Nanoscale thermometers have revealed for the first time that individual cells inside the human body register various temperatures and do not adhere to the familiar 98.6 °F norm. For many years, scientists have suspected that temperatures vary inside individual cells because many chemical reactions and physical changes take place there, producing energy and heat. Some cells are more active than others, and the unused energy is discharged as heat. Parts of an individual cell may be warmer because they harbor biochemical power plants, known as mitochondria. “We have been very interested in understanding molecular reactivity inside living cells,” said Haw Yang, associate professor at Princeton University. “One key aspect in chemical reactions is temperature. Considering the highly compartmentalized and heterogeneous nature of intracellular space, one might expect that temperature response be nonuniform. Yet, before our work, there was no experimental evidence to show whether it is true.” To measure the temperature of individual cells, Yang and Liwei Lin of the University of California, Berkeley, developed “nanothermometers” consisting of quantum dots, in this case cadmium and selenium, which emit different wavelengths of light depending on the temperature. They inserted the dots into some mouse cells growing in lab dishes and found a range of temperatures throughout the cell. Yang and his colleagues stimulated cellular activity to watch the changes, reporting a difference of a few degrees Fahrenheit in some cells. The team does not yet have enough data to give exact calculations, however. The temperature changes could have a major impact on how cells work and survive, Yang said. Temperature increases could affect how DNA works, for instance, and change how protein molecular machines operate. Yang also hypothesized that the cells may use differences in temperature as a means of communication. The team is working to determine how cellular temperature is regulated, with the goal of applying the information to improving prevention, diagnosis and treatment of diseases. “We hope that this experiment will change the view of intracellular thermodynamics, encouraging researchers to ask questions about temperature gradient and its possible roles in signaling,” Yang said. The research was presented Aug. 28 at the American Chemical Society’s annual meeting in Denver.