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Breathalyzer gets the nanotech treatment
Materials Today Volume 18, Number 8 October 2015
trast, with crystallites 10–100 nm in size, appear to be preferred by proliferating cells. ‘‘The reasons are not clear,’’ admits May, ‘‘but it may be something to do with the surface needing to be slightly rough (but not too rough) in order for cells to grip on and adhere.’’
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The final piece of the jigsaw is to grow neurons on diamond surfaces. Instead of culturing human neurons directly on diamond, the team devised a protocol to culture stem cells and then convert them into neurons later, as required. Electrical signals could then passed between the conducting diamond substrate and the neurons.
‘‘We still have a lot more fundamental studies of the neuron/diamond interface to perform,’’ says May. ‘‘[But] the long term possibilities for this work are exciting. Longlifetime diamond bio-implants may offer treatments for Parkinson’s, Alzheimer’s, stroke or even epilepsy.’’ Cordelia Sealy
New research has shown that the color vision of the human eye has the ability to see differences even down to the nanoscale. Scientists from the University of Stuttgart in Germany and the University of Eastern Finland have carried out tests that show the color-sensing abilities of the human eye allow it to distinguish between objects that differ in thickness by only a few nanometers. The research, as reported in Optica [Peterha¨nsel, et al., Optica (2015) doi:10.1364/ OPTICA.2.000627], assessed the limits of unaided human vision for small variations using volunteers to identify subtle color differences in light passing through thin films of titanium dioxide under highly controlled lighting conditions. A series of these thin films, which are key to many commercial and manufacturing applications such as anti-reflective coatings on solar panels, were produced one layer at a time through
atomic deposition, allowing careful control of their thickness and therefore how small a variation could be identified. The team were able to determine the sample thickness from the observed color based on a color-matching experiment between the thin film samples and a simulated color field presented on an LCD monitor that displayed a pure white color, apart from a colored reference area that could be calibrated to match the apparent surface colors of the thin films with various thicknesses. The color of the reference field could then be changed by the test subject until it matched accurately the reference sample. The human color observation was found to provide a very accurate evaluation, comparable to more sophisticated instrumental methods such as vapor deposition. As principal author Sandy Peterha¨nsel said, ‘‘Although the spatial resolving power of the
human eye is orders of magnitude too weak to directly characterize film thicknesses, the interference colors are well known to be very sensitive to variations in the film.’’ The tests only took a couple of minutes, with some test subjects managing to estimate the thickness of the samples which differed by only one or two nanometers from the actual value measured through conventional methods. Compared to common automated methods of determining thickness, the approach also performed very favorably. However, it is doubtful if this method will replace automated methods in the near future as eyes tend to tire very easily, but could be seen as complementary if used in fabrication control as a quick check by an experienced technician, with any deviations detected needing further characterization through other techniques. Laurie Donaldson
Breathalyzer gets the nanotech treatment Results from the Chinese Academy of Sciences suggest that tomorrow’s alcohol breath tests may be self-powered and nano-enhanced. Small-scale gas sensors are used in countless applications around the word – from monitoring the air quality in tunnels and in labs, to the detection of disease or explosives. Since the 1950s, they’ve also found widespread use in roadside breath tests for drivers. Despite many changes in design, today’s breathalyzers still operate on the original principle. Based on a chemical reaction between ethyl alcohol (ethanol) and potassium dichromate, these portable sensors produce a color change directly related to the level of alcohol present in the person’s breath. When compared to a known sample of gas, they can also provide a quantitative measure of the alcohol content in the person’s blood.
Device structure of the blow-driven triboelectric nanogenerator.
