Liquid Core Waveguide Research Articles

A LONG PATHLENGTH SPECTROPHOTOMETRIC TEGAFUR DETECTOR USING A LIQUID-CORE WAVEGUIDE

A Liquid-Core Waveguide (LCW) detection system for high sensitive determination of tegaful (FT) was developed. In this system the LCW cell was connected to the end of a hollow cathode lump and the other end to a UV spectrometer. A sample solution containing FT was pumped to the LCW cell through a T-shaped connector. A UV absorption of analyte was detected by the UV spectrometer. The configuration of connectors of LCW cell to the light source and the UV detector was designed. Stable and high responses of FT were obtained in a double tube system in which an edge of LCW cell was covered with another tube with large diameter was set in the T-connector. It was found that the UV absorption response of FT obtained in this LCW system depends on the core length and the concentration of FT. The sensitivity of FT obtained by using 65 cm of the LCW cell length was 10-fold higher than that of using 1 cm cell which was often used with a conventional UV-visible detector.

A novel long path length absorbance spectroscopy for the determination of ultra trace organophosphorus pesticides in vegetables and fruits

A simple, rapid, sensitive and reproducible spectrophotometry for determination of ultra trace organophosphorus pesticides (OPs) with liquid core waveguide light intensity technique is presented. OPs were degraded into phosphate with UV light, potassium peroxydisulphate as oxidant and nanosized titanium dioxide as catalyst. Under the optimum selected conditions, linear light intensity response was obtained in the range of 2.0 × 10 −11 to 8.0 × 10 −10 g mL −1 phosphate, and the limit of detection (LOD) 6.7 × 10 −12 g mL −1 was achieved. Both the low limit of linear range and the LOD of the proposed method were lower over 1000-fold than that of classical spectrophotometry. The proposed method was applied to the determination of ultra trace OPs in vegetables and fruits samples.

Single-molecule detection sensitivity using planar integrated optics on a chip

We present a fully planar integrated optical approach to single-molecule detection based on microfabricated planar networks of intersecting solid and liquid-core waveguides. We study fluorescence from dye molecules in liquid-core antiresonant reflecting optical waveguides, and demonstrate subpicoliter excitation volumes, parallel excitation through multiple pump waveguides, and single-molecule detection sensitivity. Integrated silicon photonics combined with single-molecule detection in solution create a compact, robust, and sensitive platform that has applications in numerous fields ranging from atomic physics to the life sciences.

Spectrophotometric Measurements of pH in-Situ: Laboratory and Field Evaluations of Instrumental Performance

Automated in-situ instrumentation has been developed for precise and accurate measurements of a variety of analytes in natural waters. In this work we describe the use of 'SEAS' (spectrophotometric elemental analysis system) instrumentation for measurements of solution pH. SEAS-pH incorporates a CCD-based spectrophotometer, an incandescent light source, and dual pumps for mixing natural water samples with a sulfonephthalein indicator. The SEAS-pH optical cell consists of either a liquid core waveguide (LCW, Teflon AF-2400) or a custom-made PEEK cell. Long optical path lengths allow use of indicators at low concentrations, thereby precluding large indicator-induced pH perturbations. Laboratory experiments show that pH measurements obtained using LCW and PEEK optical cells are indistinguishable from measurements obtained using conventional spectrophotometric cells and high-performance spectrophotometers. Deployments in the Equatorial Pacific and the Gulf of Mexico demonstrate that SEAS-pH instruments are capable of obtaining vertical pH profiles with high spatial resolution. SEAS-pH deployments at a fixed river-site (Hillsborough River, FL) demonstrate the capability of SEAS for observations of diel pH cycles with high temporal resolution. The in-situ precision of SEAS-pH is assessed as 0.0014 pH units, and the system's measurement frequency is approximately 0.5 Hz. This work indicates that in-situ instrumentation can be used to provide accurate, precise, and highly resolved observations of carbon-system transformations in the natural environment.

Liquid Core Waveguide Spectrophotometry for the Sensitive Determination of Nitrite in River Water Samples

A flow injection analysis system was built with a liquid core waveguide spectrophotometric detector using an 80 cm Teflon AF-1600 capillary tube (2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole/tetrafluoroethylene). The system was applied to determine nitrite ion in river water samples. The lower limit of detection for nitrite was 2.1 nmol dm(-3) (0.1 ng dm(-3) as NO(2)(-)) and the relative standard deviation of measurements was typically 0.56% (n = 5) at 0.21 micromol dm(-3).

