Speaker: Sharon M. Weiss, Vanderbilt University, Nashville, TN
Date & Time: July 7, 2006 - 2:00pm
Location: Room 260, Wright-Rieman Chemistry Laboratory
A New Platform for Silicon-Based Biosensing
Laboratory for Surface Modification
Sharon M. Weiss
Friday, July 7th, 2:00 PM, Room 260, Wright-Rieman Chemistry Laboratory
The development of optical sensors for the ultra-sensitive detection of chemical and biological species is critically important for disease detection, food safety analysis, and biowarfare agent recognition. Sensing on a silicon platform allows simple and inexpensive fabrication techniques, small device size, and suitability for integration with silicon microelectronics. Porous silicon is a promising silicon-based material for label-free biosensing applications because of its high surface-area-to-volume ratio and its versatility as a thin film optical material. Porous silicon, described as a nanostructured matrix of silicon with void spaces, is primarily fabricated by electrochemical etching. A large range of refractive indices, from approximately 1.2 to 2.5, can be obtained by varying the pore size and density.
Two-layer porous silicon planar waveguides have been designed and fabricated as highly sensitive platforms for biosensing applications. Guided waves travel in a high refractive index porous silicon layer and are bound by total internal reflection with a low refractive index porous silicon layer below and air above. Biomolecules are infiltrated directly into the porous silicon waveguide, such that the optical energy is confined exactly where the biomolecules are immobilized. Any change of the refractive index of the waveguide, for example due to DNA hybridization in the pores, will alter the way light propagates in the waveguide and will cause a measurable deviation in the angle at which light is coupled into and out of the sensor. Theory indicates that porous silicon waveguide sensors should perform with a substantial increase in sensitivity over both surface plasmon resonance sensors and other waveguide sensors for which the optical wave is attenuating as it penetrates the biomolecules. Experimental demonstrations of the porous silicon waveguide sensor response to the binding of DNA sequences will be presented.