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First gold-iron alloy shows power of magnetic attraction
TECHNOLOGY
How collapsing bubbles could shoot cancer cells dead in close proximity, they interact in a predictable way. Using successive pulses from two lasers, one with a wavelength of 1064 nanometres and the other radiating at 532 nanometres, the team rapidly heated a sample of fluid containing the dye trypan blue. The first pulse produced a bubble of vapour 50 micrometres
First gold-iron alloy shows power of magnetic attraction GOLD readily forms alloys with the precious metals silver and palladium, but it normally blends with cheap iron about as well as oil mixes with water. That has now changed, with the creation of a gold-iron alloy that is held together by magnetism. The arrangement of atoms in an alloy changes the chemical properties of its constituent metals and makes it potentially useful to catalyse reactions. This prompted Sylvie Rousset and colleagues at the Denis Diderot University, Paris, and the French National Centre for Scientific Research to explore creating one from gold and iron. But creating a gold-iron 22 | NewScientist | 21 August 2010
Zhong says. “We want to produce a tiny jet that can penetrate a cell without killing it,” he adds. Zhong and his team tested their bubble needle on cells obtained from a rat tumour. High-speed photography showed that the microbubble pair could be made to collapse in such a way that the jet of blue dye created a hole between 0.2 and 2 micrometres across – allowing the jet of liquid to enter without instantly destroying the cell (Physical Review Letters, DOI: 10.1103/ PhysRevLett.105.078101). This shows the jets are suitable for targeting drugs at cells within the body, Zhong says. He says that it should be possible to use microbubble pairs generated by ultrasound rather than lasers as a clinical drugdelivery system. Not everyone is convinced that the system will work in a clinical setting, however. In the presence of biological tissues, the oscillating bubbles may be less stable than in the test solution, making it difficult to deliver drugs with any accuracy, says Constantin Coussios, a biomedical engineer at the University of –Uncontrolled collapse– Oxford. Jamie Condliffe n Christopher Stevenson/photonica
JETS of fluid propelled by the collapse of microscopic bubbles could deliver drugs directly into cancer cells, if an idea from a team of engineers pays off. They have made the bubbles project a fine jet that is powerful enough to puncture the cell wall and enter the cell. Applying a pulse of heat or ultrasound to a fluid can produce bubbles that initially expand rapidly, before collapsing suddenly when the pulse ends. Pei Zhong and his team at Duke University in Durham, North Carolina, knew that the collapsing bubbles send a pressure wave through the surrounding fluid, and that oscillations at the surface of the bubble can generate a needle-like jet. The problem is predicting where the jet will go, and how powerful it will be. “Previously, there has been little control in jetting direction, and it has been hard to control the strength of the jet,” Zhong says. Now the team has shown that when pairs of bubbles collapse
across, and the second produced another bubble close to the first. As the bubbles cooled and contracted, their surfaces began to oscillate, creating vortices in the surrounding fluid. The interaction between neighbouring bubbles caused them to collapse, creating a pair of jets shooting out in opposite directions. This should provide the degree of control necessary for a targeted drug delivery system, Zhong says. The size of the bubble is crucial, as it dictates the size of the jet,
alloy is problematic because of the differing sizes of the atoms. Locked in a crystal lattice, each gold atom has an effective radius of 0.29 nanometres, while an iron atom has a radius of just 0.256 nanometres. The researchers overcame this obstacle by using ruthenium as a “bridge” between the two. With an effective atomic radius of 0.273 nanometres, a bed of ruthenium can guide the growth of a gold-iron lattice. Rousset’s team vaporised iron and gold and deposited them on a slab of ruthenium, before heating the slab to 330 °C to allow the atoms to migrate into a single-layered lattice.
