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Accelerator-on-a-chip
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Materials Today Volume 16, Number 12 December 2013
Bubbles split about how best to empty oil wells A better understanding of how bubbles form in a foam may enable the extraction of every last drop from an oil reservoir, say US scientists. Industry currently struggles to fully drain oil reservoirs, finding it technically difficult and expensive to do so. Gas – such as carbon dioxide – together with foam is often used to flush out some of the hard-to-reach oil. But a proportion of it remains elusive. Sibani Lisa Biswal and her team at Rice University used microfluidic channels and high-speed imaging to watch how gas bubbles change as they move through small spaces such as those found in the permeable rock containing oil reservoirs. These observations may help in the design of foams better able to fully extract oil wells. ‘Typically, it is difficult to recover oil from the tight pores in the lower permeable regions of the rock,’ explains Biswal. Ideally, a foam would block all the channels in the highly permeably sections of the rock, forcing pressure to flow through the regions of lower permeability flushing out any oil trapped there. ‘Foam able to block high permeable regions will lead to better recovery of oil in the low permeable regions,’ she says. The Soft Matter paper [Liontas, et al., Soft Matter (2013), doi:10.1039/c3sm51605a] described two previously unknown
Accelerator-on-a-chip Forget campus-sized particle accelerators, a nanostructured glass chip smaller than a grain of rice developed by researchers at the SLAC National Accelerator Laboratory and Stanford University in the USA uses a laser to accelerate electrons ten times more quickly than much bigger conventional instruments. Many scientists are familiar with the huge particle accelerators used to generate beams of particles for X-ray and other structural studies in science and medicine and with the microelectromechanical systems (MEMS) colloquially known as lab-on-achip devices. However, when these two technologies at opposite ends of the scientific size scale meet, countless new opportunities could arise for studying materials. ‘We still have a number of challenges before this technology becomes practical 462
mechanisms through which gas bubbles split as they flow through a constriction such a pore in a rock. ‘We fabricated a microfluidic channel with a narrow constriction and flowed foam through it at different rates,’ Biswal told Materials Today. ‘We captured the events using a high-speed camera and then analyzed the resulting images.’ By taking 10 000 pictures per second, the team saw that a bubble pinched between another bubble and the wall would split in to two smaller bubbles just before it entered the 20 mm wide channel. They also saw that a bubble squeezed and pinched between two other bubbles would also split in two before going into the channel. ‘We found neighboring bubbles that are basically karate-chopping a third one as it tries to go through,’ Biswal explains. ‘No one has seen these mechanisms [before]’. The next step in the quest for improved foams for oil extraction is to develop microfluidic models that allow the visualization of how foams displace oil in porous rocks, she says. T F]I$DT2_[1 wo previously unseen bubble-splitting mechanisms. Credit: Biswal Lab/Rice University. Nina Notman
Materials Today Volume 16, Number 12 December 2013
for real-world use, but eventually it would substantially reduce the size and cost of future high-energy particle colliders,’ explains SLAC’s Joel England. ‘It could help enable compact accelerators and X-ray devices for security scanning, medical therapy and imaging, and research in biology and materials science,’ he adds. The system was built using the same fabrication techniques used for making silicon computer chips and other microelectronic devices [Peralta, et al., Nature (2013), doi:10.1038/ nature12664]. The accelerator-on-a-chip uses a commercial laser and low-cost, mass-production techniques and could give scientists a ‘bench-top’ system to rival the twomile-long SLAC linear accelerator, delivering a million more electron pulses per second for the next generation of highpower X-ray beams, for instance. The team’s prototype demonstrated an energy gain of 300 megaelectronvolts per metre, which is about ten times that pos-
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sible with the main SLAC accelerator, which is powered by microwaves instead of lasers. In the accelerator-on-a-chip experiments, the team first accelerates electrons to near light-speed in a conventional accelerator. Then they focus this beam into a tiny, half-micrometer-wide channel within a fused silica glass chip just half a millimeter long. Nanoscale ridges that pattern the interior of the channel generate a specific electric field environment when irradiated by an infrared laser, which gives the electrons an energy boost. Obviously, turning this system into a truly benchtop accelerator will require a far more compact instrument to carry out the initial electron acceleration. A solution may come from the work of collaborators in Germany, led by Peter Hommelhoff of the Friedrich Alexander University and the Max Planck Institute of Quantum Optics. That team has demonstrated how a laser can accelerate lower-
energy electrons [Phys Rev Lett 111 (2013) 134803]. Aside from opening up powerful methods for structural studies in materials science, the accelerator-on-a-chip might find applications in medical diagnostics. ‘The next step is to demonstrate acceleration using very short particle bunches (shorter than the laser wavelength) so that all of the particles in the beam are accelerated at once, and then to do this with several successive accelerator chips fabricated together, in order to show that the process can be scaled to longer chains of structures and thereby provide higher total energy gain,’ England told Materials Today. ‘We have also developed compatible concepts for maintaining control of the particles (focusing and steering) inside the microaccelerator and these concepts need to be demonstrated as well.’ Nanofabricated accelerator chips of fused silica. Credit: Brad Plummer/SLAC. David Bradley
