Microfluidic sorting system based on optical waveguide integration and diode laser bar trapping

Effective methods for manipulating, isolating and sorting cells and particles are essential for the development of microfluidic-based life science research and diagnostic platforms. We demonstrate an integrated optical platform for cell and particle sorting in microfluidic structures. Fluorescent-dyed particles are excited using an integrated optical waveguide network within micro-channels. A diode-bar optical trapping scheme guides the particles across the waveguide/micro-channel structures and selectively sorts particles based upon their fluorescent signature. This integrated detection and separation approach streamlines microfluidic cell sorting and minimizes the optical and feedback complexity commonly associated with extant platforms.     

Planar silicon microrings as wavelength-multiplexed optical traps for storing and sensing particles

We demonstrate the trapping of particles with silicon microring resonators integrated with waveguides. Multiple microrings with different resonant wavelengths are integrated with each waveguide. We demonstrate that tuning the laser wavelength to the resonance wavelengths of different rings enables trapped particles to be transferred back and forth between the rings. We demonstrate that the change in output power arising from particle-induced resonance shift enables the real-time monitoring of trapped particles, such as their number and velocities, without the need for an external imaging system. The techniques we describe here could form the basis for small footprint systems in which objects are moved between multiple locations on a chip, at each of which different operations are performed and the objects' properties sensed.     

Development and characterization of an integrated silicon micro flow cytometer

This paper describes an innovative integrated micro flow cytometer that presents a new arrangement for the excitation/detection system. The sample liquid, containing the fluorescent marked particles/cells under analysis, is hydrodynamically squeezed into a narrow stream by two sheath flows so that the particles/cells flow individually through a detection region. The detection of the particles/cells emitted fluorescence is carried out by using a collection fiber placed orthogonally to the flow. The device is based on silicon hollow core antiresonant reflecting optical waveguides (ARROWs). ARROW geometry allows one to use the same channel to guide both the sample stream and the fluorescence excitation light, leading to a simplification of the optical configuration and to an increase of the signal-to-noise ratio. The integrated micro flow cytometer has been characterized by using biological samples marked with standard fluorochromes. The experimental investigation confirms the success of the proposed microdevice in the detection of cells. An erratum to this article can be found at     

Optical trapping of microparticles using silicon nitride waveguide junctions and tapered-waveguide junctions on an optofluidic chip

We study optical trapping of microparticles on an optofluidic chip using silicon nitride waveguide junctions and tapered-waveguide junctions. We demonstrate the trapping of single 1 μm-sized polystyrene particles using the evanescent field of waveguide junctions connecting a submicrometer-sized input-waveguide and a micrometer-sized output-waveguide. Particle trapping is localized in the vicinity of the junction. We also demonstrate trapping of one and two 1μm-sized polystyrene particles using tapered-waveguide junctions connecting a submicrometer-sized singlemode input-waveguide and a micrometer-sized multimode output-waveguide. Particle trapping occurs near the taper output end, the taper center and the taper input end, depending on the taper aspect ratio.     

An integrated optical oxygen sensor fabricated using rapid-prototyping techniques

This paper details the design and fabrication of an integrated optical biochemical sensor using a select oxygen-sensitive fluorescent dye, tris(2,2'-bipyridyl) dichlororuthenium(ii) hexahydrate, combined with polymeric waveguides that are fabricated on a glass substrate. The sensor uses evanescent interaction of light confined within the waveguide with the dye that is immobilized on an SU-8 waveguide surface. Adhesion of the dye to the integrated waveguide surface is accomplished using a unique process of spin-coating/electrostatic layer-by-layer formation. The SU-8 waveguide was chemically modified to allow the deposition process. Exposure of the dye molecules to the analyte and subsequent chemical interaction is achieved by directly coupling the fluid channel to the integrated waveguide. The completed sensor was linear in the dissolved oxygen across a wide range of interest and had a sensitivity of 0.6 ppm. A unique fabrication aspect of this sensor is the inherent simplicity of the design, and the resulting rapidity of fabrication, while maintaining a high degree of functionality and flexibility.     

