Jaisree Moorthy

Alternative Approaches to Microfluidic Systems Design, Construction and Operation

An alternative approach (µFluidic Tectonics) to microfluidic device construction that utilizes liquid phase photopolymerization and responsive materials is presented. Ultra rapid (3 min) microchannel fabrication is demonstrated. Filtering, flow control, and mixing components are demonstrated.

In situ fabricated porous filter - characterization and biological applications

Porous filter was fabricated inside a microchannel by phase separation photo-polymerization. The porosity of the filter varies with the composition of the prepolymer mixture. Four different filter compositions varying in water and crosslinker concentration was characterized using confocal microscopy and resistance measurements. Preliminary studies showed that the porous filter can separate blood cells from whole blood and the large surface area can be utilized for protein detection assays.

Polymer Microfluidic Valves, Membranes and Coatings

We present work in two areas of practical importance in polymer-based microfluidic systems — normally closed valves and reduction of swelling in organic solvents. A normally closed valve was designed, fabricated and characterized. The valve consists of three laminated layers (two polydimethylsiloxane (PDMS) micro-molded layers and a microscope cover glass). A flexible membrane (diaphragm) creates a tight seal against a channel/dam structure. If sufficient driving pressure is present in the fluid channel, the membrane diaphragm is pushed upward allowing flow. The pressures required to open a variety of valves designs were measured. The hold off pressure of the valve can be controlled by adjusting the pressure that is applied externally to the top of diaphragm. No leaking in the off state was observed. Another issue in polymer microfluidic systems is polymer swelling in organic solvents. To make the inner walls of the devices hydrophilic and resistant to organic solvents, a flow through process is used to create a thin silicate barrier layer. The swelling of a square pattern in toluene was tested for different number of coatings. The coating decreased the swelling by a factor of 2.

Autonomous Colorimetric Readout for Microfluidic Devices

Autonomous readouts that work on colorimetric principles were fabricated inside a microchannel by immobilizing dyes (congo red and phenolphthalein) in a hydrogel matrix. The response time of the readout varied between 20 s and 45 s depending on the dye. To test for reusability, the phenolphthalein containing gels were recycled between acidic and basic solutions at different flow rates (0.1, 0.25 and 0.5 mL/min).

TiO2 Surface Modifications for Light Modulated Control of Flow Velocity

Controlling flow in microchannels is an important part of microfluidics. TiO2 is a direct semiconductor that exhibits a change in surface charge upon irradation with UV light. We have exploited this phenomenon to control flow in micro channels. Light is used to modulate bulk and local velocities. The bulk velocity was measured using current monitoring techniques in the presence and absence of UV irradiation in different buffer solutions. The largest velocity change was observed at 4.7 pH with smaller changes observed at higher and lower pH values. A preliminary demonstration of localized flow control is also presented.