Lens-coupled liquid core waveguide for ultraviolet-visible absorption spectroscopy

We have developed and characterized a modular liquid core waveguide (LCW) assembly for use in a commercial spectrophotometer to measure very low light absorbance values for dilute aqueous solutions in both the ultraviolet and visible wavelengths. The sample cell in this assembly is composed of a ∼1m, pure Teflon® AF 2400 tube that is coupled to the spectrophotometer light path with a quartz lens and windows. Spectrophotometric absorbance measurements of test solutions (e.g., dilute sodium nitrate and hydrogen peroxide) produce clear and distinct spectra that exhibit a lower limit of detection of 3mAU between 240 and 640nm. At absorbances above 10mAU our LCW system produces spectra from multiple independent injections that have a relative standard deviation of less than 10% and average absorbances within 5% of calculated values based on published molar absorptivities.

Kinetic Monitoring of Electrophoretically Induced Solute Reaction by Axial Absorption Detection with Liquid-Core Waveguide

Teflon AF-2400 capillary has been used for capillary electrophoretic separation as well as for liquid-core waveguide for axial absorption detection. This separation/detection scheme has allowed continuous monitoring of electrophoretically induced reactions. In this paper, the decomposition of Cd2+ complex with 4-(2-pyridylazo)resorcinol has been tested, and its decomposition kinetics has been studied. A simple modeling has predicted the single-exponential decay of the absorbance detected by the present axial absorption detector and has allowed the estimation of the decomposition rate constant for this reaction.

Microfluidic liquid–liquid extraction system based on stopped-flow technique and liquid core waveguide capillary

In this work, a miniaturized liquid–liquid extraction system under stopped-flow manipulation mode with spectrometric detection was developed. A Teflon AF liquid-core waveguide (LCW) capillary was used to serve as both extraction channel for organic solvent flow and adsorption detection flow cell. Gravity induced hydrostatic pressure was used to drive the organic and aqueous phases through the extraction channels. During extraction process, a stable organic and aqueous phase interface was formed at the outlet of the capillary, through which the analyte in the flowing aqueous stream was extracted into the stationary organic solvent in capillary. The absorbance of the analyte extracted into the organic solvent was measured in situ by a spectrometric detection system with light emitting diode (LED) as light source and photodiode as absorbance detector. The performance of the system was demonstrated in the determination of sodium dodecyl sulfate (SDS) extracted as an ion pair with methylene blue into chloroform. The precision of the measured absorbance for a 5 mg L −1 SDS standard was 6.1% R.S.D. ( n = 5). A linear response range of 1–10 mg L −1 SDS was obtained with 5 min extraction period. The limit of detection (LOD) for SDS based on three times standard deviation of the blank response was 0.25 mg L −1.

Liquid core modal interferometer integrated with silica waveguides

An integrated structure is demonstrated as a refractive index sensor. The structure consists of a liquid-filled elliptical microchannel embedded in silica glass and integrated with waveguides. The microchannel features entry points that are open to the top surface of the device and distinct from the optical input. The structure allows light to couple from a solid-core input waveguide to the liquid-core waveguide formed by the microchannel, and back to a solid-core output waveguide. Bimodal interference allows the structure to be sensitive to the refractive index of the liquid, with a full beat corresponding to a refractive index change of /spl sim/10/sup -4/. The structure allows the direct integration of optical fluids with silica waveguides for sensing and optical processing applications.

A miniaturized wide‐angle 2D cytometer

We present an optical waveguide based cytometer that is capable of simultaneously collecting the light scattered by cells over a wide range of solid angles. Such comprehensive scattering data are a prerequisite for the microstructural characterization of cells. We use latex beads as cell mimics, and demonstrate the ability of this new cytometer to collect back-scattered light in two dimensions (2D). This cytometer is based on a liquid-core optical waveguide, excited by prism coupling, that also serves as the microfluidic channel. In principle, our use of a hemispherical lens allows the collection of scattered light from 0 to 180 degrees in 2D. The experimentally observed positions of the intensity peaks of the back-scattered light agree well with theoretical prediction of scattering from both 4.0- and 9.6-mum diameter latex beads. The position of the bead, relative to the axes of the hemispherical lens and the microchannel, strongly affects the scattering pattern. We discuss a computational method for determining these offsets. We show that wide-angle 2D light scattering patterns of cell-sized latex beads can be observed in a microfluidic-based optical cytometer that uses leaky waveguide mode excitation. This chip-based system is compatible with emerging chip-based technologies.

Comment: Analysis of cellular structure by light scattering measurements in a new cytometer design based on a liquid-core waveguide

Comment: Analysis of cellular structure by light scattering measurements in a new cytometer design based on a liquid-core waveguide

Reply: Analysis of cellular structure by light scattering measurements in a new cytometer design based on a liquid-core waveguide

The results of applying a novel microfluidic optical cytometer to generate and observe the light scattered from biological cells over a wide range of angles are presented. This cytometer incorporates a waveguide that increases the intensity of the scattered light to the extent that an inexpensive digital camera can be used to detect the light over a large solid angle. This device was applied to yeast cells and latex beads and experimental data were compared with the results of a finite difference time-domain (FDTD) method of simulation. The simulated scattering patterns were calculated from reported values of optical parameters and are in good qualitative agreement with experiment. It is demonstrated that this system could be used to acquire information on the microstructure and potentially the nanostructure of cells.