Polymer waveguide backplanes for optical sensor interfaces in microfluidics

A polymer optical backplane capable of generic luminescence detection within microfluidic chips is demonstrated using large core polymer waveguides and vertical couplers. The waveguides are fabricated through a new process combining mechanical machining and vapor polishing with elastomer microtransfer molding. A backplane approach enables general optical integration with planar array microfluidics since optical backplanes can be independently designed but still integrated with planar fluidic circuits. Fabricated large core waveguides exhibit a loss of 0.1 dB cm(-1) at 626 nm, a measured numerical aperture of 0.50, and a collection efficiency of 2.86% in an n = 1.459 medium, comparable to a 0.50 NA microscope objective. In addition to vertical couplers for out-of-plane collection and excitation, polymer waveguides are doped with organic dyes to provide wavelength selective filtering within waveguides, further improving optical device integration. With large core low loss waveguides, luminescence collection is improved and measurements can be performed with simple LEDs and photodetectors. Fluorescein detection via fluorescence intensity with a limit of detection (3sigma) of 200 nM in a 1 microL volume is demonstrated. Phosphorescence lifetime based oxygen detection in water in an oxygen controllable microbial cell culture chip with a limit of detection (3sigma) of 0.08% or 35 ppb is also demonstrated utilizing the waveguide backplane. Single waveguide luminescence collection performance is equivalent to a back collection geometry fiber bundle consisting of nine 500 microm diameter collection fibers.     

Optical Response of Porous Titania‐Silica Waveguides to Surface Charging in Electrolyte Filled Pores

In this work, we present a novel method for in situ investigation of surface charging and ion transport inside nanopores of titania‐silica waveguide by means of the optical‐waveguide‐lightmode spectroscopy. Porous oxide waveguides show a strong optical response when exposed to electrolyte solutions, and this response is consistent with oxide surface charging due to changes in ionic strength and pH of the solution in contact with the waveguide. The optical response to pH or electrolyte concentration change is stabilized within several minutes when the solution ionic strength is sufficiently high (0.1M ), while it takes two orders of magnitude longer to reach stable optical response at very low ionic strengths (<0.1mM ). The relaxation times at the high ionic strength are still by several orders of magnitude slower than expected from bulk diffusion coefficients of electrolytes in water. Our results indicate that diffusion of electrolytes is severely hindered (and more so with decreasing ionic strength) in charged pores inside waveguides.     

Gravitation-driven stress-reduced cell handling

We present a simple lab-on-chip device for handling small samples of delicate cells, e.g. stem cells. It uses a combination of sedimentation and dielectrophoresis. The transport of cells is driven by gravitation. Dielectrophoresis uses radio-frequency electric fields for generating particle-selective forces dependent on size and polarisability. Electrodes along the channels hold particles and/or cells in a defined position and deflect them towards different outlets. The absence of external pumping and the integration of injection and sampling ports allow the processing of tiny sample volumes. Various functions are demonstrated, such as contact-free cell trapping and cell/particle sorting. Pairs of human cells and antibody-coated beads, as they are formed for T cell activation, are separated from unbound beads. The cells experience only low stress levels compared with the stress levels in dielectrophoresis systems, where transport depends on external pumping. Our device is a versatile yet simple tool that finds applications in cellular biotechnology, in particular when an economic solution is required. Figure A simple gravitation-driven lab-on-chip device for the separation of mixed populations of microparticles or cells by negative dielectrophoresis.     

Controlled optical manipulation and sorting of nanomaterials enabled by photonic and plasmonic nanodevices

Precise manipulation and sorting of nanomaterials cannot rely on techniques used for micro- and macro-scale objects because of their nanoscale size, which is smaller than the diffraction limit, and their fast Brownian diffusion. To overcome the limitations of standard optical tweezers, new techniques have recently emerged that make use of optical forces acting on nanomaterials in the vicinity of photonic and plasmonic nanostructures. This review focuses on the techniques that have been recently developed to either optically transport, sort, trap, rotate, assemble, or deposit nanomaterials using photonic or plasmonic devices. The first part is dedicated to the optical transport and sorting of nanomaterials using photonic waveguides. The second part provides an overview of the recent work on optical trapping and manipulation of nanomaterials using photonic and plasmonic nanoresonators. The third part provides a short summary of recent work on optical trapping and manipulation using metalenses and metasurfaces. This review aims to highlight some specific functionalities enabled by photonic and plasmonic devices that make it possible to tailor the optical forces acting on nanomaterials.     

