Liquid Core Waveguide Research Articles

Analysis of liquid-to-solid coupling and other performance parameters for microfluidically reconfigurable photonic systems

In this paper, we analytically investigate the coupling of light from liquid-core waveguides to conventional solid-core waveguides and a series of other optical properties of liquid waveguides in order to gauge the practicality of such a system for use in microfluidically reconfigurable photonic systems. A finite element model of the system was constructed and relevant properties such as mode field diameter, attenuation, bending loss, and efficiency of evanescent and end-fire coupling were investigated as a function of the liquid waveguide Peclet number and the relative difference in refractive index. For pure liquid systems we show that the mode field diameter decreases monotonically with increasing Peclet number and that bending losses could be significantly reduced by increasing the Peclet number. More critically, we observed irreversible evanescent coupling, in which the light coupled in the solid waveguide is entrapped within the solid rather than coupled back into the liquid waveguide. This effect was caused by the lengthwise variation in the propagation constant of the liquid core due to downstream diffusion. We demonstrate that coupling efficiencies as high as 84% can be obtained for fluid based end-fire coupling by taking advantage of the tunable mode field diameter. By developing techniques for coupling light between liquid and solid states we hope to be able to overcome the drawbacks of solid waveguide systems (e.g. unchangeable structure and properties) and liquid waveguide systems (e.g. diversion and attenuation) yielding a new paradigm for reconfigurable photonics.

Development of a Compact System for the Determination of Lead Using a Liquid Core Waveguide and a Blue Diode as a Light Source

A simple and compact system was developed for the on-site analysis of lead in environmental water samples. The system consisted of a custom-made blue diode as a light source, a liquid core waveguide (LCW) as spectrophotometric cell and a compact UV-visible spectrometer. It weighed within 1.5 kg in total. Lead was detected using a spectrophotometric indicator reagent (TPPS: 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid, disulfuric acid, tetrahydrate) after masking interfering ions by coprecipitation with magnesium hydroxide. With an increase in the length of the LCW cell, the detection limit of lead was almost linearly enhanced, and the linear calibration range was shifted to a lower concentration range. The detection limit of lead by using 100 cm of a LCW cell was 2 nmol dm(-3). The observed value (9.6 +/- 0.4 microg dm(-3)) of lead in a river-water reference material (JSAC 0302-3) with this system was in good agreement with the certified value (9.9 +/- 0.2 microg dm(-3)).

Hand-held Photometer Based on Liquid-Core Waveguide Absorption Detection for Nanoliter-scale Samples

This paper reports a fully integrated hand-held photometer based on the liquid-core waveguide (LCW) detection principle for nanoliter-scale samples. All components of the photometer including light-emitting diode (LED) light source, LCW flow cell, photodiode detector, dropper pump, electronic circuit, liquid-crystal display screen, and battery were fully integrated into a small-sized (12 x 4.5 x 2.1 cm) instrument. A bent optical coupler was developed to conduct the detection light into or out of the LCW flow cell through its sidewall. This design allowed the sampling probe, input and output optical couplers, and LCW flow cell to be integrated in a single Teflon AF capillary, which significantly simplified system structure, improved working reliability, and reduced sample consumption. Two UV-LEDs were used as light source in the photometer to achieve dual wavelength detection at 260 and 280 nm, which was applied to assess on-site the quality and quantity of DNA samples. The effective optical path length of the photometer was approximately 15 mm with a sample consumption of only 350 nL. The potential of the photometer applied in point of care testing was also demonstrated in the measurement of total cholesterol in serum samples.

Optofluidic notch filter integration by lift-off of thin films

Optofluidic platforms used for biomolecular detection require spectral filtering for distinguishing analyte signals from unwanted background. Towards a fully integrated platform, an on-chip filter is required. Selective deposition of dielectric thin films on an optofluidic sensor based on antiresonant reflecting optical waveguide (ARROW) technology provides the means for localized, on-chip optical filtering. We present a lift-off technique, compatible with thin-film processing including plasma-enhanced chemical vapor and sputtering deposition. The resulting optofluidic notch filters exhibited a 20 dB rejection with linewidths as low as 20 nm for ~1 cm long chips consisting of liquid-core and solid-core waveguides.

