NewScientist.com has a brief article today about the work done by Nicholas Kotov at the University of Michigan in developing a nanoscale spring thermometer. Traditional spring thermometers, also known as bimetal thermometers, consist of two thin metallic layers, usually iron and copper joined together to make a strip that is often formed into a coil. Because the two metals have different constants of expansion, the coil will expand if heated and contract when cooled. The change can measured and calibrated allowing the coil to act as a thermometer. Unfortunately these types of thermometers are notoriously insensitive, sometimes exhibiting errors of up to ±10 °C. Kotov’s nanoscale version functions in much the same way but is accurate to ±3 °C over the range of 20 – 80 °C.
Kotov uses polyethylene glycol chains in place of the bi-metallic strip. He has also developed an ingenious way to detect the physical change in the spring. A 20 nm diameter gold sphere is attached to one end of the chain, and small amount of cadmium telluride (CdTe) is attached to the other. When struck with a laser, the CdTe glows inverse proportionally to its distance from the gold sphere. At colder temperatures when the spring is contracted and the gold sphere is close, the CdTe glows brighter than at warmer temperatures when the spring has expanded, and the gold is further away.