Single Nanoparticle Sensing using Whispering-Gallery Microresonators and Microlasers

L. Yang
Washington University, US

Keywords: sensors, nanotechnology

Summary:

Microsystems for detecting biomolecules will play important roles in biomedical research, clinical diagnosis, food safety, pharmaceutical testing, and environmental monitoring. Optical sensors based on Whispering-Gallery-Mode (WGM) resonators have emerged as front-runners for label-free, ultra-sensitive detection of nanomaterials and nanoscale phenomena due to their superior capability to significantly enhance the interactions of light with the sensing targets by confining light photons in small volumes for long periods of time. A WGM resonator traps light in circular orbits in a way similar to a whisper, i.e., a sound wave, traveling along a circular wall, an effect found in the whispering gallery of St. Paul’s Cathedral in London. This talk will introduce ultra-high-quality (Q) optical WGM microresonators and their fabrication process. The basis for resonator sensors is that the physical associations and interactions of nanomaterials on the surface of a high-Q optical WGM resonator alter the trajectory and lifetime of photons in a way that can be measured and quantified. I will first present a laser-assisted processing method to create Si-chip based optical microresonators with Q-factors in excess of 100 million, followed by the adaptation of this process to create active devices based on a sol-gel oxide delivery process. This new step enables spin-coating of high quality oxide films to achieve ultra-high-Q resonators on silicon wafers. It is also a convenient and efficient method to incorporate optical gain dopants into the oxide layer deposited on a silicon wafer, providing a route to achieve arrays of microlasers on silicon wafer with emission spectral windows from visible to infrared. I will then present a recent discovery of using ultra-high-Q microresonators and microlasers for ultra-sensitive self-referencing detection and sizing of single virion, dielectric and metallic nanoparticles. Finally, I will discuss using optical gains in a microlaser to improve the detection limit beyond the reach of a passive microresonator. These recent advancements in WGM microresonators will enable a new class of ultra-sensitive and low-power sensors for investigating the properties and kinetic behaviors of nanomaterials, nanostructures, and nanoscale phenomena.