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NEWS & TECHNOLOGY BIOCHEMICAL SENSING Meta-lenses for hand-held spectrometers RBy Nick Flaherty esearchers from Harvard University have used nanolenses to develop new hand-held spectrometers capable of the same performance as large benchtop instruments. There is an inherent trade-off between the size and performance of the spectrometer. To maintain performance while reducing spectrometer size, the researchers used ‘meta-lenses’ that combine a traditional grating and focusing mirror into a single component, as well as having much greater ability to separate wavelengths. “This research has its roots all the way back to 2011, when we were investigating the fundamental properties of light as it interacts with two dimensional metamaterials (metasurfaces) and discovered generalized laws for the refraction and reflection of light for metasurface, which are powerful generalizations of the textbook laws valid for ordinary surfaces,” said Federico Capasso of Harvard. Unlike traditional refractory lenses that are millimetres thick and have a characteristic curved surface, a meta-lens is a completely flat or planar lens made up of millions of nanostructures. Using lithographic techniques, proper placement and fabrication of these nanostructures enables similar or better functionalities compared to traditional lenses. These meta-lenses can be customized to a user’s specifications, and mass-produced using the same foundries that produce computer chips. “For these reasons, we believe meta-lenses to be game-changers,” said Capasso. “The potential applications of these new smaller spectrometers are significant for portable monitoring of biological and chemical compounds” said researcher Alex Zhu. “For example, doctors could bring hospital-level diagnostic capabilities to patients in the field where sophisticated equipment and highly trained personnel are not available, providing data on a timescale of minutes to hours, as opposed to days or weeks from usual chemistry-based methods.” The same is true for environmental monitoring: Data about pollutants, or toxic chemicals could be collected and processed in real time on site at various locations with ultra-compact, high performance spectrometers. The next step is to improve the performance of the prototype for both the working wavelength range and spectral resolution. This would allow it to be used for a wide variety of analyses, including highly specialized ones to identify proteins or gene markers using Raman spectroscopy. “The goal is to be able to achieve comparable levels of performance with a simple ‘plug-and-play’ two-component device, i.e., a meta-lens and a detector, which together function as a meta-spectrometer,” said Zhu. “The potential for this already exists in the meta-lens technology; it is simply a question of finding the right configurations and making it work.” Living sensor lights up upon pathogen exposure By Julien Happich A multidisciplinary team of researchers from MIT combined the special properties of hydrogels (consisting of up to 95 percent water) with genetically modified living cells programmed to light up in the presence of certain chemicals to create a new type of living sensors. The researchers fabricated various wearable sensors from cell-infused hydrogels, including a rubber glove with fingertips that glow after touching a chemically contaminated surface, and bandages that light up when pressed against chemicals on a person’s skin. Their paper published this week in the Proceedings of the National Academy of Sciences, demonstrates the new material’s potential for sensing chemicals, both in the environment and in the human body. According to Xuanhe Zhao, the Robert N. Noyce Career Development associate professor of mechanical engineering at MIT, such hybrid “living materials” could be adapted to sense a variety chemicals and contaminants, for uses ranging from crime scene investigation and forensic science, to pollution monitoring and medical diagnostics. Glove finger tips and bandage made of a hybrid elastomer/hydrogel compound host reactive biochemistries that light up upon pathogen detection. Courtesy of the researchers While the hydrogel efficiently confines the living cells in a moist and nutrient-rich environment, it is tough and compliant enough to be co-designed with other flexible rubbery materials to design versatile biochemical sensors. In the past, scientists could only maintain the reactive cells alive in the carefully controlled environment of a Petri dish, making it difficult to exploit their fluorescent properties within synthetic materials. Here the researchers first fabricated layers of hydrogel and patterned narrow channels within the layers using 3-D printing and micro-moulding techniques. They fused the hydrogel to a layer of elastomer porous enough to let in oxygen and injected in the channels purposely modified E. coli cells that would fluoresce when in contact with certain chemicals (those would pass through the hydrogel). Soaking the hydrogel/ elastomer hybrid material in a bath of nutrients was enough to infuse the nutrients throughout the hydrogel and maintain the bacterial cells alive and active for several days. Embedding narrow channels, the hybrid material was designed to host various biochemistries (each with a bacteria engineered to glow green in response to a different chemical compound), shaped to form wearable patches or even gloves with sensing tips. The “living patches” instantly lit up in response to the presence of their respective chemical sensitivity. 22 Electronic Engineering Times Europe March 2017 www.electronics-eetimes.com


EETE MAR 2017
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