An environmentally friendly flow system for high-sensitivity spectrophotometric determination of free chlorine in natural waters

A green and highly sensitive analytical procedure was developed for the determination of free chlorine in natural waters, based on the reaction with N,N-diethyl-p-phenylenediamine (DPD). The flow system was designed with solenoid micro-pumps in order to improve mixing conditions by pulsed flows and to minimize reagent consumption as well as waste generation. A 100-cm optical path flow cell based on a liquid core waveguide was employed to increase sensitivity. A linear response was observed within the range 10.0 to 100.0 µg L − 1 , with the detection limit, coefficient of variation and sampling rate estimated as 6.8 µg L − 1 (99.7% confidence level), 0.9% ( n = 20) and 60 determinations per hour, respectively. The consumption of the most toxic reagent (DPD) was reduced 20,000-fold and 30-fold in comparison to the batch method and flow injection with continuous reagent addition, respectively. The results for natural and tap water samples agreed with those obtained by the reference batch spectrophotometric procedure at the 95% confidence level.

Optofluidic device monitoring and fluid dynamics simulation for the spread of viral pathogens in a livestock environment

Rapid monitoring of the spreads of porcine reproductive and respiratory syndrome virus (PRRSV) was attempted using samples collected from nasal swabs of pigs and air samplers within an experimental swine building. An optofluidic device containing liquid-core waveguides was used to detect forward Mie light scattering caused by the agglutination of anti-PRRSV-conjugated submicron particles, with enhanced sensitivity, signal reproducibility, and reusability (reusable up to 75 assays). These results were compared with reverse transcription polymerase chain reaction (RT-PCR) assays (35 cycles) and showed excellent agreements to them. Each assay took less than 10 min including all necessary sample pre-processing, while the RT-PCR assays took up to 4 h including sample pre-processing and gel imaging for PCR products. A 3-D computational fluid dynamics (CFD) simulation was utilized to track the transport and distribution of PRRSV (from the mouths of pigs to the exhaust fans) within a swine building, and compared with the readings from an optofluidic device. Simulation results corresponded well with the experimental data, validating our 3-D CFD model for the spread of viral pathogens in a livestock environment. The developed optofluidic device and 3-D CFD model can serve as a good model for monitoring the spread of influenza A (swine and avian) within animal and human environments.

Multi-mode mitigation in an optofluidic chip for particle manipulation and sensing

A new waveguide design for an optofluidic chip is presented. It mitigates multi-mode behavior in solid and liquid-core waveguides by increasing fundamental mode coupling to 82% and 95%, respectively. Additionally, we demonstrate a six-fold improvement in lateral confinement of optically guided dielectric microparticles and double the detection efficiency of fluorescent particles.

A greener and highly sensitive flow-based procedure for carbaryl determination exploiting long pathlength spectrophotometry and photochemical waste degradation

An environmentally friendly analytical procedure with high sensitivity for determination of carbaryl pesticide in natural waters was developed. The flow system was designed with solenoid micro-pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation. A long pathlength (100 cm) flow cell based on a liquid core waveguide (LCW) was employed to increase the sensitivity in detection of the indophenol formed from the reaction between carbaryl and p-aminophenol (PAP). A clean-up step based on cloud-point extraction was explored to remove the interfering organic matter, avoiding the use of toxic organic solvents. A linear response was observed within the range 5-200 microg L(-1) and the detection limit, coefficient of variation and sampling rate were estimated as 1.7 microg L(-1) (99.7% confidence level), 0.7% (n=20) and 55 determinations per hour, respectively. The reagents consumption was 1.9 microg of PAP and 5.7 microg of potassium metaperiodate, with volume of 2.6 mL of effluent per determination. The proposed procedure was selective for the determination of carbaryl, without interference from other carbamate pesticides. Recoveries within 84% and 104% were estimated for carbaryl spiked to water samples and the results obtained were also in agreement with those found by a batch spectrophotometric procedure at the 95% confidence level. The waste of the analytical procedure was treated with potassium persulphate and ultraviolet irradiation, yielding a colorless residue and a decrease of 94% of total organic carbon. In addition, the residue after treatment was not toxic for Vibrio fischeri bacteria.

