Florent Colas

Chalcogenide glass optical waveguides for infrared biosensing.

Due to the remarkable properties of chalcogenide (Chg) glasses, Chg optical waveguides should play a significant role in the development of optical biosensors. This paper describes the fabrication and properties of chalcogenide fibres and planar waveguides. Using optical fibre transparent in the mid-infrared spectral range we have developed a biosensor that can collect information on whole metabolism alterations, rapidly and in situ. Thanks to this sensor it is possible to collect infrared spectra by remote spectroscopy, by simple contact with the sample. In this way, we tried to determine spectral modifications due, on the one hand, to cerebral metabolism alterations caused by a transient focal ischemia in the rat brain and, in the other hand, starvation in the mouse liver. We also applied a microdialysis method, a well known technique for in vivo brain metabolism studies, as reference. In the field of integrated microsensors, reactive ion etching was used to pattern rib waveguides between 2 and 300 μm wide. This technique was used to fabricate Y optical junctions for optical interconnections on chalcogenide amorphous films, which can potentially increase the sensitivity and stability of an optical micro-sensor. The first tests were also carried out to functionalise the Chg planar waveguides with the aim of using them as (bio)sensors.

RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy

The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, hetero-structures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As2S3 and Ge25Sb10Se65 amorphous chalcogenide thin films are prepared by radio-frequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm−1.

First Steps of in situ Surface-Enhanced Raman Scattering during Shipboard Experiments

It is shown that the surface-enhanced Raman scattering (SERS) technique can be applied to detect organic molecules during in situ experiments. To this purpose, we used trans-1,2-bis(4-pyridyl)ethylene (BPE) as a target molecule. Adsorbed on the SERS chemosensor surface and excited under laser, the vibration modes of the molecules can be identified. SERS chemosensors are based on quartz substrates functionalized by silanization and partially coated with gold nanoparticles. SERS measurements during shipboard experiments were made with a home-made in situ Raman spectrometer connected to a marinized micro-fluidic system. The device was designed to host chemosensors in order to ensure measurements with a flow cell. A theoretical limit of detection was estimated in the range of picomolar (pM) concentrations based on Freundlich isotherm calculations.

Comparison of adhesion layers of gold on silicate glasses for SERS detection

Gold is one of the most widely used metals for building up plasmonic devices. Although slightly less efficient than silver for producing sharp resonance, its chemical properties make it one of the best choices for designing sensors. Sticking gold on a silicate glass substrate requires an adhesion layer, whose effect has to be taken into account. Traditionally, metals (Cr or Ti) or dielectric materials (TiO2 or Cr2O3) are deposited between the glass and the nanoparticle. Recently, indium tin oxide and (3-mercaptopropyl)trimethoxysilane (MPTMS) were used as a new adhesion layer. The aim of this work is to compare these six adhesion layers for surface-enhanced Raman scattering sensors by numerical modeling. The near-field and the far-field optical responses of gold nanocylinders on the different adhesion layers are then calculated. It is shown that MPTMS leads to the highest field enhancement, slightly larger than other dielectric materials. We attributed this effect to the lower refractive index of MPTMS compared with the others.

Chalcogenide waveguide for IR optical range

Due to remarkable properties of the chalcogenide glasses, especially sulphide glasses, amorphous chalcogenide films should play a motivating role in the development of integrated planar optical circuits and their components. This paper describes the fabrication and properties of optical waveguides of pure and rare earth doped sulphide glass films prepared by two complementary techniques: RF magnetron sputtering and pulsed laser deposition (PLD). The deposition parameters were adjusted to obtain, from sulphide glass targets with a careful control of their purity, layers with appropriate compositional, morphological, structural characteristics and optical properties. These films have been characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray measurements (EDX). Their optical properties were measured thanks to m-lines prism coupling and near field methods. Rib waveguides were produced by dry etching under CF4, CHF3 and SF6 atmosphere. The photo-luminescence of rare earth doped GeGaSbS films were clearly observed in the n-IR spectral domain and the study of their decay lifetime will be presented. First tests were carried out to functionalise the films with the aim of using them as sensor.

Surface enhanced infrared absorption by nanoantenna on chalcogenide glass substrates

In recent years, nanowires have been proven efficient to enhanced IR absorption of molecules and opened prospects of new ultrasensitive IR sensors. The development of integrated components requires the use of special IR glasses such as chalcogenide or silver halide glasses. In this study, we report the fabrication of a surface enhanced IR absorption substrate composed of nanowires deposited onto a chalcogenide glass slide. It enabled us to detect 4-nitrophenol at the femtomolar level and enhancement factor close to 106 was calculated.

