Scientists in the United Kingdom have developed a way to monitor the health of individual cells by recording their electrical activity in much the same way that an electrocardiogram (EKG) monitors the heart. They say that the technique could revolutionize the way we test drugs and carry out environmental sensing.
Using extremely sensitive equipment, the scientists have captured the last pulse of electrical activity in a cell, the equivalent of a final heartbeat, before the cell died.
To stay alive, cells need to maintain an electrical flow of charged particles, called ions, through their cell membranes. Detecting the flow of these ions can be used to help gauge the health of that cell, says Andre Geim, a professor of physics at University of Manchester, in the United Kingdom.
But measuring electrical activity at this level requires extremely sensitive equipment, says Geim. “To reliably detect the charge of one ion, you need a sensitivity of just a few percent of that charge.”
While electron microscopes offering this level of resolution do exist, they require cryogenic temperatures in order to operate, making it impossible to study the activity of living cells. Instead, Geim and his colleagues modified a sensor usually used to measure charge in superconductors so that it could be used to study a single cell at room temperature. The device consists of an array of semiconductor electrodes spaced very close together to form a cross, upon which a cell is placed. The tip of an atomic force microscope, made out of a semiconductor material designed to measure charge from the electrodes, is placed on top of the cell.
“Essentially, it is a semiconductor cross that is specially arranged to have a very high conductance,” says Geim. This means that the arrangement can not only detect minute amounts of charge, but it can also function like leads of an EKG by recording differences in electrical activity at different points across the cell’s membrane. So although each electrode may detect more than an individual electron’s worth of charge, the variations between each of their readings make it sensitive enough to detect far smaller quantities.
The researchers initially set out to record ion flow in a cell. After attempts to record ionic activity of a single yeast cell were unsuccessful, they doused the cell in ethanol to try to elicit a response.
The trick worked: the cell finally showed some electrical activity. But the ethanol also poisoned and killed the cell, allowing the researchers to record the cell’s ultimate demise. “It was probably the last gasp of a dying cell,” says Geim. “Life in the eyes of a physicist is the motion of charges.”
Still, Geim is upbeat about the results. The experiment showed that the device could detect ion flow, down to the resolution of about 10 ions. Measuring the flow of individual ions should also be possible, but it would require the use of a more sensitive semiconductor material in the electrodes, he says.
Ultimately, Geim believes that it will be possible to record different telltale patterns of electrical activity from different cells to indicate responses to drugs or environmental chemicals. The equipment could easily be made into a portable device, and it could be useful for sensing harmful substances, says Geim. “Some cells could be used as cellular canaries for detecting changes in the environment.”
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