Michel Lehaitre

In-situ depth profiling of particle sizes

A new in-situ particle-size profiling system is presented. It allows direct determination of particle distribution spectra in 30 size classes ranging from 0.7 to 400 μm-equivalent diameter as well as an unbiased estimation of the total particle load. This profiler includes among standard probes a particle-size analyser. This new probe uses the well-known principle of diffraction pattern analysis previously used in bench-top instruments. However, the rigorous mechanical tolerances imposed by oceanographic use required a completely new design. Its description and validation is presented as well as some oceanographic applications. This instrument presents numerous advantages in oceanographic research. Its use in different European waters has demonstrated its reliability and allowed the description of common features of the profiles, particularly the accumulation of aggregates or mucilages and, in some cases, the confinement of dinoflagellates at the pycnocline. This makes possible a new sampling strategy for toxic dinoflagellates and improvements in the study of sedimentation and flocculation processes.

Detection of polycyclic aromatic hydrocarbon (PAH) compounds in artificial sea-water using surface-enhanced Raman scattering (SERS)

This paper reports an accurate synthesis of surface-enhanced Raman scattering (SERS) active substrates, based on gold colloidal monolayer, suitable for in situ environmental analysis. Quartz substrates were functionalized by silanization with (3-mercaptopropyl)trimethoxysilane (MPMS) or (3-aminopropyl)trimethoxysilane (APTMS) and they subsequently reacted with colloidal suspension of gold metal nanoparticles: respectively, the functional groups SH and NH(2) bound gold nanoparticles. Gold nanoparticles were prepared by the chemical reduction of HAuCl(4) using sodium tricitrate and immobilized onto silanized quartz substrates. Active substrate surface morphology was characterized with scanning electron microscopy (SEM) measurements and gold nanoparticles presented a diameter in the range 40-100 nm. Colloidal hydrophobic films, allowing nonpolar molecule pre-concentration, were obtained. The surfaces 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 (ASW) with limits of detection (LODs) of 10 ppb for both on MPMS silanized substrates.

Characterization and reduction of interferences in flow-injection analysis for the in situ determination of nitrate and nitrite in sea water

Abstract The aim of this work is to improve the precision and the sensitivity of nitrite and nitrate determination by flow-injection analysis (FIA) for an in situ utilization. Two kinds of signal treatment are proposed in order to eliminate the refractive index provoked by the heterogeneous flow in FIA and the errors induced by temperature, salinity and pressure variations. The concentration range of this method is 0–100 μ M NO − 3 -N with a detection limit (3 σ b ) of 0.45 μ M NO − 3 -N ( A t = 0.151 C NO3 + 0.072, n = 40, r 2 = 0.997). The relative standard deviation is 5% for nitrate solutions containing 0.5 μ M NO − 3 -N. The sampling rate is about 45 h −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.

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.

Biofilm prevention on optics by chlorine compound generation on tin oxide coating

Biofilm reduction is still a major problem for underwater instrumentation and more specifically in the case of optical measurements or viewing. The aim of the present work which is supported by the EC-MAST III programme BROS, is to assess the effectiveness of a window protection technique against biofilm growth. This technique is based on the generation of hypochlorous acid and hypochlorite ions by sea water electrolysis on a transparent conductive tin oxide coating. The work has been first focused on tin oxide corrosion resistance. Then, in house and in situ experiments have been carried out to assess the efficiency against natural biofilm. The original optical set-up, allowing the authors to check continuously the evolution the protected and unprotected optical path on different glass samples described elsewhere has been used. In house and in situ experiments have been performed. In situ experiments have been performed with two underwater video cameras. A tin oxide coated window has been set up on first one, an unprotected reference window was set up on the second. Cameras have been deployed on sea floor at Ifremer marine test station (Brest Bay) for four months. The different results presented allow the authors to conclude that generation of chlorine biocide compounds by sea water electrolysis on a transparent conductive tin oxide coating is a good strategy to prevent biofilm growth on optical surfaces. The surface treatment is efficient after a long time in use, the window optical characteristics were not strongly affected and the overall energy demand is low enough to enable application of this technique to a large range of equipment.

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.

Toward in situ detection of algae species

For the last few years there is a more and more pressing need to develop system for detecting HAB at their early stage. Researchers have then been working on new in situ sensor. In this paper a submarine transducer based on surface plasmon resonance is reported. It demonstrated a refractive index resolution of 3.10−6, which is promising for later phytoplankton detection.

Optical fiber spectrofluorimetry for in-situ algae discriminations

Nowadays it becomes more and more necessary to identify suspended matter in oceans in order to increase knowledge about primary productivity as well as the transfer of contaminants or to discriminate toxic phytoplanctonic species. It has been demonstrated for many years that fluorescence can be a well suited method to obtain specific signatures of organic matter in the sea. The paper presented here describes an interesting design of instrumentation based on optical fiber use and multiwavelength analysis which will offer wide possibilities for in situ monitoring of algae. Combining the flexibility of optical fibers and video as data carrier, results show great promise for new oceanographic equipment. In addition to technical descriptions, responses of some different grown species like dinoflagelates or diatoms families will be presented and discussed.