Integrated wavelength-selective optical waveguides for microfluidic-based laser-induced fluorescence detection

We demonstrate the fabrication and characterization of a novel, inexpensive microchip capable of laser induced fluorescence (LIF) detection using integrated waveguides with built-in optical filters. Integrated wavelength-selective optical waveguides are fabricated by doping poly(dimethysiloxane) (PDMS) with dye molecules. Liquid-core waveguides are created within dye-doped PDMS microfluidic chips by filling channels with high refractive index liquids. Dye molecules are allowed to diffuse into the liquid core from the surrounding dye-doped PDMS. The amount of diffusion is controlled by choosing either polar (low diffusion) or apolar (high diffusion) liquid waveguide cores. The doping dye is chosen to absorb excitation light and to transmit fluorescence emitted by the sample under test. After 24 h, apolar waveguides demonstrate propagation losses of 120 dB cm(-1) (532 nm) and 4.4 dB cm(-1) (633 nm) while polar waveguides experience losses of 8.2 dB cm(-1) (532 nm) and 1.1 dB cm(-1) (633 nm) where 532 and 633 nm light represent the excitation and fluorescence wavelengths, respectively. We demonstrate the separation and detection of end-labelled DNA fragments using polar waveguides for excitation light delivery and apolar waveguides for fluorescence collection. We demonstrate that the dye-doped waveguides can provide performance comparable to a commercial dielectric filter; however, for the present choice of dye, their ultimate performance is limited by autofluorescence from the dye. Through the detection of a BK virus polymerase chain reaction (PCR) product, we demonstrate that the dye-doped PDMS system is an order of magnitude more sensitive than a similar undoped system (SNR: 138 vs. 9) without the use of any external optical filters at the detector.     

Fabrication of Erbium-Doped Channel Waveguides by a Combination of Ion Exchange and Sol-Gel Techniques

Erbium-doped germano-silicate thin films of good optical quality were produced by the sol-gel technique. High refractive index changes of up to 0.018 were obtained by sodium-silver ion exchange. Monomode optical waveguides with Gaussian mode profile were fabricated by this technique. It is shown that, if the ion exchange process parameters are well chosen, the influence of the waveguide fabrication on the active properties of the material is negligible.     

Electrical field induced phase-matched second harmonic generation in low Tg polymer waveguides

Second-harmonic generation in the guided waveguide configuration is very attractive because a high fundamental power density can be coupled over long propagation length therefore remarkably high conversion efficiencies can be expected compared to bulk materials.¹ Organic SHG devices in optical waveguides have not been developed extensively because of the difficulty encountered in phase-matching. To avoid this problem, the use of an artificial periodic structure, Cerenkov radiation, and non-colinear light path geometry have already been demonstrated. Recently, we reported an electric field-induced dynamic phase-matching in a guided wave configuration using a main-chain polymer in which the effective phase-matching thickness can be controlled by an applied electric field.² This technique is able to increase the waveguide dimension tolerances of phase-matching condition. In the case of a main-chain polymer, the thermal optic effects due to the heating prevent to satisfy the optimum phase-matching conditions, which causes a reduction in the conversion efficiency of devices. In order to overcome this problem, we have synthesized novel low glass transition temperature (Tg) nonlinear optical (NLO) polymers. In this presentation, we will discuss an electric field-induced dynamic phase-matching of a multilayer waveguide at room temperature using a low Tg NLO polymer which can increase both the waveguide dimension tolerances and overlap integral. Using this technique, efficient phase-matched SHG was generated from p-nitroaniline grafted NLO materials. The dimension tolerance of waveguides under an electric field will be described.     