Seeing a Deep Ocean CO2 Enrichment Experiment in a New Light: Laser Raman Detection of Dissolved CO2 in Seawater

We used a newly developed in situ laser Raman spectrometer (LRS) for detection of elevated levels of dissolved CO2 in seawater. The experiment was carried out at 500 m depth, 6 degrees C, to examine new protocols for detection of CO2-enriched seawater emanating from a liquid CO2 source in the ocean, and to determine current detection limits under field conditions. A system of two interconnected 5 L chambers was built, with flow between them controlled by a valve and pump system, and this unit was mounted on an ROV. The first chamber was fitted with a pH electrode and the optical probe of the LRS. In the second chamber approximately 580 mL of liquid CO2 was introduced. Dissolution of CO2 across the CO2-seawater interface then occurred, the valves were opened, and a fixed volume of low-pH/CO2-enriched seawater was transferred to the first chamber for combined pH/Raman sensing, where we estimate a mean dissolution rate of approximately 0.5 (micromol/cm2)/s. This sequence was repeated, resulting in measurement of a progressively CO2 enriched seawater sample. The rapid in-growth of CO2 was readily detected as the Fermi dyad of the dissolved state with a detection limit of approximately 10 mM with spectral acquisition times of 150 s. The detection of background levels of CO2 species in seawater (approximately 2.2 mM, dominantly HCO3-) will require an improvement in instrument sensitivity by a factor of 5-10, which could be obtained by the use of a liquid core waveguide.

A simple microfluidic system for efficient capillary electrophoretic separation and sensitive fluorimetric detection of DNA fragments using light-emitting diode and liquid-core waveguide techniques

A miniaturized CE system has been developed for fast DNA separations with sensitive fluorimetric detection using a rectangle type light-emitting diode (LED). High sensitivity was achieved by combining liquid-core waveguide (LCW) and lock-in amplification techniques. A Teflon AF-coated silica capillary on a compact 6x3 cm baseplate served as both the separation channel for CE separation and as an LCW for light transmission of fluorescence emission to the detector. An electronically modulated LED illuminated transversely through a 0.2 mm aperture, the detection point on the LCW capillary without focusing, and fluorescence light was transmitted to the capillary outlet. To simplify the optics and enhance collection of light from the capillary outlet, an outlet reservoir was designed, with a light transmission window, positioned directly in front of a photomultiplier tube (PMT), separated only by a high pass filter. Automated sample introduction was achieved using a sequential injection system through a split-flow interface that allowed effective release of gas bubbles. In the separation of a phiX174 HaeIII DNA digest sample, using ethidium bromide as labeling dye, all 11 fragments of the sample were effectively resolved in 400 s, with an S/N ratio comparable to that of a CE system with more sophisticated LIF.

Fluorescence detection system for capillary separations utilizing a liquid core waveguide with an optical fibre-coupled compact spectrometer

A fluorescence detection system for capillary liquid separation methods is described. The system is based on a silica capillary coated with a low refractive index fluoropolymer Teflon AF that serves both as a separation channel and as a liquid core waveguide (LCW). A fibre-coupled laser excites separated analytes in a detection point and arising fluorescence is collected at one end of the LCW capillary into the other optical fibre which brings it to a compact charge-coupled device (CCD) array spectrometer installed in a desktop computer. No additional components such as focusing optics or filters are necessary. This system was used for detecting isoelectrically focused fluorescent low-molecular-mass p I (isoelectric point) markers and fluorescein isothiocyanate (FITC) labelled proteins. The ability of the system to acquire fluorescent spectra is also demonstrated.

Integrating functional components into capillary electrophoresis systems using liquid-core waveguides

Miniaturization and integration have become strong trends in the development of analytical devices, particularly over the past decade. Miniaturized total analysis systems (lTAS), lab-on-a-chip, and analytical microfluidics are all newly established concepts and methods of realizing such goals, which not only imply the production of portable and wearable analytical devices, but also dramatic enhancements in analysis speed and sample or reagent economy. Various platforms have been developed or adapted for achieving such aims, the most important of which are those based on MEMS (Micro-electromechanical Systems) techniques. However, MEMS techniques have still not quite fulfilled expectations in terms of fully integrating functional sample processing and detection components onto single microdevices. In particular, optical detection components, most commonly employed in analytical systems, have often proved to be too complicated, bulky, and/or costly to be microfabricated and integrated on a chip without sacrificing considerable analytical performance. This is especially true when minimum detection windows and volumes are vital for ensuring optimum performance, as in chip-based capillary electrophoresis (CE) separations, or when highly multiplexed detections are required. In fact, the first few generations of commercialized lab-chip CE products, albeit successful, have not yet attempted on-chip integration of detection components (except for the detection window itself). Among various possible routes towards complete integration, techniques based on liquid-core waveguides (LCW) have recently shown great promise. The state-ofart of CE with LCW is briefly reviewed in this article, and the potential for and perspectives on the miniaturization and integration of CE systems with light-emitting diode (LED)-excited fluorimetric detectors are discussed.

