Light-driven droplet-based microfluidic platforms for lab-on-a-chip applications

In this dissertation, I present several light-driven droplet manipulation mechanisms for active control of individual droplets; (1) floating electrode optoelectronic tweezers (FEOET), (2) single-sided continuous optoelectrowetting (SCOEW), and (3) high-speed pulse laser-driven droplet generators (PLDG).;A floating electrode optoelectronic tweezers (FEOET) mechanism enables, for the first time, optical actuation of aqueous droplets using light-induced dielectrophoretic (DEP) force on a single-sided photoconductive surface. A circular laser beam was able to transport a 681-microm de-ionized water droplet immersed in corn oil medium with a light intensity as low as 4.08 microW/mm2 at a speed of 85.1 microm/sec. We also study the shape effect of light patterns to achieve two-dimensional (2D) droplet manipulation on FEOET.;A single-sided continuous optoelectrowetting (SCOEW) mechanism is also described. It enables optical modulation of the surface tension for droplet manipulation on a featureless photoconductive surface. Since surface tension-based droplet actuation provides larger forces than the DEP forces provided in FEOET, SCOEW permits a higher droplet transport speed on the order of cm/sec and allows more droplet manipulation functions such as droplet splitting and injection from reservoirs, which were not achieved in the previous FEOET devices. Various droplet-based functions have been demonstrated including, the continuous transport, splitting, merging, and mixing of droplets with volumes ranging from 50 microL to 250 pL, over 5-orders of magnitude. Light-triggered, parallel, and volume-tunable droplet injection with volume variation less than 1% has also been demonstrated with a dispensing speed of 7 droplets/min using SCOEW.;Lastly, I present a novel ultra-fast, pulse laser-driven droplet generation (PLDG) mechanism that enables on-demand droplet generation up to 10,000 droplets/sec, continuous tuning of droplet volume ranging from 1pL to 150pL with precise volume control (0.26% volume variation), and single-particles or cells encapsulation with a 92.07% cell viability in a single layer PDMS based microfluidic device without any mechanical valves or pumps. Device reliability testing of continuous excitation for more than 3.6 million laser pulsing cycles without device damage is also achieved. PLDG promises a high-speed droplet generator for high-throughput and quantitative single-cell based analysis.