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Micromachines, Volume 4, Issue 4 (December 2013), Pages 357-443

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Research

Open AccessArticle Polydimethylsiloxane (PDMS) Sub-Micron Traps for Single-Cell Analysis of Bacteria
Micromachines 2013, 4(4), 357-369; doi:10.3390/mi4040357
Received: 25 July 2013 / Revised: 12 September 2013 / Accepted: 23 September 2013 / Published: 11 October 2013
Cited by 11 | PDF Full-text (3816 KB) | HTML Full-text | XML Full-text
Abstract
Microfluidics has become an essential tool in single-cell analysis assays for gaining more accurate insights into cell behavior. Various microfluidics methods have been introduced facilitating single-cell analysis of a broad range of cell types. However, the study of prokaryotic cells such as Escherichia
[...] Read more.
Microfluidics has become an essential tool in single-cell analysis assays for gaining more accurate insights into cell behavior. Various microfluidics methods have been introduced facilitating single-cell analysis of a broad range of cell types. However, the study of prokaryotic cells such as Escherichia coli and others still faces the challenge of achieving proper single-cell immobilization simply due to their small size and often fast growth rates. Recently, new approaches were presented to investigate bacteria growing in monolayers and single-cell tracks under environmental control. This allows for high-resolution time-lapse observation of cell proliferation, cell morphology and fluorescence-coupled bioreporters. Inside microcolonies, interactions between nearby cells are likely and may cause interference during perturbation studies. In this paper, we present a microfluidic device containing hundred sub-micron sized trapping barrier structures for single E. coli cells. Descendant cells are rapidly washed away as well as components secreted by growing cells. Experiments show excellent growth rates, indicating high cell viability. Analyses of elongation and growth rates as well as morphology were successfully performed. This device will find application in prokaryotic single-cell studies under constant environment where by-product interference is undesired. Full article
Open AccessArticle Resistless Fabrication of Nanoimprint Lithography (NIL) Stamps Using Nano-Stencil Lithography
Micromachines 2013, 4(4), 370-377; doi:10.3390/mi4040370
Received: 5 May 2013 / Revised: 27 July 2013 / Accepted: 10 October 2013 / Published: 15 October 2013
Cited by 2 | PDF Full-text (3467 KB) | HTML Full-text | XML Full-text
Abstract
In order to keep up with the advances in nano-fabrication, alternative, cost-efficient lithography techniques need to be implemented. Two of the most promising are nanoimprint lithography (NIL) and stencil lithography. We explore here the possibility of fabricating the stamp using stencil lithography, which
[...] Read more.
In order to keep up with the advances in nano-fabrication, alternative, cost-efficient lithography techniques need to be implemented. Two of the most promising are nanoimprint lithography (NIL) and stencil lithography. We explore here the possibility of fabricating the stamp using stencil lithography, which has the potential for a cost reduction in some fabrication facilities. We show that the stamps reproduce the membrane aperture patterns within ±10 nm and we validate such stamps by using them to fabricate metallic nanowires down to 100 nm in size. Full article
(This article belongs to the Special Issue Micromachined Tools for Nanoscale Science and Technology)
Open AccessArticle Guard Cell and Tropomyosin Inspired Chemical Sensor
Micromachines 2013, 4(4), 378-401; doi:10.3390/mi4040378
Received: 26 May 2013 / Revised: 30 September 2013 / Accepted: 11 October 2013 / Published: 18 October 2013
Cited by 1 | PDF Full-text (921 KB) | HTML Full-text | XML Full-text
Abstract
Sensors are an integral part of many engineered products and systems. Biological inspiration has the potential to improve current sensor designs as well as inspire innovative ones. This paper presents the design of an innovative, biologically-inspired chemical sensor that performs “up-front” processing through
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Sensors are an integral part of many engineered products and systems. Biological inspiration has the potential to improve current sensor designs as well as inspire innovative ones. This paper presents the design of an innovative, biologically-inspired chemical sensor that performs “up-front” processing through mechanical means. Inspiration from the physiology (function) of the guard cell coupled with the morphology (form) and physiology of tropomyosin resulted in two concept variants for the chemical sensor. Applications of the sensor design include environmental monitoring of harmful gases, and a non-invasive approach to detect illnesses including diabetes, liver disease, and cancer on the breath. Full article
(This article belongs to the Special Issue Bioinspired Microsensors and Micromachines)
Open AccessCommunication Monodisperse Water-in-Oil-in-Water (W/O/W) Double Emulsion Droplets as Uniform Compartments for High-Throughput Analysis via Flow Cytometry
Micromachines 2013, 4(4), 402-413; doi:10.3390/mi4040402
Received: 5 September 2013 / Revised: 5 November 2013 / Accepted: 19 November 2013 / Published: 3 December 2013
Cited by 7 | PDF Full-text (1181 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Here we report the application of monodisperse double emulsion droplets, produced in a single step within partially hydrophilic/partially hydrophobic microfluidic devices, as defined containers for quantitative flow cytometric analysis. Samples with varying fluorophore concentrations were generated, and a clear correlation between dye concentration
[...] Read more.
Here we report the application of monodisperse double emulsion droplets, produced in a single step within partially hydrophilic/partially hydrophobic microfluidic devices, as defined containers for quantitative flow cytometric analysis. Samples with varying fluorophore concentrations were generated, and a clear correlation between dye concentration and fluorescence signals was observed. Full article
(This article belongs to the collection Lab-on-a-Chip)
Figures