explain that adding the enzyme acetylcholinesterase to a nanorod growth system can be exploited to detect molecules that inhibit the enzyme, such as toxic nerve agents. The enzyme hydrolyses the substrate acetylthiocholine, for instance, generating thiocholine, which then interferes with nanorod growth – by blocking reduction of the gold ions – in a controlled manner. Their experimental setup for testing for nerve-agent type chemicals involves three steps. First, they generate small amounts of thiocholine using the enzyme to hydrolyse acetylthiocholine. Next, they mix the generated thiocholine with a gold seed solution. Finally, they transfer this mixture into the gold nanorod growth medium. The team adds that depending on the conditions of the enzymatic reaction they get a particular mix of gold nanorods, cubes and spheres, as revealed by transmission electron microscopy. Inhibition of acetylcholinesterase can
be monitored by the same procedure modified by pre-incubation of the enzyme with nerve gas analogues. In the field, of course, actual nerve agents would be the target of the detection. UV/Vis (ultraviolet/visible) spectroscopic monitoring of colloidal nanoparticles reveals changes in the plasmon resonance of the growing nanoparticles. The presence of sub-nanomolar concentrations of the inhibitor correlates with the spectra; down to 280 picomolar for the enzyme inhibitor ‘‘paraoxon’’, the team reports. Tests with two other nerve agent analogues were also successful, the team says. ‘‘This represents a significant improvement with respect to previous works for acetylcholinesterase inhibitors biosensing using metal nanoparticles,’’ the team concludes. Potentially, this work could be extended by the use of different types of nanoparticles. David Bradley
Gold nanorods find chemical weapons The way in which gold nanorods grow can be used as the basis of a sensitive, colorimetric test for tiny concentrations of nerve agent type chemicals that inhibit the enzyme acetylcholinesterase, according to a study by researchers in Spain [Coronado-Puchau, et al., Nano Today(2013), doi:10.1016/ j.nantod.2013.08.008]. Various external factors can affect the seed-mediated growth of gold nanorods in particular the absorption on the metal surface of thiol-containing molecules. The autocatalytic reduction of metal ions on to 2-nanometre seed particles in a gold salt solution further catalyses growth but at the same time provides the nucleation points for this growth. Luis Liz-Marza´n, Ikerbasque Professor at CIC biomaGUNE, in Donostia, Spain and colleagues Marc Coronado-Puchau, Laura Saa, Marek Grzelczak, and Valeri Pavlov have now coupled these two phenomena. They
463
Materials Today Volume 16, Number 12 December 2013
Bubbles split about how best to empty oil wells A better understanding of how bubbles form in a foam may enable the extraction of every last drop from an oil reservoir, say US scientists. Industry currently struggles to fully drain oil reservoirs, finding it technically difficult and expensive to do so. Gas – such as carbon dioxide – together with foam is often used to flush out some of the hard-to-reach oil. But a proportion of it remains elusive. Sibani Lisa Biswal and her team at Rice University used microfluidic channels and high-speed imaging to watch how gas bubbles change as they move through small spaces such as those found in the permeable rock containing oil reservoirs. These observations may help in the design of foams better able to fully extract oil wells. ‘Typically, it is difficult to recover oil from the tight pores in the lower permeable regions of the rock,’ explains Biswal. Ideally, a foam would block all the channels in the highly permeably sections of the rock, forcing pressure to flow through the regions of lower permeability flushing out any oil trapped there. ‘Foam able to block high permeable regions will lead to better recovery of oil in the low permeable regions,’ she says. The Soft Matter paper [Liontas, et al., Soft Matter (2013), doi:10.1039/c3sm51605a] described two previously unknown
Accelerator-on-a-chip Forget campus-sized particle accelerators, a nanostructured glass chip smaller than a grain of rice developed by researchers at the SLAC National Accelerator Laboratory and Stanford University in the USA uses a laser to accelerate electrons ten times more quickly than much bigger conventional instruments. Many scientists are familiar with the huge particle accelerators used to generate beams of particles for X-ray and other structural studies in science and medicine and with the microelectromechanical systems (MEMS) colloquially known as lab-on-achip devices. However, when these two technologies at opposite ends of the scientific size scale meet, countless new opportunities could arise for studying materials. ‘We still have a number of challenges before this technology becomes practical 462
mechanisms through which gas bubbles split as they flow through a constriction such a pore in a rock. ‘We fabricated a microfluidic channel with a narrow constriction and flowed foam through it at different rates,’ Biswal told Materials Today. ‘We captured the events using a high-speed camera and then analyzed the resulting images.’ By taking 10 000 pictures per second, the team saw that a bubble pinched between another bubble and the wall would split in to two smaller bubbles just before it entered the 20 mm wide channel. They also saw that a bubble squeezed and pinched between two other bubbles would also split in two before going into the channel. ‘We found neighboring bubbles that are basically karate-chopping a third one as it tries to go through,’ Biswal explains. ‘No one has seen these mechanisms [before]’. The next step in the quest for improved foams for oil extraction is to develop microfluidic models that allow the visualization of how foams displace oil in porous rocks, she says. T F]I$DT2_[1 wo previously unseen bubble-splitting mechanisms. Credit: Biswal Lab/Rice University. Nina Notman
