August R&D Round UpAugust 8, 2008 By: Melanie Martella, Sensors
This month, integrated nanowire circuitry, better ad hoc networking for first responders, a curved image sensor that mimics the human retina, and a new salivary sensor to ferret out disease.
Nanowires show great promise as highly efficient sensing elements for light, chemicals, and some electrical properties. However, as anyone who's worked with traditional sensors knows, adding electronics is critical to getting a useful signal from a sensing element. The same holds true with nanowire-based sensors. Researchers at the U.S. DoE's Lawrence Berkeley Lab and the University of California at Berkeley, led by Ali Javey, have successfully created a nanowire-based integrated sensor circuit ("A First in Integrated Nanowire Sensor Circuitry" at BrightSurf.com has more details). The team developed methods of printing the desired nanowires on to a donor substrate and then transferring them to the desired target substrate. To get an idea of why this is so important, I'll quote Javey, "Our main objective is a route toward integrated nanowire arrays that we can produce on any substrate—even paper!—and to reproduce them uniformly on a large scale." In other words, we're another step closer to mass-produced nanosensors, with supporting electronics, that you can place on almost any surface.
A Better Breadcrumb Trail
Ad Hoc wireless networks can be used by first responders to maintain two-way communications as they travel into fires, collapsed buildings, mines, or other radio-hostile environments. One way to maintain the communication is to lay down wireless relays ("breadcrumbs") at specified points to work around radio dead spots and other obstacles. However, that's not necessarily the best approach because of all the factors that can affect signal strength. NIST researchers Nader Moayeri, Michael Souryal, and their compatriots have developed software that, when incorporated into these relays, can monitor signal strength and alert responders when to drop the next relay. Not only that, it can also advise the responder where to place the relay for best results. Finally, and maybe most importantly, it automates the placement leaving the first responder concentrating on the task at hand.
Curved Image Sensors
The human eye's curved retina provides us with wide-angle images, without distortion, in a remarkably compact form factor. As reported in New Scientist, researchers at the University of Illinois at Urbana - Champaign have discovered how to mimic that curve (and the resulting benefits) in a digital image sensor. They built 500 µm by 500 µm by 1 µm photodiodes (using conventional photolithography) and then created a 1 cm wide stretch plastic hemisphere. Then, stretching the hemisphere flat they laid it over the photodioes, which glommed on to the surface (no, that's not the technical term but it's an accurate description). When the hemisphere was released it bounced back into it's curved shape, bringing its cargo of sensors with it. Supported by a curved glass substrate and with a conventional lens attached, the result was an electronic eyeball.
Drool Here for Diagnosis
Researchers supported by the National Institute of Health's National Institute of Dental and Craniofacial Research (NIDCR), have developed an ultra-sensitive optical protein sensor. The device is intended to act as a salivary diagnostic test when incorporated into a lab-on-chip; certain medical conditions have protein markers that show up in saliva, allowing doctors to diagnose the illness without having to take blood. The sensor in question is primed to bind with the protein of interest, fluorescing more strongly as the protein's concentration increases. More interestingly, the researchers figured out how to boost the SNR by finding the optimal location at which to collect the light, increasing the limit of detection by two orders of magnitude.
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