Tuesday, February 28, 2017
Image: Georgia Institute of Technology/Nature Nanotechnology
Mass spectrometry is a chemical analysis and detection tool that has been around for 130 years. In that time there have been so many tweaks and improvements that observers have become a bit blasé about the next big leap in its development.
But the latest improvement out of the Georgia Institute of Technology may be the biggest yet for the venerable old analytical tool. In research described Nature Nanotechnology, the Georgia Tech researchers have managed to make mass spectrometry more sensitive than ever before, more portable, cheaper and even safer. All of these advancements were accomplished by replacing the direct current power source typically used as power source with triboelectric nanogenerators (TENGs). You can see a demonstration of the technology at work in the video below.
While the researchers concede the mechanism by which the enhancement takes place demands more investigation, they believe the unique aspects of the TENG output—oscillating high voltage and controlled current—should enable improvements in the ionization process, increasing the voltage applied without damaging samples.
The so-called TENGs were developed at Georgia Tech back in 2012 and Zhong Lin Wang and his colleagues at Georgia Tech have been improving the technology and expanding its applications ever since. TENGs essentially harvest static electricity from friction. The TENG devices consist of two different materials that are rubbed together. In this way, materials that tend to give off electrons, such as glass or nylon, will donate them to materials that tend to absorb them, such as silicon or teflon. By converting mechanical energy from friction to electricity the TENGs can power small electronic devices.
Applied to mass spectrometry, the TENGs replace the direct current power source for generating the ions. This takes the advantage of a fixed input charge in each cycle of the operation of the TENG regardless of the current or voltage, allowing the mass spectrometer to analyze the smallest possible sample at the highest possible sensitivity.
“The sensitivity has been increased to being able to detect down to 100 molecules,” said Wang in an e-mail interview with IEEE Spectrum. “This is the highest ever.”
Wang also points out how efficient the TENG power source is in using samples. In mass spectrometry, a sample is ionized and the ions are sorted according to their mass-to-charge ratio. But with DC voltages, the number of generated ions does not depend on the applied voltage in a straightforward fashion. As a result, controlling the number of charges used in the ionization of neutral species is usually impossible. The fixed number of charges provided by TENGs offer unprecedented control over ion generation. This makes it very efficient in how it uses the sample.
“The key here is that the total charge delivered in each cycle is entirely controlled and constant regardless of the speed at which the TENG is triggered,” said Wang in a press release.
Facundo Fernández, a professor in Georgia Tech’s School of Chemistry and Biochemistry, added: “Our discovery is basically a new and very controlled way of putting charge onto molecules. We know exactly how much charge we produce using these nanogenerators, allowing us to reach sensitivity levels that are unheard of – at the zeptomole scale (10-21th part of a mole or about 600 molecules). We can measure down to literally hundreds of molecules without tagging.”
The Georgia Tech team has measured the TENGs generating as much as 6000 and 8000 volts as a mass spectrometry ionizer. Standard ionizers normally operate at less than 1500 volts.
“Because the voltage from these nanogenerators is high, we believe that the size of the sample droplets can be much smaller than with the conventional way of making ions,” Fernández said. “That increases the ion generation efficiency. We are operating in a completely different electrospray regime, and it could completely change the way this technology is used.”
By eliminating the often high-voltage power supplies, mass spectrometry could become more portable, leading the researchers to speculate that they could be used in extreme and harsh environments since they would become a durable self-contained unit.
While dramatically improving sensitivity, portability and adding a bit of safety by replacing the high-voltage power supplies, the TENGs also enable the deposition of ions onto surfaces, including non-conducting ones. This becomes possible because the TENGs are creating an oscillating ionization that produces a sequence of alternating positive and negative charges, resulting in a net neutral surface.
Wang added: “This opens a new field for applying TENG in portable and mobile instruments with high performance. The next phase of research is to optimize the performance of the system so that it can be used for sophisticated analytical chemistry and biochemistry.”
Monday, February 27, 2017
Boqu He, Junyi Nan, Min Li, Shuai Yuan, and Heping Zeng
Full Article | PDF Article
In this paper, a switched-capacitor readout circuit topology integrated with a THz antenna and field-effect transistor detector is analyzed, designed, and fabricated in a 0.13-μm standard CMOS technology. The main objective is to perform amplification and filtering of the signal, as well as subtraction of background in case of modulated source, in order to avoid the need for an external lock-in amplifier, in a compact implementation. A maximum responsivity of 139.7 kV/W, and a corresponding minimum NEP of 2.2 nW/√Hz, was obtained with a two-stage readout circuit at 1 kHz modulation frequency. The presented switched-capacitor circuit is suitable for implementation in pixel arrays due to its compact size and power consumption (0.014 mm and 36 μW).
Test made in a vineyard. Credit: Elhuyar Fundazioa
Researchers at the NUP/UPNA-Public University of Navarre have designed two types of sensors whose innovative technologies obtain information on the water status of a vineyard. The work has been developed by a NUP/UPNA multidisciplinary team in collaboration with various Navarrese companies.
The first of these sensors does not require contact with the plant, and works by capturing information in the terahertz range. "These devices transmit a terahertz signal and measure what proportion of the signal is returned by the trunk of the vine," explained Gonzaga Santesteban-García, lecturer in the Department of Agricultural Production and leader of the research project. "It involves reflectance technology without any contact with the plant. That way, we can check the plant's water status. It is a technique that has not been used before for this purpose." The results of this development have been published in the journals Frontiers in Plant Science and the Journal of Infrared, Millimeter and Terahertz Waves.
The sensor design is simple because high bandwidth is not needed; it uses planar technology, which allows a high degree of miniaturization and thus considerably cuts the cost per unit, since many of its chips can be obtained commercially at a low price.
The second of the sensors is based on a totally different principle. In this case, the aim was to use magnetoelastic sensors to detect the changes that take place throughout the day and night in the size of the trunk or branches of the vine. Gonzaga-Santiesteban explained that sensors of this type offer two advantages over the classical dendrometers used by some wineries. "Firstly, this is a different technology enabling costs to be reduced and, secondly, we have made it more flexible so that these devices can be fitted not only to the trunk, as until now, but also to different parts of the vine, such as, for example, the cluster," he added. The results of this development have also been partially published in the journal IEEE Transactions on Magnetics.