Friday July 8, 2005
10 AM - 11 AM
ENG Z-50 Auditorium

Office Hours:
Friday July 8, 2005
3:30 PM - 4 PM
ENG 208

"Resonant Cavity Biosensor"
Prof. M. Selim Unlu
Boston University

There exists today a critical need to perform high-throughput, efficient bio-molecular binding studies. The Resonant Cavity Imaging Biosensor (RCIB) addresses this need by detecting binding between target molecules in a sample and probe molecules fixed to a surface in a microarray format. This detection is performed label-free, meaning that there is no need to fix molecular labels to the sample molecules being detected. RCIB works by resonantly coupling light through a 1 cm square cavity constructed from Si-SiO2 Bragg reflectors. The microarray is synthesized on one of these reflectors and modulates the local resonant condition of the cavity. As the wavelength of the probe beam is swept, an IR camera monitors cavity transmittance at each pixel. RCIB improves on existing biosensing techniques by offering a solution that is label-free, fast, high- throughput, cost effective, and highly sensitive.

The principle of resonant cavity imaging biosensor (RCIB) relies on the use of an optical cavity. Two partially reflecting mirrors are positioned with their reflecting surfaces facing one another to form the cavity. A large diameter collimated beam of light enters the cavity through the backside of one of the reflectors. The wavelength of the incident light is swept in time. At specific wavelengths, the resonant condition of the cavity is met. Light resonates within the cavity when the condition is met, building up energy and coupling transmitted light through the structure. Beyond the cavity structure, a camera is positioned to image the transmitted intensity from each spot of the cavity surface. The optical cavity formed can be thought to be divided into many subunits or cells where each cell is excited equally by the large incident beam, has two reflecting surfaces, and whose transmission is detected by a single pixel on the camera. Each cell will act like an independent optical cavity so long as the lateral dimension of the cell is much greater than the wavelength of light used.

In the present application, the resonant condition along the cavity will be modulated by the local binding of probe biomolecules to spots of target biomolecules patterned and fixed to one of the reflectors. First a microarray will be fabricated on the surface of one of the reflectors in the cavity so that it has fixed spots of different target biomolecules. Next the wavelength is swept and the wavelength-transmission curve that characterizes the resonant condition of the cavity will be recorded for each pixel. The probe biomolecules will then be introduced to the microarray surface, the wavelength-transmission curves will be re-recorded, and binding will be determined by a shift in the wavelength of the resonant response. It is important to note that the spots are being recorded simultaneously by the pixels on the camera, so that the system is truly high-throughput allowing for hundreds of thousands of spots to be monitored simultaneously using currently available cameras.