Better Packaging for Miniature Immersible Diagnostic Systems

NASA's Jet Propulsion Laboratory, Pasadena, California

A method of packaging now under development would afford improved protection and functionality for miniature immersible diagnostic systems (MIDS). The method involves covering a MIDS with a thin hermetic film that, if necessary, can be broken on command to expose one or more sensor(s) in the MIDS to the environment to be sensed.

One or More Actuator(s) Around the Inlet would, on command, disrupt the polymer film that surrounds the MIDS to allow ambient liquid to enter the inlet.

MIDS are members of a growing class of advanced microelectromechanical systems (MEMS) that have been and are being developed for use primarily as biosensors, including (but not limited to) chemical and temperature. Conceptually, MIDS are designed to be fully immersed in water to sense water-borne toxicity or biohazards, or in bodily fluids (e.g., in the gastrointestinal tract) to gather information on patients' health. In addition, the basic MIDS concept will likely be extended to the development of miniature immersible systems for delivering drugs and/or acquiring liquid samples.

Some MIDS are designed to be permanently encapsulated for protection, and yet able to function without direct contact between their environments and delicate sensor components; a body-temperature sensor is an example of this kind of MIDS. Other MIDS (e.g., those for detecting water-borne biohazards) must be at least partly immersed in order to function; therefore, their operational lifetimes can be limited and the onset of operation cannot be delayed. The present developmental method would make it possible to delay the onset of operation; in other words, a delicate MIDS could be kept sealed against hostile surroundings until commanded to expose itself to the surroundings to perform its sensory function.

The figure schematically illustrates a conceptual MIDS packaged according to the present developmental method. The MIDS would include a microfluidic sample-preparation device that would acquire one or more sample(s) of the ambient liquid to one or more sensor(s). The sensor outputs would be processed and telemetered to an external hand-held receiving unit or portable computer. The entire exterior surface of the MIDS would be protected by a thin polymer film. The portion of the film covering the inlet to the sample-preparation device would be delineated by an underlying electric-heating wire or other actuator. Upon command, the actuator would melt, tear, and/or otherwise disrupt the film to allow the surrounding liquid to enter the inlet.

Thus far, films of an amorphous fluoropolymer with thicknesses of 0.8±0.2 µm have been applied to silicon substrates and analyzed with respect to adhesion, protective properties, amena-bility to patterning, and amenability to disruption on command. Experiments have shown that disruption on command is more difficult than had been anticipated. It may be possible to overcome this difficulty through a combination of patterning and increasing actuation force.

This work was done by Gisela Lin, Kevin King, and H. L. Kim of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.

NPO-20954