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Special Issue "Microfluidic Devices"

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A special issue of Sensors (ISSN 1424-8220).

Deadline for manuscript submissions: closed (31 December 2012)

Special Issue Editor

Guest Editor
Dr. Bruce K. Gale (Website)

Utah State Center of Excellence for Biomedical Microfluidics, Mechanical Engineering Department, 50 S Central Campus Drive Room 2110, Salt Lake City, UT 84112-9208, USA
Interests: highly parallel microfluidics; micro-total analysis systems; microscale medical devices; nanoparticle characterization; low resource area medical diagnostics

Special Issue Information

Dear Colleagues,

Sensors are becoming smaller and smaller every year, and new applications of sensors are being developed. Many of these sensors are designed to work with liquid samples, such as in the medical, environmental monitoring, and quality control fields. These miniature sensors are thus integrated with microfluidic systems that often perform sample preparation steps before delivering the prepared sample to the sensing portion of the device. Many future sensors will be multiplexed with the ability to sense multiple analytes simultaneously. These integrated devices will be the future of many liquid based sensors and will provide a wide range of new functionality allowing penetration into broad range of commercial markets and applications.

This current special issue will address microfluidic sensors and integration of sensors with microfluidic systems. In addition, multiplexed microfluidic sensors, the systems and packaging aspects of microfluidic sensors, and the integration of microfluidic sensors into more complex, complete devices are appropriate topics. We also solicit review articles and original research papers on new microfluidic sensing and actuating concepts, which are especially suited for systems integration or which make use of recently discovered phenomena.

Dr. Bruce K. Gale
Guest Editor

Published Papers (13 papers)

