Special Issue "Optofluidics 2018"

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (10 April 2019)

Special Issue Editors

Guest Editor
Prof. Limin Xiao

Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China
Website | E-Mail
Interests: fiber-based optofluidics; all-fiber optic devices; specialty fiber sensors and lasers
Guest Editor
Prof. Lingling Shui

South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
Website | E-Mail
Interests: droplet; microcapsule; electrowetting; self-assembly
Guest Editor
Prof. Changyuan Yu

Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Website | E-Mail
Interests: optical fiber communcations; optical fiber devices; optical sensors

Special Issue Information

Dear Colleagues,

Optofluidics is the study of interactions between light and fluids in the use of either light to control the flow of fluids or fluids to guide the flow of light, particularly at the micro-scale. Specific applications of the former one include optowetting, optical trapping, particle and cell sorting, and nanoparticle assisted optical flow control. Notable applications of the latter one are in waveguides, displays, optical switches, sensors, as well as in lab-on-a-chip, lab-in-fiber, and smart optical devices. In this special issue, we invite insight from investigators and scientists in the field to show your work with research papers, short communications, and review articles that focus on the new technology, fundamental research, concept, and application cases in the area of Optofluidics.

Prof. Limin Xiao
Prof. Lingling Shui
Prof. Changyuan Yu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • lab on a chip
  • lab in fiber
  • microfluidics and droplets
  • optofluidics
  • functional optical devices

Published Papers (9 papers)

