Polymer makes NO sense

Portable nitric oxide sensor could diagnose diseases.
3 July 2002
PHILIP BALL


Nitric oxide (NO) makes blood vessels dilate.

A new polymer could lead to cheap, hand-held sensors that can detect ailments from respiratory infections to Alzheimer's disease. The material responds to molecules of nitric oxide (NO), high levels of which in human breath can be diagnostic for certain diseases.

Takeshi Shioya and Tim Swager of the Massachusetts Institute of Technology in Cambridge, Massachusetts, have built a prototype NO sensor incorporating their new polymer, which conducts electricity1. All the necessary electronics can be mounted on a single microchip, the researchers say.

The device is basically a small transistor with very low power consumption. The maximum electrical current that will flow through it increases when it comes into contact with NO. The polymer's chainlike molecules are studded with cobalt ions. The way the chains conduct electrical charge changes when NO binds to the cobalt.

Sensors that measure NO in breath exist already, but are cumbersome and costly, and so are not used routinely.

Our bodies produce NO for a variety of purposes. It relaxes the tension in blood-vessel walls, allowing the vessels to dilate. Heart-disease medications such as nitroglycerin reproduce this effect, as does the impotence drug Viagra.

The body also produces more NO when our immune system fights infection. So measuring NO levels in a patient's breath can signal infection. Such monitoring might also spot early signs of exposure to biological-warfare agents.

NO controls the activity of some cells in the central nervous system. Changes in NO levels can signify neuron death, as induced by degenerative diseases such as Alzheimer's. Shioya and Swager believe that their new conducting polymer could be used to make electrode microsensors that could be inserted into a patient near to NO-producing cells to detect such changes.


References
Shioya, T. & Swager, T. M. A reversible resistivity-based nitric oxide sensor. Chemical Communications, 2002, 1364 - 1365, (2002).


© Nature News Service / Macmillan Magazines Ltd 2002