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Research

Open AccessArticle Position Measurement/Tracking Comparison of the Instrumentation in a Droplet-Actuated-Robotic Platform
Sensors 2013, 13(5), 5857-5869; doi:10.3390/s130505857
Received: 4 April 2013 / Revised: 25 April 2013 / Accepted: 25 April 2013 / Published: 7 May 2013
Cited by 2 | PDF Full-text (598 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports our work on developing a surface tension actuated micro-robotic platform supported by three bubbles (liquid environment) or droplets (gaseous environment). The actuation principle relies on the force developed by surface tension below a millimeter, which benefits from scaling laws, [...] Read more.
This paper reports our work on developing a surface tension actuated micro-robotic platform supported by three bubbles (liquid environment) or droplets (gaseous environment). The actuation principle relies on the force developed by surface tension below a millimeter, which benefits from scaling laws, and is used to actuate this new type of compliant robot. By separately controlling the pressure inside each bubble, three degrees of freedom can be actuated. We investigated three sensing solutions to measure the platform attitude in real-time (z-position of each droplet, leading to the knowledge of the z position and Θx and Θy tilts of the platform). The comparison between optical, resistive, and capacitive measurement principles is hereafter reported. The optical technique uses SFH-9201 components. The resistive technique involves measuring the electrical resistance of a path flowing through two droplets and the platform. This innovative technique for sensing table position combines three pairs of resistances, from which the resistance in each drop can be deduced, thus determining the platform position. The third solution is a more usual high frequency (~200 MHz) capacitive measurement. The resistive method has been proven reliable and is simple to implement. This work opens perspectives toward an interesting sensing solution for micro-robotic platforms. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle Microflow Cytometers with Integrated Hydrodynamic Focusing
Sensors 2013, 13(4), 4674-4693; doi:10.3390/s130404674
Received: 1 March 2013 / Revised: 22 March 2013 / Accepted: 28 March 2013 / Published: 9 April 2013
Cited by 12 | PDF Full-text (943 KB) | HTML Full-text | XML Full-text
Abstract
This study demonstrates the suitability of microfluidic structures for high throughput blood cell analysis. The microfluidic chips exploit fully integrated hydrodynamic focusing based on two different concepts: Two-stage cascade focusing and spin focusing (vortex) principle. The sample—A suspension of micro particles or [...] Read more.
This study demonstrates the suitability of microfluidic structures for high throughput blood cell analysis. The microfluidic chips exploit fully integrated hydrodynamic focusing based on two different concepts: Two-stage cascade focusing and spin focusing (vortex) principle. The sample—A suspension of micro particles or blood cells—is injected into a sheath fluid streaming at a substantially higher flow rate, which assures positioning of the particles in the center of the flow channel. Particle velocities of a few m/s are achieved as required for high throughput blood cell analysis. The stability of hydrodynamic particle positioning was evaluated by measuring the pulse heights distributions of fluorescence signals from calibration beads. Quantitative assessment based on coefficient of variation for the fluorescence intensity distributions resulted in a value of about 3% determined for the micro-device exploiting cascade hydrodynamic focusing. For the spin focusing approach similar values were achieved for sample flow rates being 1.5 times lower. Our results indicate that the performances of both variants of hydrodynamic focusing suit for blood cell differentiation and counting. The potential of the micro flow cytometer is demonstrated by detecting immunologically labeled CD3 positive and CD4 positive T-lymphocytes in blood. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle An Optofluidic Temperature Probe
Sensors 2013, 13(4), 4289-4302; doi:10.3390/s130404289
Received: 26 January 2013 / Revised: 18 March 2013 / Accepted: 22 March 2013 / Published: 28 March 2013
Cited by 5 | PDF Full-text (529 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report the application of a microfluidic device for semi-contact temperature measurement in picoliter volumes of aqueous media. Our device, a freely positionable multifunctional pipette, operates by a hydrodynamic confinement principle, i.e., by creating a virtual flow cell of micrometer dimensions [...] Read more.
We report the application of a microfluidic device for semi-contact temperature measurement in picoliter volumes of aqueous media. Our device, a freely positionable multifunctional pipette, operates by a hydrodynamic confinement principle, i.e., by creating a virtual flow cell of micrometer dimensions within a greater aqueous volume. We utilized two fluorescent rhodamines, which exhibit different fluorescent responses with temperature, and made ratiometric intensity measurements. The temperature dependence of the intensity ratio was calibrated and used in a model study of the thermal activation of TRPV1 ion channels expressed in Chinese hamster ovary cells. Our approach represents a practical and robust solution to the specific problem of measuring temperature in biological experiments in vitro, involving highly localized heat generation, for example with an IR-B laser. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle A Strip-Type Microthrottle Pump: Modeling, Design and Fabrication
Sensors 2013, 13(3), 3092-3108; doi:10.3390/s130303092
Received: 16 January 2013 / Revised: 13 February 2013 / Accepted: 27 February 2013 / Published: 4 March 2013
Cited by 4 | PDF Full-text (1122 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A novel design for a strip-type microthrottle pump with a rectangular actuator geometry is proposed, with more efficient chip surface consumption compared to existing micropumps with circular actuators. Due to the complex structure and operation of the proposed device, determination of detailed [...] Read more.
