylsioxane (PDMS) is an attractive low cost material for making substrates of the micro-fluidic package. The disposable PDMS Package consists of PDMS substrates, which are fabricated by soft-lithography. The PDMS substrates are bonded together to form the disposable package with the use of a thin-film, coated both side with adhesive material. The adhesive material is selected by chemical soaking test, peel test and bio-analysis. The tests reveal that the adhesive material can handle all chemical reagents without causing blockage or discoloration to the package. The disposable PDMS package uses a plug-in concept as the macro-micro fluidic interconnects that allows easy detachment of package from the external fluidic system. The developed disposable PDMS package has demonstrated a fluidic leak-proof package that handles up to 100kPa pressure with flow-rate of 200µl/min. The package has also demonstrated that it can filter out Viral Ribonucleic Acids (RNA) from spiked blood sample. This micro fluidic package forms an integral part of the bio micro fluidic system.

We report a force field on a particle in a concentration (conductivity) gradient under an externally applied oscillating electric field. The conductivity gradient was established through integrated microcapillaries bridging high- and low-conductivity streams in dedicated microchannels. Particles in low-conductivity electrolyte were observed to experience a strong force with the application of an oscillating field and pulled to the microcapillary openings where they were held against the flow. Particle trapping was accompanied by a concurrent electrolyte injection from high- to low-conductivity channel, triggered with the externally applied field and further contributed to the conductivity gradient near the trapping sites. We experimentally evaluated the force dependence on the magnitude and frequency of the excitation field for 10 μm polystyrene particles immersed at various conductivity levels. The experiments suggest that the observed force cannot be simply explained by dielectrophoresis or diffusiophoresis alone and further requires the consideration of a so-called concentration polarization force. This force has been rather recently postulated based on a theoretical treatment and yet to be experimentally validated. Using the theoretical treatment of this force, together with fluidic drag and diffusiophoresis, we correctly predicted trapping trajectories of particles based on a simultaneous solution of Poisson-Nernst-Planck and Stokes equations. The predicted and measured trapping velocities were found in reasonable agreement (within a factor of

As metal nanorods show much higher metal enhanced fluorescence (MEF) than metal nanospheres, microfluidic-based MEF is first explored with Ag nanorod (ND) arrays made by oblique angle deposition. By measuring the fluorescein isothiocyanate (FITC) solution sandwiched between the Ag NDs and a piece of cover slip, the enhancement factors (EFs) are found as 3.7 ± 0.64 and 6.74 ± 2.04, for a solution thickness at 20.8 μm and 10 μm, respectively. Because of the strong plasmonic coupling between the adjacent Ag NDs, only the emission of the fluorophores present in the three-dimensional NDs array gets enhanced. Thus, the corresponding effective enhancement factors (EEFs) are revealed to be relatively close, 259 ± 92 and 340 ± 102, respectively. To demonstrate the application of MEF in microfluidic systems, a multilayer of SiO2 NDs/Ag NDs is integrated with a capillary electrophoresis device. At a microchannel depth of 10 μm, an enhancement of 6.5 fold is obtained for amino acids separation detection. These results are very encouraging and open the possibility of MEF applications for the Ag ND arrays decorated microchannels. With the miniaturization of microfluidic devices, microfluidic-based MEF by Ag ND arrays will likely find more applications with further enhancement.

Among the electrophysiology techniques, the voltage clamp and its subsequent scaling to smaller mammalian cells, the so-called patch clamp, led to fundamental discoveries in the last century, revealing the ionic mechanisms and the role of single-ion channels in the generation and propagation of action potentials through excitable membranes (e.g. nerves and muscles). Since then, these techniques have gained a reputation as the gold standard of studying cellular ion channels owing to their high accuracy and rich information content via direct measurements under a controlled membrane potential. However, their delicate and skill-laden procedure has put a serious constrain on the throughput and their immediate utilization in the discovery of new cures targeting ion channels until researchers discovered 'lab-on-a-chip' as a viable platform for the automation of these techniques into a reliable high-throughput screening functional assay on ion channels. This review examines the innovative 'lab-on-a-chip' microtechnologies demonstrated towards this target over a period of slightly more than a decade. The technologies are categorically reviewed according to their considerations for design, fabrication, as well as microfluidic integration from a performance perspective with reference to their ability to secure G Ω seals (gigaseals) on cells, the norm broadly accepted among electrophysiologists for quality recordings that reflect ion-channel activity with high fidelity.

