CBE Doctoral Dissertation Defense: “Controlled Deposition of Cargo-Carrying Colloids from Dispersed Liquid to Solid Surfaces” (Paradorn Rummaneethorn)

Abstract:

Great advances have been made in encapsulation of (biological) analytes at extremely high throughput via techniques such as microfluidics and/or conjugation. In parallel, analytical techniques such as mass spectrometry have advanced to analyze biochemical components of complex mixtures with high resolutions. Both capabilities are essential for enabling biology at subcellular scales; rather than engineering a new integrated system possessing both capabilities, the path of lower resistance may be to bridge such high-throughput encapsulation to high-resolution analytical platforms. However, existing encapsulation techniques yield colloids in dispersions, whereas analytical techniques require sample preparation on surfaces.

In this work, we addressed two types of colloids dispersed in liquid medium – liquid droplets and solid particles. For droplets, we employed a charge injection technique to study the reversible wetting state modulation of water droplets on hydrophobic polydimethylsiloxane (PDMS) surfaces. The system exhibits a high range of wetting modulation (from nonwetting to 20°), and we were able to demonstrate two-way cargo transfer between droplet and surface. For dispersed particles, we employed two techniques to array particles in a patterned microwell array: capillary assembly and dielectrophoretic assembly. For capillary assembly, we studied the effects of coating speed, coating passes, particle concentration, surface temperature, and presence of surfactants to optimize yield (% of occupied wells) and selectivity (% of particles inside microwells) of particle arraying. As for dielectrophoretic (DEP) assembly, we studied the number of particles deposited as a function of peak-to-peak voltage (DEP force) and alternating current frequency (DEP polarity) to the arraying of carboxylate-conjugated polystyrene particles.

The physical nature of these technologies enables robustness against combinations of colloid-surface chemical characteristics, with a tunable parameter space that empowers broad use cases involving different colloid-surface combinations. Beyond the colloid deposition use case described here, the technologies studied here can also be applied to separations, heterogeneous reaction engineering, and fundamental colloid-surface studies. When colloids and surfaces come together, possibilities are imagination-limited.