421
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Human eye capable of distinguishing to the nanoscale
NEWS
NEWS
But work from a team of US and Chinese researchers suggests there may be an even better way to test a person’s breath – a nanowire ‘whistle’ that powers itself. Published in Nano Energy [Wen, et al., Nano Energy (2015), doi:10.1016/j.nanoen. 2015.06.006], the paper describes the development of a rotating triboelectric generator and gas sensor, that can to detect alcohol at concentrations as low as 10 parts per million (ppm). In its simplest form, the ‘whistle’ is assembled from three main components – a rotator (a rotating acrylic wheel coated with polymer nanowires), a stator (a pair of stationary, copper-coated acrylic
Materials Today Volume 18, Number 8 October 2015
disks) and a spacer (soft elastic O-rings to sit between them). It works by the triboelectric effect – blowing into the whistle causes the wheel to rotate. Because copper is an electron-donating material and the fluorinated ethylene propylene (FEP) nanowires are electron-accepting, as the nanowirecoated wheel spins, there is an exchange of electrons between the materials. This produces a large enough current to power a Co3O4 based gas sensor. The team found that the output voltage of the gas sensor was constant and independent of the user, or the speed at which the user exhaled. Powered by the triboelectric
whistle, the sensor could detect a range of different gases at very low concentrations, and connecting a low-cost alarm to it (also powered by blowing into the whistle) minimized the risk of interference by the user. So, what’s the catch? Well, this system is optimized to operate at 1608C – not the typical roadside temperature! The next stage of the work is to investigate a series of alternative materials for a system that can operate at ambient temperatures – only then will the system be considered selfpowered! Laurie Winkless
Reconfiguring graphene to improve biosensors A new study has produced a reconfigurable and very sensitive molecule sensor by manipulating the optical and electronic properties of graphene. A team from the E´cole Polytechnique Fe´de´rale De Lausanne and the Institute of Photonic Sciences in Spain used graphene to make improvements to infrared absorption spectroscopy, a common technique for detecting molecules. Although light is normally used to excite molecules, which vibrate differently depending on their nature, this approach is impractical for detecting nanometrically sized molecules. However, with the right geometry, graphene can focus the light on a specific area on its surface and pick up the vibration of a nanometric molecule attached to it. The team patterned nanostructures on the graphene surface by bombarding it with electron beams before etching it with oxygen ions. When the light arrives, electrons in the graphene nanostructures start to oscillate, a phenomenon known as ‘localized surface plasmon resonance’. This focuses light into tiny spots that are comparable to the dimensions of the target molecules, helping to detect nanometric structures. The process can also determine the nature of the bonds connecting the atoms that the molecule is made up of. When a
molecule vibrates, it produces a range of vibrations that are generated by the bonds connecting the different atoms. Each vibration can be identified by nuances that provide information on the nature of each bond as well as the health of the whole molecule, acting as a fingerprint for identifying the molecule.
The researchers, whose work was published in Science [Rodrigo, et al., Science (2015), doi:10.1126/science.aab2051], ‘tuned’ the graphene to different frequencies by applying voltage. With graphene’s electrons oscillating differently, it is possible to ‘read’ all the vibrations of the molecule on its surface. The method demonstrates how to carry out complex analysis with one device rather than many, and with no stress or modification of the biological sample, highlighting graphene’s potential in the field of detection. Combining tunable spectral selectivity with enhanced sensitivity of graphene could lead to many applications, especially as the sensor detects molecular vibrations in the infrared range, which are found for practically any material. As researcher Hatice Altug points out, ‘‘We believe that this new level of light confinement and the dynamical tunability of graphene offer great opportunities for infrared biosensing.’’ The sensor could also be suitable for applications involving non-destructive tests to distinguish between materials of a different chemical nature, such as in clinics and diagnostics, biotechnology, material science, food safety, pharmaceutics and environmental monitoring. Laurie Donaldson
this electronically complex and unstable heavy metal does indeed display magnetism, but it is in constant flux, hence the difficulties in attempting to observe it since the metal was first produced 75 years ago.
Plutonium famously is a fissile material and was first produced in 1940 by Glenn Seaborg and Edwin McMillan at the University of California, Berkeley, by bombarding uranium-238 with deuterons. Not only is it
Detecting molecules using improved infrared absorption spectroscopy based on graphene.