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Research

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Open AccessArticle
Comparison of Micro-Mixing in Time Pulsed Newtonian Fluid and Viscoelastic Fluid
Micromachines 2019, 10(4), 262; https://doi.org/10.3390/mi10040262
Received: 17 February 2019 / Revised: 12 April 2019 / Accepted: 16 April 2019 / Published: 18 April 2019
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Abstract
Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher [...] Read more.
Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher than that in the Newtonian fluid. Particularly, the mixing in Newtonian fluid with time pulsing is decreased when the Reynolds number Re is between 0.002 and 0.01, while it is enhanced when Re is between 0.1 and 0.2 compared with that at a constant flow rate. In the viscoelastic fluid, on the other hand, the time pulsing does not change the mixing degree when the Weissenberg number Wi 20, while a larger mixing degree is realized at a higher pulsing frequency when Wi = 50. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessArticle
Higher-Order Mode Suppression in Antiresonant Nodeless Hollow-Core Fibers
Micromachines 2019, 10(2), 128; https://doi.org/10.3390/mi10020128
Received: 16 January 2019 / Accepted: 14 February 2019 / Published: 15 February 2019
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Abstract
Negative curvature hollow-core fibers (NC-HCFs) are useful as gas sensors. We numerically analyze the single-mode performance of NC-HCFs. Both single-ring NC-HCFs and nested antiresonant fibers (NANFs) are investigated. When the size of the cladding tubes is properly designed, higher-order modes (HOMs) in the [...] Read more.
Negative curvature hollow-core fibers (NC-HCFs) are useful as gas sensors. We numerically analyze the single-mode performance of NC-HCFs. Both single-ring NC-HCFs and nested antiresonant fibers (NANFs) are investigated. When the size of the cladding tubes is properly designed, higher-order modes (HOMs) in the fiber core can be coupled with the cladding modes effectively and form high-loss supermodes. For the single-ring structure, we propose a novel NC-HCF with hybrid cladding tubes to enable suppression of the first two HOMs in the core simultaneously. For the nested structure, we find that cascaded coupling is necessary to maximize the loss of the HOMs in NANFs, and, as a result, NANFs with five nested tubes have an advantage in single-mode guidance performance. Moreover, a novel NANF with hybrid extended cladding tubes is proposed. In this kind of NANF, higher-order mode extinction ratios (HOMERs) of 105 and even 106 are obtained for the LP11 and LP21 modes, respectively, and a similar level of 105 for the LP02 modes. Good single-mode performance is maintained within a broad wavelength range. In addition, the loss of the LP01 modes in this kind of NANF is as low as 3.90 × 10−4 dB/m. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessCommunication
Self-Healing Flexible Conductive Film by Repairing Defects via Flowable Liquid Metal Droplets
Micromachines 2019, 10(2), 113; https://doi.org/10.3390/mi10020113
Received: 10 December 2018 / Revised: 18 January 2019 / Accepted: 1 February 2019 / Published: 11 February 2019
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Abstract
Self-healing flexible conductive films have been fabricated, evaluated, and applied. The film is composed of a fragile indium tin oxide (ITO) layer covered with sprayed liquid metal (LM) droplets. Self-healing of electrical conductivity is achieved via spontaneous capillary wicking of LM droplets into [...] Read more.
Self-healing flexible conductive films have been fabricated, evaluated, and applied. The film is composed of a fragile indium tin oxide (ITO) layer covered with sprayed liquid metal (LM) droplets. Self-healing of electrical conductivity is achieved via spontaneous capillary wicking of LM droplets into cracks/defects of the ITO film. The liquid metal adhering onto the ITO layer can also connect the ITO fragments during bending to keep the overall conductivity of the composite LM/ITO film stable. Stable and reversible electrowetting performance has been achieved with the composite LM/ITO as the conductive film, in either flat or curved states. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessArticle
High Sensitivity Photonic Crystal Fiber Refractive Index Sensor with Gold Coated Externally Based on Surface Plasmon Resonance
Micromachines 2018, 9(12), 640; https://doi.org/10.3390/mi9120640
Received: 31 October 2018 / Revised: 22 November 2018 / Accepted: 30 November 2018 / Published: 3 December 2018
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Abstract
In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is [...] Read more.
In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is used for the performance analysis, and the numerical results show that the thickness of the gold film, the refractive index of the analyte, the radius of the air hole in the first layer, the second layer, and the central air hole can affect the sensing properties of the sensor. By optimizing the sensor structure, the maximum wavelength sensitivity can reach 11000 nm/RIU and the maximum amplitude sensitivity can reach 641 RIU−1. Due to its high sensitivity, the proposed sensor can be used for practical biological and chemical sensing. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessArticle
A Diffusion-Based pH Regulator in Laminar Flows with Smartphone-Based Colorimetric Analysis
Micromachines 2018, 9(12), 616; https://doi.org/10.3390/mi9120616
Received: 20 October 2018 / Revised: 7 November 2018 / Accepted: 19 November 2018 / Published: 23 November 2018
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Abstract
A strategy for an on-chip pH regulator is demonstrated computationally and experimentally, based on the diffusion characteristics of aqueous ionic solutions. Micro-flows with specific pH values are formed based on the diffusion behaviors of hydrogen and hydroxide ions in laminar flows. The final [...] Read more.
A strategy for an on-chip pH regulator is demonstrated computationally and experimentally, based on the diffusion characteristics of aqueous ionic solutions. Micro-flows with specific pH values are formed based on the diffusion behaviors of hydrogen and hydroxide ions in laminar flows. The final achieved pH value and its gradient in the channel can be regulated by the amount of ions transported between laminar flows, and the experimental results can be further generalized based on the normalized Nernst-Planck equation. A smartphone was applied as an image capture and analysis instrument to quantify pH values of liquids in a colorimetric detection process, with monotonic response range of ~1–13. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessFeature PaperArticle
Cell Density Detector Based on Light Beam Focusing
Micromachines 2018, 9(11), 592; https://doi.org/10.3390/mi9110592
Received: 17 October 2018 / Revised: 1 November 2018 / Accepted: 5 November 2018 / Published: 13 November 2018
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Abstract
Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter [...] Read more.
Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter based on light beam focusing to measure the density of adherent cells. In this sensor, the light emitted from the optical fibers is collimated by the collimating lens formed in polydimethylsiloxane (PDMS). The uniformly attached adherent cells act as a convex lens, focusing the collimated light propagated through them. The intensity of the focused light indicates the density of the adherent cells. For Hela cells, a detection limit of 8.3 × 104 cells/mL with a detection range from 0.1 × 106 cells/mL to 1.0 × 106 cells/mL is achieved. This sensor is particularly useful for drug screening, cell pathology analysis, and cancer pre-diagnosis. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Review

