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Title:High-throughput sensing of bulk fluids and freely flowing particles with opto-mechano-fluidics
Author(s):Han, Kewen
Director of Research:Bahl, Gaurav
Doctoral Committee Chair(s):Bahl, Gaurav
Doctoral Committee Member(s):Saif, Taher; Bashir, Rashid; Toussaint, Kimani
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Particle sensing
Abstract:High-Q optical resonators have revolutionized label-free sensing of nanoparticles, down to the resolution of individual viruses and single molecules. However, these laboratory demonstrations commonly encounter practical constraints that remain unresolved. Specifically, optical resonator detection techniques rely on random diffusion of particles to the sensing region, occasionally also necessitating adsorption onto the resonator. This implies severe reduction in detection speed and only a small number of analyte particles can be detected or quantified in a sample, at speeds no faster than a few particles per second. Furthermore, the mechanical properties of sample fluids or particles do not couple directly to optical fields. Yet, many disease states correlate with mechanical properties such as compressibility and viscoelasticity (e.g. in anemia and cancers). These mechanical properties are usually measured with microelectromechanical sensors (MEMS). In particular, mass, compressibility, and viscoelasticity of analyte particles can be measured by binding them on a vibrating structure (Nat Commun 7:13452, 2016; Appl Phys Lett 108, 11, 2016). These methods, however, suffer from the severe reduction in detection speed as well. Fast non-contact measurement is made possible with a hollow type of MEMS device, which weighs bio-analytes in real-time as they flow through the internal channel of the device (Nat Commun 6:7070, 2015). However, the fastest achieved detection speed is still less than 10 events/s. Generating meaningful data on practical samples, for instance a liquid suspension containing a few viral nanoparticles amongst millions of particles of debris, requires ultra-high throughput measurements with nearly 100\% detection efficiency. To address this fundamental measurement challenge, we have developed a novel class of solid-liquid hybrid optomechanical resonators that perform phonon-mediated optical detection of fluids and nanoparticles at extremely high speed. The microcapillary-type resonators support ultrahigh-Q optical modes that are coupled to co-localized mechanical (phonon) modes, while fluid analytes are flowed internally without influencing the optics. Thus we also call this resonator opto-mechano-fluidic resonator (OMFR). In this thesis, we first provide the detailed methodology to fabricate these OMFRs, perform optomechanical testing, and measure optomechanical vibrations. Fundamentally, OMFR interfaces with bulk fluids acoustically through the shell-fluid hybrid mechanical modes. A numerical setup for an eigenfrequency analysis of the OMFR system in the acoustic regime is developed. This model unifies the solid shell domain and the inner fluid domain by applying interactive boundary conditions on the shell-fluid interface. As a result, we can simulate the hybrid fluid-shell vibrational modes and investigate the acoustic sensitivity of the OMFRs to fluid density and speed of sound. With the simulation results, we are able to identify of the hybrid fluid-shell modes from experiment and extract fluid properties. In addition, based on the simulation results, a perturbation model is built to predict the OMFR's acoustic sensitivity to micro- and nano-particles. Experimental determination of fluid viscosity is also demonstrated, through optomechanical measurement of the vibrational noise spectrum of the resonator mechanical modes. A linear relationship between the spectral linewidth and root-viscosity is predicted and experimentally verified in the low viscosity regime. The bioanalyte particles perturbs the acoustic field in the fluid domain by density and compressibility contrast with the ambient fluid. Phonons permeate the entire cross-section of the resonator, casting a near-perfect net for measuring particles flowing along the fluid streamlines. All particles in the sample must transit and perturb these phonon modes, in turn perturbing the optical readout due to the strong optomechanical coupling. In our first experimental report, we show that detection rates exceeding 10,000 particles-per-second are reachable with noise floor (size) better than 660 nm, without any binding, labeling, or reliance on random diffusion. This optomechanical method also uniquely quantifies mechanical parameters of single nanoparticles such as density, viscoelasticity, and compressibility, which are not accessible through traditional optical measurements. Later, an electro-opto-mechanical driving and lock-in technique is adopted and real-time operation of the OMFR is enabled. Particle detection with transit time scale as short as 490 um is experimentally demonstrated. Furthermore, the initial results on high-throughput measurement of particle compressibility using OMFR are shown at last.
Issue Date:2017-04-19
Rights Information:Copyright 2017 Kewen Han
Date Available in IDEALS:2017-08-10
Date Deposited:2017-05

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