Enhancement of signal-to-noise level by synchronized dual wavelength modulation for light emitting diode fluorimetry in a liquid-core-waveguide microfluidic capillary electrophoresis system

The signal-to-noise level of light emitting diode (LED) fluorimetry using a liquid-core-waveguide (LCW)-based microfluidic capillary electrophoresis system was significantly enhanced using a synchronized dual wavelength modulation (SDWM) approach. A blue LED was used as excitation source and a red LED as reference source for background-noise compensation in a microfluidic capillary electrophoresis (CE) system. A Teflon AF-coated silica capillary served as both the separation channel and LCW for light transfer, and blue and red LEDs were used as excitation and reference sources, respectively, both radially illuminating the detection point of the separation channel. The two LEDs were synchronously modulated at the same frequency, but with 180°-phase shift, alternatingly driven by a same constant current source. The LCW transferred the fluorescence emission, as well as the excitation and reference lights that strayed through the optical system to a photomultiplier tube; a lock-in amplifier demodulated the combined signal, significantly reducing its noise level. To test the system, fluorescein isothiocyanate (FITC)-labeled amino acids were separated by capillary electrophoresis and detected by SDWM and single wavelength modulation, respectively. Five-fold improvement in S/N ratio was achieved by dual wavelength modulation, compared with single wavelength modulation; and over 100-fold improvement in S/N ratio was achieved compared with a similar LCW-CE system reported previously using non-modulated LED excitation. A detection limit (S/N = 3) of 10 nM FITC-labeled arginine was obtained in this work. The effects of modulation frequency on S/N level and on the rejection of noise caused by LED-driver current and detector were also studied.

Detection and quantification of Pu(III, IV, V, and VI) using a 1.0-meter liquid core waveguide

SummaryDetection and quantification of the aquo ions of Pu in 1 M HClO4was carried out using a 1-meter liquid core waveguide (LCW) coupled to a fiber optic UV-Vis spectrometer. Detection limits of 7 × 10−7M for Pu(VI), 1.6 × 10−5M for Pu(V), 5 × 10−6M for Pu(IV) and 8 × 10−6M for Pu(III) were achieved. The limits of detection represent increases of 18 to 33 times those achievable using a conventional 1-cm path length. Because of the much lower detection limits of the LCW, routine identification of the oxidation states in dilute Pu solutions can be made.

Raman spectroscopy as a detection method for liquid-separation techniques

Raman spectroscopy has considerable identification power but is, nevertheless, seldom used for detection in liquid-separation methods such as column liquid chromatography and capillary electrophoresis. This is mainly due to its poor analyte detectability. This review gives attention to the improved performance effected by instrumental developments (e.g., laser technology and liquid-core waveguide detector cells) and the proper use of analyte-enrichment techniques. However, the main emphasis is on the benefits that derive from using special Raman modes, such as resonance Raman and surface-enhanced (resonance) Raman spectroscopy. The most promising on-line and at-line set-ups are highlighted, and the detectability vs. identification dilemma is explained. To achieve a real breakthrough, relevant real-life applications will be crucial.

Trace and ultratrace analysis methods for the determination of phosphorus by flow-injection techniques

Trace (≤1 mg/l or 30 μM) and ultratrace (≤1 μg/l or 30 nM) analysis methods for phosphorus determination by flow-injection analysis are reviewed. Most of the methods cited in this review are fundamentally based on the reaction of orthophosphate with molybdate to form heteropoly acids, such as molybdenum yellow and molybdenum blue, and some of the methods are based on the formation of such secondary reactions as ion associates and their aggregates with bulky cations, such as cationic dyes and quaternary ammonium ions. The heteropoly acids themselves can be measured by spectrophotometry, and the ion associate formed with a cationic dye, Malachite Green (MG), can be measured based on the coloration of MG. Light scattering detection methods can be used for measuring the aggregates of ion associates formed with bulky cations. Highly sensitive detection of phosphorus can be accomplished by fluorophotometry; Rhodamine B (RB) and its analogues react with molybdophosphate to form ion associates, which shows fluorescence quenching of RB: LOD is about 5 nM. The detection method based on the chemiluminescence of luminal oxidized with molybdophosphoric acids is probably the most sensitive of all the detection methods reported so far: LOD of the method is as low as 1 nM. The LOD of the molybdenum blue method can be improved by using a liquid core waveguide: LOD is 0.5 nM.