Elastomer based tunable optofluidic devices

The synergetic integration of photonics and microfluidics has enabled a wide range of optofluidic devices that can be tuned based on various physical mechanisms. One such tuning mechanism can be realized based on the elasticity of polydimethylsiloxane (PDMS). The mechanical tuning of these optofluidic devices was achieved by modifying the geometry of the device upon applying internal or external forces. External or internal forces can deform the elastomeric components that in turn can alter the optical properties of the device or directly induce flow. In this review, we discuss recent progress in tunable optofluidic devices, where tunability is enabled by the elasticity of the construction material. Different subtypes of such tuning methods will be summarized, namely tuning based on bulk or membrane deformations, and pneumatic actuation.     

Optofluidic detection for cellular phenotyping

Quantitative analysis of the output of processes and molecular interactions within a single cell is highly critical to the advancement of accurate disease screening and personalized medicine. Optical detection is one of the most broadly adapted measurement methods in biological and clinical assays and serves cellular phenotyping. Recently, microfluidics has obtained increasing attention due to several advantages, such as small sample and reagent volumes, very high throughput, and accurate flow control in the spatial and temporal domains. Optofluidics, which is the attempt to integrate optics with microfluidics, shows great promise to enable on-chip phenotypic measurements with high precision, sensitivity, specificity, and simplicity. This paper reviews the most recent developments of optofluidic technologies for cellular phenotyping optical detection.     

Recent applications of AC electrokinetics in biomolecular analysis on microfluidic devices

AC electrokinetics is a generic term that refers to an induced motion of particles and fluids under nonuniform AC electric fields. The AC electric fields are formed by application of AC voltages to microelectrodes, which can be easily integrated into microfluidic devices by standard microfabrication techniques. Moreover, the magnitude of the motion is large enough to control the mass transfer on the devices. These advantages are attractive for biomolecular analysis on the microfluidic devices, in which the characteristics of small space and microfluidics have been mainly employed. In this review, I describe recent applications of AC electrokinetics in biomolecular analysis on microfluidic devices. The applications include fluid pumping and mixing by AC electrokinetic flow, and manipulation of biomolecules such as DNA and proteins by various AC electrokinetic techniques. Future prospects for highly functional biomolecular analysis on microfluidic devices with the aid of AC electrokinetics are also discussed.     

Logic digital fluidic in miniaturized functional devices: Perspective to the next generation of microfluidic lab‐on‐chips

Microfluidics has emerged following the quest for scale reduction inherent to micro‐ and nanotechnologies. By definition, microfluidics manipulates fluids in small channels with dimensions of tens to hundreds of micrometers. Recently, microfluidics has been greatly developed and its influence extends not only the domains of chemical synthesis, bioanalysis, and medical researches but also optics and information technology. In this review article, we will shortly discuss an enlightening analogy between electrons transport in electronics and fluids transport in microfluidic channels. This analogy helps to master transport and sorting. We will present some complex microfluidic devices showing that the analogy is going a long way off toward more complex components with impressive similarities between electronics and microfluidics. We will in particular explore the vast manifold of fluidic operations with passive and active fluidic components, respectively, as well as the associated mechanisms and corresponding applications. Finally, some relevant applications and an outlook will be cited and presented.     

Multifunctional Features of Organic Charge-Transfer Complexes: Advances and Perspectives

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.     

Optoelectrofluidic platforms for chemistry and biology

Extraordinary advances in lab on a chip systems have been made on the basis of the development of micro/nanofluidics and its fusion with other technologies based on electrokinetics and optics. Optoelectrofluidic technology, which has been recently introduced as a new manipulation scheme, allows programmable manipulation of particles or fluids in microenvironments based on optically induced electrokinetics. Herein, the behaviour of particles or fluids can be controlled by inducing or perturbing electric fields on demand in an optical manner, which includes photochemical, photoconductive, and photothermal effects. This elegant scheme of the optoelectrofluidic platform has attracted attention in various fields of science and engineering. A lot of research on optoelectrofluidic manipulation technologies has been reported and the field has advanced rapidly, although some technical hurdles still remain. This review describes recent developments and future perspectives of optoelectrofluidic platforms for chemical and biological applications.     

Nanomanipulation using near field photonics

In this article we review the use of near-field photonics for trapping, transport and handling of nanomaterials. While the advantages of traditional optical tweezing are well known at the microscale, direct application of these techniques to the handling of nanoscale materials has proven difficult due to unfavourable scaling of the fundamental physics. Recently a number of research groups have demonstrated how the evanescent fields surrounding photonic structures like photonic waveguides, optical resonators, and plasmonic nanoparticles can be used to greatly enhance optical forces. Here, we introduce some of the most common implementations of these techniques, focusing on those which have relevance to microfluidic or optofluidic applications. Since the field is still relatively nascent, we spend much of the article laying out the fundamental and practical advantages that near field optical manipulation offers over both traditional optical tweezing and other particle handling techniques. In addition we highlight three application areas where these techniques namely could be of interest to the lab-on-a-chip community, namely: single molecule analysis, nanoassembly, and optical chromatography.     

