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.     

Tailorable integrated optofluidic filters for biomolecular detection

Spectral filtering is an essential component of biophotonic methods such as fluorescence and Raman spectroscopy. Predominantly utilized in bulk microscopy, filters require efficient and selective transmission or removal of signals at one or more wavelength bands. However, towards highly sensitive and fully self-contained lab-on-chip systems, the integration of spectral filters is an essential step. In this work, a novel optofluidic solution is presented in which a liquid-core optical waveguide both transports sample analytes and acts as an efficient filter for advanced spectroscopy. To this end, the wavelength dependent nature of interference-based antiresonant reflecting optical waveguide technology is exploited. An extinction of 37 dB, a narrow rejection band of only 2.5 nm and a free spectral range of 76 nm using three specifically designed dielectric layers are demonstrated. These parameters result in an 18.4-fold increase in the signal-to-noise ratio for on-chip fluorescence detection. In addition, liquid-core waveguide filters with three operating wavelengths were designed for F?rster resonance energy transfer detection and demonstrated using doubly labeled oligonucleotides. Incorporation of high-performance spectral processing illustrates the power of the optofluidic concept where fluidic channels also perform optical functions to create innovative and highly integrated lab-on-chip devices.     

An integrated optofluidic platform for Raman-activated cell sorting

We report on integrated optofluidic Raman-activated cell sorting (RACS) platforms that combine multichannel microfluidic devices and laser tweezers Raman spectroscopy (LTRS) for delivery, identification, and simultaneous sorting of individual cells. The system allows label-free cell identification based on Raman spectroscopy and automated continuous cell sorting. Two optofluidic designs using hydrodynamic focusing and pinch-flow fractionation are evaluated based on their sorting design and flow velocity effect on the laser trapping efficiency at different laser power levels. A proof-of-principle demonstration of the integrated optofluidic LTRS system for the identification and sorting of two leukemia cell lines is presented. This functional prototype lays the foundation for the development of a label-free cell sorting platform based on intrinsic Raman markers for automated sampling and sorting of a large number of individual cells in solution.     

A high-discernment microflow cytometer with microweir structure

Using a simple and reliable isotropic wet etching process, we fabricated a microflow cytometer in which cells/particles are concentrated in the center of the sample stream using a 2-D hydrodynamic focusing technique and an microweir structure. Having focused the cells/particles, they are detected and counted using a LIF method. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in squeezing the cells/particles into a narrow stream in the horizontal X-Y plane. Furthermore, it is shown numerically that the microweir structure results in the separation of the cells/particles in the vertical X-Z plane such that they pass through the detection region in a sequential fashion and can therefore be counted with a high degree of precision. The experimental results obtained using fluorescent polystyrene beads with diameters of 5 and 10 microm, respectively, confirm the suitability of the proposed device for microfluidic applications requiring the high-precision counting of particles or cells within a sample flow.     

Measurements of scattered light on a microchip flow cytometer with integrated polymer based optical elements

Flow cytometry is widely used for analyzing microparticles, such as cells and bacteria. In this paper, we report an innovative microsystem, in which several different optical elements (waveguides, lens and fiber-to-waveguide couplers) are integrated with microfluidic channels to form a complete microchip flow cytometer. All the optical elements, the microfluidic system, and the fiber-to-waveguide couplers were defined in one layer of polymer (SU-8, negative photoresist) by standard photolithography. With only a single mask procedure required, all the fabrication and packaging processes can be finished in one day. Polystyrene beads were measured in the microchip flow cytometer, and three signals (forward scattering, large angle scattering and extinction) were measured simultaneously for each bead. To our knowledge this is the first time forward scattered light and incident light extinction were measured in a microsystem using integrated optics. The microsystem can be applied for analyzing different kinds of particles and cells, and can easily be integrated with other microfluidic components.     

A microfabricated deformability-based flow cytometer with application to malaria

Malaria resulting from Plasmodium falciparum infection is a major cause of human suffering and mortality. Red blood cell (RBC) deformability plays a major role in the pathogenesis of malaria. Here we introduce an automated microfabricated "deformability cytometer" that measures dynamic mechanical responses of 10(3) to 10(4) individual RBCs in a cell population. Fluorescence measurements of each RBC are simultaneously acquired, resulting in a population-based correlation between biochemical properties, such as cell surface markers, and dynamic mechanical deformability. This device is especially applicable to heterogeneous cell populations. We demonstrate its ability to mechanically characterize a small number of P. falciparum-infected (ring stage) RBCs in a large population of uninfected RBCs. Furthermore, we are able to infer quantitative mechanical properties of individual RBCs from the observed dynamic behavior through a dissipative particle dynamics (DPD) model. These methods collectively provide a systematic approach to characterize the biomechanical properties of cells in a high-throughput manner.     

