Microfluidics

The Microelectronics Laboratory silicon facilities were used to develop microfluidic integrated circuits, in which fluids move around in channels on a substrate to accomplish a variety of tasks. Fluids can be pumped and their paths switched using no moving parts and no external pressure. The underlying principle is electrowetting. Potential applications of this new field range from chemical lasers, to implantable drug delivery systems, to detection of biological or chemical hazards, to DNA analysis.

The ability to efficiently control and manipulate the shape and composition of microfluidic elements on a surface or in a system provides a powerful toolset for multiple scientific and engineering applications. The Chemical, Microsystem, and Nanoscale Technologies Group has a large portfolio of projects in this field, encompassing basic interface materials science, specialized microfabrication methods, and unique applications in support of Lincoln Laboratory’s mission areas.

need captionImage of a helically shaped 20-µm-wide strand of hydrophobic liquid (oil) embedded in a hydrophilic conductive medium. This shape was formed by prepatterning the substrate. Other optofluidic elements, such as microlens arrays, have also been formed and their optical properties characterized.

Many microfluidic lab-on-a-chip devices target the miniaturization of chemical or biomedical sample processing. The projects in the Chemical, Microsystem, and Nanoscale Technologies Group extend this approach to complex two-dimensional and three-dimensional microfluidic circuits that can enable fast combinatorial analysis of a large number of components such as genes, miRNAs, and proteins. This approach can be a game changer in applications that the group is exploring, ranging from cancer research to defense against chemical agents, and it holds the promise of providing orders of magnitude advantage in speed and cost. Furthermore, microfluidic design and fabrication is an integral part of effective synthesis of biomolecules in the growing field of synthetic biology, which is being pursued at Lincoln Laboratory.

A related microfluidic fabrication technology that has been developed at Lincoln Laboratory is low-voltage electrowetting. In this process, a thin dielectric layer is applied to the walls of microfluidic channels, and the application of suitable voltages enables the switching and propagation of two-component fluids (such as oil drops in water) in complex paths. Electrically controlled microfluidic circuits can be designed and implemented, including pumps, valves, mixing elements, and filters. Besides biomedical applications, the Chemical, Microsystem, and Nanoscale Technologies Group is pursuing applications of low-voltage electrowetting in microoptics and microhydraulics. In microoptics, the group has demonstrated the fabrication and functionality of switchable liquid lens arrays, with dimensions of individual lenses down to 50 µm and even less, capable of changing focus over a wide range as the applied voltage changes the shape of the oil-water interface. A related application envisions electrowetting-based optical beam steering, where the variable-focus liquid microlenses are replaced with variable-angle liquid microprisms. The group's initial studies into microhydraulics applications have recently shown efficient fluid displacement through arrays of microchannels in a conductive matrix, leading to the development of pistons and actuators.

Other applications of microfluidics in the Chemical, Microsystem, and Nanoscale Technologies Group include the implementation of fluidic valves and channels with liquid metals, thus enabling reconfigurable radio-frequency antennas; and the design and fabrication of one-phase and two-phase fluidic cooling manifolds, which provide much needed power dissipation to advanced microelectronic circuits, high-power radio-frequency amplifiers, and new solid-state lasers. 

 

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