Surface migration of monocrystalline silicon has been applied to demonstrate self-formed cylindrical microcapillaries with diameters from 0.8 to 2.8 μm based on the microstructured substrate topography. The microcapillaries are entirely enclosed in silicon and can be conveniently etched to create fluidic access ports and microchannels for their subsequent integration into functional microfluidic devices. Moreover, the microcapillaries can be thermally oxidized through their access ports with silica walls remain intact upon release from surrounding silicon in an effort to enhance optical clarity. Straight microcapillaries and microcapillaries with perpendicular turns and crossings (junctions) have all been fabricated and validated for fluidic continuity with a fluorescein solution pumped through. The utility of the microcapillaries has been showcased on particle traps in which biological cells are probed for single-cell impedance spectroscopy. The approach disclosed, given its full compatibility with semiconductor device fabrication, offers great potential towards intelligent cell and molecule-based devices merging microelectronics and microfluidics. (Some figures may appear in colour only in the online journal)

We have designed, fabricated and characterized poly(dimethylsiloxane) (PDMS) arrayed waveguide grating (AWG) with four-channel output for operation in the visible light wavelength range. The PDMS AWG was realized based on the single-mode PDMS rib waveguide. The device was designed for 1 nm channel spacing with the wavelength ranging from 639 to 644 nm. The measured insertion loss is 11.4 dB at the peak transmission spectrum and the adjacent crosstalk is less than -16 dB. The AWG device occupies an area of 7.5 × 15 mm(2). PDMS AWG has the potential for integration with microfluidics in a monolithic PDMS lab-on-a-chip device for visible light spectroscopy applications.

This paper reports the formation and manipulation of ferrofluid droplets at a microfluidic T-junction in the presence of a permanent magnetic field. A small circular permanent magnet with a diameter of 3 mm is used to control the size of the ferrofluid droplets within a microfluidic device. In the absence of a magnetic field, the size of the ferrofluid droplets decreases linearly with the increase of the flow rate of the continuous phase. In the presence of a magnetic field, the size of the droplets depends on the magnetic field strength, magnetic field gradient and the magnetization of the ferrofluid. The magnetic field strength is adjusted in our experiment by the location of the magnet. The induced attractive magnetic force affects the droplet formation process leading to the change in the size of the formed droplets. Experimental observation also shows that the relative change in the size of the droplet depends on the flow rate of the continuous phase. Furthermore, the paper compares the evolving shape of the ferrofluid droplet during the formation process with and without the magnetic field.

In this paper, silicon-based devices with a step structure integrated at the flow-focusing junction were designed, fabricated and characterized for droplet generation. A two-step silicon etching method was demonstrated to create the step structure. During fabrication, undesirable spikes encountered at the step edge were removed by oxygen plasma ashing and silicon isotropic etching. With this method, two types of step profile (flat and triangular profiles) were fabricated. These two profiles were compared for their differences in droplet-generation behavior. The device with the flat-step profile was found to make larger droplets and at a lower frequency compared to the device with the triangular-step profile. Additionally, polydimethylsiloxane and glass were tested as capping materials for the devices and the impact of their surface characteristics (hydrophobic and hydrophilic) on the type of droplets (water-in-oil or oil-in-water) formed was investigated.

Lateral patch-clamping has emerged as a chip-based platform for automation of the conventional patch-clamp technique, the 'gold' standard for studying cellular ion channels. The conventional technique, as it relies on skilled-maneuver of glass micropipettes to patch cells, is extremely delicate, low in throughput, and thus cannot be used for primary screening of compounds against ion channels. Direct integration of glass capillaries on silicon provides lateral junctions for automated trapping and patching of cells. We demonstrate here a method of scaling up the lateral junctions to a standard 1536-well microtiter plate format. A single unit of 1536-well plate has been formed here on a 9 mm by 9 mm microstructured silicon with the inclusive of 16 wells molded in a capping layer made of polydimethylsiloxane (PDMS). The silicon substrate provides integrated glass capillaries (total 12) and their associated microfluidic network. Each glass capillary has an independent access through a dedicated well in PDMS and leads to a centralized channel in which cell suspension can be delivered through one of the remaining 4 wells. The unit has been tested on RBL-1 cells by recording whole-cell activity from inwardly rectifying endogenous potassium channels. A revised test protocol has been prescribed to avoid inaccurate readings due to altered ionic composition of the recording buffer when a typical suction is applied to capture cells.

