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.
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
This Brief includes a Technical Support Package (TSP).
Better Packaging for Miniature Immersible Diagnostic Systems
(reference NPO-20954) is currently available for download from the TSP library.
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Overview
The document presents a technical support package detailing advancements in packaging for miniature immersible diagnostic systems (MIDS) developed at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a NASA contract. The primary focus is on improving the packaging methods used for these diagnostic systems, which are essential for in-situ analysis of liquids without the need for sample transfer to benchtop machines.
Current MIDS typically employ complete encapsulation, which, while protective, limits the sensing capabilities of the devices. The new approach aims to reconfigure this encapsulation to allow sensors to access the liquid environment more effectively while maintaining their protection. This is achieved through the development of a packaging system that can expose sensors or inlets to microfluidic circuits on command, enhancing their operational flexibility.
The document outlines the novelty of the work, emphasizing that the proposed system eliminates the need for transferring samples, thus streamlining the analysis process. The packaging is designed to protect sensors from environmental factors while allowing for dynamic exposure to the liquid being analyzed. This capability is crucial for applications such as environmental monitoring and medical diagnostics.
To address the challenges of encapsulation, the team conducted extensive literature reviews to identify suitable inert, protective polymers. Teflon AF (DuPont) was selected as the initial polymer for testing due to its desirable properties. The document describes the development of thin film processing capabilities for this polymer and the challenges encountered in breaking or tearing the Teflon-coated films to facilitate sensor exposure. The team is exploring various actuation methods to achieve the desired functionality.
In summary, the document highlights a significant advancement in the design and functionality of miniature immersible diagnostic systems through innovative packaging solutions. By allowing sensors to operate in an in-situ manner while being protected from environmental factors, this work represents a step forward in the field of diagnostic technology, with potential applications in both environmental and medical fields. The ongoing research and development efforts aim to refine these packaging techniques further, ensuring that MIDS can deliver reliable and accurate data in real-time.
