Total protein measurement using a fiber-optic evanescent wave-based biosensor

A novel method and instrumental system to determine the total protein concentration in a liquid sample is described. It uses a fiber optic total protein sensor (FOPS) based on the principles of fiber optic evanescent wave spectroscopy. The FOPS applies a dye-immobilized porous glass coating on a multi-mode optical fiber. The evanescent waves at the fiber optic core-cladding interface are used to monitor the protein-induced changes in the sensor element. The FOPS offers a single-step method for quantifying protein concentrations without destroying the sample. The response time and reusability of the FOPS are evaluated. This unique sensing method presents a sensitive and accurate platform for the quantification of protein.     

Aerobiological pathogen detection by evanescent wave fibre optic sensor

An evanescent field fibre optic sensor was employed for detecting and monitoring aerobiological pathogen contamination in hospital environment. Measurements of methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae colonies were detected in 6 and 13 h, respectively, faster than those obtained by means of conventional techniques. All of the bacteria growth phases were clearly time resolved by means of the optical sensor. The 0.33 cm² sensitive surface area fibre optic transducer also exhibited reproducibility, was of easy construction and low cost, which greatly enhances its potential and usefulness.     

Evanescent wave absorbance based fiber optic biosensor for label-free detection of E. coli at 280 nm wavelength

A novel label-free technique for the detection of pathogens based on evanescent wave absorbance (EWA) changes at 280 nm from a U-bent optical fiber sensor is demonstrated. Bending a decladded fiber into a U-shaped structure enhances the penetration depth of evanescent waves and hence sensitivity of the probe. We show that the enhanced EWA response from such U-bent probes, caused by the inherent optical absorbance properties of bacterial cells or biomolecules specifically bound to the sensor surface, can be exploited for the detection of pathogens. A portable optical set-up with a UV light emitting diode, a spectrometer and U-bent fiber optic probe of 200 μm core diameter, 0.75 mm bend radius and effective probe length of 1cm demonstrated an ability to detect less than 1000 cfu/ml.     

倏逝波光纤免疫传感器的光纤再生

倏逝波光纤免疫传感器作为一种新兴的检测技术,在环境检测、食品卫生检测及生物医学检测等领域具有广泛的应用前景。为了降低检测成本并达到快速检测,光纤再生问题就显得尤为重要。我们在对倏逝波光纤免疫传感器原理和光纤再生原理介绍的基础上,对光纤再生的酸性碱性溶液、高浓度盐溶液、去污剂等方法进行简要综述,探讨了光纤再生存在的问题,并展望了解决光纤重生后倏逝波光纤免疫传感器的应用前景。     

光纤倏逝波生物传感器及其应用

介绍光纤倏逝波生物传感器的基本原理、常用试验方法、基本仪器构建及应用进展。光纤倏逝波生物传感器是基于光波在光纤内以全反射方式传输时产生倏逝波的原理,以生物分子作为敏感元件进行检测的一类新兴传感器。光纤倏逝波生物传感器有望应用于环境监控、食品卫生监控、临床疾病监测、DNA检测和生物战剂检测。     

Development of evanescent wave all-fiber immunosensor for environmental water analysis

A compact and portable evanescent wave all-fiber immunosensor is developed, which employs a novel single-multi-mode fiber optic coupler for exciting and collecting fluorescence emission from the fiber optic probe. Combination tapered fiber probes are produced by tube-etching method and the best tapered ratio of the probe determined is approximately 0.37. Calibration curves obtained for 2,4-dichlorophenoxyacetic acid (2,4-D) and Microcystin-LR (MC-LR) have detection limits of 0.09 microgL(-1)and 0.03 microgL(-1), respectively. The 50% inhibition concentration (IC(50)) for MC-LR and 2,4-D were 1.12+/-0.01 microgL(-1)and 3.81+/-0.03 microgL(-1), respectively. A reusable immunosurface is provided via the covalent attachment of the analyte derivative to a self-assembled monolayer formed onto the fiber optic probe. The regeneration of the sensor surface allows the performance of more than 100 assay cycles within an analysis time of about 20 min for each assay cycle.     

Dual wavelength optical fibre sensor for ph measurement

A rapid response, inexpensive, fibre optic pH sensor which uses a two-wavelength time division multiplexed system to measure the change in absorption of an indicator dye and provide a reference channel for other losses in the light path has been constructed and described, for use in solution, with solid state LED sources and detectors being employed.     