This paper reports experimental investigations on the droplet formation of deionized water and a nanofluid in a heat-induced microfluidic flow focusing device. Besides the effect of temperature, the effects of nanoparticle suspension (nanofluid) and the flow rate of aqueous fluid on the droplet formation and size manipulation were studied. At constant flow rates of the two liquids, three different droplet breakup regimes were observed and their transition capillary numbers as well as temperatures were identified. The heat generated by an integrated microheater changes the droplet formation process. Increasing the temperature enlarges the size of the droplets significantly. These results also demonstrate that the titanium oxide (15 nm)/deionized water-based nanofluid exhibits similar characteristics in droplet formation at different temperatures and any small change in the flow rate of this nanofluid has little impact on the size of the droplets formed in a flow focusing geometry. Accepted version

We demonstrate a simple planar peristaltic pump fabricated in poly(dimethylsiloxane) (PDMS) via soft lithography and suitable for microfluidic integration.

Precise dispensing of microdroplets is an important process for droplet-based microfluidics. The droplet formation by shear force between two immiscible fluids depends on their flow rates, the viscosities, and the interfacial tension. In this letter, the authors report the use of integrated microheater and temperature sensor for controlling the droplet formation process. The technique exploits the dependency on temperature of viscosities and interfacial tension. Using a relatively low heating temperature ranging from 25 to 70 °C, the droplet diameter can be adjusted to over two times of its original value. The relatively low temperature range makes sure that this concept is applicable for droplets containing biological samples Published version

The authors present microfluidic logic gates based on two-phase flows at low Reynold’s number. The presence and the absence of a dispersed phase liquid (slug) in a continuous phase liquid represent 1 and 0, respectively. The working principle of these devices is based on the change in hydrodynamic resistance for a channel containing droplets. Logical operations including AND, OR, and NOT are demonstrated, and may pave the way for microfludic system automation and computation.

The authors present a microfluidic device towards an integrated patch-clamping assay. The device replaces conventional glass patch pipette with a buried microfluidic channel on silicon substrate. The microchannel fabrication involves reforming doped glass under heat and pressure, a process, in principle, analogous to the heat-pulling/polishing of glass patch pipettes. Unlike etching substrate, this process leaves a smooth glass surface for seal formation with cell membrane. The microchannel is evolved from a trapped void inside the trench during nonconformal deposition of the doped glass. The results of seal formation with mammalian cells captured at such microchannel opening are presented.

A high-performance flow-focusing geometry for spontaneous generation of monodispersed droplets is demonstrated. In this geometry, a two-phase flow is forced through a circular orifice integrated inside a silicon-based microchannel. The orifice with its cusp-like edge exerts a ring of maximized stress around the flow and ensures controlled breakup of droplets for a wide range of flow rates, forming highly periodic and reproducible dispersions. The droplet generation can be remarkably rapid, exceeding 10(4) s(-1) for water-in-oil droplets and reaching 10(3) s(-1) for oil-in-water droplets, being largely controlled by flow rate of the continuous phase. The droplet diameter and generation frequency are compared against a quasi-equilibrium model based on the critical Capillary number. The droplets are obtained despite the low Capillary number, below the critical value identified by the ratio of viscosities between the two phases and simple shear-flow.

This study demonstrates precise profile control of 3D lateral junction traps in silicon by exploiting a 2D mask layout and isotropic etching. The traps penetrate through silicon partitions and laterally link microfluidic channels. Since the trap constrictions cannot be registered directly by planar lithography, they are not trivial to define but critical for capturing cells in suspension. A special mask layout introduced here when combined with isotropic etching can form elliptic and circular constrictions. The mask layout offers three design parameters: two geometric angles and a separation distance between them. The design parameters have been systematically varied and a set of corresponding trap structures have been fabricated. Mapping of the constriction profiles to design parameters indicates that the constriction shape is mainly determined by the two design angles whereas the constriction size is controlled by the separation distance and total isotropic etching. It is shown that a circular constriction can be fabricated by setting the two angles such that their harmonic mean yields a critical value of about 45°. The constriction size may vary from several micrometers to tenths of micrometers depending on the separation distance and isotropically etched amount.