Performance of an in-plane detection cell with integrated waveguides for UV/Vis absorbance measurements on microfluidic separation devices

A microfluidic device with integrated waveguides and a long path length detection cell for UV/Vis absorbance detection is presented. The 750 microm U-cell detection geometry was evaluated in terms of its optical performance as well as its influence on efficiency for electrophoretic separations in the microdevice. Stray light was found to have a strong effect on both, the sensitivity of the detection and the available linear range. The long path length U-cell showed a 9 times higher sensitivity when compared to a conventional capillary electrophoresis (CE) system with a 75 microm inner diameter (ID) capillary, and a 22 times higher sensitivity than with a 50 microm ID capillary. The linear range was comparable to that achieved in a 75 microm ID capillary and more than twice as large as in a 50 microm ID capillary. The use of the 750 microm U-cell did not contribute significantly to band broadening; however, a clear quantification was made difficult by the convolution of several other band broadening sources.     

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.     

Towards a portable microchip system with integrated thermal control and polymer waveguides for real-time PCR

A novel real-time PCR microchip platform with integrated thermal system and polymer waveguides has been developed. The integrated polymer optical system for real-time monitoring of PCR was fabricated in the same SU-8 layer as the PCR chamber, without additional masking steps. Two suitable DNA binding dyes, SYTOX Orange and TO-PRO-3, were selected and tested for the real-time PCR processes. As a model, cadF gene of Campylobacter jejuni has been amplified on the microchip. Using the integrated optical system of the real-time PCR microchip, the measured cycle threshold values of the real-time PCR performed with a dilution series of C. jejuni DNA template (2 to 200 pg/microL) could be quantitatively detected and compared with a conventional post-PCR analysis (DNA gel electrophoresis). The presented approach provided reliable real-time quantitative information of the PCR amplification of the targeted gene. With the integrated optical system, the reaction dynamics at any location inside the micro reaction chamber can easily be monitored.     

A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection

We have developed a planar, optofluidic Mach-Zehnder interferometer for the label-free detection of liquid samples. In contrast to most on-chip interferometers which require complex fabrication, our design was realized via a simple, single-layer soft lithography fabrication process. In addition, a single-wavelength laser source and a silicon photodetector were the only optical equipment used for data collection. The device was calibrated using published data for the refractive index of calcium chloride (CaCl(2)) in solution, and the biosensing capabilities of the device were tested by detecting bovine serum albumin (BSA). Our design enables a refractometer with a low limit of detection (1.24 × 10(-4) refractive index units (RIU)), low variability (1 × 10(-4) RIU), and high sensitivity (927.88 oscillations per RIU). This performance is comparable to state-of-the-art optofluidic refractometers that involve complex fabrication processes and/or expensive, bulky optics. The advantages of our device (i.e. simple fabrication process, straightforward optical equipment, low cost, and high detection sensitivity) make it a promising candidate for future mass-producible, inexpensive, highly sensitive, label-free optical detection systems.     

Counting of Escherichia coli by a microflow cytometer based on a photonic–microfluidic integrated device

Counting of Escherichia coli DH5α‐cell suspensions in PBS is performed using a microflow cytometer based on a photonic–microfluidic integrated device. Side‐scattered light signals are used to count the E. coli cells. A detection efficiency of 92% is achieved when compared with the expected count from a hemocytometer. The detection efficiency is correlated to the ratio of sample to sheath flow rates. It is demonstrated that E. coli can be easily distinguished from beads of similar sizes (2–4 μm) as their scattering intensities are different.     

Fluorescence microscopy imaging with a Fresnel zone plate array based optofluidic microscope

We report the implementation of an on-chip microscope system, termed fluorescence optofluidic microscope (FOFM), which is capable of fluorescence microscopy imaging of samples in fluid media. The FOFM employs an array of Fresnel zone plates (FZP) to generate an array of focused light spots within a microfluidic channel. As a sample flows through the channel and across the array of focused light spots, the fluorescence emissions are collected by a filter-coated CMOS sensor, which serves as the channel's floor. The collected data can then be processed to render fluorescence microscopy images at a resolution determined by the focused light spot size (experimentally measured as 0.65 μm FWHM). In our experiments, our established resolution was 1.0 μm due to Nyquist criterion consideration. As a demonstration, we show that such a system can be used to image the cell nuclei stained by Acridine Orange and cytoplasm labeled by Qtracker(?).     

