Optical resonators have enabled the label-free measurement of nanoparticles suspended in liquids, down to the resolution of individual viruses and large molecules, but are only able to quantify optical properties (refractive index, scattering, fluorescence). Additionally, these sensors are fundamentally limited by the random diffusion of particles to the sensing region, and thus only measure a tiny fraction of the analyte. We have developed a microfluidic optomechanical resonator capable of sensing freely flowing nanoparticles using the action of phonons that are coupled to light. The phonon mode of the system casts a nearly perfect net for measuring density, viscoelasticity, and compressibility of the particles that flow through, without being limited by random diffusion. Information on the mechanical properties of the particles is encoded in the light scattered from the thermal fluctuations of the phonon mode. We have also developed a new electro-opto-mechanical method for improving the sensing speed achievable with this technique. We demonstrate real-time particle transit measurements as fast as 400 microseconds, without any post-processing. We discuss how this novel technique can be used for ultra-high throughput analysis of mechanical properties of biological particles in liquids, enabling a new form of flow cytometry.
(invited by Prof. Giuseppe Leo)
Kewen Han, Jeewon Suh, Alan Luo, and Gaurav Bahl, "Ultra-high throughput microfluidic optomechanical sensors (Conference Presentation)," Proc. SPIE 10111, Quantum Sensing and Nano Electronics and Photonics XIV, 101112A (Presented at SPIE OPTO: February 01, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2253534.5394049049001.
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