- Email: [email protected]
Neuronal nanotubes
RESEARCH NEWS
Neuronal nanotubes NANOTECHNOLOGY
Could nanotechnology be the key to developing an interface between nerve cells and microelectronic circuitry? US scientists have recently demonstrated that signals can be recorded from rat neurons using conducting polymer nanotubes. The research carried out at the University of Michigan might one day help in the development of sensors and treatments for neurological disorders including Parkinson’s disease and paralysis. Conventional neural electrodes can have operational times of hours or even years but all of them trigger an initial in inflammatory response once they are inserted into the brain. After that, the brain settles into a chronic, wound-healing process, which can isolate the electrode from surrounding neurons as new tissue encapsulates it. Metal electrodes are obviously conducting but lack the biocompatibility that precludes this chronic wound-healing problem. Now, nanotubes coated with the polymer poly(3,4-ethylenedioxythiophene) (PEDOT) have been used to record neural signals [Abidian et al., Adv. Mater. (2009) 21, 3764-3770]. Mohammad Reza Abidian and colleagues explain that PEDOT is not only electrically conductive but is also biocompatible, which they hoped would prevent encapsulation. “Microelectrodes implanted in the brain are increasingly being used to treat neurological disorders,” explains Abidian. “Moreover, these
The image depicts neurons firing (green structures in the foreground) and communicating with nanotubes in the background. (Illustration courtesy of Mohammad Reza Abidian.)
electrodes enable neuroprosthetic devices, which hold the promise to return functionality to individuals with spinal cord injuries and neurodegenerative diseases.” The challenge is to find ways to make robust and reliable
neural electrodes that could monitor symptoms and perhaps even deliver the appropriate medication automatically. The researchers have demonstrated the ability of PEDOT nanotubes to act as drug carriers previously. The team has now tested their PEDOT nanotube electrodes in laboratory rats. In the experiment, they implanted two neural microelectrodes in the brains of three rats. They then monitored the electrical impedance of the recording sites and measured the quality of recording signals over a seven-week period. They found that not only was the signal-tonoise ratio of the coated electrodes 30% higher than with uncoated electrodes, but the coated electrodes operated with less electrical resistance. This meant that the electrodes could communicate more clearly with individual surrounding neurons. “Conducting polymers are biocompatible and have both electronic and ionic conductivity,” Abidian explains. “Therefore, these materials are good candidates for biomedical applications such as neural interfaces, biosensors and drug delivery systems.” He adds that, “This study paves the way for smart recording electrodes that can deliver drugs to alleviate the immune response of encapsulation.” David Bradley
Magnetricity is taken for a spin MAGNETISM At long last there is experimental evidence that magnetic charges exist and that they have measurable currents or magnetricity, just like an electric charge [Bramwell et al., Nature (2009) 461, 956]. A team from the UK and France used Dy2Ti2O7, a material known as a spin ice, to test the new technique. Spin ices are predicted to have sharply defined magnetic point charge (magnetic monopole) excitations, making them good test materials. In their recent paper, the researchers explained how they applied Onsager’s theory of electrolytes,
14
which describes the conductivity of liquid and lattice electrolytes, to set up an experiment that can detect the magnetic monopoles in spin ice. They replaced the electrical quantities described in Onsager’s theory with magnetic quantities, based on the assumption that there is equivalence between electricity and magnetism. A spin ice sample was cooled to temperatures close to zero and then probed using muons, negatively charged elementary particles. Single crystals of spin ice were aligned parallel to the muon spin direction and a magnetic field was applied at right angles to this axis. The asymmetry of muon beta decay was then
DECEMBER 2009 | VOLUME 12 | NUMBER 12
measured as a function of time, leading to information on internal magnetic fields. Results so far have yielded a value of 5 μB Å-1 for the elementary unit of magnetic charge. The technique has not only been used to prove the existence of magnetic charges in spin ice but is also capable of measuring relative changes in magnetic conductivity. While the new technique is a good proof of theory, can be used to determine deviations from Ohm’s law, and demonstrates good correlation between electricity and magnetism, it may also lead the way to controlling magnetic charges in the future.