Plutonium’s missing magnetism found Scientists have long thought that plutonium should be magnetic but observing that property experimentally seemed impossible. Now, a neutron scattering study by researchers in the USA has revealed that 422
trast, with crystallites 10–100 nm in size, appear to be preferred by proliferating cells. ‘‘The reasons are not clear,’’ admits May, ‘‘but it may be something to do with the surface needing to be slightly rough (but not too rough) in order for cells to grip on and adhere.’’
NEWS
The final piece of the jigsaw is to grow neurons on diamond surfaces. Instead of culturing human neurons directly on diamond, the team devised a protocol to culture stem cells and then convert them into neurons later, as required. Electrical signals could then passed between the conducting diamond substrate and the neurons.
‘‘We still have a lot more fundamental studies of the neuron/diamond interface to perform,’’ says May. ‘‘[But] the long term possibilities for this work are exciting. Longlifetime diamond bio-implants may offer treatments for Parkinson’s, Alzheimer’s, stroke or even epilepsy.’’ Cordelia Sealy
New research has shown that the color vision of the human eye has the ability to see differences even down to the nanoscale. Scientists from the University of Stuttgart in Germany and the University of Eastern Finland have carried out tests that show the color-sensing abilities of the human eye allow it to distinguish between objects that differ in thickness by only a few nanometers. The research, as reported in Optica [Peterha¨nsel, et al., Optica (2015) doi:10.1364/ OPTICA.2.000627], assessed the limits of unaided human vision for small variations using volunteers to identify subtle color differences in light passing through thin films of titanium dioxide under highly controlled lighting conditions. A series of these thin films, which are key to many commercial and manufacturing applications such as anti-reflective coatings on solar panels, were produced one layer at a time through
atomic deposition, allowing careful control of their thickness and therefore how small a variation could be identified. The team were able to determine the sample thickness from the observed color based on a color-matching experiment between the thin film samples and a simulated color field presented on an LCD monitor that displayed a pure white color, apart from a colored reference area that could be calibrated to match the apparent surface colors of the thin films with various thicknesses. The color of the reference field could then be changed by the test subject until it matched accurately the reference sample. The human color observation was found to provide a very accurate evaluation, comparable to more sophisticated instrumental methods such as vapor deposition. As principal author Sandy Peterha¨nsel said, ‘‘Although the spatial resolving power of the
human eye is orders of magnitude too weak to directly characterize film thicknesses, the interference colors are well known to be very sensitive to variations in the film.’’ The tests only took a couple of minutes, with some test subjects managing to estimate the thickness of the samples which differed by only one or two nanometers from the actual value measured through conventional methods. Compared to common automated methods of determining thickness, the approach also performed very favorably. However, it is doubtful if this method will replace automated methods in the near future as eyes tend to tire very easily, but could be seen as complementary if used in fabrication control as a quick check by an experienced technician, with any deviations detected needing further characterization through other techniques. Laurie Donaldson
Breathalyzer gets the nanotech treatment Results from the Chinese Academy of Sciences suggest that tomorrow’s alcohol breath tests may be self-powered and nano-enhanced. Small-scale gas sensors are used in countless applications around the word – from monitoring the air quality in tunnels and in labs, to the detection of disease or explosives. Since the 1950s, they’ve also found widespread use in roadside breath tests for drivers. Despite many changes in design, today’s breathalyzers still operate on the original principle. Based on a chemical reaction between ethyl alcohol (ethanol) and potassium dichromate, these portable sensors produce a color change directly related to the level of alcohol present in the person’s breath. When compared to a known sample of gas, they can also provide a quantitative measure of the alcohol content in the person’s blood.
Device structure of the blow-driven triboelectric nanogenerator.