Sensitive and rapid detection of 2,4-dicholorophenoxyacetic acid in water samples by using evanescent wave all-fiber immunosensor

Sensitive and rapid detection of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was achieved with a newly developed evanescent wave all-fiber immunosensor (EWAI). A reusable functional sensing surface of the immunosensor is prepared by covalent binding of 2,4-D-bovine serum albumin (2,4-D-BSA) conjugate to a self-assembled alkanethiol monolayer formed onto the fiber optic probe through heterobifunctional reagent. The quantification of free 2,4-D in samples was based on indirect competitive immunoreaction principle. Under optimum conditions, calibration curve obtained for 2,4-D had detection limits of 0.07 microg L(-1), the 50% inhibition concentration (IC(50)) was 3.93+/-0.03 microg L(-1) and the quantitative detection range was 0.22-69.5 microg L(-1). The antibodies binding on the sensor surface could be removed simply by the flow of a pepsin solution (pH 1.9), facilitating reuse of the same probe. The regeneration of the sensor surface allowed the performance of more than 100 assay cycles without significant loss of reactivity. The antibody showed negligible cross-reactivity against a few compounds structurally similar to 2,4-D. The immunosensor developed was successfully applied to the monitoring of 2,4-D in spiked water samples without significant effect of the matrix. The proposed portable immunosensor is promising for real-time on-site analysis of small molecules of environmental interest.     

Detection of recombinant growth hormone by evanescent cascaded waveguide coupler on silica‐on‐silicon

An evanescent wave based biosensor is developed on the silica‐on‐silicon (SOS) with a cascaded waveguide coupler for the detection of recombinant growth hormone. So far, U ‐bends and tapered waveguides are demonstrated for increasing the penetration depth and enhancing sensitivity of the evanescent wave sensor. In this work, a monolithically integrated sensor platform containing a cascaded waveguide coupler with optical power splitters and combiners designed with S ‐bends and tapper waveguides is demonstrated for an enhanced detection of recombinant growth hormone. In the cascaded waveguide coupler, a large surface area to bind the antibody with increased penetration depth of evanescent wave to excite the tagged‐rbST is obtained by splitting the waveguide into multiple paths using Y splitters designed with s ‐bends and subsequently combining them back to a single waveguide through tapered waveguide and combiners. Hence a highly sensitive fluoroimmunoassay sensor is realized. Using the 2D FDTD (Finite‐difference time‐domain method) simulation of waveguide with a point source in Rsoft FullWAVE, the fluorescence coupling efficiency of straight and bend section of waveguide is analyzed. The sensor is demonstrated for the detection of fluorescently‐tagged recombinant growth hormone with the detection limit as low as 25 ng/ml. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol-gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be rho=-0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.     

Plasmonic Coating on Chemically Treated Optical Fiber Probe in the Presence of Evanescent Wave: a Novel Approach for Designing Sensitive Plasmonic Sensor

Plasmonics - A new approach has been proposed for monolayer plasmonic coating on optical fiber for sensor application. It uses evanescent wave in addition to chemical linker while the chemically...     

Sensitivity of ex situ and in situ spectral surface plasmon resonance sensors in the analysis of protein arrays

We have investigated the sensitivity of ex situ (analysis under air condition) and in situ (analysis under liquid condition) spectral SPR sensors, which were self-constructed with fiber optic spectrometers. The sensitivity of SPR sensors was analyzed in the wavelength range of 550-780 nm by the interactions of streptavidin and biotinylated IgG, and the sensitivity was dependent on the wavelength of measurements. The sensitivity of an ex situ SPR sensor operated at the long wavelength range from 712 nm was approximately 2.6 times higher than that at the short wavelength range from 571 nm. In addition, the sensitivity of an ex situ spectral SPR sensor was about twice as high as that of an in situ spectral SPR sensor for the same resonance wavelength range. This was interpreted in that the difference in sensitivity between two SPR sensors was significantly caused by the evanescent field intensity at the metal/dielectric interface. Thus, it was suggested that ex situ spectral SPR sensors operated at the long wavelength range are sensitive biosensors for the high-throughput analysis of protein interactions on protein arrays.     

Evanescent wave biosensors

Optical biosensors, based on evanescent wave technology, are analytical devices that measure the interactions between biomolecules in real time, without the need for any labels. Specific ligands are immobilized to a sensor surface, and a solution of receptor or antibody is injected over the top. Binding is measured by recording changes in the refractive index, caused by the molecules interacting near the sensor surface within the evanescent field. Evanescent wave-based biosensors are being used to study an increasing number of applications in the life sciences, including the binding and dissociation kinetics of antibodies and receptor-ligand pairs, protein-DNA and DNA-DNA interactions, epitope mapping, phage display libraries, and whole cell- and virus-protein interactions. There are currently four commercially available avanescent wave biosensors on the market. This article describes the technology behind their sensing techniques, as well as the range of applications in which they are employed.     

A single mode fibre-optic evanescent wave biosensor.