Active particle control through silicon using conventional optical trapping techniques

Functional integration of optical trapping techniques with silicon surfaces and environments can be realized with minimal modification of conventional optical trapping instruments offering a method to manipulate, track and position cells or non-biological particles over silicon substrates. This technique supports control and measurement advances including the optical control of silicon-based microfluidic devices and precision single molecule measurement of biological interactions at the semiconductor interface. Using a trapping laser in the near infra-red and a reflective imaging arrangement enables object control and measurement capabilities comparable to trapping through a classical glass substrate. The transmission efficiency of the silicon substrate affords the only reduction in trap stiffness. We implement conventional trap calibration, positioning, and object tracking over silicon surfaces. We demonstrate control of multiple objects including cells and complex non-spherical objects on silicon wafers and fabricated surfaces.     

Halide Perovskite Single Crystals and Nanocrystal Films as Electron Donor-Acceptor Heterojunctions

Halide perovskites are materials for future optical displays and solar cells. Electron donor-acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined e-beam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trapping-assisted band gap engineering at the desired locations in MAPbBr₃ microrods, microplates, or nanocrystal thin films. The built-in donor-acceptor double and multi-heterojunction structures let us transport and trap photogenerated charge carriers from wide-band gap bromide to narrow-band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single-, double- and multi-heterojunction donor-acceptor halide perovskites for photovoltaic, photonic, and electronic applications.     

Vapour‐Phase Epitaxial Growth of Dual‐Colour‐Emitting DCM‐Perylene Micro‐Heterostructure Optical Waveguides

Organic micro‐heterostructures (MHS) with dual optical emissions are essential to produce miniaturized optical waveguides for wavelength division multiplexing technologies. The bimolecular MHS produced by solution‐based bottom‐up self‐assembly technique often leads to poor surface smoothness, edge imperfection, defects, and unwanted thin films deposits. Conversely, sequential sublimation technique at ambient pressure facilitates effective integration of α‐perylene micro‐square with dicyanomethylene‐2‐methyl‐6‐(p‐dimethylaminostyryl) 4H‐pyran (DCM) microrods in an epitaxial manner to produce MHS. The obtained DCM/perylene MHS act as optical waveguides to produce red (λ_max≈670 nm) or/and yellow (λ_max≈607 nm) dual optical outputs via an energy transfer mechanism depending upon the heterostructures geometry and optical excitation positions. The presented dual‐color emitting MHS optical waveguides are essential for the integrated nano‐photonic and optoelectronic device structures.     

Viscosity and refractive index adjustment of poly(methyl methacrylate‐co‐ethyleneglycol dimethacrylate) for application in microoptics

Polymer optical components like waveguides or lenses are gaining more and importance as passive or active devices enabling the formation of a sensor and detector platform, e.g. for monitoring the health of large area functional surfaces, which are difficult to access like the wings of an off‐shore wind energy plant. With respect to low‐loss waveguiding and the use of chemical and mechanical stable polymers there is a need to tailor the optical as well as the thermomechanical properties. The given approach describes the addition of electron‐rich small organic molecules like phenanthrene to a poly(methyl methacrylate)‐based polymer matrix enabling a significant refractive index increase from 1.49 up to almost 1.55 (@589 nm). As undesirable side effects the optical transmittance in the visible range at higher guest molecule content is reduced, and a pronounced plasticizing occurs. Both hamper the application of the mixture, e.g. as optical waveguide material. The plasticizing and the accompanied drop of the glass transition temperature, determining the maximum operation temperature, can be partially compensated by the copolymerization of the methyl methacrylate monomer (MMA) with the difunctional monomer ethyleneglycol dimethacrylate (EGDMA) at certain crosslinker content. The resulting new developed guest–host mixtures enable the realization of optical devices with adjusted rheological behavior prior to curing and tailored optical properties after polymerization. Copyright © 2015 John Wiley & Sons, Ltd.     

