Long period grating working in transition mode as promising technological platform for label-free biosensing

We present the development of a platform for label-free biosensing based on overlayered Long Period Gratings (LPGs) working in transition mode. Nano-scale layers of Polystyrene (PS) with different thicknesses were deposited onto the same LPG to test the performances of the device in different working points of its modified sensitivity characteristic. Adsorption dynamic of biotinylated bovine serum albumin (BBSA) onto the PS overlays was on-line monitored as well as a subsequent streptavidin (SA) binding dynamic on the biotinylated sites of the protein ad-layer. Experimental results show that overlayered LPGs are among the most sensitive refractive index transducers to be employed in label-free biochemical detection and that wide margins of further optimization exist.

Monitoring the dispersion process of SWNTs in aqueous solutions by UV-vis and Raman spectroscopies

The current bottleneck to carbon nanotubes (CNT) application in composite materials field consists in the difficulty of dispersing them in solvents. As a result of strong van der Waals interactions, as produced CNTs are tightly bundled in ropes of several tubes, rendering the carbon-powder insoluble in aqueous and organic liquids and thus unprocessable. The interest in applications that require water-soluble CNTs is growing and much attention is being directed to the study of surfactant aqueous solutions. In a typical dispersion procedure, after the surfactant has been adsorbed on the nanotube surface by hydrophobic or pi-pi interactions, ultrasonication helps nanotubes debundling, providing a mechanical energy able to overcome van der Waals interactions in CNT bundles. The electrostatic repulsion between surfactant polar heads that remain in solution allows the colloidal stability. In this work the dispersibility of HiPCO Single Walled Carbon Nanotubes (SWNT) in different surfactant solutions has been evaluated by using UV-vis and Raman spectroscopies. UV absorbance as well as intensity of SWNTs characteristic Raman bands have been studied as a function of sonication time for each type of surfactant. Moreover the surface morphology of SWNTs films obtained by solutions drying has been observed by using Scanning Electron and Atomic Force Microscopies.

Near field behavior of SnO(2) particle-layer deposited on standard optical fiber by electrostatic spray pyrolysis method

We report the emergent optical near field profiles from standard single mode optical fibers on the cleaved end of which were deposited particle layers of SnO(2). The layers, composed of micron and sub-micron sized particles, were deposited by means of Electrostatic Spray Pyrolysis (ESP) technique. Powerful analytical tools such as Atomic Force Microscopy (AFM) and Scanning Near-field Optical Microscopy (SNOM) were used to obtain simultaneously the SnO(2) layers topography and the related optical near field intensity distribution, when the fiber-substrate is illuminated by a light radiation in NIR range. We show that isolated microstructures, positioned in correspondence of the fiber core, reveal highly unusual capability of locally enhancing the collected optical near field. The observed phenomenon leads to new concepts of fiber optic chemical sensors and in fiber microsystems as well.