Surface Functionalization with Polymer Membrane or SEIRA Interface to Improve the Sensitivity of Chalcogenide-Based Infrared Sensors Dedicated to the Detection of Organic Molecules.

Priority substances likely to pollute water can be characterized by mid-infrared spectroscopy based on their specific absorption spectral signature. In this work, the detection of volatile aromatic molecules in the aqueous phase by evanescent-wave spectroscopy has been optimized to improve the detection efficiency of future optical sensors based on chalcogenide waveguides. To this end, a hydrophobic polymer was deposited on the surface of a zinc selenide prism using drop and spin-coating methods.

Enhanced second harmonic generation of gold nanostars: optimizing multipolar radiation to improve nonlinear properties.

We report a detailed investigation on the second harmonic generation (SHG) emission from single 150 nm diameter non-centrosymmetric gold nanoparticles. Polarization-resolved analysis together with scanning electron microscopy images shows that these nanostructures exhibit a unique polarization-sensitive SHG that depends strongly on the particle's shape. An analytical approach based on multipolar analysis is introduced to link SHG properties to the nanoparticles' shape.

Fast and reliable fabrication of gold tips with sub-50 nm radius of curvature for tip-enhanced Raman spectroscopy.

We have developed a new electrochemical etching procedure to fabricate gold tips with sub-50 nm apical radius of curvature with a production yield of 80% and production time lower than 5 min. The technique is based on a two-step self-terminating process in which a gold wire is first quickly (<1 min) pre-etched in an hydrochloric acid (HCl)∕ethanol solution at high voltage (10 VDC), and then slowly (2-4 min) etched at lower voltages (<2.5 VDC).

Nanoscale optical properties of metal nanoparticles probed by Second Harmonic Generation microscopy.

We report spatial and vectorial imaging of local fields' confinement properties in metal nanoparticles with branched shapes, using Second Harmonic Generation (SHG) microscopy. Taking advantage of the coherent nature of this nonlinear process, the technique provides a direct evidence of the coupling between the excitation polarization and both localization and polarization specificities of local fields at the sub-diffraction scale. These combined features, which are governed by the nanoparticles' symmetry, are not accessible using other contrasts such as linear optical techniques or two-photon luminescence.

Optimized plasmonic nanostructures for improved sensing activities.

The paper outlines the optimization of plasmonic nanostructures in order to improve their sensing properties such as their sensitivity and their ease of manipulation. The key point in this study is the optimization of the localized surface plasmon resonance (LSPR) properties essential to the sensor characteristics, and more especially for surface-enhanced Raman scattering (SERS). Two aspects were considered in order to optimize the sensing performance: apolar plasmonic nanostructures for non polarization dependent detection and improvements of SERS sensitivity by using a molecular adhesion layer between gold nanostructures and glass.

Fabrication of an atrazine acoustic immunosensor based on a drop-deposition procedure.

Among the various novel analytical systems, immunosensors based on acoustic waves are of emerging interest because of their good sensitivity, real-time monitoring capability, and experimental simplicity. In this work, piezoelectric immunosensors were constructed for the detection of atrazine through the immobilization of specific monoclonal anti-atrazine antibodies on thiolated modified quartz crystal microbalances (QCMs). The immunoassay was conducted by a novel drop-deposition procedure using different atrazine dilutions in phosphate buffer solution ranging from 10(-10) to 10(-1) mg/mL.

A lower limit of detection for atrazine was obtained using bioluminescent reporter bacteria via a lower incubation temperature.

The present article reports on the influence of various atrazine concentrations to the response of genetically modified Escherichia coli TV1061 bacterial cells while modulating the experimental conditions. Interesting increases of bioluminescence signals are recorded for E. coli TV1061 bacteria in the presence of 10 μg/mL atrazine concentration named "high-toxicity bacteria alert" when compared with 1 μg/mL -10 fg/mL atrazine termed "low-toxicity bacteria alert".

SERS detection of biomolecules using lithographed nanoparticles towards a reproducible SERS biosensor.

In this paper we highlight the accurate spectral detection of bovine serum albumin and ribonuclease-A using a surface-enhanced Raman scattering (SERS) substrate based on gold nanocylinders obtained by electron-beam lithography (EBL). The nanocylinders have diameters from 100 to 180 nm with a gap of 200 nm. We demonstrate that optimizing the size and the shape of the lithographed gold nanocylinders, we can obtain SERS spectra of proteins at low concentration.

Design of nanostructures for imaging and biomedical applications by plasmonic optimization.

An adapted method of optimization of coated metallic nanoparticles is introduced to perform the optimal choice of material and sizes for better scattering or absorption efficiency. This design of nanoshells, involving plasmon resonance, is achieved to maximize the efficiency factors. The presented method is turned to tune the efficiency of nanoshells for biomedical applications and an increasing of the efficiency factors by 1 or 2 orders of magnitude is predicted with realistic materials.

Electro-optical microscopy: mapping nonlinear polymer films with micrometric resolution.

The first demonstration, to the best of our knowledge, of electro-optical microscopy is presented and applied to a polymer-based optical device. A confocal transmission microscope with interferometric homodyne detection is implemented to measure Pockels phase shifts with micrometric spatial resolution and an accuracy level down to 4 x 10(-7) rad. This technique is applied to poled polymer films in which noncentrosymmetric molecular orientation is preliminarily achieved in the sample plane between transverse planar electrodes.