Taking measurements of nanoscale objects is no easy task. Last month, researchers at IBM Zurich reported a breakthrough that leveraged an atomic force microscope (AFM) to measure the temperature of an object at the nanoscale. For the IBM researchers, the advance came when they stopped trying to make a nanoscale thermometer and instead focused on a macroscale thermometer for the nanoscale.
Now, researchers at the University of Montreal have turned that back around and produced the smallest thermometer yet. They had a skilled accomplice in accomplishing this feat: nature. The Canadian researchers have built a thermometer out of DNA that takes advantage of the molecule’s tendency to unfold in response to heat.
“In recent years, biochemists also discovered that biomolecules such as proteins or RNA (a molecule similar to DNA) are employed as nanothermometers in living organisms and report temperature variation by folding or unfolding,” said professor Alexis Vallée-Bélisle, a senior member of the University of Montreal team, in a press release. “Inspired by those natural nanothermometers, which are typically 20,000x smaller than a human hair, we have created various DNA structures that can fold and unfold at specifically defined temperatures.”
In research described in the journal ACS Nano, the researchers didn’t simply get the DNA to unfold in the presence of heat, but programmed it to have either have a precise response over a small temperature interval of around 0.05 degrees Celsius or an extended linear response over a wide temperature range between 25 to 90 degrees Celsius.
To achieve these responses at differing temperatures, the researchers exploited the relatively simple and programmable chemistry of DNA.
“DNA is made from four different monomer molecules called nucleotides: nucleotide A binds weakly to nucleotide T, whereas nucleotide C binds strongly to nucleotide G,” explained Arnaud Desrosiers, co-author of the study, in a press release.
Desrosiers added: “Using these simple design rules we are able to create DNA structures that fold and unfold at a specifically desired temperature...By adding optical reporters to these DNA structures, we can therefore create 5-nm-wide thermometers that produce an easily detectable signal as a function of temperature.”
These DNA-based nanoscale thermometers are initially targeted for biological measurements where they can be used to measure temperature variations inside each individual cell.
“Tumor cells are known to be warmer than healthy cells, so our thermometer could be used to identify these tumor cells,” said Vallée-Bélisle in an e-mail interview with IEEE Spectrum.
While it appears biological applications for the DNA thermometers are first up, the researchers believe that they could also be used for monitoring local temperature variations at the nanoscale in electronic devices.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.