DISSERTATION DEFENSE
Theodore Anyika, Electrical and Computer Engineering
*under the supervision of Justus Ndukaife
鈥淢ultiphysics Nanotweezers for Manipulation and Characterization of Individual Nanoparticles: From Nanoplastics to Extracellular Vesicles鈥�
9.29.26 | 10:00 am | 308 Featheringill Hall |
Devices that enable single-particle trapping, manipulation, and characterization have become indispensable tools for investigating nanoscopic phenomena across the physical and life sciences and have enabled several applications including the directed assembly of colloidal structures, deterministic positioning of individual quantum emitters at engineered photonic hotspots, and the in-situ chemical characterization of nanoplastics and extracellular vesicles in solution. Extracellular vesicles (EVs) are key mediators of intercellular communication and carry complex molecular signatures that make them valuable for noninvasive biomarker discovery and targeted drug delivery, yet their clinical translation remains limited by pronounced heterogeneity in size, cargo and membrane composition which are not easily resolved by bulk characterization techniques. Likewise, Nanoplastics pose a similar challenge in the context of environmental contamination. The global plastic production currently exceeds 400 million tonnes per year, of which 19 to 23 million tonnes reach aquatic ecosystems and fragment under photo-oxidation, abrasion and biodegradation into micro-and nanoplastics capable of transversing biological barriers to induce cytotoxic and inflammatory effects. In both cases critical information carried by individual particles is lost in standard bulk measurements.
This dissertation addresses these challenges developing by developing multiphysics nanotweezers for trapping and characterization of nanoparticles that leverage optical, thermal, electrohydrodynamic and mass-transport phenomena. The first part is focused on developing various trapping strategies, while the later part geared towards applications to single-particle characterization. First, we leverage electrothermoplasmonic (ETP) flow-assisted trapping to achieve rapid trapping of 25 nm polystyrene particles using a double nanohole (DNH) plasmonic aperture, overcoming the diffusion limit that constrains plasmonic trapping. Next, we build on this design to develop a mirror-enhanced DNH aperture that amplifies the field enhancement while significantly suppressing thermal effects and demonstrate low-power trapping of single extracellular vesicles in solution. Lastly, instead of avoiding photothermal effects in plasmonic antennas, we exploit these effects using bowtie plasmonic antennas to induce sharp diffusiophoretic potentials that enabled stable trapping and 2D manipulation of nanoplastics and extracellular vesicles at sub-milliwatt powers.
In the second part, we first develop an automated Raman trapping and characterization platform built around an interferometric electrohydrodynamic trapping (IET) device that uses a patterned Au electrode to induce engineered AC electroosmotic flows for massively parallel trapping of nanoparticles. We then demonstrate an 聽suppression of Raman background from nanoparticles by coupling the Raman scattered light into a core fiber that pushes the detection limit down to 200 nm particles. 聽Next, we apply the same IET device to quantify the loading efficiency of doxorubicin (DOX) in tomato-derived extracellular vesicles, using label-free interferometric imaging to discriminate between loaded and unloaded vesicles when compared with fluorescence imaging. We also propose that, by lithographically placing nanoantennas at the IET trapping the detection limit below 200 nm, using a ring-coupled bowtie design that raises the simulated field enhancement from as high as 85 at a steady-state temperature rise below 1.5 , we can further push the Raman detection limit of Automated Raman trapping platform, creating a new modality for efficient single nanoplastics characterization and analysis.