Development of a Miniaturized Liquid Core Waveguide System With Nanoporous Dielectric Cladding—A Potential Biosensing Platform

We present a high-throughput optofluidic light waveguide system consisting of etched microchannels in silicon using water as the core and an ultra low refractive index nanoporous dielectric (ND) as the cladding organosilicate nanoparticulate films with refractive index of 1.16 have been used as the cladding layer. Although NDs offers many advantages over Teflon AF for use as the cladding layer, integration of these coatings to the waveguide design is not trivial. In this paper, we address the various integration issues of the NDs to the liquid core waveguide architecture followed by testing of these waveguides for their light guiding capability. Compared to uncoated channels, ND clad channels offer a high light guiding efficiency. In addition, the high surface areas associated with them could be potentially used to immobilize higher density of sensor probes implying a great potential for biosensor applications in an integrated system.

A Compact Spectrophotometer Using Liquid Core Waveguide and Handheld Charge Coupled Device: For Green Method and Ultrasensitive Speciation Analysis of Cr(III) and Cr(VI)

ABSTRACT In this short letter, we report a compact spectrophotometer consisting of a liquid core waveguide as the optical cell and a handheld charge coupled device spectrometer as the detector. This instrumentation features portability, ultrahigh sensitivity, simultaneous multicomponent detection, and minimal analyte solution. Its ultrahigh sensitivity permits the measurement of Cr(III) without coloration with any reagents. Therefore, a simple, fast, cost-effective, and green analytical method was developed for the ultrasensitive and simultaneous speciation analysis of Cr(III) and Cr(VI) in water samples, with the limits of detection down to the ppb level.

Sequential injection trace determination of iron in natural waters using a long‐pathlength liquid core waveguide and different spectrophotometric chemistries

We developed a sequential injection analysis (SIA) method for the determination of iron in coastal, ground, and surface fresh waters using two different reagents (ferrozine and 1,10‐phenathroline). The methodology uses a double‐line SIA system to improve mixing conditions between sample and reagent solutions. A liquid wave‐guide capillary cell (LWCC) with 1.0 m pathlength, 550 µm i.d., and 250 µL internal volume was used to enhance the sensitivity of the determination. The detection limits for the ferrozine and 1,10‐phenanthroline reagent were 0.15 and 0.35 µg L−1, respectively. The system provides a linear response up to 20 µg L−1 and has a high throughput rate (41 h−1), low reagent consumption, and also low effluent production for both reagents. The developed method was applied to natural waters (river, well, ground, potable, and sea waters) and one reference water sample.

Flow cytometry without alignment of collection optics

This study describes the performance of a new waveguide flow cell constructed from Teflon AF (TFC) and the potential use of fiber optic splitters to replace collection objectives and dichroic mirrors. The TFC has the unique optical property that the refractive index of the polymer is lower than water and therefore, water filled TFC behaves and functions as a liquid core waveguide. Thus, as cells flow through the TFC and are illuminated by a laser orthogonal to the flow direction, scattered and fluorescent light is directed down the axis of the TFC to a fiber optic. The total signal in the fiber optic is then split into multiple fibers by fiber optic splitters to enable measurement of signal intensities at different wavelengths. Optical filters are placed at the terminus of each fiber before measurement of specific wavelengths by a PMT. The constructed system was used to measure DNA content of CHO and yeast cells. Polystyrene beads were used for alignment and to assess the performance of the system. Polystyrene beads were observed to produce light scattering signals with unique bimodal characteristics dependent on the direction of flow relative to the collecting fiber optic.