Katerina Busuttil
Neuronal nanotubes NANOTECHNOLOGY
Could nanotechnology be the key to developing an interface between nerve cells and microelectronic circuitry? US scientists have recently demonstrated that signals can be recorded from rat neurons using conducting polymer nanotubes. The research carried out at the University of Michigan might one day help in the development of sensors and treatments for neurological disorders including Parkinson’s disease and paralysis. Conventional neural electrodes can have operational times of hours or even years but all of them trigger an initial in inflammatory response once they are inserted into the brain. After that, the brain settles into a chronic, wound-healing process, which can isolate the electrode from surrounding neurons as new tissue encapsulates it. Metal electrodes are obviously conducting but lack the biocompatibility that precludes this chronic wound-healing problem. Now, nanotubes coated with the polymer poly(3,4-ethylenedioxythiophene) (PEDOT) have been used to record neural signals [Abidian et al., Adv. Mater. (2009) 21, 3764-3770]. Mohammad Reza Abidian and colleagues explain that PEDOT is not only electrically conductive but is also biocompatible, which they hoped would prevent encapsulation. “Microelectrodes implanted in the brain are increasingly being used to treat neurological disorders,” explains Abidian. “Moreover, these
The image depicts neurons firing (green structures in the foreground) and communicating with nanotubes in the background. (Illustration courtesy of Mohammad Reza Abidian.)
electrodes enable neuroprosthetic devices, which hold the promise to return functionality to individuals with spinal cord injuries and neurodegenerative diseases.” The challenge is to find ways to make robust and reliable
neural electrodes that could monitor symptoms and perhaps even deliver the appropriate medication automatically. The researchers have demonstrated the ability of PEDOT nanotubes to act as drug carriers previously. The team has now tested their PEDOT nanotube electrodes in laboratory rats. In the experiment, they implanted two neural microelectrodes in the brains of three rats. They then monitored the electrical impedance of the recording sites and measured the quality of recording signals over a seven-week period. They found that not only was the signal-tonoise ratio of the coated electrodes 30% higher than with uncoated electrodes, but the coated electrodes operated with less electrical resistance. This meant that the electrodes could communicate more clearly with individual surrounding neurons. “Conducting polymers are biocompatible and have both electronic and ionic conductivity,” Abidian explains. “Therefore, these materials are good candidates for biomedical applications such as neural interfaces, biosensors and drug delivery systems.” He adds that, “This study paves the way for smart recording electrodes that can deliver drugs to alleviate the immune response of encapsulation.” David Bradley
Magnetricity is taken for a spin MAGNETISM At long last there is experimental evidence that magnetic charges exist and that they have measurable currents or magnetricity, just like an electric charge [Bramwell et al., Nature (2009) 461, 956]. A team from the UK and France used Dy2Ti2O7, a material known as a spin ice, to test the new technique. Spin ices are predicted to have sharply defined magnetic point charge (magnetic monopole) excitations, making them good test materials. In their recent paper, the researchers explained how they applied Onsager’s theory of electrolytes,
14
which describes the conductivity of liquid and lattice electrolytes, to set up an experiment that can detect the magnetic monopoles in spin ice. They replaced the electrical quantities described in Onsager’s theory with magnetic quantities, based on the assumption that there is equivalence between electricity and magnetism. A spin ice sample was cooled to temperatures close to zero and then probed using muons, negatively charged elementary particles. Single crystals of spin ice were aligned parallel to the muon spin direction and a magnetic field was applied at right angles to this axis. The asymmetry of muon beta decay was then
DECEMBER 2009 | VOLUME 12 | NUMBER 12
measured as a function of time, leading to information on internal magnetic fields. Results so far have yielded a value of 5 μB Å-1 for the elementary unit of magnetic charge. The technique has not only been used to prove the existence of magnetic charges in spin ice but is also capable of measuring relative changes in magnetic conductivity. While the new technique is a good proof of theory, can be used to determine deviations from Ohm’s law, and demonstrates good correlation between electricity and magnetism, it may also lead the way to controlling magnetic charges in the future.
Katerina Busuttil