A fixed-grid approach for modeling the motion of a particle-encapsulated droplet carried by a pressure driven immiscible carrier fluid in a microchannel is presented. Three phases (the carrier fluid, the droplet and the particle), and two different moving boundaries (the droplet-carrier fluid and droplet-particle interfaces), are involved. This is a moving boundaries problem with the motion of the three phases strongly coupled. In the present article, the particle is assumed to be a fluid of high viscosity and constrained to move with rigid body motion. A combined formulation using one set of governing equations to treat the three phases is employed. The droplet-carrier fluid interface is represented and evolved using a level-set method with a mass correction scheme. Surface tension is modeled using the Continuum Surface Force model. An additional signed distance function is employed to define the droplet-particle interface. Its evolution is determined from the particle motion governed by the Newton-Euler equations. The governing equations are solved numerically using a Finite Volume method on a fixed Cartesian grid. For demonstration purpose, the flows of particle-encapsulated droplets through a constricted microchannel and through a microchannel system are presented.Copyright © 2007 by ASME

Significant efforts have been targeted towards developing a droplet-based microfluidic system and understanding the droplet formation process and the physics behind it and yet the underlying physics of the droplet formation in terms of evolution of pressures in both the continuous phase and dispersed phase has received less attention over the years and is not understood clearly. A numerical investigation on the mechanism of droplet formation in a microfluidic T-junction has been conducted and validated against the experimental flow visualisation. From the computational results it is shown that the pressure profile of the dispersed phase and the continuous phase in the squeezing regime changes as the droplet break-up process proceeds. New insights on the droplet break-up process such as the minimum pressure difference between the continuous phase and the dispersed phase happens at the last moment of the the droplet break-up and not during the second and third stage of the droplet formation mechanism in the squeezing regime have been identified. As a next step in the analysis, reagent addition to microfluidic droplets is a fundamental operation in high-throughput screenings. Adding precise amount of reagents to droplets poses difficulties and many of the available designs use complicated structures and fabrication methods. A design that reliably adds reagents into droplets by exploiting the physics of fluid flow at an expanded section right after the T-junction which enhances merging of a stream with a droplet, eliminates the drawbacks such as extra droplet formation and long mixing time is demonstrated. Experimental results show that the expanded section minimizes the tendency to form extra droplets; the reactants are in axial arrangement inside the droplets which leads to faster mixing; reliable addition of reagent to the droplets happens for the combination of flow rates in a broad range of both substrate and reagent streams. To understand the physics behind the reliable operation of reagent addition, a numerical investigation using VOF model has been conducted. The flow field and the pressure measurements show that when an expanded section is used, the dynamics of droplet formation mechanism undergoes a significant change and is dominated by the combination of both shear stress and pressure buildup-based droplet breakup from a pure pressured buildup-based droplet breakup in the squeezing regime; and the expanded section plays the role in creating low Laplace pressure jump across the interface of the droplet forming from the T-junction which reduces the probability of forming extra droplet in the merging process. DOCTOR OF PHILOSOPHY (MAE)

In this thesis, PDMS-based AWG microspectrometer for LOC application was demonstrated by foremost developing planar waveguide in PDMS material. The development of planar waveguide focused primarily in design and fabrication of novel PDMS waveguide with single-mode propagation as the basic building block for complex devices. By selecting the appropriate geometrical parameters, single-mode propagation can be generated even in a large cross section PDMS rib waveguide (> 5 μm). The fabrication of PDMS single-mode waveguide involved precise controlled of the slab and rib height to the accuracy of ±0.1 μm as well as the modification of the refractive index from 1.408 to 1.429. The characterization ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library VIII of the PDMS waveguide corroborated single-mode propagation at the wavelength of 635 nm with the propagation loss measured to be 0.48 dB/cm for low refractive index contrast waveguides (Δ=0.07%) and 0.2 dB/cm for high refractive index contrast waveguides (Δ=1.18%). DOCTOR OF PHILOSOPHY (EEE)