Optofluidic particle concentration by a long-range dual-beam trap

Ultrahigh sensitivity detection of particles in solution implies the ability to detect at very low concentrations. At the single-particle level, this is achieved through fluorescence detection, reaching down to single fluorophores. Sensitivity may also be improved by concentrating many particles into a compact cluster, thus "integrating" the signal of many particles. We show how both ways can be combined on an optofluidic chip in a fully planar geometry utilizing counterpropagating liquid-core waveguide modes to form a loss-based optical trap. This all-optical concentrator can increase the concentration of particles by more than 2 orders of magnitude and also provides a convenient, nondispersive means of transport for particle ensembles.

A versatile total internal reflection photometric detection cell for flow analysis

A total internal reflection (TIR) flow-through cell that is highly tolerant of schlieren effects, has limited hydrodynamic dispersion and does not trap gas bubbles, and which is suitable for sensitive photometric measurements in flow analysis, is described. Light from an optical fibre is introduced into a short length of quartz capillary through the sidewall at an incident angle of ca. 53°. Under this condition, incident light undergoes total internal reflection from the external air–quartz interface and is propagated by successive reflections from the external walls through the aqueous liquid core of the cell. Detection of the transmitted beam is enabled by intentionally introducing an optical coupling medium at a predetermined distance along the capillary wall, which allows the internally reflected light to be captured by a second optical fibre connected to a charge-couple device detector.This configuration embodies a number of the desirable features of a liquid core waveguide cell (i.e. total internal reflection), a multi-reflection (MR) flow cell (i.e. minimum susceptibility to schlieren effects, low hydrodynamic dispersion and little tendency to trap bubbles), and a conventional Z-cell (wide dynamic range). When employed with a flow injection system, a limit of detection of 2.0μgPL−1 was achieved for the determination of reactive phosphate using the TIR cell, compared with LOD values of 3.8μgPL−1 and 4.9μgPL−1 obtained using the MR and Z-cells with same manifold.The combined advantages of schlieren-tolerance and lack of bubble entrapment of the MR cell with the higher S/N ratio and wider dynamic range of a conventional Z-cell, make the TIR cell eminently useful for photometric measurements of samples with widely differing refractive indices.

Surface enhanced Raman scattering of amino acids and peptides

AbstractSurface Enhanced Raman Scattering (SERS) has been used to observe spectra of several amino acids and peptides. SERS signals from amino acids (tryptophan, phenylalanine and glycine) and peptides (Trp‐Trp and Gly‐Gly‐Gly) in silver colloids have been studied in three experimental configurations 1) free volume 2) liquid core waveguide (LCW) and 3) microfluidic channel. Even though all amino acids contain carboxyl and amine functional groups, the conditions for observing the SERS spectra are different for different amino acids. The impact of the type of electrolyte used for colloid aggregation and the experimental procedures for mixing of the components on the amplitude and the stability of the SERS signal have been studied. The optimum conditions for observing SERS signals for the above mentioned amino acids and peptides have been found. For Trp amino acid a SERS enhancement of Raman signal up to 107 was observed. Additional enhancement of 10 to 50 times can be obtained with the help of a liquid core waveguide technique. The results obtained will be useful in the development and optimization of microfluidic chip devices utilizing SERS. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analytical intercomparison between type I and type II long‐pathlength liquid core waveguides for the measurement of chromophoric dissolved organic matter

In the past decade, technological advances in optical sensors have facilitated an increased understanding of the relationship between optical characteristics and biogeochemistry of our oceans. In particular, long‐pathlength liquid core waveguide cells (LCWs) are being used to “map” chromophoric dissolved organic matter (CDOM), as a biogeochemical tracer, in various coastal and open ocean regions. At present, two LCW cell types are used in the study of marine CDOM, and concerns about discrepancies in data collected with the different cell types and problems with baseline offsets have arisen. We conducted a direct comparison of absorption coefficient spectra of a dissolved spectrophotometric standard, molecular weight standard (MWS), and dilution series of natural seawater obtained in type I and type II LCWs to assess data agreement and potential colloid‐mediated biases. Although no statistical difference was observed for the dissolved standard, we found the type I to have a slight bias toward higher absorption coefficient values for MWS 14–150 kDa (within 95% confidence interval) and natural seawater. Seawater CDOM spectral slopes differed significantly between type I and type II LCWs, with a maximum difference in slope of 0.0006 nm−1. Fastidious elimination of microbubbles from the capillary cells greatly reduced baseline offsets and markedly improved CDOM spectral slope precision.