A novel design for a strip-type microthrottle pump with a rectangular actuator geometry is proposed, with more efficient chip surface consumption compared to existing micropumps with circular actuators. Due to the complex structure and operation of the proposed device, determination of detailed structural parameters is essential. Therefore, we developed an advanced, fully coupled 3D electro-fluid-solid mechanics simulation model in COMSOL that includes fluid inertial effects and a hyperelastic model for PDMS and no-slip boundary condition in fluid-wall interface. Numerical simulation resulted in accurate virtual prototyping of the proposed device only after inclusion of all mentioned effects. Here, we provide analysis of device operation at various frequencies which describes the basic pumping effects, role of excitation amplitude and backpressure and provides optimization of critical design parameters such as optimal position and height of the microthrottles. Micropump prototypes were then fabricated and characterized. Measured characteristics proved expected micropump operation, achieving maximal flow-rate 0.43 mL·min−1 and maximal backpressure 12.4 kPa at 300 V excitation. Good agreement between simulation and measurements on fabricated devices confirmed the correctness of the developed simulation model. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle Characterization of Microparticle Separation Utilizing Electrokinesis within an Electrodeless Dielectrophoresis Chip
Sensors 2013, 13(3), 2763-2776; doi:10.3390/s130302763
Received: 5 January 2013 / Revised: 6 February 2013 / Accepted: 22 February 2013 / Published: 27 February 2013
Cited by 5 | PDF Full-text (709 KB) | HTML Full-text | XML Full-text
Abstract
This study demonstrated the feasibility of utilizing electrokinesis in an electrodeless dielectrophoresis chip to separate and concentrate microparticles such as biosamples. Numerical simulations and experimental observations were facilitated to investigate the phenomena of electrokinetics, i.e., electroosmosis, dielectrophoresis, and electrothermosis. Moreover, the [...] Read more.
This study demonstrated the feasibility of utilizing electrokinesis in an electrodeless dielectrophoresis chip to separate and concentrate microparticles such as biosamples. Numerical simulations and experimental observations were facilitated to investigate the phenomena of electrokinetics, i.e., electroosmosis, dielectrophoresis, and electrothermosis. Moreover, the proposed operating mode can be used to simultaneously convey microparticles through a microfluidic device by using electroosmotic flow, eliminating the need for an additional micropump. These results not only revealed that the directions of fluids could be controlled with a forward/backward electroosmotic flow but also categorized the optimum separating parameters for various microparticle sizes (0.5, 1.0 and 2.0 μm). Separation of microparticles can be achieved by tuning driving frequencies at a specific electric potential (90 Vpp·cm−1). Certainly, the device can be designed as a single automated device that carries out multiple functions such as transportation, separation, and detection for the realization of the envisioned Lab-on-a-Chip idea. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle Detection of Micrococcus Luteus Biofilm Formation in Microfluidic Environments by pH Measurement Using an Ion-Sensitive Field-Effect Transistor
Sensors 2013, 13(2), 2484-2493; doi:10.3390/s130202484
Received: 26 December 2012 / Revised: 8 February 2013 / Accepted: 10 February 2013 / Published: 18 February 2013
Cited by 5 | PDF Full-text (653 KB) | HTML Full-text | XML Full-text
Abstract
Biofilm formation in microfluidic channels is difficult to detect because sampling volumes are too small for conventional turbidity measurements. To detect biofilm formation, we used an ion-sensitive field-effect transistor (ISFET) measurement system to measure pH changes in small volumes of bacterial suspension. [...] Read more.
Biofilm formation in microfluidic channels is difficult to detect because sampling volumes are too small for conventional turbidity measurements. To detect biofilm formation, we used an ion-sensitive field-effect transistor (ISFET) measurement system to measure pH changes in small volumes of bacterial suspension. Cells of Micrococcus luteus (M. luteus) were cultured in polystyrene (PS) microtubes and polymethylmethacrylate (PMMA)-based microfluidic channels laminated with polyvinylidene chloride. In microtubes, concentrations of bacteria and pH in the suspension were analyzed by measuring turbidity and using an ISFET sensor, respectively. In microfluidic channels containing 20 μL of bacterial suspension, we measured pH changes using the ISFET sensor and monitored biofilm formation using a microscope. We detected acidification and alkalinization phases of M. luteus from the ISFET sensor signals in both microtubes and microfluidic channels. In the alkalinization phase, after 2 day culture, dense biofilm formation was observed at the bottom of the microfluidic channels. In this study, we used an ISFET sensor to detect biofilm formation in clinical and industrial microfluidic environments by detecting alkalinization of the culture medium. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle Numerical Simulation of Optically-Induced Dielectrophoresis Using a Voltage-Transformation-Ratio Model
Sensors 2013, 13(2), 1965-1983; doi:10.3390/s130201965
Received: 13 December 2012 / Revised: 16 January 2013 / Accepted: 29 January 2013 / Published: 4 February 2013
Cited by 5 | PDF Full-text (788 KB) | HTML Full-text | XML Full-text
Abstract
Optically-induced dielectrophoresis (ODEP) has been extensively used for the manipulation and separation of cells, beads and micro-droplets in microfluidic devices. With this approach, non-uniform electric fields induced by light projected on a photoconductive layer can be used to generate attractive or repulsive [...] Read more.
