Microsystems for detection of biomolecules can play important roles in biomedical research, clinical diagnosis, food safety, homeland security and pharmaceutical testing. It has been demonstrated that single molecule detection can be achieved by an optical resonator with Q factor over 10^8. However, traditional sensing mechanisms based on monitoring the frequency shift and linewidth variation of a single mode are difficult to implement in practice. The resonant frequency is sensitive not only to the desired sensing signal but also to instrumental noises and many types of disturbances in the environment, such as temperature variation, mechanical instability and irrelevant molecules. Hence the incredible sensitivity inherent to resonator biosensing has been difficult to implement because of the necessity to eliminate nonspecific adsorption of contaminating biomolecules onto the resonator surface in order to report the capture of a specific target. We develop a silicon chip-based ‘self-reference sensing’technique that enables ultrasensitive detection and characterization of nanoparticles. The basis for the technology is that the physical associations and interactions of nanoparticles on a high- Q optical resonator surface alter the trajectory and lifetime of photons in a way that can be measured and quantified. The novel sensing mechanism is based on mode splitting, a phenomenon resulting from the interactions of nanoparticles and an ultra-high-quality Whispering-Gallery-Mode resonator. I will explain how a single nanoparticle can ‘split’ a high-quality optical mode in a microtoroid resonator into two modes, which reside in the same resonator, forming a self-referencing detection scheme more immune to noises than traditional single-frequency resonator sensor. I will discuss how to use the mode-splitting technique to achieve accurate sizing of single nanoparticles down to 30nm in a single-shot measurement.

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Dr. Lan Yang is an assistant professor in the Preston M. Green Department of Electrical and Systems Engineering at Washington University, St. Louis, MO. She received the M.S. degree in materials science and the Ph.D. degree in applied physics from the California Institute of Technology, Pasadena, in 2000 and 2005, respectively, after she received B.S from University of Science and Technology of China. Her current research interests include novel photonic materials and nano/micro photonic devices for lasing, sensing, and optomechanics. She received the NSF CAREER Award in 2010 for her work on real-time particle detection using an on-chip optical resonator.