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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Physical Chemistry, Theoretical and Computational Chemistry".

Deadline for manuscript submissions: closed (31 March 2011)

Special Issue Editor

Guest Editor
Prof. Dr. Axel Guenther (Website)

Department of Mechanical and Industrial Engineering, University of Toronto, 5 King\'s College Road, Toronto, Ontario M5S 3G8, Canada

Published Papers (11 papers)

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Research

Jump to: Review

Open AccessArticle Evaluation of a Centrifuged Double Y-Shape Microfluidic Platform for Simple Continuous Cell Environment Exchange
Int. J. Mol. Sci. 2012, 13(1), 819-827; doi:10.3390/ijms13010819
Received: 7 December 2011 / Revised: 6 January 2012 / Accepted: 9 January 2012 / Published: 13 January 2012
Cited by 2 | PDF Full-text (796 KB) | HTML Full-text | XML Full-text
Abstract
We have demonstrated the efficacy of a microfluidic medium exchange method for single cells using passive centrifugal force of a rotating microfluidic-chip based platform. At the boundary of two laminar flows at the gathering area of two microfluidic pathways in a Y-shape, [...] Read more.
We have demonstrated the efficacy of a microfluidic medium exchange method for single cells using passive centrifugal force of a rotating microfluidic-chip based platform. At the boundary of two laminar flows at the gathering area of two microfluidic pathways in a Y-shape, the cells were successfully transported from one laminar flow to the other, without mixing the two microfluidic mediums of the two laminar flows during cell transportation, within 5 s with 1 g (150 rpm) to 36.3 g (900 rpm) acceleration, with 93.5% efficiency. The results indicate that this is one of the most simple and precise tools for exchanging medium in the shortest amount of time. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessArticle A Rapid Method for Optimizing Running Temperature of Electrophoresis through Repetitive On-Chip CE Operations
Int. J. Mol. Sci. 2011, 12(7), 4271-4281; doi:10.3390/ijms12074271
Received: 6 April 2011 / Revised: 16 June 2011 / Accepted: 20 June 2011 / Published: 1 July 2011
Cited by 2 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a rapid and simple method to determine the optimal temperature conditions for denaturant electrophoresis using a temperature-controlled on-chip capillary electrophoresis (CE) device is presented. Since on-chip CE operations including sample loading, injection and separation are carried out just by [...] Read more.
In this paper, a rapid and simple method to determine the optimal temperature conditions for denaturant electrophoresis using a temperature-controlled on-chip capillary electrophoresis (CE) device is presented. Since on-chip CE operations including sample loading, injection and separation are carried out just by switching the electric field, we can repeat consecutive run-to-run CE operations on a single on-chip CE device by programming the voltage sequences. By utilizing the high-speed separation and the repeatability of the on-chip CE, a series of electrophoretic operations with different running temperatures can be implemented. Using separations of reaction products of single-stranded DNA (ssDNA) with a peptide nucleic acid (PNA) oligomer, the effectiveness of the presented method to determine the optimal temperature conditions required to discriminate a single-base substitution (SBS) between two different ssDNAs is demonstrated. It is shown that a single run for one temperature condition can be executed within 4 min, and the optimal temperature to discriminate the SBS could be successfully found using the present method. Full article
(This article belongs to the Special Issue Microfluidics)
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Open AccessArticle Fully Automated On-Chip Imaging Flow Cytometry System with Disposable Contamination-Free Plastic Re-Cultivation Chip
Int. J. Mol. Sci. 2011, 12(6), 3618-3634; doi:10.3390/ijms12063618
Received: 31 March 2011 / Revised: 18 May 2011 / Accepted: 26 May 2011 / Published: 7 June 2011
Cited by 9 | PDF Full-text (1523 KB) | HTML Full-text | XML Full-text
Abstract
We have developed a novel imaging cytometry system using a poly(methyl methacrylate (PMMA)) based microfluidic chip. The system was contamination-free, because sample suspensions contacted only with a flammable PMMA chip and no other component of the system. The transparency and low-fluorescence of [...] Read more.
We have developed a novel imaging cytometry system using a poly(methyl methacrylate (PMMA)) based microfluidic chip. The system was contamination-free, because sample suspensions contacted only with a flammable PMMA chip and no other component of the system. The transparency and low-fluorescence of PMMA was suitable for microscopic imaging of cells flowing through microchannels on the chip. Sample particles flowing through microchannels on the chip were discriminated by an image-recognition unit with a high-speed camera in real time at the rate of 200 event/s, e.g., microparticles 2.5 μm and 3.0 μm in diameter were differentiated with an error rate of less than 2%. Desired cells were separated automatically from other cells by electrophoretic or dielectrophoretic force one by one with a separation efficiency of 90%. Cells in suspension with fluorescent dye were separated using the same kind of microfluidic chip. Sample of 5 μL with 1 × 106 particle/mL was processed within 40 min. Separated cells could be cultured on the microfluidic chip without contamination. The whole operation of sample handling was automated using 3D micropipetting system. These results showed that the novel imaging flow cytometry system is practically applicable for biological research and clinical diagnostics. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessArticle Optimal Designs of Staggered Dean Vortex Micromixers
Int. J. Mol. Sci. 2011, 12(6), 3500-3524; doi:10.3390/ijms12063500
Received: 1 April 2011 / Revised: 19 May 2011 / Accepted: 25 May 2011 / Published: 3 June 2011
Cited by 5 | PDF Full-text (1513 KB) | HTML Full-text | XML Full-text
Abstract
A novel parallel laminar micromixer with a two-dimensional staggered Dean Vortex micromixer is optimized and fabricated in our study. Dean vortices induced by centrifugal forces in curved rectangular channels cause fluids to produce secondary flows. The split-and-recombination (SAR) structures of the flow [...] Read more.
A novel parallel laminar micromixer with a two-dimensional staggered Dean Vortex micromixer is optimized and fabricated in our study. Dean vortices induced by centrifugal forces in curved rectangular channels cause fluids to produce secondary flows. The split-and-recombination (SAR) structures of the flow channels and the impinging effects result in the reduction of the diffusion distance of two fluids. Three different designs of a curved channel micromixer are introduced to evaluate the mixing performance of the designed micromixer. Mixing performances are demonstrated by means of a pH indicator using an optical microscope and fluorescent particles via a confocal microscope at different flow rates corresponding to Reynolds numbers (Re) ranging from 0.5 to 50. The comparison between the experimental data and numerical results shows a very reasonable agreement. At a Re of 50, the mixing length at the sixth segment, corresponding to the downstream distance of 21.0 mm, can be achieved in a distance 4 times shorter than when the Re equals 1. An optimization of this micromixer is performed with two geometric parameters. These are the angle between the lines from the center to two intersections of two consecutive curved channels, θ, and the angle between two lines of the centers of three consecutive curved channels, φ. It can be found that the maximal mixing index is related to the maximal value of the sum of θ and φ, which is equal to 139.82°. Full article
(This article belongs to the Special Issue Microfluidics)
Figures

