Lan Yang, Ph.D.
Edwin H. and Florence G. Skinner Professor
Department of Electrical & Systems Engineering
Washington University in St. Louis
“Leveraging Whispering-Gallery-Mode Optical Resonators for Biomedical Applications: Ultrasensitive and Label-Free Detection of Nanoparticles and Cells”

Lan Yang, Ph.D.
Optical sensors are at the forefront of advancements in biomedical research, clinical diagnostics, and environmental monitoring. Among the diverse sensing technologies, whispering-gallery-mode (WGM) resonators have gained prominence for their unique ability to amplify interactions between light and biological targets. Like a whisper traveling along a circular wall, photons in WGM resonators propagate along a curved surface. Ultra-high-quality (Q) optical WGM microresonators significantly enhance light-matter interactions, presenting new opportunities for ultra-sensitive and label-free detection of small objects, such as nanoparticles, molecules, and cells, in biomedical research. This seminar will explain how nanomaterial interactions with a high-Q WGM resonator can alter photon trajectories and lifetimes, offering precise and quantifiable measurements. Groundbreaking applications, such as the detection and sizing of nanoparticles—including single virions—using ultra-sensitive, self-referencing microresonators and microlasers, will be explored. Furthermore, the seminar will highlight how optical gains in microlasers can push detection limits beyond conventional passive resonators. Innovative sensing strategies, including barcode technology leveraging collective responses of multiple resonances to enhance sensitivity and dynamic range of sensing measurement, label-free detection via photoacoustic spectroscopy, and AI-enhanced target classification, will be discussed for their transformative potential in biomedical sensing. The versatility of WGM sensors will be demonstrated through a probe-type configuration capable of scanning surfaces to collect resonance-enhanced Raman signals. In particular, a WGM microprobe that enhances the sensitivity of commercial Surface-Enhanced Raman Spectroscopy (SERS) test papers will be presented, demonstrating its potential for highly sensitive, label-free molecular detection. The presentation will conclude with the introduction of a handheld sensing platform, a compact evolution of traditional setups, promising to expand the accessibility and applicability of WGM sensor technology.