Optofluidic modulator based on peristaltic nematogen microflows
TL;DR: Based on peristaltic nematogen microflows in polydimethylsiloxane, the authors demonstrate an optofluidic modulator that exhibits a symmetric 250 µs response and can operate at frequencies of up to 1 kHz.
Abstract: Based on peristaltic nematogen microflows in polydimethylsiloxane, scientists demonstrate an optofluidic modulator that exhibits a symmetric 250 µs response and can operate at frequencies of up to 1 kHz.
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TL;DR: The emerging field of optofluidics seeks to create new ways of uniting solid and non-solid materials in a single photonic system whose optical properties are typically defined by the fluidic component as discussed by the authors.
Abstract: Photonics has long been used to study non-solid materials such as liquids, gases and plasmas, but these fluidic media have traditionally not comprised a functional part of the photonic device or system. The emerging field of optofluidics seeks to create new ways of uniting solid and non-solid materials in a single photonic system whose optical properties are typically defined by the fluidic component. This Review summarizes the current state of optofluidics from a photonics perspective. First, we describe a new class of photonic elements based on the combination of fluidic media and integrated optical structures. We then discuss the applications of optofluidic principles to particle sensing and manipulation in fluids, and finally assess current challenges and potential directions for future developments.
282 citations
TL;DR: This work employs the nanohole array geometry and the conducting nature of the film to actively concentrate analyte within the sensor to achieve 180-fold enrichment of a dye, and 100-fold enriched and simultaneous sensing of a protein in less than 1 min.
Abstract: The integration of fluidics and optics, as in flow-through nanohole arrays, has enabled increased transport of analytes to sensing surfaces. Limits of detection, however, are fundamentally limited by local analyte concentration. We employ the nanohole array geometry and the conducting nature of the film to actively concentrate analyte within the sensor. We achieve 180-fold enrichment of a dye, and 100-fold enrichment and simultaneous sensing of a protein in less than 1 min. The method presents opportunities for an order of magnitude increase in sensing speed and 2 orders of magnitude improvement in limit of detection.
119 citations
TL;DR: The LC environment enables new mechanisms of particle transport that are reviewed, among them the motion of particles caused by gradients of the director, and effects in the electric field: backflow powered by director reorientations, dielectrophoresis in LC with varying dielectric permittivity and LC-enabled nonlinear electrophoresIS with velocity that depends on the square of the applied electric field and can be directed differently from the field direction.
Abstract: Colloidal particles in a liquid crystal (LC) behave very differently from their counterparts in isotropic fluids. Elastic nature of the orientational order and surface anchoring of the director cause long-range anisotropic interactions and lead to the phenomenon of levitation. The LC environment enables new mechanisms of particle transport that are reviewed in this work. Among them the motion of particles caused by gradients of the director, and effects in the electric field: backflow powered by director reorientations, dielectrophoresis in LC with varying dielectric permittivity and LC-enabled nonlinear electrophoresis with velocity that depends on the square of the applied electric field and can be directed differently from the field direction.
118 citations
TL;DR: Liquid crystals (LCs)-integrated metaholograms for ultracompact dynamic holographic displays are proposed, which will provide a path to external stimuli-driven "smart" sensing and display applications such as hologram labels for temperature/pressure/touch monitoring and interactive holographic shows with haptic motion recognition.
Abstract: Flat optics, realized by the artificially created 2D material platform called optical metasurfaces, is currently undergoing a science-to-technology transition. However, "real-time" active operations of such flat optical devices remain yet unresolved. Here, liquid crystals (LCs)-integrated metaholograms for ultracompact dynamic holographic displays are proposed. The anisotropic nature of the LCs allows facile and repeatable manipulation of the polarization of light. Specifically designed ("designer") LCs and efficient helicity-encoded metaholograms are combined to realize stimuli-responsive dynamic displays. The designer LC modulators are used as switches that enable a variety of external stimuli (e.g., electric field, heat, surface pressure) to operate holographic images in real-time. Such a dynamic metaholographic platform will provide a path to external stimuli-driven "smart" sensing and display applications such as hologram labels for temperature/pressure/touch monitoring and interactive holographic displays with haptic motion recognition.
101 citations
18 Sep 2014
TL;DR: The hydrodynamic properties of nematic liquid crystals are characterized by a complex mutual coupling between flow, viscosity, and nematic order, and the presence of the four confining channel walls adds new phenomena to the already rich and multifaceted flow behavior as discussed by the authors.
