Chemical Sensing Using a Polymer Coated Long-Period Fiber Grating Interrogated by Ring-Down Spectroscopy

An etched long-period grating was used as a refractive index sensor for vapours of four volatile organic compounds, i.e. m-xylene, cyclohexane, trichloroethylene and commercial gasoline. The sensitivity to the vapours was further increased by solid-phase microextraction into a coating made of polydimethylsiloxane (PDMS)/polymethyl-octylsiloxane (PMOS) co-polymer. By further amplification of the optical loss in an optical cavity made of two identical fiber-Bragg gratings and interrogation by phase-shift cavity ring-down spectroscopy we could detect and distinguish xylene (detection limit: 134ppm) from trichloroethylene (3300ppm), cyclohexane (1850ppm) and gasoline (10,500ppm).

Detection of Lead Contamination of Water and VOC Contamination of Air Using SOI Micro-Optical Devices

Micro-photonic SOI Mach-Zehnder interferometers were coated with solid-phase micro-extraction materials derived from polydimethylsiloxane to enable sensing of volatile organic compounds of the BTEX class in air. A different coating based on functionalized mesoporous silicates is used to detect lead Pb(II) with a detection limit of <;; 100 ppb in water.

Absorption Detection Using Optical Waveguide Cavities

Cavity ring-down spectroscopy is a spectroscopic method that uses a high quality optical cavity to amplify the optical loss due to the light absorption by a sample. In this presentation we highlight two applications of phase-shift cavity ring-down spectroscopy that are suited for absorption measurements in the condensed phase and make use of waveguide cavities. In the first application, a fiber loop is used as an optical cavity and the sample is introduced in a gap in the loop to allow absorption measurements of nanoliters of solution at the micromolar level. A second application involves silica microspheres as high finesse cavities. Information on the refractive index and absorption of a thin film of ethylene diamine on the surface of the microresonator is obtained simultaneously by the measurements of the wavelength shift of the cavity mode spectrum and the change in optical decay time, respectively.

Thin film composite optical waveguides for sensor applications: a review

We review the design and fabrication of thin-film composite optical waveguides (OWG) with high refractive index for sensor applications. A highly sensitive optical sensor device has been developed on the basis of thin-film, composite OWG. The thin-film OWG was deposited onto the surface of a potassium-ion-exchanged (K+) glass OWG by sputtering or spin coating (5-9 mm wide, and with tapers at both ends). By allowing an adiabatic transition of the guided light from the secondary OWG to the thin-film OWG, the electric field of the evanescent wave at the thin film was enhanced. The attenuation of the guided light in the thin film layer was small, and the guided light intensity changed sensitively with the refractive index of the cladding layer. Our experimental results demonstrate that thin-film, composite OWG gas sensors or immunosensors are much more sensitive than sensors based on other technologies. (c) 2004 Elsevier B.V. All rights reserved.

Plasmonic nanorod metamaterials for biosensing.

Label-free plasmonic biosensors rely either on surface plasmon polaritons or on localized surface plasmons on continuous or nanostructured noble-metal surfaces to detect molecular-binding events(1-4). Despite undisputed advantages, including spectral tunability(3), strong enhancement of the local electric field(5,6) and much better adaptability to modern nanobiotechnology architectures(7), localized plasmons demonstrate orders of magnitude lower sensitivity compared with their guided counterparts(3). Here, we demonstrate an improvement in biosensing technology using a plasmonic metamaterial that is capable of supporting a guided mode in a porous nanorod layer. Benefiting from a substantial overlap between the probing field and the active biological substance incorporated between the nanorods and a strong plasmon-mediated energy confinement inside the layer, this metamaterial provides an enhanced sensitivity to refractive-index variations of the medium between the rods (more than 30,000nm per refractive-index unit). We demonstrate the feasibility of our approach using a standard streptavidin-biotin affinity model and record considerable improvement in the detection limit of small analytes compared with conventional label-free plasmonic devices.

