Label-free detection techniques are widely used in biological and environmental sensing. In particular, whispering gallery mode microtoroid resonators have been used to detect single nanoparticles and molecules by relying on the ultrahigh quality factor of these resonators together with frequency locking for ultra-precise resonance tracking. However, material property characterization on a particle-by-particle basis remains a challenge in these label-free schemes. Here we characterize single particle material properties using microtoroid optical resonators combined with spectroscopic techniques.
Whispering gallery mode (WGM) optical microresonators with high quality (Q) factors have been widely used to sense biomolecules due to their small mode volume and narrow linewidth resonance. Previously, we reported a frequency locked optical whispering evanescent resonator (FLOWER) system for real time single macromolecule detection. Here, we explore the detection limit of FLOWER via numerical simulation based on coupled mode theory. These results predict that frequency locked microcavities with ultra-high-Q can detect resonance shifts as small as 0.05 attometers at 1 millisecond time interval and are limited by shot noise and laser intensity noise.
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