Recent advances in droplet microfluidics for microbiology

Advances in microbiology rely on innovations in technology. Droplet microfluidics, as a versatile and powerful technique that allows high-throughput generation and manipulation of subnanoliter volume droplets, has become an indispensable tool shifting experimental paradigms in microbiology. Droplet microfluidics has opened new avenues to various microbiological research, from resolving single-cell heterogeneity to investigating spatiotemporal dynamics of microbial communities, from precise quant...     

Optofluidic differential spectroscopy for absorbance detection of sub-nanolitre liquid samples

We present a novel optofluidic differential method for carrying out absorbance spectroscopy of sub-nanolitre volumes of liquid samples on a microfluidic chip. Due to the reduction of liquid volume, the absorbance detection in microfluidics is often hindered by either low sensitivity or complex fabrication. To address this issue, we introduced an optofluidic modulator which can be easily integrated into a PDMS (polydimethylsiloxane) based microfluidic chip. The modulator was controlled by the fluid pressure and the absorbance spectrum of the analyte was obtained by taking differential measurements between the analyte and reference medium. An advantage is that this method doesn't need a complicated fabrication step. It is compatible with conventional microfluidic chips and measurements can be carried out on a normal transmission microscope. The performance of the device was tested by measuring solutions containing methylene blue, with concentrations as low as 13 μM.     

Electropatterning—Contemporary developments for selective particle arrangements employing electrokinetics

The selective positioning and arrangement of distinct types of multiscale particles can be used in numerous applications in microfluidics, including integrated circuits, sensors and biochips. Electrokinetic (EK) techniques offer an extensive range of options for label-free manipulation and patterning of colloidal particles by exploiting the intrinsic electrical properties of the target of interest. EK-based techniques have been widely implemented in many recent studies, and various methodologies and microfluidic device designs have been developed to achieve patterning two- and three-dimensional (3D) patterned structures. This review provides an overview of the progress in electropatterning research during the last 5 years in the microfluidics arena. This article discusses the advances in the electropatterning of colloids, droplets, synthetic particles, cells, and gels. Each subsection analyzes the manipulation of the particles of interest via EK techniques such as electrophoresis and dielectrophoresis. The conclusions summarize recent advances and provide an outlook on the future of electropatterning in various fields of application, especially those with 3D arrangements as their end goal.     

Microfluidic flows of wormlike micellar solutions

The widespread use of wormlike micellar solutions is commonly found in household items such as cosmetic products, industrial fluids used in enhanced oil recovery and as drag reducing agents, and in biological applications such as drug delivery and biosensors. Despite their extensive use, there are still many details about the microscopic micellar structure and the mechanisms by which wormlike micelles form under flow that are not clearly understood. Microfluidic devices provide a versatile platform to study wormlike micellar solutions under various flow conditions and confined geometries. A review of recent investigations using microfluidics to study the flow of wormlike micelles is presented here with an emphasis on three different flow types: shear, elongation, and complex flow fields. In particular, we focus on the use of shear flows to study shear banding, elastic instabilities of wormlike micellar solutions in extensional flow (including stagnation and contraction flow field), and the use of contraction geometries to measure the elongational viscosity of wormlike micellar solutions. Finally, we showcase the use of complex flow fields in microfluidics to generate a stable and nanoporous flow-induced structured phase (FISP) from wormlike micellar solutions. This review shows that the influence of spatial confinement and moderate hydrodynamic forces present in the microfluidic device can give rise to a host of possibilities of microstructural rearrangements and interesting flow phenomena.     

Catalytic micropumps: microscopic convective fluid flow and pattern formation

As innovations continue to be made in the fields of microfluidics and the colloidal assembly, new strategies for moving particles and fluids may be needed. Heterogeneous catalysis provides means of locally converting the stored chemical energy of fuels to mechanical energy. We report an ambient temperature stationary "pump" that generates a proton concentration gradient through the bipolar electrochemical decomposition of hydrogen peroxide on patterned silver-gold surfaces. The resulting electric field drives convective fluid flow and pattern formation of colloidal tracer particles at the microscopic level by a combination of electroosmotic and electrophoretic forces.     

Magnetism and microfluidics

Magnetic forces are now being utilised in an amazing variety of microfluidic applications. Magnetohydrodynamic flow has been applied to the pumping of fluids through microchannels. Magnetic materials such as ferrofluids or magnetically doped PDMS have been used as valves. Magnetic microparticles have been employed for mixing of fluid streams. Magnetic particles have also been used as solid supports for bioreactions in microchannels. Trapping and transport of single cells are being investigated and recently, advances have been made towards the detection of magnetic material on-chip. The aim of this review is to introduce and discuss the various developments within the field of magnetism and microfluidics.     

Planar optofluidic chip for single particle detection, manipulation, and analysis

We present a fully planar integrated optofluidic platform that permits single particle detection, manipulation and analysis on a chip. Liquid-core optical waveguides guide both light and fluids in the same volume. They are integrated with fluidic reservoirs and solid-core optical waveguides to define sub-picoliter excitation volumes and collect the optical signal, resulting in fully planar beam geometries. Single fluorescently labeled liposomes are used to demonstrate the capabilities of the optofluidic chip. Liposome motion is controlled electrically, and fluorescence correlation spectroscopy (FCS) is used to determine concentration and dynamic properties such as diffusion coefficient and velocity. This demonstration of fully planar particle analysis on a semiconductor chip may lead to a new class of planar optofluidics-based instruments.     