Optically-induced dielectrophoresis (ODEP) has been extensively used for the manipulation and separation of cells, beads and micro-droplets in microfluidic devices. With this approach, non-uniform electric fields induced by light projected on a photoconductive layer can be used to generate attractive or repulsive forces on dielectric materials. Then, moving these light patterns can be used for the manipulation of particles in the microfluidic devices. This study reports on the results from numerical simulation of the ODEP platform using a new model based on a voltage transformation ratio, which takes the effective electrical voltage into consideration. Results showed that the numerical simulation was in reasonably agreement with experimental data for the manipulation of polystyrene beads and emulsion droplets, with a coefficient of variation less than 6.2% (n = 3). The proposed model can be applied to simulations of the ODEP force and may provide a reliable tool for estimating induced dielectrophoretic forces and electric fields, which is crucial for microfluidic applications. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle Analysis of Detection Enhancement Using Microcantilevers with Long-Slit-Based Sensors
Sensors 2013, 13(1), 681-702; doi:10.3390/s130100681
Received: 21 November 2012 / Revised: 26 December 2012 / Accepted: 30 December 2012 / Published: 7 January 2013
Cited by 1 | PDF Full-text (910 KB) | HTML Full-text | XML Full-text
Abstract
The present work analyzes theoretically and verifies the advantage of utilizing rectangular microcantilevers with long-slits in microsensing applications. The deflection profile of these microcantilevers is compared with that of typical rectangular microcantilevers under the action of dynamic disturbances. Various force-loading conditions are [...] Read more.
The present work analyzes theoretically and verifies the advantage of utilizing rectangular microcantilevers with long-slits in microsensing applications. The deflection profile of these microcantilevers is compared with that of typical rectangular microcantilevers under the action of dynamic disturbances. Various force-loading conditions are considered. The theory of linear elasticity for thin beams is used to obtain the deflection-related quantities. The disturbance in these quantities is obtained based on wave propagation and beam vibration theories. It is found that detections of rectangular microcantilevers with long-slits based on maximum slit opening length can be more than 100 times the deflections of typical rectangular microcantilevers. Moreover, the disturbance (noise effect) in the detection quantities of the microcantilever with long-slits is found to be always smaller than that of typical microcantilevers, regardless of the wavelength, force amplitude, and the frequency of the dynamic disturbance. Eventually, the detection quantities of the microcantilever with long-slits are found to be almost unaffected by dynamic disturbances, as long as the wavelengths of these disturbances are larger than 3.5 times the microcantilever width. Finally, the present work recommends implementation of microcantilevers with long-slits as microsensors in robust applications, including real analyte environments and out of laboratory testing. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle Flow Cell Design for Effective Biosensing
Sensors 2013, 13(1), 58-70; doi:10.3390/s130100058
Received: 23 November 2012 / Revised: 11 December 2012 / Accepted: 12 December 2012 / Published: 20 December 2012
Cited by 5 | PDF Full-text (595 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The efficiency of three different biosensor flow cells is reported. All three flow cells featured a central channel that expands in the vicinity of the sensing element to provide the same diameter active region, but the rate of channel expansion and contraction [...] Read more.
The efficiency of three different biosensor flow cells is reported. All three flow cells featured a central channel that expands in the vicinity of the sensing element to provide the same diameter active region, but the rate of channel expansion and contraction varied between the designs. For each cell the rate at which the analyte concentration in the sensor chamber responds to a change in the influent analyte concentration was determined numerically using a finite element model and experimentally using a flow-fluorescence technique. Reduced flow cell efficiency with increasing flow rates was observed for all three designs and was related to the increased importance of diffusion relative to advection, with efficiency being limited by the development of regions of recirculating flow (eddies). However, the onset of eddy development occurred at higher flow rates for the design with the most gradual channel expansion, producing a considerably more efficient flow cell across the range of flow rates considered in this study. It is recommended that biosensor flow cells be designed to minimize the tendency towards, and be operated under conditions that prevent the development of flow recirculation. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle Mass Transport Effects in Suspended Waveguide Biosensors Integrated in Microfluidic Channels
Sensors 2012, 12(11), 14327-14343; doi:10.3390/s121114327
Received: 23 August 2012 / Revised: 20 September 2012 / Accepted: 17 October 2012 / Published: 25 October 2012
Cited by 3 | PDF Full-text (522 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Label-free optical biosensors based on integrated photonic devices have demonstrated sensitive and selective detection of biological analytes. Integrating these sensor platforms into microfluidic devices reduces the required sample volume and enables rapid delivery of sample to the sensor surface, thereby improving response [...] Read more.
