With a diameter of about 30 nanometers, the spherical device is 1,000-fold smaller than existing voltmeters, said Kopelman who is the Richard Smalley Distinguished University Professor of Chemistry, Physics and Applied Physics. It is a photonic instrument, meaning that it uses light to do its work, rather than the electrons that electronic devices employ.
Kopelman's former postdoctoral fellow Katherine Tyner, now at the U.S. Food and Drug Administration, used the nano-voltmeter to measure electric fields deep inside a cell - a feat that until now was impossible. Scientists have measured electric fields in the membranes that surround cells, but not in the interior, Kopelman said.
With the new approach, the researchers don't simply insert a single voltmeter; they're able to deploy thousands of voltmeters at once, spread throughout the cell. Each unit is a single nano-particle that contains voltage-sensitive dyes. When stimulated with blue light, the dyes emit red and green light, and the ratio of red to green corresponds to the strength of the electric field in the area of interest.
Tyner's measurements revealed surprisingly high electric fields in cytosol - the jellylike material that makes up most of a cell's interior. "The standard paradigm has been that there are zero electric fields in cytosol", Kopelman said, "but all of the 13 regions we measured had high electric field strength - as high as 15 million volts per meter." In comparison, the electrical field strength inside a typical home is five to 10 volts per meter; directly under a power transmission line, it's 10,000 volts per meter.
Those findings leave the researchers wondering why electrical fields exist inside cells. "I don't know the answer to that," Kopelman said. "I suspect that finding out exactly what's going on will keep a lot of people working for a long time." But the ability to measure internal cellular electrical fields should aid in that endeavor.
COMPAMED.de; Source: University of Michigan