High-Performance Biosensing Using Arrays of Plasmonic Nanotubes

We show that aligned gold nanotube arrays capable of supporting plasmonic resonances can be used as high performance refractive index sensors in biomolecular binding reactions. A methodology to examine the sensing ability of the inside and outside walls of the nanotube structures is presented. The sensitivity of the plasmonic nanotubes is found to increase as the nanotube walls are exposed, and the sensing characteristic of the inside and outside walls is shown to be different. Finite element simulations showed good qualitative agreement with the observed behavior. Free standing gold nanotubes displayed bulk sensitivities in the region of 250 nm per refractive index unit and a signal-to-noise ratio better than 1000 upon protein binding which is highly competitive with state-of-the-art label-free sensors.

Determination of the Tolman length in the improved Derjaguin-Broekhoff-de Boer theory for capillary condensation of ethanol in mesoporous thin films by ellipsometric porosimetry

Ethanol adsorption-desorption isotherms on well-organized mesoporous silica and titania films with hexagonal pores structure were studied by ellipsometric porosimetry. The mesopore volume Was calculated from the change of the effective refractive index at the end points of the isotherm. An improved Derjaguin-Broekhoff-de Boer (IDBdB) model for cylindrical pores is proposed for the determination of the pore size. In this model, the disjoining pressure isotherms were obtained by measuring the thickness of the ethanol film on a non-porous film with the same chemical composition. This approach eliminates uncertainties related to the application of the statistical film thickness determined via t-plots in previous versions of the DBdB model. The deviation in the surface tension of ethanol in the mesopores from that of a flat interface was described by the Tolman parameter in the Gibbs-Tolman-Koening-Buff equation. A positive value of the Tolman parameter of 0.2 nm was found from the fitting of the desorption branch of the isotherms to the experimental data obtained by Low Angle X-ray Diffraction (LA-XRD) and Transmission Electron Microscopy (TEM) measurements in the range of pore diameters between 2.1 and 8.3 nm. (C) 2009 Elsevier Inc. All rights reserved.

Resonant Rayleigh light scattering response of individual Au nanoparticles to antigen--antibody interaction

A proof-of-concept study was reported on analysis of antigen–antibody recognition based on resonant Rayleigh scattering response of single Au nanoparticles in an imaging chamber. As benefited by a traditional dark-field microscope and a spectrograph, individual Au nanoparticles (30 nm) were observed with high signal-to-noise ratio and they were effectively utilized to monitor changes in refractive index induced by specific binding of the adsorbates. Using PSA antigen as a model, a LSPR ?max shift of about 2.85 nm was recorded for a molecular binding corresponding to 0.1 pg ml-1 of the protein biomarker. This result successfully demonstrates a non-labeling detection system for proteins as well as thousands of different chemical or biological species, and it possesses a great potential as a sensitive, on-chip and multiplexing detection.

The ultrasensitive detection of prostate cancer biomarker based on resonant Rayleigh light-scattering response of single Au nanoparticle

A proof-of-concept study was reported on analysis of antigen-antibody recognition based on resonant Rayleigh scattering response of single Au nanoparticles on a microimaging chamber. As benefited by a traditional dark-field microscope and a spectrograph, tiny 30 nm Au nanoparticles were effectively used as nanosensors to monitor changes in refractive index induced by every single binding of the adsorbates. The individual Au nanoparticles were observed with very high signal-to-noise ratio, and a LSPR ?max shift of about 2.5 nm accounting for the detection of PSA antigen with concentration as low as 0.1 pg ml-1 was recorded. This resulted in the successful demonstration of a non-labelling detection system for proteins as well as thousands of different chemical or biological species with possibility of miniaturization and multiplexing scheme.