Open AccessArticle Hydrodynamic Cell Trapping for High Throughput Single-Cell Applications
Micromachines 2013, 4(4), 414-430; doi:10.3390/mi4040414
Received: 31 August 2013 / Revised: 15 November 2013 / Accepted: 25 November 2013 / Published: 3 December 2013
Cited by 3 | PDF Full-text (900 KB) | HTML Full-text | XML Full-text
Abstract
The possibility to conduct complete cell assays under a precisely controlled environment while consuming minor amounts of chemicals and precious drugs have made microfluidics an interesting candidate for quantitative single-cell studies. Here, we present an application-specific microfluidic device, cellcomb, capable of conducting high-throughput
[...] Read more.
The possibility to conduct complete cell assays under a precisely controlled environment while consuming minor amounts of chemicals and precious drugs have made microfluidics an interesting candidate for quantitative single-cell studies. Here, we present an application-specific microfluidic device, cellcomb, capable of conducting high-throughput single-cell experiments. The system employs pure hydrodynamic forces for easy cell trapping and is readily fabricated in polydimethylsiloxane (PDMS) using soft lithography techniques. The cell-trapping array consists of V-shaped pockets designed to accommodate up to six Saccharomyces cerevisiae (yeast cells) with the average diameter of 4 μm. We used this platform to monitor the impact of flow rate modulation on the arsenite (As(III)) uptake in yeast. Redistribution of a green fluorescent protein (GFP)-tagged version of the heat shock protein Hsp104 was followed over time as read out. Results showed a clear reverse correlation between the arsenite uptake and three different adjusted low = 25 nL min−1, moderate = 50 nL min−1, and high = 100 nL min−1 flow rates. We consider the presented device as the first building block of a future integrated application-specific cell-trapping array that can be used to conduct complete single cell experiments on different cell types. Full article
Open AccessArticle A Bi-Directional Out-of-Plane Actuator by Electrostatic Force
Micromachines 2013, 4(4), 431-443; doi:10.3390/mi4040431
Received: 1 July 2013 / Revised: 21 August 2013 / Accepted: 30 October 2013 / Published: 5 December 2013
PDF Full-text (911 KB) | HTML Full-text | XML Full-text
Abstract
Presented in this paper is a bi-directional out-of-plane actuator which combines the merits of the electrostatic repulsive principle and the electrostatic attractive principle. By taking advantage of the electrostatic repulsive mode, the common “pull-in” instability can be lessened to enlarge the displacement, and
[...] Read more.
Presented in this paper is a bi-directional out-of-plane actuator which combines the merits of the electrostatic repulsive principle and the electrostatic attractive principle. By taking advantage of the electrostatic repulsive mode, the common “pull-in” instability can be lessened to enlarge the displacement, and by applying the electrostatic attractive mode, the out-of-plane displacement is further enlarged. The implications of changing the actuator’s physical dimensions are discussed, along with the two-layer polysilicon surface microfabrication process used to fabricate such an actuator. The static characteristics of the out-of-plane displacement versus the voltage of both modes are tested, and displacements of 1.4 μm and 0.63 μm are obtained at 130 V and 15 V, respectively. Therefore, a total stroke of 2.03 μm is achieved, more than 3 fold that of the electrostatic attractive mode, making this actuator useful in optical Micro-Electro-Mechanical Systems (MEMS) and Radio Frequency (RF) MEMS applications. Full article
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