Open AccessArticle Experimental and Numerical Analysis of High-Resolution Injection Technique for Capillary Electrophoresis Microchip
Int. J. Mol. Sci. 2011, 12(6), 3594-3605; doi:10.3390/ijms12063594
Received: 30 March 2011 / Revised: 11 May 2011 / Accepted: 25 May 2011 / Published: 3 June 2011
Cited by 6 | PDF Full-text (576 KB) | HTML Full-text | XML Full-text
Abstract
This study presents an experimental and numerical investigation on the use of high-resolution injection techniques to deliver sample plugs within a capillary electrophoresis (CE) microchip. The CE microfluidic device was integrated into a U-shaped injection system and an expansion chamber located at [...] Read more.
This study presents an experimental and numerical investigation on the use of high-resolution injection techniques to deliver sample plugs within a capillary electrophoresis (CE) microchip. The CE microfluidic device was integrated into a U-shaped injection system and an expansion chamber located at the inlet of the separation channel, which can miniize the sample leakage effect and deliver a high-quality sample plug into the separation channel so that the detection performance of the device is enhanced. The proposed 45° U-shaped injection system was investigated using a sample of Rhodamine B dye. Meanwhile, the analysis of the current CE microfluidic chip was studied by considering the separation of Hae III digested φx-174 DNA samples. The experimental and numerical results indicate that the included 45° U-shaped injector completely eliminates the sample leakage and an expansion separation channel with an expansion ratio of 2.5 delivers a sample plug with a perfect detection shape and highest concentration intensity, hence enabling an optimal injection and separation performance. Full article
(This article belongs to the Special Issue Microfluidics)

