Enhancing whispering gallery mode biosensing

First, years of work on advancing the device physics and engineering of WGM biosensors has improved the ultimate physical detection limits of WGM transducers, yet the limits for DNA detection by hybridization has plateaued. Molecular recognition of DNA at a surface limits the biosensors' sensitivity, specificity, and reusability. It is therefore imperative to integrate novel molecular approaches with existing label-free transducers to overcome those limitations. I will demonstrate this concept by integrating a DNA strand displacement circuit with a whispering gallery mode (WGM) biosensor. Second, by perfecting the fabrication of a glass microsphere WGM resonators by melting optical fibers, we are able to achieve Q factors close to this physical theoretical limit in solution, resulting in, for example, a detection limit of single Influenza-A virus particles with a molecular weight MW ∼ 300,000 kD. This is impressive, but falls several orders of magnitude short of being able to, for example, detect individual biomolecules. I will speak about the theoretical and experimental approaches for further enhancing the already extreme sensitivity of optical resonators with the principle of plasmon resonance, creating regions of high field intensity with subwavelength plasmonic nanoparticles and setting up hybrid photonic-plasmonic modes.