Transformation optofluidics for large-angle light bending and tuning

Transformation optics is a new art of light bending by designing materials with spatially variable parameters for developing wave-manipulation devices. Here, we introduce a transformation optofluidic Y-branch splitter with large-angle bending and tuning based on the design of a spatially variable index. Differing from traditional splitters, the optofluidic splitter is achieved in an inhomogeneous medium by coordinate transformation. The designed bidirectional gradient index (GRIN) distribution can be achieved practically by the convection-diffusion process of liquid flowing streams. The transformation optofluidic splitter can achieve a much larger split angle with little bend loss than the traditional ones. In the experiments, a large tunable split angle up to 30° is achieved by tuning the flow rates, allowing optical signals to be freely transferred to different channels. Besides the symmetrical branch splitting, asymmetrical Y-branch splitting with approximately equal power splitting is also demonstrated by changing the composition of the liquids. The optofluidic splitter has high potential applications in biological, chemical and biomedical solution measurement and detection.     

Electroosmotic transport of immiscible binary system with a layer of non‐conducting fluid under interfacial slip: The role applied pressure gradient

We investigate the transport of immiscible binary fluid layers, constituted by one conducting (top layer fluid) and another non‐conducting (bottom layer fluid) fluids in a microfluidic channel under the combined influences of an applied pressure gradient and imposed electric field. We solve the transport equation governing the flow dynamics analytically and obtain the closed‐form expressions of the velocity fields. We bring out the alteration in the flow dynamics, mainly attributable to the non‐linear interaction between interfacial slip and the electrical double layer effect over small scales as modulated by the applied pressure gradient. In particular, we show the augmentation in the net volume transport rate through the channel, emerging from an intricate competition among electrical forcing, applied pressure gradient and the viscous resistance as modulated by the interfacial slip. We believe that the results of this study may be of immense consequence for the design of various microfluidic devises, which are often used for the manipulation of two immiscible fluids in different biomedical/biochemical processes.     

Polymer chemistry in flow: New polymers,beads, capsules,and fibers

The union between polymer science and microfluidics is reviewed. Fluids in microreactors allow the synthesis of a wide range of polymeric materials with unique properties. We begin by discussing the important fluid dynamics that dominate the behavior of fluids on the micrometer scale. We then progress through a comprehensive analysis of the polymeric materials synthesized to date. This highlight concludes with an overview of the methods used to make microreactors. We enthusiastically endorse microreactors as a powerful approach to making materials with controlled properties, although we have tried to provide a critical eye to help the nonexpert enter the field. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6505–6533, 2006     

Nanomaterials meet microfluidics

Nanomaterials and lab-on-a-chip platforms have undergone enormous development during the past decade. Here, we present an overview of how microfluidics benefited from the use of nanomaterials for the enhanced separation and detection of analytes. We also discuss how nanomaterials benefit from microfluidics in terms of synthesis and in terms of the simulation of environments for nanomotors and nanorobots. In our opinion, the "marriage" of nanomaterials and microfluidics is highly beneficial and is expected to solve vital challenges in related fields.     

Surface‐Tension‐Confined Microfluidics and Their Applications

This article is a brief overview of the emerging microfluidic systems called surface‐tension‐confined microfluidic (STCM) devices. STCM devices utilize surface energy that can control the movement of fluid droplets. Unlike conventional poly(dimethylsiloxane)‐based microfluidics which confine the movement of fluids by three‐dimensional (3D) microchannels, STCM systems provide two‐dimensional (2D) platforms for microfluidics. A variety of STCM devices have been prepared by various micro‐/nanofabrication strategies. Advantages of STCM devices over conventional microfluidics are significant reduction of energy consumption during device operation, facile introduction of fluids onto 2D microchannels without the use of a micropump, increased flow rate in a special type of STCM device, among others. Thus, STCM devices can be excellent alternatives for certain areas in microfluidics. In this Minireview, fabrication methods, operating modes, and applications of STCM devices are introduced.     

Hybrid materials for optics and photonics

The interest in organic-inorganic hybrids as materials for optics and photonics started more than 25 years ago and since then has known a continuous and strong growth. The high versatility of sol-gel processing offers a wide range of possibilities to design tailor-made materials in terms of structure, texture, functionality, properties and shape modelling. From the first hybrid material with optical functional properties that has been obtained by incorporation of an organic dye in a silica matrix, the research in the field has quickly evolved towards more sophisticated systems, such as multifunctional and/or multicomponent materials, nanoscale and self-assembled hybrids and devices for integrated optics. In the present critical review, we have focused our attention on three main research areas: passive and active optical hybrid sol-gel materials, and integrated optics. This is far from exhaustive but enough to give an overview of the huge potential of these materials in photonics and optics (254 references).