Label-free optical biosensors based on integrated photonic devices have demonstrated sensitive and selective detection of biological analytes. Integrating these sensor platforms into microfluidic devices reduces the required sample volume and enables rapid delivery of sample to the sensor surface, thereby improving response times. Conventionally, these devices are embedded in or adjacent to the substrate; therefore, the effective sensing area lies within the slow-flow region at the floor of the channel, reducing the efficiency of sample delivery. Recently, a suspended waveguide sensor was developed in which the device is elevated off of the substrate and the sensing region does not rest on the substrate. This geometry places the sensing region in the middle of the parabolic velocity profile, reduces the distance that a particle must travel by diffusion to be detected, and allows binding to both surfaces of the sensor. We use a finite element model to simulate advection, diffusion, and specific binding of interleukin 6, a signaling protein, to this waveguide-based biosensor at a range of elevations within a microfluidic channel. We compare the transient performance of these suspended waveguide sensors with that of traditional planar devices, studying both the detection threshold response time and the time to reach equilibrium. We also develop a theoretical framework for predicting the behavior of these suspended sensors. These simulation and theoretical results provide a roadmap for improving sensor performance and minimizing the amount of sample required to make measurements. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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Open AccessArticle Cooperative Suction by Vertical Capillary Array Pump for Controlling Flow Profiles of Microfluidic Sensor Chips
Sensors 2012, 12(10), 14053-14067; doi:10.3390/s121014053
Received: 23 August 2012 / Revised: 27 September 2012 / Accepted: 10 October 2012 / Published: 18 October 2012
Cited by 4 | PDF Full-text (677 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A passive pump consisting of integrated vertical capillaries has been developed for a microfluidic chip as an useful component with an excellent flow volume and flow rate. A fluidic chip built into a passive pump was used by connecting the bottoms of [...] Read more.
A passive pump consisting of integrated vertical capillaries has been developed for a microfluidic chip as an useful component with an excellent flow volume and flow rate. A fluidic chip built into a passive pump was used by connecting the bottoms of all the capillaries to a top surface consisting of a thin layer channel in the microfluidic chip where the thin layer channel depth was smaller than the capillary radius. As a result the vertical capillaries drew fluid cooperatively rather than independently, thus exerting the maximum suction efficiency at every instance. This meant that a flow rate was realized that exhibited little variation and without any external power or operation. A microfluidic chip built into this passive pump had the ability to achieve a quasi-steady rather than a rapidly decreasing flow rate, which is a universal flow characteristic in an ordinary capillary. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle Electromagnetically-Actuated Reciprocating Pump for High-Flow-Rate Microfluidic Applications
Sensors 2012, 12(10), 13075-13087; doi:10.3390/s121013075
Received: 31 July 2012 / Revised: 28 August 2012 / Accepted: 22 September 2012 / Published: 26 September 2012
Cited by 5 | PDF Full-text (810 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study presents an electromagnetically-actuated reciprocating pump for high-flow-rate microfluidic applications. The pump comprises four major components, namely a lower glass plate containing a copper microcoil, a middle PMMA plate incorporating a PDMS diaphragm with a surface-mounted magnet, upper PMMA channel plates, [...] Read more.
This study presents an electromagnetically-actuated reciprocating pump for high-flow-rate microfluidic applications. The pump comprises four major components, namely a lower glass plate containing a copper microcoil, a middle PMMA plate incorporating a PDMS diaphragm with a surface-mounted magnet, upper PMMA channel plates, and a ball-type check valve located at the channel inlet. When an AC current is passed through the microcoil, an alternating electromagnetic force is established between the coil and the magnet. The resulting bi-directional deflection of the PDMS diaphragm causes the check-valve to open and close; thereby creating a pumping effect. The experimental results show that a coil input current of 0.4 A generates an electromagnetic force of 47 mN and a diaphragm deflection of 108 μm. Given an actuating voltage of 3 V and a driving frequency of 15 Hz, the flow rate is found to be 13.2 mL/min under zero head pressure conditions. Full article
(This article belongs to the Special Issue Microfluidic Devices)
Open AccessArticle Modular Architecture of a Non-Contact Pinch Actuation Micropump
Sensors 2012, 12(9), 12572-12587; doi:10.3390/s120912572
Received: 13 July 2012 / Revised: 18 August 2012 / Accepted: 28 August 2012 / Published: 13 September 2012
Cited by 7 | PDF Full-text (1252 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates a modular architecture of a non-contact actuation micropump setup. Rapid hot embossing prototyping was employed in micropump fabrication by using printed circuit board (PCB) as a mold material in polymer casting. Actuator-membrane gap separation was studied, with experimental investigation [...] Read more.
This paper demonstrates a modular architecture of a non-contact actuation micropump setup. Rapid hot embossing prototyping was employed in micropump fabrication by using printed circuit board (PCB) as a mold material in polymer casting. Actuator-membrane gap separation was studied, with experimental investigation of three separation distances: 2.0 mm, 2.5 mm and 3.5 mm. To enhance the micropump performance, interaction surface area between plunger and membrane was modeled via finite element analysis (FEA). The micropump was evaluated against two frequency ranges, which comprised a low driving frequency range (0–5 Hz, with 0.5 Hz step increments) and a nominal frequency range (0–80 Hz, with 10 Hz per step increments). The low range frequency features a linear relationship of flow rate with the operating frequency function, while two magnitude peaks were captured in the flow rate and back pressure characteristic in the nominal frequency range. Repeatability and reliability tests conducted suggest the pump performed at a maximum flow rate of 5.78 mL/min at 65 Hz and a backpressure of 1.35 kPa at 60 Hz. Full article
(This article belongs to the Special Issue Microfluidic Devices)

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