Researchers have known for more than 60 years now that DNA molecules unfold when heated and refold when cooled down again. More recently they also discovered that living organisms employ biomolecules such as proteins or RNA (a molecule similar to DNA) as nanothermometers thanks to this unfolding and folding. “Inspired by these natural nanothermometers, we have now created various DNA structures that can fold and unfold at specifically defined temperatures,” explains team leader Alexis Vallée-Bélisle.

The team used the simple Watson–Crick base pair code of DNA and the so-called Hoogsteen interactions to create their DNA structures. The good thing about DNA is that its chemistry is relatively simple and programmable, says team member David Garreau. “DNA is made from four different nucleotide molecules, A, C, G and T. Nucleotide A binds weakly to nucleotide T, whereas nucleotide C binds strongly to nucleotide G. Using these simple rules, we were able to create DNA structures that can be programmed to fold and unfold at specific temperatures.”

Easily detectable fluorescence signal

By then adding optical reporter molecules to these DNA structures, the researchers have succeeded in creating thermometers just 5 nm wide that produce an easily detectable fluorescence signal as a function of temperature.

As well as real-world applications, the new devices might even help us better understand molecular biology, says Vallée-Bélisle. “There are still many unanswered questions in biology. For example, we know that the temperature inside the human body is maintained at 37°C, but we have no idea whether there is a large temperature variation at the nanoscale inside each individual cell.”

“Nearer-term applications could involve using these thermometers to monitor local temperature variations in nanometric circuits – for example to detect hotspots caused by defects in electronic materials,” Vallée-Bélisle tells nanotechweb.org.

The team says that it is now looking into whether natural nanomachines and nanomotors, which developed over millions of years during evolution, overheat (like their artificial counterparts do) when functioning at a high rate.

The DNA thermometer is described in Nano Letters DOI: 10.1021/acs.nanolett.6b00156.