Metamaterials-Based Label-Free Nanosensor for Conformation and Affinity Biosensing

Analysis of molecular interaction and conformational dynamics of biomolecules is of paramount importance in understanding of their vital functions in complex biological systems, disease detection, and new drug development. Plasmonic biosensors based upon surface plasmon resonance and localized surface plasmon resonance have become the predominant workhorse for detecting accumulated biomass caused by molecular binding events. However, unlike surface-enhanced Raman spectroscopy (SERS), the plasmonic biosensors indeed are not suitable tools to interrogate vibrational signatures of conformational transitions required for biomolecules to interact. Here, we show that highly tunable plasmonic metamaterials can offer two transducing channels for parallel acquisition of optical transmission and sensitive SERS spectra at the biointerface, simultaneously probing the conformational states and binding affinity of biomolecules, e.g. G-quadruplexes, in different environments. We further demonstrate the use of the metamaterials for fingerprinting and detection of arginine-glycine-glycine domain of nucleolin, a cancer biomarker which specifically binds to a G-quadruplex, with the picomolar sensitivity.

The controlled fabrication and geometry tunable optics of gold nanotube arrays

Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15–30 nm, wall thicknesses of 5–15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600–900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

Plasmonic Sensing Using Nanodome Arrays Fabricated by Soft Nanoimprint Lithography

Arrays of gold-coated nanodomes were fabricated on glass substrates using a soft
nanoimprint lithography technique. Optical transmission measurements revealed complex
plasmonic resonances that proved highly sensitive to the array dimensions, the thickness of
the gold layer, and the refractive index of the surrounding medium. As one promising
application for these structures, the refractive index sensing capabilities of the nanodome
arrays were assessed.

Polarisabilities of alkylimidazolium ionic liquids

The molar polarisability and molar volume for 71 ionic liquids were extracted from 157 measurements of their refractive index and density, which were then further deconstructed into atomic contributions by means of a Designed Regression analysis. Using this approach, the density and refractive index for any chosen ionic liquid with alkyl-substituted imidazolium cations can be predicted in good agreement with experimental data.

Irradiation of oxygen and water ices at by 4 keV singly and doubly charged ions; sputtering and molecular synthesis

The icy surfaces of dust grains in the Interstellar Medium and those of comets, satellites and Kuiper Belt Objects are continuously exposed tophoton and charged particle irradiation. These energetic particles maysputter and induce chemical changes in the ices and the underlyingsurfaces.In the present work 258 nm thick O2 and H2O ices were deposited at 10 K with the thickness measured by a laser interferometer method. Asimple model fit to the reflected laser intensity as measured by aphotodiode detector enabled the refractive index of the ices to bedetermined. The ices were then irradiated with various singly and doublycharged ions such as He+, 13C+, N+, O+ , Ar+, 13C2+, N2+ and O2+ at 4keV. The decrease in ice thickness as a function of ion dose wasmonitored by a laser interferometer and the model used to determine thesputtering yield as shown in Figure 1.In the case of O2 ice thesputtering yields increased with increasing ion mass in good agreementwith a model calculation [Fama, J, Shi, R.A Baragiola, Surface Sci.,602, 156 (2007)]. In the case of O2 ice, O2+ has a significant lowersputtering yield when compared to O+. The sputtering yields for O2 icewere found to be at least 9 times larger compared to those for H2O ice.For H2O ice the sputter yields for C, N and O ions were found todecrease with increasing mass. Doubly charged C, N and O ions which werefound to have the same sputtering yield as the singly charged ionswithin the experimental errors. A preliminary TPD study was carried outusing a QMS to detect the desorbed species from water ice afterirradiation by 6 × 10^15 ions of 13C+ and 13C2+. The formation of13CO and 13CO2 was observed with the yield of 13CO almost of a factor of100 larger than of 13CO2. This is in contrast to our earlier work whereonly CO¬2 was observed.

Zero-Reflectance Metafilms for Optimal Plasmonic Sensing

An ultrathin layer of metasurface that almost completely annihilates the reflection of light (>99.5%) over a wide range of incident angles (>80°) is experimentally demonstrated. Such zero-reflectance metafilms exhibit optimal performance for plasmonic sensing, since their sensitivity to changes of local refractive index is far superior to films of nonzero reflectance. Since both main detection mechanisms tracking intensity changes and wavelength shifts are improved, zero-reflectance metafilms are optimal for localized surface plasmon resonance molecular sensing. Such nanostructures have significant opportunities in many areas, including enhanced light harvesting as well as in developing high-performance molecular sensors for a wide range of chemical and biomedical applications.