Review

Jump to: Research

Open AccessReview Enhancing Single Molecule Imaging in Optofluidics and Microfluidics
Int. J. Mol. Sci. 2011, 12(8), 5135-5156; doi:10.3390/ijms12085135
Received: 31 March 2011 / Revised: 23 May 2011 / Accepted: 25 July 2011 / Published: 12 August 2011
Cited by 11 | PDF Full-text (781 KB) | HTML Full-text | XML Full-text
Abstract
Microfluidics and optofluidics have revolutionized high-throughput analysis and chemical synthesis over the past decade. Single molecule imaging has witnessed similar growth, due to its capacity to reveal heterogeneities at high spatial and temporal resolutions. However, both resolution types are dependent on the [...] Read more.
Microfluidics and optofluidics have revolutionized high-throughput analysis and chemical synthesis over the past decade. Single molecule imaging has witnessed similar growth, due to its capacity to reveal heterogeneities at high spatial and temporal resolutions. However, both resolution types are dependent on the signal to noise ratio (SNR) of the image. In this paper, we review how the SNR can be enhanced in optofluidics and microfluidics. Starting with optofluidics, we outline integrated photonic structures that increase the signal emitted by single chromophores and minimize the excitation volume. Turning then to microfluidics, we review the compatible functionalization strategies that reduce noise stemming from non-specific interactions and architectures that minimize bleaching and blinking. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessReview Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications
Int. J. Mol. Sci. 2011, 12(6), 3648-3704; doi:10.3390/ijms12063648
Received: 10 April 2011 / Revised: 3 May 2011 / Accepted: 19 May 2011 / Published: 7 June 2011
Cited by 48 | PDF Full-text (1503 KB) | HTML Full-text | XML Full-text
Abstract
Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this [...] Read more.
Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessReview Microfluidic Technologies for Synthetic Biology
Int. J. Mol. Sci. 2011, 12(6), 3576-3593; doi:10.3390/ijms12063576
Received: 7 April 2011 / Revised: 20 May 2011 / Accepted: 26 May 2011 / Published: 3 June 2011
Cited by 22 | PDF Full-text (937 KB) | HTML Full-text | XML Full-text
Abstract
Microfluidic technologies have shown powerful abilities for reducing cost, time, and labor, and at the same time, for increasing accuracy, throughput, and performance in the analysis of biological and biochemical samples compared with the conventional, macroscale instruments. Synthetic biology is an emerging [...] Read more.
Microfluidic technologies have shown powerful abilities for reducing cost, time, and labor, and at the same time, for increasing accuracy, throughput, and performance in the analysis of biological and biochemical samples compared with the conventional, macroscale instruments. Synthetic biology is an emerging field of biology and has drawn much attraction due to its potential to create novel, functional biological parts and systems for special purposes. Since it is believed that the development of synthetic biology can be accelerated through the use of microfluidic technology, in this review work we focus our discussion on the latest microfluidic technologies that can provide unprecedented means in synthetic biology for dynamic profiling of gene expression/regulation with high resolution, highly sensitive on-chip and off-chip detection of metabolites, and whole-cell analysis. Full article
(This article belongs to the Special Issue Microfluidics)
Figures

Open AccessReview Microfluidic Mixing: A Review
Int. J. Mol. Sci. 2011, 12(5), 3263-3287; doi:10.3390/ijms12053263
Received: 25 March 2011 / Revised: 2 May 2011 / Accepted: 5 May 2011 / Published: 18 May 2011
Cited by 167 | PDF Full-text (1461 KB) | HTML Full-text | XML Full-text
Abstract
The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes [...] Read more.
The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessReview Droplets Formation and Merging in Two-Phase Flow Microfluidics
Int. J. Mol. Sci. 2011, 12(4), 2572-2597; doi:10.3390/ijms12042572
Received: 17 February 2011 / Revised: 11 March 2011 / Accepted: 2 April 2011 / Published: 15 April 2011
Cited by 49 | PDF Full-text (839 KB) | HTML Full-text | XML Full-text
Abstract
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two [...] Read more.
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed. Full article
(This article belongs to the Special Issue Microfluidics)
Open AccessReview Non-Linear Electrohydrodynamics in Microfluidic Devices
Int. J. Mol. Sci. 2011, 12(3), 1633-1649; doi:10.3390/ijms12031633
Received: 24 January 2011 / Revised: 10 February 2011 / Accepted: 24 February 2011 / Published: 3 March 2011
Cited by 3 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
Since the inception of microfluidics, the electric force has been exploited as one of the leading mechanisms for driving and controlling the movement of the operating fluid and the charged suspensions. Electric force has an intrinsic advantage in miniaturized devices. Because the [...] Read more.
Since the inception of microfluidics, the electric force has been exploited as one of the leading mechanisms for driving and controlling the movement of the operating fluid and the charged suspensions. Electric force has an intrinsic advantage in miniaturized devices. Because the electrodes are placed over a small distance, from sub-millimeter to a few microns, a very high electric field is easy to obtain. The electric force can be highly localized as its strength rapidly decays away from the peak. This makes the electric force an ideal candidate for precise spatial control. The geometry and placement of the electrodes can be used to design electric fields of varying distributions, which can be readily realized by Micro-Electro-Mechanical Systems (MEMS) fabrication methods. In this paper, we examine several electrically driven liquid handling operations. The emphasis is given to non-linear electrohydrodynamic effects. We discuss the theoretical treatment and related numerical methods. Modeling and simulations are used to unveil the associated electrohydrodynamic phenomena. The modeling based investigation is interwoven with examples of microfluidic devices to illustrate the applications. Full article
(This article belongs to the Special Issue Microfluidics)

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