Joshua D. Tice

Design considerations for electrostatic microvalves with applications in poly(dimethylsiloxane)-based microfluidics†

Microvalves are critical in the operation of integrated microfluidic chips for a wide range of applications. In this paper, we present an analytical model to guide the design of electrostatic microvalves that can be integrated into microfluidic chips using standard fabrication processes and can reliably operate at low actuation potentials (<250 V). Based on the analytical model, we identify design guidelines and operational considerations for elastomeric electrostatic microvalves and formulate strategies to minimize their actuation potentials, while maintaining the feasibility of fabrication and integration. We specifically explore the application of the model to design microfluidic microvalves fabricated in poly(dimethylsiloxane), using only soft-lithographic techniques. We discuss the electrostatic actuation in terms of several microscale phenomena, including squeeze-film damping and adhesion-driven microvalve collapse. The actuation potentials predicted by the model are in good agreement with experimental data obtained with a microfabricated array of electrostatic microvalves actuated in air and oil. The model can also be extended to the design of peristaltic pumps for microfluidics and to the prediction of actuation potentials of microvalves in viscous liquid environments. Additionally, due to the compact ancillaries required to generate low potentials, these electrostatic microvalves can potentially be used in portable microfluidic chips.

Control of pressure-driven components in integrated microfluidic devices using an on-chip electrostatic microvalve

Pressure-driven actuators play a critical role in many microfluidic technologies, but the ancillary equipment needed to operate pneumatic and hydraulic platforms has limited their portability. To address this issue, we created an electrostatic microvalve used to regulate pressures in hydraulic control lines. In turn, these control lines are able to actuate pressure-driven components, e.g., microvalves. The electrostatic microvalve is fabricated exclusively with soft-lithographic techniques, allowing it to be directly integrated in a microfluidic chip. The electrostatic microvalve also contains a passive structural element that balances the pressure on the top and bottom sides of the actuating membrane. This feature enables the microvalve to induce pressure changes up to 20 kPa with electric potentials less than 320 V. When the microvalve is integrated into a microfluidic “pressure amplifier” circuit, the pressure output of the circuit can be tuned with the voltage applied to the microvalve. This integration allows for different types of pressure-driven components to be actuated with variable pressures, and thus eliminates the need for off-chip pressure regulation. In the example reported here, only one actuator is required to adjust the pressure of a single hydraulic line.

Normally-Closed Electrostatic Microvalve Fabricated Using Exclusively Soft-Lithographic Techniques and Operated With Portable Electronics

We report an elastomer-based electrostatic microvalve that was fabricated using replica molding, micro-transfer printing, and plasma bonding. The microvalve can be actuated with an electric potential of ~ 220 V and can withstand pressures up to 3 kPa. Sixteen independently-operated valves were integrated on a single chip and operated with portable electronics.

Vertical-cavity surface-emitting lasers for optical sensing in microfluidic microsystems

We describe the hybrid integration of vertical-cavity surface-emitting lasers with a network of microfluidic channels to form a compact microfluidic microsystem. VCSEL dies, created by standard fabrication techniques, are integrated on a silicon substrate which is merged with a micro-fluidic network of PDMS channels to form an opto-fluidic microsystem. The fabrication and integration process of VCSEL dies, silicon host substrate, and microfluidic network are discussed. Absorption measurements of the laser output power using IR absorbing dyes indicate a detection limit of 13 μM of dye concentration. A future integration scheme using monolithically integrated VCSEL / PIN photodetector dies is proposed.

Optofluidic microchip with VCSELs and edge emitting laser sources

We discuss two approaches for integration of light sources into microfluidic chips. 780 nm VCSELs and fiber pigtailed edge emitting lasers are integrated for fluorescent measurements.