421
NEWS
Human eye capable of distinguishing to the nanoscale
NEWS
NEWS
But work from a team of US and Chinese researchers suggests there may be an even better way to test a person’s breath – a nanowire ‘whistle’ that powers itself. Published in Nano Energy [Wen, et al., Nano Energy (2015), doi:10.1016/j.nanoen. 2015.06.006], the paper describes the development of a rotating triboelectric generator and gas sensor, that can to detect alcohol at concentrations as low as 10 parts per million (ppm). In its simplest form, the ‘whistle’ is assembled from three main components – a rotator (a rotating acrylic wheel coated with polymer nanowires), a stator (a pair of stationary, copper-coated acrylic
Materials Today Volume 18, Number 8 October 2015
disks) and a spacer (soft elastic O-rings to sit between them). It works by the triboelectric effect – blowing into the whistle causes the wheel to rotate. Because copper is an electron-donating material and the fluorinated ethylene propylene (FEP) nanowires are electron-accepting, as the nanowirecoated wheel spins, there is an exchange of electrons between the materials. This produces a large enough current to power a Co3O4 based gas sensor. The team found that the output voltage of the gas sensor was constant and independent of the user, or the speed at which the user exhaled. Powered by the triboelectric
whistle, the sensor could detect a range of different gases at very low concentrations, and connecting a low-cost alarm to it (also powered by blowing into the whistle) minimized the risk of interference by the user. So, what’s the catch? Well, this system is optimized to operate at 1608C – not the typical roadside temperature! The next stage of the work is to investigate a series of alternative materials for a system that can operate at ambient temperatures – only then will the system be considered selfpowered! Laurie Winkless
Reconfiguring graphene to improve biosensors A new study has produced a reconfigurable and very sensitive molecule sensor by manipulating the optical and electronic properties of graphene. A team from the E´cole Polytechnique Fe´de´rale De Lausanne and the Institute of Photonic Sciences in Spain used graphene to make improvements to infrared absorption spectroscopy, a common technique for detecting molecules. Although light is normally used to excite molecules, which vibrate differently depending on their nature, this approach is impractical for detecting nanometrically sized molecules. However, with the right geometry, graphene can focus the light on a specific area on its surface and pick up the vibration of a nanometric molecule attached to it. The team patterned nanostructures on the graphene surface by bombarding it with electron beams before etching it with oxygen ions. When the light arrives, electrons in the graphene nanostructures start to oscillate, a phenomenon known as ‘localized surface plasmon resonance’. This focuses light into tiny spots that are comparable to the dimensions of the target molecules, helping to detect nanometric structures. The process can also determine the nature of the bonds connecting the atoms that the molecule is made up of. When a
molecule vibrates, it produces a range of vibrations that are generated by the bonds connecting the different atoms. Each vibration can be identified by nuances that provide information on the nature of each bond as well as the health of the whole molecule, acting as a fingerprint for identifying the molecule.
The researchers, whose work was published in Science [Rodrigo, et al., Science (2015), doi:10.1126/science.aab2051], ‘tuned’ the graphene to different frequencies by applying voltage. With graphene’s electrons oscillating differently, it is possible to ‘read’ all the vibrations of the molecule on its surface. The method demonstrates how to carry out complex analysis with one device rather than many, and with no stress or modification of the biological sample, highlighting graphene’s potential in the field of detection. Combining tunable spectral selectivity with enhanced sensitivity of graphene could lead to many applications, especially as the sensor detects molecular vibrations in the infrared range, which are found for practically any material. As researcher Hatice Altug points out, ‘‘We believe that this new level of light confinement and the dynamical tunability of graphene offer great opportunities for infrared biosensing.’’ The sensor could also be suitable for applications involving non-destructive tests to distinguish between materials of a different chemical nature, such as in clinics and diagnostics, biotechnology, material science, food safety, pharmaceutics and environmental monitoring. Laurie Donaldson
this electronically complex and unstable heavy metal does indeed display magnetism, but it is in constant flux, hence the difficulties in attempting to observe it since the metal was first produced 75 years ago.
Plutonium famously is a fissile material and was first produced in 1940 by Glenn Seaborg and Edwin McMillan at the University of California, Berkeley, by bombarding uranium-238 with deuterons. Not only is it
Detecting molecules using improved infrared absorption spectroscopy based on graphene.
Plutonium’s missing magnetism found Scientists have long thought that plutonium should be magnetic but observing that property experimentally seemed impossible. Now, a neutron scattering study by researchers in the USA has revealed that 422