Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development

Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and time-dependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered. Received: 19 January 1998 / Revised: 15 May 1998 / Accepted: 21 May 1998     

Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development

Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and time-dependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered.     

Surface transport and stable trapping of particles and cells by an optical waveguide loop

Waveguide trapping has emerged as a useful technique for parallel and planar transport of particles and biological cells and can be integrated with lab-on-a-chip applications. However, particles trapped on waveguides are continuously propelled forward along the surface of the waveguide. This limits the practical usability of the waveguide trapping technique with other functions (e.g. analysis, imaging) that require particles to be stationary during diagnosis. In this paper, an optical waveguide loop with an intentional gap at the centre is proposed to hold propelled particles and cells. The waveguide acts as a conveyor belt to transport and deliver the particles/cells towards the gap. At the gap, the diverging light fields hold the particles at a fixed position. The proposed waveguide design is numerically studied and experimentally implemented. The optical forces on the particle at the gap are calculated using the finite element method. Experimentally, the method is used to transport and trap micro-particles and red blood cells at the gap with varying separations. The waveguides are only 180 nm thick and thus could be integrated with other functions on the chip, e.g. microfluidics or optical detection, to make an on-chip system for single cell analysis and to study the interaction between cells.     

八乙基卟啉膜/K~+交换玻璃光波导传感器的制备及对甲胺的气敏性研究

利用旋转-甩涂法(Spin-coating)将八乙基卟啉固定在K+交换玻璃光波导表面,制成八乙基卟啉膜/K+交换玻璃光波导敏感元件。利用该敏感元件考察不同有机挥发性气体的响应,同时优化了敏感元件的制备条件。结果表明,该敏感元件对甲胺具有较高的灵敏度,检出限(信噪比S/N=5.1)为1.0×10-8V/V0,响应时间为1.2 s,恢复时间为2.3 s,在平行试验中,其结果具有良好的线性关系,相对标准偏差为1.1%,证明了该元件对甲胺气体检测的准确性。     

Vapor zone velocities measurement using a capillary optical fiber sensor with an application to gas chromatography

A fiber optic sensor has been used for real-time measurement of the migration rates of all the compounds in a mixture separated by gas chromatography. The sensor makes use of a coated capillary optical fiber as the column. This new type of waveguide consists in a polarization-maintaining optical core positioned close to the capillary edge along the entire fiber length. The optical detection is performed through the coupling of the two polarization modes of the waveguide and this coupling is detected by a polarimetric interferometry technique. Through some signal processing, the resulting interferogram provides the migration rates of the various compounds of a gas mixture flowing in the capillary. One of the major benefits of this optical migration rate sensing is that the detection of each velocity peak appears as soon as the analyte enters the capillary fiber and the peaks are constantly measured during the whole separation process. Carrier gas acceleration occurring in the column is plainly demonstrated. This paper presents a proof-of-concept on a qualitative basis. The experiments were done at 29 °C because the current opto-fluidic set-up cannot withstand a higher temperature.     

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.     

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.     

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.     

氧化锌薄膜/锡掺杂玻璃光波导元件及其对氯苯的气敏性研究

建立了玻璃光波导气敏元件检测氯苯气体的方法.采用浸渍-提拉法将ZnO敏感膜固定在锡掺杂玻璃光波导表面,研制出了检测氯苯气体的ZnO薄膜/锡掺杂玻璃光波导气敏元件,并用该玻璃光波导气敏元件对挥发性有机气体进行了检测.实验结果表明,在室温下,气敏元件对氯苯气体有明显的响应,而对相同浓度的其它挥发性有机气体的响应相对较小,对...     

Design of new integrated optical substrates for immuno-analytical applications

Integrated optical Mach-Zehnder interferometers supply information on changes in refractive index and/or thickness of a film placed as a superstrate on top of one of its surface wave-guides. The internal propagation of light is influenced by the evanescent field reaching into the superstrate. This propagating light interferes with an uninfluenced wave in the second arm after recombination. The result is an intensity modulation depending on the refractive index parameters of the substrate, the waveguide itself and the properties of the superstrate. Taking an antigen layer as the superstrate, its interaction with antibodies changes its thickness by several nanometers. This can be observed by recording the change in intensity of the signal of the interferometer. The sensitivity of such a device depends on particular values of the optical parameters of substrate and waveguide with respect to the given superstrate properties. Computer calculations help to select optimum glass and waveguide fabrication conditions. The numerical results of a variety of assumed conditions have been tested experimentally. The application to the improved detection of triazines is discussed.     

