Special Issue "Microfluidics"

Guest Editor
Prof. Dr. Axel Guenther
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King\'s College Road, Toronto, Ontario M5S 3G8, Canada
Website: http://www.mie.utoronto.ca/faculty/guenther/
E-Mail:

Submission

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Type of Paper: Review
Title: Microfluidic Mixing: A Review
Authors: Chia-Yen Lee and Lung-Ming Fu
Affiliation: Department of Materials Engineering, National Pingtung University of Science and Technology, Pingtung, 912, Taiwan;
E-Mail: loudyfu@mail.npust.edu.tw (L.-M.F.)
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 can be categorized as either “active”, i.e., an external energy force is applied to perturb the species samples, or “passive”, i.e., the contact area and contact time of the species are increased through the use of 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 microfluidic mixing device field and then describes some of the more significant proposals for active and passive mixers.

Type of Paper: Review
Title: Droplets in Two-Phase Flow Microfluidics
Authors: Hao Gu, Michel H. G. Duits and Frieder Mugele
Affiliation: Physics of Complex Fluids, MESA+ Institute, University of Twente, PO Box 217, 7500 AE, Enschede, The Netherlands; E-Mails: H.Gu@utwente.nl (H.G.); f.mugele@utwente.nl (F.M.)
Abstract: Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput, for example in chemical synthesis and bio-chemical assays. Within the two-phase flow platform, the formation and merging of droplets are the two key procedures for (i) emulsification at a controlled drop size and (ii) the use of droplet as microreactors. Besides purely hydrodynamic manipulation, also electric signals transmitted via microelectrodes are increasingly used to enhance control. With the latter, the formation and merging of droplets can be achieved on-demand and with high precision. Here we review the state-of-the-art in two-phase flow micro-fluidics with particular emphasis on droplet formation and droplet merging under both the hydrodynamic and electric control conditions. Also innovative microfabrication methods for two-phase flow micro-fluidics will be discussed.

Type of Paper: Review
Title: Single Molecule Detection in Microfluidics
Authors: A. E. Vasdekis, G. Laporte and D. Psaltis
Affiliation: Optics Laboratory, School of Engineering, Ecole Polytechnique Federale de Lausanne (EPFL), Station 17, Lausanne, Switzerland;
E-Mail: andreas.vasdekis@epfl.ch (A.E.V.)
Abstract: Microfluidics have revolutionised high-throughput analysis and chemical synthesis the past decade. In this paper, we will discuss strategies aiming at detecting single molecules inside microfluidic channels. Single molecule detection represents the ultimate optical detection limit, and has enabled a variety of studies within the fields of biophysics and systems biology. However certain optical and chemical approaches are essential for detecting individual fluorescent molecules. We will review the optical methods currently available and discuss our approach for enhancing single molecule detection via a copolymer immobilization strategy [1]. The latter is uniquely introduced within the microfluidic channels, once these are fabricated, enabling thus a wide range of post-processing functionalization routes. We will focus on the performance of the aforementioned copolymer functionalization strategy to manipulate and detect single fluorescent molecules.

Title: MEMS based Microfluidic Devices for Biomedical Applications
Authors: Muhammad Waseem Ashraf, Shahzadi Tayyaba and Nitin Afzulpurkar
Affiliation: School of Engineering and Technology, Asian Institute of Technology (AIT), Bangkok, Thailand;
E-Mails: Muhammad.Waseem.Ashraf@ait.ac.th (M.W.A.); Shahzadi.Tayyaba@ait.ac.th (S.T.)
Abstract: MEMS based microfluidic devices are gaining popularity from last few years in biomedicine field. In this paper, a brief 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 aspects of micropumps and microneedles. The important features of micropumps are working principles, actuation methods, fabrication techniques, construction, performance parameters and applications. Based on the actuation mechanisms, the micropumps are classified into two main types such as mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, materials, overall shape, tip shape, size and applications. 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.

Title: A Rapid Method for Optimizing Running Temperature of Electrophoresis through Repetitive On-Chip CE Operations
Authors: Shohei Kaneda, Koichi Ono, Tatsuhiro Fukuba, Takahiko Nojima, Takatoki Yamamoto and Teruo Fujii
Affiliation: Institute of Industrial Science, University of Tokyo, LIMMS/CNRS-IIS (UMI 2820), Japan; E-Mails: shk@iis.u-tokyo.ac.jp (S.K.);
tfujii@iis.u-tokyo.ac.jp (T.F.)
Abstract: In this paper, a rapid and simple method for optimizing running temperature of electrophoresis on a temperature-controlled on-chip CE device is presented. Since on-chip CE operations including sample loading, injection and separation are carried out just by switching of electric field, we can repeat consecutive run to run CE operations on single on-chip CE device by programming the voltage sequences. By utilizing the high-speed separation and its repeatability of the on-chip CE, consecutive electrophoresis with different CE running temperature condition can be implemented rapidly. Using separations of reaction products of a single-stranded DNA (ssDNA) with a peptide nucleic acid (PNA) oligomer, the effectiveness of the presented method to find out the optimal temperature condition 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 in 4 min, and the optimal temperature to discriminate the SBS can be found within 16 min by the present method.

Type of Paper: Article
Title: Position Sensing of Aqueous Droplets in Digital Microfluidic Devices Using Capacitive Measurements
Authors: Justin D. Gullotta ¹, Jeffrey G. Martin ², William Fergus ², Julie M. Beaudet ², John T. Wen ¹, Jonathan S. Dordick ² and Robert J. Linhardt ²
Affiliations: ¹ Center for Automation Technologies and Systems, Rensselaer Polytechnic Institute, 110 8^th Street, Troy, NY, USA
² Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, 110 8^th Street, Troy, NY, USA;
E-Mails: dordick@rpi.edu (J.S.D.); linhar@rpi.edu (R.J.L.)
Abstract: The artificial Golgi is currently being developed as a screening platform for the development of glycan-based pharmaceuticals, including a bioengineered heparin. Capacitance offers a highly sensitive method for the positioning of droplets on digital microfluidic devices. This communication describes the use of capacitance as a detection method that can facilitate the implementation of feedback control in an artificial Golgi device and other digital microfluidic platforms.