The next time I look at a guitar it will be with an entirely new perspective. This is thanks to a recent conversation I had with Northeastern’s Steve Cranford.

Let’s make one thing clear. I’m not a musician. Not even close. Cranford is the guitar player. He’s also an assistant professor in the Department of Civil and Environmental Engineering, and in our talk he explained how plucking the strings on his guitar one day led to a fascinating research idea.

He wondered: If we shrink the scale of the physics involved in a guitar string’s pitch down to the molecular level, can molecular strings produce musical notes?

Cranford’s lab focuses on the study and mechanical characterization of nanoscale materials and systems, and he had just finished a research paper on what happens when you put carbyne into compression.

Carbyne served as the ideal candidate for trying to produce molecular music. It is a one-dimensional chain of carbon atoms that vibrates similar to an elastic string when put in tension. Those vibrations, Cranford posited, could perhaps be predicted based on length and tension.

The molecules played along and music was born
“When you tune guitar strings, you effectively increase or decrease their tension, which results in a change in their vibrational frequency,” he explained. “I made the connection between tuning the guitar strings and tuning the strings of carbyne. I thought that if you can manipulate the tension in the carbyne at the molecular scale, you can get predictable vibration frequencies.”

Here’s how it works
In their study, Cranford and his graduate student, Ashley Kocsis, MS’15, set forth to determine the accessible frequency range of carbyne. They started by considering a single carbyne chain akin to a single nanoscale guitar string. They then set the carbyne chain to specific tensions—similar to tuning a guitar string—and “plucked” the carbyne chain at those tensions. They were able to demonstrate that different frequencies can be produced and compared to a standard musical scale by adjusting the chain’s tension and length.

Earlier this year, Cranford and Kocsis presented their molecular music in a paper published in the journal MRS Communications.

“Mary Had a Little Lamb” – performed by Carbyne Chain
Cranford believes this is the first research to “tune a molecule” to achieve actual sound. He and Kocsis observed a range of vibration frequencies from putting tension on this carbyne chain before it broke. And then converted those frequencies to a musical scale with audible notes—in the form of the classic nursery rhyme “Mary Had a Little Lamb.”

Listen:

“The sounds we are recording are at much higher frequencies than typical sound waves,” Cranford explained. “Even dogs couldn’t hear these. We’d need to slow down frequency in order to emit an actual sound. But the scale still works.”
 
More than just for show
The musical platform Cranford and Kocsis present merely provides a demonstration of the ability to tune the vibrational frequency, they explained. In other words, Cranford doesn’t envision developing nanoscale Fender guitars. But, he noted, the research does have implications for developing vibration-based nanoscale biosensors or signaling/emitting devices that could be used, for example, in medical diagnostics or airport security screening.

“By determining the frequency of the one-dimensional carbyne, we can determine its sensitivity to other molecules and demonstrate its function as a biosensor, force transducer, or signaling device,” they wrote in their paper. “Ultimately, we wish to set out the design rules and performance limits for this new ‘instrument’ and compose our own desired ‘music.’”