Detection in near-field domain of biomolecules adsorbed on a single metallic nanoparticle.

In this paper, we study the performances of nanosensors based on Localized Surface Plasmon Resonance in the context of biological sensing. We demonstrate the sensitivity and the selectivity of our designed nanosensors by studying the influence of the concentration of Streptavidin on the shift of Localized Surface Plasmon Resonance wavelength. In addition, to study the detection of biomolecules on a single Au nanoparticle, we used a Scanning Near-field Optical Microscope. These results represent new steps for applications in biological research and medical diagnostics.

How nanoparticles encapsulating fluorophores allow a double detection of biomolecules by localized surface plasmon resonance and luminescence.

The paper shows how polysiloxane particles encapsulating fluorophores can be successfully used to detect biotin-streptavidin binding by two types of technique. After functionalization of the particles by streptavidin, the fixation of the biomolecule can indeed be detected by a shift of the localized surface plasmon resonance of the biotinylated gold dots used as substrate and by the luminescence of the fluorophores evidenced by scanning near-field optical microscopy. The development of particles allowing such a double detection opens a route for increasing the reliability of biological detection and for multi-labelling strategies crossing both detection principles.

Characterization of strong electromagnetic field confinement on gold nanostructures by apertureless scanning near-field optical microscopy.

We report on the detection of the optical near field of a 1D gold particle array by using an apertureless scanning near-field optical microscope. The strong near-field confinement measured above the grating proves unambiguously the near-field origin of the detected optical signal. Comparing the experiment with theory leads us to assign the optical near field to the first diffracted order of the grating, which is evanescent.

Near-field reflection backscattering apertureless optical microscopy: application to spectroscopy experiments on opaque samples, comparison between lock-in and digital photon counting detection techniques.

An apertureless scanning near-field optical microscope (ASNOM) in reflection backscattering configuration is designed to conduct spectroscopic experiments on opaque samples constituted of latex beads. The ASNOM proposed takes advantage of the depth-discrimination properties of confocal microscopes to efficiently extract the near-field optical signal. Given their importance in a spectroscopic experiment, we systematically compare the lock-in and synchronous photon counting detection methods. Some results of Rayleigh's scattering in the near field of the test samples are used to illustrate the possibilities of this technique for reflection backscattering spectroscopy.

Apertureless near-field optical microscopy: influence of the illumination conditions on the image contrast.

We report a hybrid microscope composed of an apertureless scanning near-field optical microscope and a commercial atomic force microscope. We discuss the optical origin of the near-field images of a test sample. We show that the optical images have a sharp contrast that depends on the illumination parameters: the state of polarization and the angle of incidence of the incident light.