The team tested a number of combinations of iron and gold to see which led to the most stable arrangement. Theoretically, stability should be found in a mix containing about 80 per cent iron, as this minimises the mechanical strain caused by the atoms’ different sizes. However, to their surprise they found that the most stable lattice contained
“The absolute dominance of the magnetic interaction in a gold-iron alloy is remarkable” approximately one iron atom to every two gold atoms (Physical Review Letters, DOI: 10.1103/ PhysRevLett.105.056101). In this combination there was evidence of long-range order: a
repeating pattern of interconnected hexagons of gold, each with an iron atom at its centre. Rousset suggests that iron’s magnetism is behind this stability. The iron atoms have their strongest magnetic properties when they make up one-third of the alloy, she says. “What is remarkable is the absolute dominance of the magnetic interaction,” says Gayle Thayer of Sandia National Laboratories in Albuquerque, New Mexico. “The long-range order is also spectacular.” If the magnetism can be switched between two orientations when a magnetic field is applied, and maintain that orientation at the temperatures found inside computers, the alloy could function as a high-density computer memory array, says Rousset. Kate McAlpine n
How collapsing bubbles could shoot cancer cells dead in close proximity, they interact in a predictable way. Using successive pulses from two lasers, one with a wavelength of 1064 nanometres and the other radiating at 532 nanometres, the team rapidly heated a sample of fluid containing the dye trypan blue. The first pulse produced a bubble of vapour 50 micrometres
First gold-iron alloy shows power of magnetic attraction GOLD readily forms alloys with the precious metals silver and palladium, but it normally blends with cheap iron about as well as oil mixes with water. That has now changed, with the creation of a gold-iron alloy that is held together by magnetism. The arrangement of atoms in an alloy changes the chemical properties of its constituent metals and makes it potentially useful to catalyse reactions. This prompted Sylvie Rousset and colleagues at the Denis Diderot University, Paris, and the French National Centre for Scientific Research to explore creating one from gold and iron. But creating a gold-iron 22 | NewScientist | 21 August 2010
Zhong says. “We want to produce a tiny jet that can penetrate a cell without killing it,” he adds. Zhong and his team tested their bubble needle on cells obtained from a rat tumour. High-speed photography showed that the microbubble pair could be made to collapse in such a way that the jet of blue dye created a hole between 0.2 and 2 micrometres across – allowing the jet of liquid to enter without instantly destroying the cell (Physical Review Letters, DOI: 10.1103/ PhysRevLett.105.078101). This shows the jets are suitable for targeting drugs at cells within the body, Zhong says. He says that it should be possible to use microbubble pairs generated by ultrasound rather than lasers as a clinical drugdelivery system. Not everyone is convinced that the system will work in a clinical setting, however. In the presence of biological tissues, the oscillating bubbles may be less stable than in the test solution, making it difficult to deliver drugs with any accuracy, says Constantin Coussios, a biomedical engineer at the University of –Uncontrolled collapse– Oxford. Jamie Condliffe n Christopher Stevenson/photonica
JETS of fluid propelled by the collapse of microscopic bubbles could deliver drugs directly into cancer cells, if an idea from a team of engineers pays off. They have made the bubbles project a fine jet that is powerful enough to puncture the cell wall and enter the cell. Applying a pulse of heat or ultrasound to a fluid can produce bubbles that initially expand rapidly, before collapsing suddenly when the pulse ends. Pei Zhong and his team at Duke University in Durham, North Carolina, knew that the collapsing bubbles send a pressure wave through the surrounding fluid, and that oscillations at the surface of the bubble can generate a needle-like jet. The problem is predicting where the jet will go, and how powerful it will be. “Previously, there has been little control in jetting direction, and it has been hard to control the strength of the jet,” Zhong says. Now the team has shown that when pairs of bubbles collapse
across, and the second produced another bubble close to the first. As the bubbles cooled and contracted, their surfaces began to oscillate, creating vortices in the surrounding fluid. The interaction between neighbouring bubbles caused them to collapse, creating a pair of jets shooting out in opposite directions. This should provide the degree of control necessary for a targeted drug delivery system, Zhong says. The size of the bubble is crucial, as it dictates the size of the jet,
alloy is problematic because of the differing sizes of the atoms. Locked in a crystal lattice, each gold atom has an effective radius of 0.29 nanometres, while an iron atom has a radius of just 0.256 nanometres. The researchers overcame this obstacle by using ruthenium as a “bridge” between the two. With an effective atomic radius of 0.273 nanometres, a bed of ruthenium can guide the growth of a gold-iron lattice. Rousset’s team vaporised iron and gold and deposited them on a slab of ruthenium, before heating the slab to 330 °C to allow the atoms to migrate into a single-layered lattice.
The team tested a number of combinations of iron and gold to see which led to the most stable arrangement. Theoretically, stability should be found in a mix containing about 80 per cent iron, as this minimises the mechanical strain caused by the atoms’ different sizes. However, to their surprise they found that the most stable lattice contained
“The absolute dominance of the magnetic interaction in a gold-iron alloy is remarkable” approximately one iron atom to every two gold atoms (Physical Review Letters, DOI: 10.1103/ PhysRevLett.105.056101). In this combination there was evidence of long-range order: a
repeating pattern of interconnected hexagons of gold, each with an iron atom at its centre. Rousset suggests that iron’s magnetism is behind this stability. The iron atoms have their strongest magnetic properties when they make up one-third of the alloy, she says. “What is remarkable is the absolute dominance of the magnetic interaction,” says Gayle Thayer of Sandia National Laboratories in Albuquerque, New Mexico. “The long-range order is also spectacular.” If the magnetism can be switched between two orientations when a magnetic field is applied, and maintain that orientation at the temperatures found inside computers, the alloy could function as a high-density computer memory array, says Rousset. Kate McAlpine n