Capacitive microsystems for biological sensing.

The growing interest in personalized medicine leads to the need for fast, cheap and portable devices that reveal the genetic profile easily and accurately. To this direction, several ideas to avoid the classical methods of diagnosis and treatment through miniaturized and label-free systems have emerged. Capacitive biosensors address these requirements and thus have the perspective to be used in advanced diagnostic devices that promise early detection of potential fatal conditions. The operation principles, as well as the design and fabrication of several capacitive microsystems for the detection of biomolecular interactions are presented in this review. These systems are micro-membranes based on surface stress changes, interdigitated micro-electrodes and electrode-solution interfaces. Their applications extend to DNA hybridization, protein-ligand binding, antigen-antibody binding, etc. Finally, the limitations and prospects of capacitive microsystems in biological applications are discussed.

Ultraviolet femtosecond, picosecond and nanosecond laser microstructuring of silicon: structural and optical properties.

The effect of laser pulse duration on the morphology, composition, crystallinity and optical properties of self-organized Si microcones fabricated using 248 nm laser pulses (500 fs, 5 ps and 15 ns) in an SF(6) atmosphere, is presented in this paper. Despite distinct differences in the morphology, the Si cones show similar structure and composition independently of the laser pulse duration used: a core of single-crystalline Si, covered by a few hundred nanometer thick, sulfur-doped nanocrystalline Si layer, where no amorphous Si is present. The obtained features exhibit strong below-bandgap absorptance, making them excellent candidates for Si based photodetectors with improved spectral response.

Plasma strings from ultraviolet laser filaments drive permanent structural modifications in fused silica.

Long self-trapped femtosecond ultraviolet filaments created in the bulk of pure fused silica are used to induce permanent structural changes in the medium. We monitor the laser pulse propagation as a filamentary structure and the plasma string left at its trail. We investigate and demonstrate the link of the filament-induced plasma to the permanent structural changes left in the medium. Specific electron density thresholds are found for the induced modifications.

Long-range filamentary propagation of subpicosecond ultraviolet laser pulses in fused silica.

We report on what is to our knowledge the first observation of subpicosecond ultraviolet laser pulse filamentation in transparent solid materials. Robust filaments were created in fused silica and observed over distances that exceed 3 cm in length. Intensities as high as 10(13) W/cm2 were found to be transported in the filamented beam without material damage in the bulk of the fused-silica sample.

Etching and printing of diffractive optical microstructures by a femtosecond excimer laser.

Diffractive optics fabrication is performed by two complementary processing methods that rely on the photoablation of materials by ultrashort UV laser pulses. The spatially selective ablation of materials permits the direct microetching of high-quality surface-relief patterns. In addition, the direct, spatially selective transfer of the ablated material onto planar and nonplanar receiving substrates provides a complementary microprinting operation. The radiation from the ultrashort pulsed excimer laser results in superior quality at relatively low-energy density levels, owing to the short absorption length and minimal thermal-diffusion effects. Computer-generated holographic structures are produced by both modes of operation. Submicrometer features, including Bragg-type structures, are microprinted onto planar and high-curvature optical-fiber surfaces, demonstrating the unique ability of the schemes for complex microstructure and potentially nanostructure development.