Multisyringe flow injection analysis hyphenated with liquid core waveguides for the development of cleaner spectroscopic analytical methods: improved determination of chloride in waters

In this work, the hyphenation of the multisyringe flow injection analysis technique with a 100-cm-long pathlength liquid core waveguide has been accomplished. The Cl-/Hg(SCN)2/Fe3+ reaction system for the spectrophotometric determination of chloride (Cl(-)) in waters was used as chemical model. As a result, this classic analytical methodology has been improved, minimizing dramatically the consumption of reagents, in particular, that of the highly biotoxic chemical Hg(SCN)2. The proposed method features a linear dynamic range composed of two steps between (1) 0.2-2 and (2) 2-8 mg Cl- L(-1), thus extended applicability due to on-line sample dilution (up to 400 mg Cl- L(-1)). It also presents improved limits of detection and quantification of 0.06 and 0.20 mg Cl- L(-1), respectively. The coefficient of variation and the injection throughput were 1.3% (n = 10, 2 mg Cl- L(-1)) and 21 h(-1). Furthermore, a very low consumption of reagents per Cl- determination of 0.2 microg Hg(II) and 28 microg Fe3+ has been achieved. The method was successfully applied to the determination of Cl- in different types of water samples. Finally, the proposed system is critically compared from a green analytical chemistry point of view against other flow systems for the same purpose.

Microfluidic device capable of sensing ultrafast chemiluminescence

Based on the principle of liquid core waveguide, a novel microfluidic device with micro-scale detection window capable of sensing flashlight emitted from rapid 1,1′-oxalyldi-4-methylimidazole (OD4MI) chemiluminescence (CL) reaction was fabricated. Light emitted from OD4MI CL reaction occurring in the micro-dimensional pentagonal detection window (length of each line segment: 900.0 μm, depth: 50.0 μm) of the microfluidic device with two inlets and one outlet was so bright that it was possible to take an image every 1/30 s at the optimal focusing distance (60 cm) using a commercial digital camera. Peaks obtained using a flow injection analysis (FIA) system with the micro-scale detection window and OD4MI CL detection show excellent resolution and reproducibility without any band-broadening observed in analytical devices having additional reaction channel(s) to measure light generated from slow CL reaction. Maximum height ( H max) and area ( A) of peak, reproducibility and sensitivity observed in the FIA system with the microfluidic device and OD4MI CL detection depends on (1) the mole ratio between bis(2,4,6-trichlorophenyl) oxalate and 4-methyl imidazole yielding OD4MI, (2) the flow rate to mix OD4MI, H 2O 2 and 1-AP in the detection window of the microfluidic device, and (3) H 2O 2 concentration. We obtained linear calibration curves with wide dynamic ranges using H max and A. The detection limit of 1-AP determined with H max and A was as low as 0.05 fmole/injection (signal/background = 3.0).

Espectrofotometria de longo caminho óptico em espectrofotômetro de duplo-feixe convencional: uma alternativa simples para investigações de amostras com densidade óptica muito baixa

We describe the design and tests of a set-up mounted in a conventional double beam spectrophotometer, which allows the determination of optical density of samples confined in a long liquid core waveguide (LCW) capillary. Very long optical path length can be achieved with capillary cell, allowing measurements of samples with very low optical densities. The device uses a custom optical concentrator optically coupled to LCW (TEFLON® AF). Optical density measurements, carried out using a LCW of ~ 45 cm, were in accordance with the Beer-Lambert Law. Thus, it was possible to analyze quantitatively samples at concentrations 45 fold lower than that regularly used in spectrophotometric measurements.

Water-ice chip with liquid-core waveguide functionality. Toward lab on ice

A liquid-core waveguide is fabricated with water-ice, which has lower refractive index than most of the solvents, as cladding, and provides a possibility as an ice chip for flow analyses.