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Access Type

WSU Access

Date of Award

January 2019

Degree Type


Degree Name



Electrical and Computer Engineering

First Advisor

Amar Basu


Since Ashkin’s invention of the optical tweezer in the 1980’s, the use of light to physically manipulate objects has remained an interest in physics and the life sciences. Optical tweezers have found tremendous applications in cellular and subcellular manipulation, and in measuring forces on biomolecules. However, optical tweezers rely on scattering and electromagnetic gradient forces, which are typically in the piconewton range. This generally limits the optical manipulation to objects in the low micron and submicron size scale. Here we report a novel optical trapping technique, the optofluidic tweezer which can trap millimeter and submillimeter scale droplets using thermocapillary forces. The OFT relies on the asymmetric Marangoni flows generated by localized heating with a focused laser. Asymmetry in the tangential stress leads to a restoring force which traps the droplet on the laser axis. The core objective of this thesis is to measure the holding force and temperature profiles of the optofluidic tweezer. Experimentally measured holding forces on a 600um oil droplet is the order of 350 nanonewtons, which is 10,000 times larger than the conventional optical tweezer. These forces are obtained with a 48mW laser, generating temperature increases of around 26 ℃. The relationship between holding force, laser power, droplet size, and liquid parameters are explored. Early applications of the optofluidic tweezer, such as bead manipulation on droplet ‘rafts,’ is also demonstrated.

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