微流控液液萃取-液液波导集成化分析系统

利用溴化1-丁基-3-甲基咪唑离子液体/碳酸钠溶液双水相体系,实现了多相层流液液萃取.以具有较高折射率的离子液体为液芯,较低折射率的盐溶液为包层,实现了液液波导吸光度检测.据此建立了一种液液萃取与液液波导检测集成化的微流控分析系统.该系统对甲酚红试样的萃取率在93%以上,对甲酚红试样检测的线性范围为0.01~0.40 mg/m L,相对标准偏差为3.4%(n=11),检出限为3.8μg/m L(3σ).该系统将萃取分离与液液波导长光程吸光度检测集成在一起,为拓展吸光度检测在微流控系统中的应用提供了新思路.     

Optical chemical sensors for the detection of explosives and associated substances

The main analytical characteristics of optical chemical sensors for detecting the vapors and microparticles of explosives and associated substances are compared. The limits of detection, sensitivity, sensor setting time (response speed) and recovery time after the action of an analyte, and the selectivity of fluorescence sensors, chemiluminescence sensors, surface-enhanced Raman sensors, surface plasmon resonance sensors, absorption integrated optical waveguide sensors, waveguide interferometric sensors, and ring resonator based sensors. The effectiveness of the use of nanosized structures and bio- and nanostructured specific coatings in optical sensors is analyzed.     

Study on the formation defect of nano imprinted optical waveguide devices and nano‐indentation detection

In this study, we try to discuss the formation defects found in the application of air‐assisted soft mold UV‐cured nano imprint lithography technology in the manufacture of optical waveguide devices, and find a solution. Meanwhile, we try to utilize the nano‐indentation technology in the material quality detection for optical waveguide devices. The results tell us that there is a corresponding relationship between the indentation hardness and procedure parameters under nano‐meter level depth. For example, the indentation tends to be harder when it is lowly loaded and shallow in depth. Closer it gets to the edge of waveguide's turning, lower the indentation hardness will be. At the same time, different exposal process results in different structural intensity. Therefore, the high structural intensity without forming defects of optical waveguide with less optical loss and better optical transmission. Copyright © 2008 John Wiley & Sons, Ltd.     

A novel C-shaped, gold nanoparticle coated, embedded polymer waveguide for localized surface plasmon resonance based detection

In this study, a novel embedded optical waveguide based sensor which utilizes localized surface plasmon resonance of gold nanoparticles coated on a C-shaped polymer waveguide is being reported. The sensor, as designed, can be used as an analysis chip for detection of minor variations in the refractive index of its microenvironment, which makes it suitable for wide scale use as an affinity biosensor. The C-shaped waveguide coupled with microfluidic channel was fabricated by single step patterning of SU8 on an oxidized silicon wafer. The absorbance due to the localized surface plasmon resonance (LSPR) of SU8 waveguide bound gold nano particle (GNP) was found to be linear with refractive index changes between 1.33 and 1.37. A GNP coated C-bent waveguide of 200 μ width with a bend radius of 1 mm gave rise to a sensitivity of ~5 ΔA/RIU at 530 nm as compared to the ~2.5 ΔA/RIU (refractive index units) of the same dimension bare C-bend SU8 waveguide. The resolution of the sensor probe was ~2 × 10(-4) RIU.     

Optical leaky waveguide biosensors for the detection of organophosphorus pesticides

Organophosphorus (OP) pesticides can be rapidly detected by integrating organophosphorus hydrolase with an optical leaky waveguide biosensor. This enzyme catalyses the hydrolysis of a wide range of organophosphorus compounds causing an increase in the pH. Thus, the direct detection of OP is possible by monitoring of the pH changes associated with the enzyme's activity. This article describes the use of an optical, leaky waveguide clad with absorbing materials for the detection of OP pesticides by measuring changes in refractive index, absorbance and fluorescence. In the most effective configuration, a thick sensing layer was used to increase the amount of immobilized enzyme and to increase the light interaction with the sensing layer, resulting in a greatly enhanced sensitivity. The platforms developed in this work were successfully used to detect paraoxon and parathion down to 4 nM concentrations.     