A compact differential isoperibol calorimeter with variable heat shields

The dynamic characteristics of an isoperibol solution calorimeter with electrical heating are discussed on a theoretical basis.The design requirements of a solution calorimeter are briefly reviewed. A calorimeter which satisfies these requirements was conducted and is described here. The dynamics of solutions heating by an electrical heater are mathematically developed and computer generated heating curves are compared to experimental curves.     

A tunable 3D optofluidic waveguide dye laser via two centrifugal Dean flow streams

This paper presents a tunable optofluidic waveguide dye laser utilizing two centrifugal Dean flows. The centrifugal Dean flow increases the light confinement of the dye laser by shaping a three-dimensional (3D) liquid waveguide from curved microchannels. The active medium with the laser dye is dissolved in the liquid core and pumped with an external pump laser to produce stimulated emission. The laser's Fabry-Pérot microcavity is formed with a pair of aligned gold-coated fiber facets to amplify the fluorescent emission. The advantage of the 3D optofluidic waveguide dye laser is its higher efficiency, thus to obtain lasing at a reduced threshold (60%) with higher output energy. The demonstrated slope efficiency is at least 3-fold higher than its traditional two-dimensional equivalent. In addition, the laser output energy can be varied on demand by tuning the flow rates of the two flows. This technique provides a versatile platform for high potential applications microfluidic biosensor and bioanalysis.     

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.     

Dye-activated hybrid organic/inorganic mesostructured titania waveguides

A room-temperature synthesis route for the fabrication of a new type of hybrid organic/inorganic mesostructured material based on titania instead of silica as the inorganic component has been developed. This approach enables facile processing of the titania/block copolymer surfactant precursor solution into optically activated, transparent, and crack-free fibers and planar waveguides with adjustable thickness. Stabilization of the structures occurs upon solvent evaporation by formation of a solid, glasslike material without heat treatment. These dye-activated, high refractive index, titania-based composites show efficient waveguiding and mirrorless lasing at low thresholds without the need of an ultralow refractive index support layer.     

A new compact interferometer design

The optical layout of a compact interferometer suitable for Fourier transform spectroscopy is presented. The constraints on the practical implementation of this design are discussed. Specifications are given for the collimating optics, the optical finish of the interferometer components, and the allowable mirror tilt.     

A compact electrode assembly for voltammetric measurements with solid electrodes

Summary An electrode assembly is presented consisting of a cell compartment of plexiglass and an electronic circuit for automatic performance. It was especially designed for the use with polarographs PAR 264, 264 A, 384 and 384 B when working with solid electrodes. A special attempt was made to reduce the metallic parts of the assembly to a minimum in order to avoid contamination risks when analyzing heavy metals.

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Kompakter Elektrodenstand für voltammetrische Messungen mit Festkörperelektroden

Zusammenfassung Ein Elektrodenstand wird beschrieben, der aus einer Meßzelleneinheit aus Plexiglas und einem elektronischen Schaltkreis für automatischen Betrieb besteht. Er wurde speziell für die Polarographen-PAR-Modelle 264 und 384 für voltammetrische Messungen mit Festkörperelektroden konzipiert. Um bei Schwermetallanalysen das Kontaminationsrisiko möglichst gering zu halten, wurden metallische Teile der Zelle weitgehendst vermieden.

     

A long pathlength spectrophotometric pCO(2) sensor using a gas-permeable liquid-core waveguide

The first long pathlength fiber optic-based sensor system to measure pCO(2) in natural waters and the atmosphere is described. The sensor is based on a liquid-core (an indicator-HCO(3)(-)/CO(3)(2-) buffer solution) waveguide made of a low refractive index amorphous fluoropolymer tubing, the wall of which serves as a gas-permeable membrane to sense pCO(2) changes. The system detects the indicator absorbance changes when the liquid-core reaches CO(2) equilibrium with the surrounding sample. Theoretical calculations demonstrate that due to indicator buffer effects, increasing the optical pathlength is a more efficient way to obtain higher sensitivity than increasing the indicator concentration. Using an 18-cm cell with low indicator concentrations (10 muM), this system achieves a precision and an accuracy of +/-2-3 muatm in the pCO(2) range of 200-500 muatm. The sensor also features a response time (99%) of only 2 min for low-level (<1000 muatm) pCO(2) measurements as a result of high CO(2) permeability of the amorphous fluoropolymer membrane. Field tests indicate that this new sensor is capable of handling both atmospheric and aquatic pCO(2) monitoring.