Towards in situ detection of PAH trace in seawater using SERS-active sensors

This paper reports the development of a sensor based on surface-enhanced Raman scattering (SERS) for analyses in seawater. Polycyclic aromatic hydrocarbons (PAHs) are targeted by these sensors and their detection in situ summons up chemical synthesis and optical development. Firstly, a relevant synthesis of SERS active substrates based on gold nanostructures is presented. Different kinds of substrates have been synthesized under variable experimental conditions to modify some parameters such as i) gold shape, size and distribution and such as ii) chemical functionalization: (i) gold nanoparticles were prepared either by chemical reduction of HAuCl4 or by physical deposition. (ii) Substrates were functionalized by hydrophobic films to allow nonpolar molecules pre-concentration. Low concentration from ppb to ppm of PAHs were detected with a Raman microscope designed for lab experiments. Sensors exhibit strong enhancement of Raman scattering from molecules adsorbed on the films. Spectra were recorded for two PAHs (naphthalene and pyrene) in artificial sea-water with limits of detection of 10ppb for both with a short integration time (10s) and a low incident laser power (~0.1mW). Active substrate surface morphology was characterized with scanning electron microscopy (SEM) measurements. Secondly, an home-made in situ Raman spectrometer was developed and has been connected to a micro-fluidic system. This system was designed to host SERS-active sensors in order to ensure measurements with a flow cell. This original configuration of in situ Raman spectroscopy was then achieved. Such a device is now ready to use to confirm the PAH detection at ppb levels during the offshore experiments thanks to SERS sensors.

Toward detection of harmful algae blooms by in situ surface plasmon resonance spectroscopy

Among marine algae species, Alexandrium minutum produces a phycotoxin called paralytic shellfish poisoning (PSP) that is introduced in the food chain through the ingestion of phytoplankton by shellfishs, and later by human consumers. Thus, in situ monitoring of A. minutum proliferation in coastal seawater is of great economical importance for marine resources exploitation. Here, we propose a rapid test for the detection of A. minutum by surface plasmon resonance spectroscopy. First, whole genomic DNA is extracted from the algae. Second, a 677 bp long portion of the 28S ribosomal DNA is amplified by PCR. Third, the PCR product is detected by surface plasmon resonance spectroscopy onto a DNA functionalized gold substrate.

Combined SPR and SERS: Otto and Kretschmann configurations

Combined surface enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) setup was proposed recently. The experimental setup requires a gold layer deposited on a glass substrate. However, due to the poor ability of sticking gold material on glass, a nanometric adhesion layer is used. In this paper we compare numerically both the SERS gain, and the SPR signal, for metallic and dielectric adhesion layers, for two substrates. We show that even if the dielectric materials can be considered as equivalent for the SPR signal, this is not the case for the SERS gain. In particular the dielectric adhesion layer reduces the sensitivity of the SERS gain to this parameter and therefore their use could be more suitable for the fabrication of the sensor. Moreover the higher the refractive index of substrate with regards to the adhesion layer is, the higher efficiency of setup is obtained, and therefore the Otto configuration seems to be more efficient than the Kretschmann one. Optimization of the thicknesses of the adhesion layer and of the gold layer can lead to a SERS gain greater than 103 without nanostructuring.

Development of integrated platform based on chalcogenides for sensing applications in the mid-infrared

Mid-Infrared (mid-IR) spectral range, spanning from 2 μm to 20 μm, is ideal for chemical sensing using spectroscopy thanks to the presence of vibrational absorption bands of many liquid and gas substances in this wavelength range. Indeed, mid-IR spectroscopy allows simultaneous qualitative and quantitative analysis by, respectively, identifying molecules from their spectral signature and relating the concentrations of different chemical agents to their absorption coefficient according to Beer-Lambert law. In the last years, photonic integrated sensors based on mid-IR spectroscopy have emerged as a cheap, accurate, and compact solution that would enable continuous real-time on-site diagnostics and monitoring of molecular species without the need to collect samples for off-site measurements. Here, we report the design, processing and characterization of a photonic integrated transducer based on selenide ridge waveguides. Evanescent wave detection of chemical substances in liquid phase (isopropyl alcohol, C3H8O, and acetic acid, C2H4O2, both dissolved in cyclohexane) is presented using their absorption at a wavelength of 7.7 μm.