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Open AccessReview
Wettability Manipulation by Interface-Localized Liquid Dielectrophoresis: Fundamentals and Applications
Micromachines 2019, 10(5), 329; https://doi.org/10.3390/mi10050329
Received: 19 April 2019 / Revised: 6 May 2019 / Accepted: 14 May 2019 / Published: 16 May 2019
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Abstract
Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a [...] Read more.
Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a non-homogeneous electric field. The LDEP technique was mainly dedicated to the actuation of dielectric and aqueous liquids in microfluidics systems. Recently, a new concept called dielectrowetting was demonstrated by which the wettability of a dielectric liquid droplet can be reversibly manipulated via a highly localized LDEP force at the three-phase contact line of the droplet. Although dielectrowetting is principally very different from electrowetting on dielectrics (EWOD), it has the capability to spread a dielectric droplet into a thin liquid film with the application of sufficiently high voltage, overcoming the contact-angle saturation encountered in EWOD. The strength of dielectrowetting depends on the ratio of the penetration depth of the electric field inside the dielectric liquid and the difference between the dielectric constants of the liquid and its ambient medium. Since the introduction of the dielectrowetting technique, significant progress in the field encompassing various real-life applications was demonstrated in recent decades. In this paper, we review and discuss the governing forces and basic principles of LDEP, the mechanism of interface localization of LDEP for dielectrowetting, related phenomenon, and their recent applications, with an outlook on the future research. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessReview
Droplet-Based Microfluidic Thermal Management Methods for High Performance Electronic Devices
Micromachines 2019, 10(2), 89; https://doi.org/10.3390/mi10020089
Received: 17 December 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 25 January 2019
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Abstract
Advanced thermal management methods have been the key issues for the rapid development of the electronic industry following Moore’s law. Droplet-based microfluidic cooling technologies are considered as promising solutions to conquer the major challenges of high heat flux removal and nonuniform temperature distribution [...] Read more.
Advanced thermal management methods have been the key issues for the rapid development of the electronic industry following Moore’s law. Droplet-based microfluidic cooling technologies are considered as promising solutions to conquer the major challenges of high heat flux removal and nonuniform temperature distribution in confined spaces for high performance electronic devices. In this paper, we review the state-of-the-art droplet-based microfluidic cooling methods in the literature, including the basic theory of electrocapillarity, cooling applications of continuous electrowetting (CEW), electrowetting (EW) and electrowetting-on-dielectric (EWOD), and jumping droplet microfluidic liquid handling methods. The droplet-based microfluidic cooling methods have shown an attractive capability of microscale liquid manipulation and a relatively high heat flux removal for hot spots. Recommendations are made for further research to develop advanced liquid coolant materials and the optimization of system operation parameters. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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Open AccessFeature PaperReview
Recent Advances in Tunable and Reconfigurable Metamaterials
Micromachines 2018, 9(11), 560; https://doi.org/10.3390/mi9110560
Received: 14 October 2018 / Accepted: 26 October 2018 / Published: 31 October 2018
Cited by 1 | PDF Full-text (3679 KB) | HTML Full-text | XML Full-text
Abstract
Metamaterials are composed of nanostructures, called artificial atoms, which can give metamaterials extraordinary properties that cannot be found in natural materials. The nanostructures themselves and their arrangements determine the metamaterials’ properties. However, a conventional metamaterial has fixed properties in general, which limit their [...] Read more.
Metamaterials are composed of nanostructures, called artificial atoms, which can give metamaterials extraordinary properties that cannot be found in natural materials. The nanostructures themselves and their arrangements determine the metamaterials’ properties. However, a conventional metamaterial has fixed properties in general, which limit their use. Thus, real-world applications of metamaterials require the development of tunability. This paper reviews studies that realized tunable and reconfigurable metamaterials that are categorized by the mechanisms that cause the change: inducing temperature changes, illuminating light, inducing mechanical deformation, and applying electromagnetic fields. We then provide the advantages and disadvantages of each mechanism and explain the results or effects of tuning. We also introduce studies that overcome the disadvantages or strengthen the advantages of each classified tunable metamaterial. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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