Materials Today Volume 16, Number 12 December 2013
for real-world use, but eventually it would substantially reduce the size and cost of future high-energy particle colliders,’ explains SLAC’s Joel England. ‘It could help enable compact accelerators and X-ray devices for security scanning, medical therapy and imaging, and research in biology and materials science,’ he adds. The system was built using the same fabrication techniques used for making silicon computer chips and other microelectronic devices [Peralta, et al., Nature (2013), doi:10.1038/ nature12664]. The accelerator-on-a-chip uses a commercial laser and low-cost, mass-production techniques and could give scientists a ‘bench-top’ system to rival the twomile-long SLAC linear accelerator, delivering a million more electron pulses per second for the next generation of highpower X-ray beams, for instance. The team’s prototype demonstrated an energy gain of 300 megaelectronvolts per metre, which is about ten times that pos-
NEWS
sible with the main SLAC accelerator, which is powered by microwaves instead of lasers. In the accelerator-on-a-chip experiments, the team first accelerates electrons to near light-speed in a conventional accelerator. Then they focus this beam into a tiny, half-micrometer-wide channel within a fused silica glass chip just half a millimeter long. Nanoscale ridges that pattern the interior of the channel generate a specific electric field environment when irradiated by an infrared laser, which gives the electrons an energy boost. Obviously, turning this system into a truly benchtop accelerator will require a far more compact instrument to carry out the initial electron acceleration. A solution may come from the work of collaborators in Germany, led by Peter Hommelhoff of the Friedrich Alexander University and the Max Planck Institute of Quantum Optics. That team has demonstrated how a laser can accelerate lower-
energy electrons [Phys Rev Lett 111 (2013) 134803]. Aside from opening up powerful methods for structural studies in materials science, the accelerator-on-a-chip might find applications in medical diagnostics. ‘The next step is to demonstrate acceleration using very short particle bunches (shorter than the laser wavelength) so that all of the particles in the beam are accelerated at once, and then to do this with several successive accelerator chips fabricated together, in order to show that the process can be scaled to longer chains of structures and thereby provide higher total energy gain,’ England told Materials Today. ‘We have also developed compatible concepts for maintaining control of the particles (focusing and steering) inside the microaccelerator and these concepts need to be demonstrated as well.’ Nanofabricated accelerator chips of fused silica. Credit: Brad Plummer/SLAC. David Bradley
explain that adding the enzyme acetylcholinesterase to a nanorod growth system can be exploited to detect molecules that inhibit the enzyme, such as toxic nerve agents. The enzyme hydrolyses the substrate acetylthiocholine, for instance, generating thiocholine, which then interferes with nanorod growth – by blocking reduction of the gold ions – in a controlled manner. Their experimental setup for testing for nerve-agent type chemicals involves three steps. First, they generate small amounts of thiocholine using the enzyme to hydrolyse acetylthiocholine. Next, they mix the generated thiocholine with a gold seed solution. Finally, they transfer this mixture into the gold nanorod growth medium. The team adds that depending on the conditions of the enzymatic reaction they get a particular mix of gold nanorods, cubes and spheres, as revealed by transmission electron microscopy. Inhibition of acetylcholinesterase can
be monitored by the same procedure modified by pre-incubation of the enzyme with nerve gas analogues. In the field, of course, actual nerve agents would be the target of the detection. UV/Vis (ultraviolet/visible) spectroscopic monitoring of colloidal nanoparticles reveals changes in the plasmon resonance of the growing nanoparticles. The presence of sub-nanomolar concentrations of the inhibitor correlates with the spectra; down to 280 picomolar for the enzyme inhibitor ‘‘paraoxon’’, the team reports. Tests with two other nerve agent analogues were also successful, the team says. ‘‘This represents a significant improvement with respect to previous works for acetylcholinesterase inhibitors biosensing using metal nanoparticles,’’ the team concludes. Potentially, this work could be extended by the use of different types of nanoparticles. David Bradley
Gold nanorods find chemical weapons The way in which gold nanorods grow can be used as the basis of a sensitive, colorimetric test for tiny concentrations of nerve agent type chemicals that inhibit the enzyme acetylcholinesterase, according to a study by researchers in Spain [Coronado-Puchau, et al., Nano Today(2013), doi:10.1016/ j.nantod.2013.08.008]. Various external factors can affect the seed-mediated growth of gold nanorods in particular the absorption on the metal surface of thiol-containing molecules. The autocatalytic reduction of metal ions on to 2-nanometre seed particles in a gold salt solution further catalyses growth but at the same time provides the nucleation points for this growth. Luis Liz-Marza´n, Ikerbasque Professor at CIC biomaGUNE, in Donostia, Spain and colleagues Marc Coronado-Puchau, Laura Saa, Marek Grzelczak, and Valeri Pavlov have now coupled these two phenomena. They
463