Graphene-Based Waveguides: Novel Method for Detecting Biological Activity

We demonstrate the fabrication of a biosensor based on graphene coupled with polydimethylsiloxane (PDMS) waveguide. Biosensors work on the principle of local evanescent graphene-coupled wave sensor. It is observed that the evanescent field shifts in the presence of chemical or biological species as evanescent waves are extremely sensitive to a change in refractive index. This method helps to monitor the target analyte by attaching the selective receptor molecules to the surface of the PDMS optical waveguide resulting in its optical intensity distribution shift. We monitor the electrical properties of graphene in the dark and under illumination of PDMS waveguide. The changes in photocurrent through the graphene film were monitored for blue, green, and red light. We observed that the fabricated graphene-coupled PDMS optical waveguide sensor is sensitive to visible light for the used bioanalytes.     

Planar waveguides for ultra-high sensitivity of the analysis of nucleic acids

In the first part of this paper, the need for analytical techniques capable of highly parallel and sensitive nucleic acid analysis, with the capability of achieving very low limits of detection (LODs) and of resolving small differences in concentration, is described. Whereas the requirement for performing simultaneously multi-analyte detection is solved by the approach of nucleic acid microarrays, requirements on sensitivity can often not be satisfied by classical detection technologies. Inherent limitations of conventional fluorescence excitation and detection schemes are identified, and the implementation of planar waveguides as analytical platforms for nucleic acid microarrays, with fluorescence excitation in the evanescent field associated with the guided excitation light, is proposed. The relevant parameters for an optimization of sensitivity are discussed.In the second part of this paper, the specific formats of our planar waveguide platforms, which are compatible with established industrial standard formats allowing for integration into industrial high throughput environments, are presented, as well as the dedicated optical system for fluorescence excitation and detection that we developed. In a direct comparison with a state-of-the-art scanner, it is demonstrated that the implementation of genomic microarrays on planar waveguide platforms allows for unprecedented, direct detection of low-abundant genes in limited amounts of sample. Otherwise, when using conventional fluorescence excitation and detection configurations, the detection of such low amounts of nucleic acids requires massive sample preparation and signal or target amplification steps.     

An optical waveguide acid vapor sensor

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.     

Micro flow modules with combined fluid flow channel and optical detection waveguide - hyper Rayleigh scattering as a case study

Micro flow modules with optical detection have been fabricated in a way which enables optical waveguiding inside and a defined interaction length along the fluid channel. Because of the usually lower refractive index of the solution compared with that of the substrate, so-called "leaky" optical wave-guiding must be employed. The combination of the fluid flow channel function with that of the optical waveguide has advantages for all miniaturized optical detection cells. It has been shown for hyper Rayleigh scattering (HRS) that improvement of the analytical principle is inherent in the miniaturization. The detection limit can be enhanced by at least a factor of 20. The applied HRS measurement procedure also enables simultaneous detection of two photon absorption (TPA) fluorescence. The severe boundary conditions of capillary electrophoresis were used as micro flow module design constraints to enable the transfer of the approach to other types of analysis.     

基于液芯波导原理的微流控芯片长光程光度检测系统

提出了一种基于液芯波导(Liquidcorewaveguide,LCW)原理的微流控芯片吸收光度检测系统.通过芯片与外界接口技术实现液芯波导管与芯片的耦合,建立了芯片上长光程(毫米至厘米级)吸收光度检测池.采用邻菲啉-铁(Ⅱ)显色体系验证系统分析性能,以5.5cm外覆TeflonAF液芯波导管作为检测池(检测池体积240nL)时,芯片系统的检测线性范围为0.03～50μmol/L,对邻菲啉-铁(Ⅱ)配合物的检出限为8nmol/L,检测池有效光程达1.7cm,分析精度RSD(n=5)为0.8%.