Abstract: The hydrodynamic properties of nematic liquid crystals are characterized by a complex mutual coupling between flow, viscosity, and nematic order. While the flow behaviour of nematic bulk samples is well known, corresponding studies in microfluidic settings are still at an early stage. The presence of the four confining channel walls – and in particular the nature of the surface anchoring of the nematic order on the walls – adds new phenomena to the already rich and multifaceted flow behaviour. We present an overview of recent studies focusing on the microfluidics of nematic liquid crystals. Particular topics are the functionalization of the channel walls for defined surface anchoring conditions and the resulting structures of the nematic director field, the controlling and tuning of the flow velocity profile and director field configuration and resulting opto-fluidic applications, and the behaviour of topological defects in the flowing nematic and their application for a guided colloidal transport.
95 citations
Cites methods from "Optofluidic modulator based on peri..."
...The flow-induced effective birefringence due to the director reorientation was also employed to realize optofluidic modulators [121] and tunable colour filters....
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References
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TL;DR: An extension to the soft lithography paradigm, multilayersoft lithography, with which devices consisting of multiple layers may be fabricated from soft materials is described, to build active microfluidic systems containing on-off valves, switching valves, and pumps entirely out of elastomer.
Abstract: Soft lithography is an alternative to silicon-based micromachining that uses replica molding of nontraditional elastomeric materials to fabricate stamps and microfluidic channels. We describe here an extension to the soft lithography paradigm, multilayer soft lithography, with which devices consisting of multiple layers may be fabricated from soft materials. We used this technique to build active microfluidic systems containing on-off valves, switching valves, and pumps entirely out of elastomer. The softness of these materials allows the device areas to be reduced by more than two orders of magnitude compared with silicon-based devices. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained.
4,218 citations
TL;DR: Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes to devices that handle aqueous solutions.
Abstract: Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
3,344 citations
TL;DR: D devices in which optics and fluidics are used synergistically to synthesize novel functionalities are described, according to three broad categories of interactions: fluid–solid interfaces, purely fluidic interfaces and colloidal suspensions.
Abstract: We describe devices in which optics and fluidics are used synergistically to synthesize novel functionalities. Fluidic replacement or modification leads to reconfigurable optical systems, whereas the implementation of optics through the microfluidic toolkit gives highly compact and integrated devices. We categorize optofluidics according to three broad categories of interactions: fluid–solid interfaces, purely fluidic interfaces and colloidal suspensions. We describe examples of optofluidic devices in each category.
1,700 citations
TL;DR: This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics and presents a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres.
Abstract: Nanodevices don't use much energy, and if the little they do need can be scavenged from vibrations associated with foot steps, heart beats, noises and air flow, a whole range of applications in personal electronics, sensing and defence technologies opens up. Energy gathering of that type requires a technology that works at low frequency range (below 10 Hz), ideally based on soft, flexible materials. A group working at Georgia Institute of Technology has now come up with a system that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing their associated nanowires together, mechanical energy is converted into electricity via a coupled piezoelectric-semiconductor process. This work shows a potential method for creating fabrics which scavenge energy from light winds and body movement. A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing, personal electronics and defence technologies1. This is in principle feasible for nanodevices owing to their extremely low power consumption2,3,4,5. Solar, thermal and mechanical (wind, friction, body movement) energies are common and may be scavenged from the environment, but the type of energy source to be chosen has to be decided on the basis of specific applications. Military sensing/surveillance node placement, for example, may involve difficult-to-reach locations, may need to be hidden, and may be in environments that are dusty, rainy, dark and/or in deep forest. In a moving vehicle or aeroplane, harvesting energy from a rotating tyre or wind blowing on the body is a possible choice to power wireless devices implanted in the surface of the vehicle. Nanowire nanogenerators built on hard substrates were demonstrated for harvesting local mechanical energy produced by high-frequency ultrasonic waves6,7. To harvest the energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and air flow, it is important to explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials. Here we present a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing the nanowires rooted on them with respect to each other, mechanical energy is converted into electricity owing to a coupled piezoelectric–semiconductor process8,9. This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics.
1,473 citations
TL;DR: Trans-cis photoisomerization of azobenzene with a laser pulse resulted in a nematic-to-isotropic phase transition with a rapid optical response of 200 microseconds.
Abstract: Liquid crystals are promising materials for optical switching and image storage because of their high resolution and sensitivity. Azobenzene liquid crystals (LCs) have been developed, in which azobenzene moieties play roles as both mesogens and photosensitive chromophores. Azobenzene LC films showed a nematic phase in trans isomers and no LC phase in cis isomers. Trans-cis photoisomerization of azobenzene with a laser pulse resulted in a nematic-to-isotropic phase transition with a rapid optical response of 200 microseconds.
1,432 citations