When many people hear the word "dust," they immediately think of a powdery substance with little intrinsic value. But my work with my adviser Michael Sailor, a professor at the University of California, San Diego (UCSD) and my advisor, demonstrates that dust-sized devices may have important scientific applications.
Sailor began working in the field of porous silicon sensors upon his arrival at UCSD in 1990. After completing my undergraduate chemistry degree at Princeton in 2000, I wanted an opportunity to work with Sailor because of his interdisciplinary approach and his interest in finding real-world applications for these devices. The current challenges of nanotechnology require creative solutions that may be based in chemistry, physics, biology, or engineering. Our work together led to my being selected as one of the world's top 100 young innovators by Technology Review, in September 2004.
The term "smart dust" commonly refers to millimeter-sized, low- power devices that are used for sensing, computing, and wireless communication. These devices typically are constructed using conventional silicon microfabrication techniques and function as the individual components within expansive wireless sensor networks for various surveillance applications.
Our version of smart dust is much smaller, and is constructed using electrochemical corrosion techniques. The sensors are photonic crystals that change color in the presence of the specific substance they are designed to detect. These sensors can be engineered to have a different color on each side, with one side designed to stick to the target and the other side designed to report information to the viewer. For example, in the presence of a chemical toxin in sewage water, or a harmful gas within a room, the green side of our crystals attaches to the pollutant and the red side becomes visible to the naked eye.
The project developed in response to emerging national needs; since 11 September, interest in environmental surveillance technologies for homeland security applications has increased dramatically. We responded by gearing part of our research toward environmental surveillance applications.
An Interview With Jamie Link
What skills did you need to enter the field and do this kind of research?
The challenges currently posed in nanotechnology will require creative solutions that may be based in chemistry, physics, biology, or engineering. What is essential is the ability to communicate with and to learn from scientists from all different backgrounds.
How did you acquire these skills?
My formal training as an undergraduate was in chemistry, but by working in such an interdisciplinary field, I have a chance to communicate almost daily with scientists from other areas. I have also had the opportunity to speak at national and international conferences, where I have learned to communicate my research to a broad audience.
What is the job outlook for this kind of work in the future? Do you see more women entering the field of materials science?
I think we're seeing more women pursuing careers in all of the scientific disciplines.
What advice would you give young women or others who are interested in following in your footsteps?
I would encourage young women interested in science to seek out role models in their fields of interest and to get hands-on experience in the laboratory as early as possible. It's only by doing independent research that you really begin to understand the scientific process.
What do you expect or hope to be doing 5 or 10 years from now?
I am interested in a career in science policy.
The Making of Smart Dust
The color of our photonic crystals is not due to pigmentation but to multiple layers of transparent material designed to reflect only particular wavelengths of light. This "structural color" is seen in nature in butterfly wings, fish scales, and iridescent abalone shells. We are able to emulate these colorful structures in silicon by porosifying the silicon in a controlled manner to generate a layered structure that displays tunable optical properties. In this way, we impart structural color to the silicon and provide an easy means of tracking and identifying our sensors once they are scattered in the environment. The colorful films can be removed from the bulk substrate and broken into tiny, "dust-sized" pieces that are small enough for use in a range of applications.
Once we've created an optical reflector in porous silicon, we perform specific surface chemistry on the structure to tailor it to detect a specific chemical or biomolecule. An array of sensors--each with a different color code--can be designed for use in a highly parallel screening application. Because the smart dust is porous and has a surface area several thousand times that of the bulk material, it functions as a "microconcentrator" and can translate detection of a low concentration of the material being analyzed into a large change in signal.
The miniaturization of the sensors from the dime-sized wafers that had been constructed in the group for many years to the micrometer-sized particles of smart dust led to new uses for porous silicon sensors. For example, the sensors could have many in vivo applications for monitoring localized drug delivery, or as tracers in the bloodstream if they are reduced to the nanoscale. Because the sensors are bioresorbable and contain no toxic materials, they are preferable to most existing technologies for these types of applications (such as quantum dots or organic fluorophores used as tracer elements). Moreover, the porous silicon smart dust can be easily probed using noninvasive techniques.
A Recommended Field
As smart dust and devices of all types continue to shrink in size, we are witnessing fascinating developments at the nexus of materials science and nanotechnology. Perhaps the greatest challenge in the field currently is to engineer devices with increasing complexity and functionality in increasingly smaller packages. The continuation of this trend toward miniaturization to the nanoscale will hinge on the development of new fabrication techniques that exceed the limits of conventional lithography. The development of tools that will allow us to manipulate individual molecules will draw on the skills of scientists from many different disciplines. As the youngest of 30 women honored by Technology Review, I hope to inspire young girls and women to pursue careers in science and technology.
Jamie Link is a graduate student in the department of chemistry and biochemistry at the University of California, San Diego. She may be reached at email@example.com .