Zinc oxide (ZnO) nanospheres with excellent sensing ability towards formaldehyde were successfully synthesized us-ing a single-capillary electrospinning method. Structural and electrical characteristics of the as-synthesized ZnO nan-ospheres were systematically investigated. The scanning electron microscope (SEM) images clearly display a novel structure of ZnO with pores distributed on the surface of the nanospheres. The results demonstrate that the ZnO nano-spheres possess excellent formaldehyde gas-sensing properties. At room temperature, the response of ZnO nano-spheres to formaldehyde with concentration of 100 ppm is determined to be 126.3. In addition, the ZnO nanosphere sensors exhibit short response time of 30 s and short recovery time of 2 s. These excellent gas-sensing properties make the ZnO nanospheres a promising material for the application in environmental monitoring devices.

We present a novel electrochemical technique for the fabrication of nano-photonic crystal structures. Based on a specially designed electrolyte, porous silicon (PSi) layers with different porosities are possible to be produced on highly-doped n-type silicon substrate by varying the applied current density which determines the size and the morphology of pores. By applying an alternative current density modulation during anodization, porous silicon photonic crystals are obtained using HF-containing electrolyte without oxidizing components. The current burst model (CBM) is employed to interpret the mechanism of the formation of the macropore porous silicon.

In order to realize the planar gradient refractive index (GRIN) microlens which is based upon porous silicon (PSi) and fabricated on silicon on insulator (SOI), a novel anodization method is used by applying lateral electric field. The microlens with smooth variation of the effective optical thickness is achieved. The lens is transparent in the infrared region, including the optical communication window (1.3 μm＜λ＜1.6 μm). This approach also allows the fabrication of an array of such lenses on SOI, and the GRIN microlens can be used as potential components in future silicon-based integrated optical circuits.

The single-layer porous silicon is prepared by electrochemistry etching method, which is used as an immunosensor for determining recombinant mouse zona pellucida 3 fusion protein (r-mZP3) by Raman spectroscopy analysis at room temperature. The molecule binding increases the effective optical thickness (EOT), and thus the Raman spectrum intensity decreases. The concentration and variation of Raman intensity show a good linear quantitative relation. The excellent sensing performance could open the way to a new family of optical sensors for biological standardization.

The enhanced sensitivity of a guided mode biosensor is analyzed by employing double-layered porous silicon grating structures. The grating-coupled waveguide structure consists of two porous silicon grating layers with different refractive indices. Simulations are carried out by changing the refractive index, which is due to the binding of biological molecules on the porous silicon pore can increase the refractive index of porous silicon. The numerical results show that this novel guided mode biosensor with a double-layered grating can provide not only a very high sensitivity but also a better reflectivity characteristic.