Researchers at Vanderbilt University have developed a sensor, based on nanotechnology, that is capable of measuring minute amounts of insulin produced by living pancreatic cells. The big clinical idea is that such a sensor will allow to assess the health of cells in real time, whether in a diseased pancreas or in a transplanted one.
…the researchers developed a new electrode for a device called a microphysiometer. The microphysiometer assesses the condition of living cells by submerging them in a saline solution, confining them in a very small chamber and then measuring variations in their metabolism. The volume of the chamber is only three microliters — about 1/20th the size of an ordinary raindrop — allowing the electrode to detect the minute amounts of insulin produced by special pancreatic cells called Islets of Langerhans.
The new electrode is built from multiwalled carbon nanotubes, which are like several flat sheets of carbon atoms stacked and rolled into very small tubes. Provided by William Hofmeister at the University of Tennessee Space Institute, the nanotubes are electrically conductive and the concentration of insulin in the chamber can be directly related to the current at the electrode and the nanotubes operate reliably at pH levels characteristic of living cells.
Current detection methods measure insulin production at intervals by periodically collecting small samples and measuring their insulin levels. The new sensor detects insulin levels continuously by measuring the transfer of electrons produced when insulin molecules oxidize in the presence of glucose. When the cells produce more insulin molecules, the current in the sensor increases and vice versa, allowing the researchers to monitor insulin concentrations in real time. It is similar to a device developed by another group of researchers that operated at acidity levels well beyond those where living cells can function.
Previous tests had shown that nanotube detectors are more sensitive at measuring insulin than conventional methods. However, the researchers had to overcome a major obstacle to adapt them to work in the microphysiometer.
In the small chamber, they found that the fluid moves across the electrode surface rather than pushing against it. These micro-currents tended to sweep the nanotubes aside rather than pinning them to the electrode surface where their electrical activity can be measured. The researchers solved this problem by coating the electrode with a chemical called dihydropyran, a small molecule that forms chains that trap the insulin molecules on the electrode surface.
"One of the key advances of this project was finding how to keep nanotubes active on the surface without being washed away by microfluidic flows," Cliffel says.
Now that the microphysiometer has demonstrated the ability to rapidly detect the small quantities of insulin produced by individual cells, the researchers hope to use it to determine the health of the islet cells used for transplantation.
More from Exploration, Vanderbilt’s Online Research Magazine: Measuring insulin in minute quantities
