Optical Biosensor based on Silicon-on-Insulator Microring Cavities for Specific Protein Binding Detection

摘要

Label-free biosensors for protein detection try to overcome the stability and reliability problems of commercialized systems relying on the detection of labeled molecules. We propose a micron sized integrated Silicon-on-Insulator optical biosensor based on a microring cavity that enables real time and sensitive measurements of protein dynamics, fast sample preparation and multiparameter detection for extremely low analyte quantities. Fabrication with Deep UV lithography for standard CMOS processing allows for cheap mass production and integration with electronic functions for complete lab-on-chip devices. The SOI material system offers a high refractive index contrast suitable for the fabrication of submicron sized optical cavities of very high quality. The shift of resonance wavelength that occurs when the dielectric surroundings of such a cavity is changed, is used for sensing. We demonstrate a SOI optical microring resonator with radius 5 micron capable of detecting bulk refractive index changes of 10~(-4). Modification of the semiconductor surface, allowing for immobilization of biomolecules, is characterized by X-ray Photoelectron Spectroscopy, ellipsometry, Scanning Contact Angle and Atomic Force Microscopy. We use the avidin/biotin high affinity couple to demonstrate good repeatability and the detection of protein concentrations down to 50 ng/ml. Negative control using low interaction protein couples shows low responses, proving the realization of real specific binding. Integration with a microfluidic setup will allow for more precise monitoring of the interaction dynamics, while lining up the microrings in arrays will allow for cheap high throughput label-free multiparameter analyses.