This paper reports experimental developments in the construction and operation of a single-mode fibre-optic evanescent wave biosensor using an exposed core silica single-mode fibre embedded in a silica block. The device was able to monitor the concentration of a blue dye, Procion Blue MX-G, in overlayers of various refractive indices. The practicality of such a biosensor has been demonstrated with a colorimetric enzyme assay system. Penicillin G in the 0-0.4 mM concentration range was monitored at 633 nm by the decoloration of the starch-iodine reagent when Bacillus cereus penicillinase was immobilized over the exposed core of the monomode fibre.     

Gene probe assays on a fibre-optic evanescent wave biosensor.

This report describes experiments to detect oligonucleotide hybridization at the surface of a fibre-optic evanescent wave biosensor. Conditions were optimized and the time course of hybridization reactions were found to be very rapid compared to conventional hybridization assays. Binding was easily reversed by heating and the sensor surface could be reused many times. Short (16- and 20-mer) oligonucleotides bound to the waveguide surface could be used to detect fluorescein-labelled complementary sequences at the nanomolar level. Polymerase chain reaction was used to generate a 204-base oligomer that was attached to the waveguide surface. Fluorescein-labelled oligos bound at either the proximal or distal ends of this probe were found to give similar outputs.     

New approaches for the analysis of molecular recognition using the IAsys evanescent wave biosensor

Trends in the analysis of molecular recognition using the IAsys evanescent wave biosensor are outlined. Diversification of sensor surface chemistry, an open cuvette format and the advent of robotics controlled by intelligent software are widening the range and throughput of applications. Analyses of binding and dissociation are now carried out across a wide spectrum of biomolecules, including protein, nucleic acid, carbohydrate and lipid. Determinations are obtained from a range of experimental formats. These include qualitative 'yes/no' screening assays, through semi quantitative ranking of kinetic association, dissociation and equilibrium constants for a family of binding partners, to deriving constants comparable with those which would be obtained in free solution. A dependence of the initial rate of biomolecular association on concentration allows analyte concentration to be measured--an increasingly common application class. This is often employed in situations where a rapid determination is required The ability to recover bound analyte from the sensor surface in sufficient amounts for subsequent characterization is opening up new routes to the parallel analysis of structure and function.     

A composite fibre optic catheter for monitoring peristaltic transit of an intra‐luminal bead

A fibre optic motion sensor has been developed for monitoring the proximity and direction of motion of a ferrous bead travelling axial to the sensor. By integrating an array of these sensors into our previously developed fibre optic manometry catheters we demonstrate simultaneous detection of peristaltic muscular activity and the associated motion of ferrous beads through a colonic lumen. This allows the motion of solid content to be temporally and spatially related to pressure variations generated by peristaltic contractions without resorting to videoflouroscopy to track the motion of a radio opaque bolus. The composite catheter has been tested in an in‐vitro animal preparation consisting of excised sections of rabbit colon.

Cut‐away image of the fibre optic motion sensor showing the location of the fibre Bragg gratings and the rare earth magnet.     

Effect of taper geometries and launch angle on evanescent wave penetration depth in optical fibers

A large penetration depth of an evanescent wave is the key to success for developing an ultra high-resolution fiber-based evanescent wave biosensor. Tapering the fiber and launching light at an angle has the potential of increasing the penetration depth of evanescent wave manifolds. The effects of tapering, launch angle and taper length of the fiber have been explored in detail using a ray-tracing model to calculate the highest possible penetration depth of the evanescent field. Evanescent wave penetration depths of the order of the size of living cells have been achieved by optimizing the parameters relating geometry of tapered fibers.     

Antibody–aptamer functionalized fibre‐optic biosensor for specific detection of Listeria monocytogenes from food

Aim: To develop antibody–aptamer functionalized fibre‐optic biosensor for specific detection of Listeria monocytogenes from food products. Methods and Results: Aptamer, a single‐stranded oligonucleotide ligand that displays affinity for the target molecule, was used in the assay to provide sensor specificity. Aptamer‐A8, specific for internalin A, an invasin protein of L. monocytogenes, was used in the fibre‐optic sensor together with antibody in a sandwich format for detection of L. monocytogenes from food. Biotinylated polyclonal anti‐Listeria antibody, P66, was immobilized on streptavidin‐coated optical waveguide surface for capturing bacteria, and Alexa Fluor 647‐conjugated A8 was used as a reporter. The biosensor was able to selectively detect pathogenic Listeria in pure culture and in mixture with other bacteria at a concentration of approx. 10³ CFU ml^?1. This sensor also successfully detected L. monocytogenes cells from artificially contaminated (initial inoculation of 10² CFU 25 g^?1) ready‐to‐eat meat products such as sliced beef, chicken and turkey after 18 h of enrichment. Conclusion: Based on the data presented in this study, the antibody–aptamer functionalized fibre‐optic biosensor could be used as a detection tool for sensitive and specific detection of L. monocytogenes from foods. Significance and Impact of the Study: The study demonstrates feasibility and novel application of aptamer on fibre‐optic biosensor platform for the sensitive detection of L. monocytogenes from food products.