Fluorescent liquid-core/air-cladding waveguides towards integrated optofluidic light sources

We have demonstrated fluorescent liquid-core/air-cladding (LA) waveguides suitable for use as integrated optofluidic light sources. These waveguides were fabricated by conventional soft lithography using poly(dimethylsiloxane) (PDMS). Two-phase stratified flows of air and ethylene glycol with fluorescent dye were generated along the PDMS channel. Compared to the liquid-core/liquid-cladding (L(2)) waveguide, the larger refractive index contrast of the LA waveguide resulted in stronger optical confinement. Specifically, the larger refractive index contrast led to experimentally achievable captured fractions (the amount of light to be coupled into the liquid core) as high as 22.8% and the measured propagation losses as low as 0.14 dB cm(-1). Furthermore, in our LA waveguides, diffusional mixing of the core and cladding fluids did not occur and the size of the core stream could be reversibly tuned simply by adjusting the flow rates of the two contiguous phases.     

Polyaniline thin film optical waveguides for integrated optics and VLSI prepared by vacuum evaporation technique

Polyaniline is emerging as an important polymer material which offers challenging opportunities for both fundamental research and new technological applications in waveguides. Metal doped polyaniline has been prepared initially in the form of powder by a solution growth technique. The emeraldine salt with doped metal was also prepared by solution growth technique. This powder was used for vacuum evaporation on optically flat glass substrate. The dark green doped (Fe, Al) polyaniline thin films were prepared by vacuum evaporation technique (10^?4 torr). Deposited waveguide thin films have been characterized structurally, using X‐ray diffraction (XRD), optically etc. Effective refractive index of the thin film waveguide was also calculated theoretically and experimentally. Waveguide parameters, namely refractive index, propagation loss and depth of vacuum deposited polyaniline thin films optical waveguide have been determined. The optical spectra and structure and waveguide parameters of vacuum deposited polyaniline thin films are strongly affected by the type of doping. It is possible to reduce the losses by addition of Fe to the vacuum deposited polyanine thin film and modify the effective refractive index (O_eff) according to particular requirements. Results are compared with the results in the literature. Copyright © 2002 John Wiley & Sons, Ltd.     

Rapid fabrication of a microfluidic device with integrated optical waveguides for DNA fragment analysis

The fabrication and performance of a microfluidic device with integrated liquid-core optical waveguides for laser induced fluorescence DNA fragment analysis is presented. The device was fabricated through poly(dimethylsiloxane) (PDMS) soft lithography and waveguides are formed in dedicated channels through the addition of a liquid PDMS pre-polymer of higher refractive index. Once a master has been fabricated, microfluidic chips can be produced in less than 3 h without the requirement for a cleanroom, yet this method provides an optical system that has higher performance than a conventional confocal optical assembly. Optical coupling was achieved through the insertion of optical fibers into fiber-to-waveguide couplers at the edge of the chip and the liquid-fiber interface results in low reflection and scattering losses. Waveguide propagation losses are measured to be 1.8 dB cm(-1) (532 nm) and 1.0 dB cm(-1) (633 nm). The chip displays an average total coupling loss of 7.6 dB due to losses at the optical fiber interfaces. In the electrophoretic separation and detection of a BK virus PCR product, the waveguide system achieves an average signal-to-noise ratio of 570 +/- 30 whereas a commercial confocal benchtop electrophoresis system achieves an average SNR of 330 +/- 30. To our knowledge, this is the first time that a waveguide-based system has been demonstrated to have a SNR comparable to a commercially available confocal-based system for microchip capillary electrophoresis.     

Quantum dot enabled thermal imaging of optofluidic devices

Quantum dot thermal imaging has been used to analyse the chromatic dependence of laser-induced thermal effects inside optofluidic devices with monolithically integrated near-infrared waveguides. We demonstrate how microchannel optical local heating plays an important role, which cannot be disregarded within the context of on-chip optical cell manipulation. We also report on the thermal imaging of locally illuminated microchannels when filled with nano-heating particles such as carbon nanotubes.