Carbon Nanotubes and the Future of Smart Sensors

Carbon nanotubes (CNTs) are among the most remarkable materials ever discovered. Thousands of times thinner than a human hair yet extraordinarily strong and electrically sensitive to specific external impacts, they have long promised breakthroughs in electronics, medicine and environmental monitoring. But turning that promise into everyday technology has proved difficult. One of the major challenges is simply finding, identifying and integrating the right nanotubes into working devices.

That is where physicist Dr. Miroslav Haluška from the Micro and Nanosystems group (MNS) at ETH Zürich believes Raman spectroscopy can make a decisive difference. In a recent QAMSS lecture, Miro Haluška described how the laser-based technique not only helps scientists “see” and characterise CNTs, but can also actively modify them during device fabrication. In a follow-up interview, he explained why this work matters far beyond the laboratory, from detecting toxic pollution to monitoring disease through breath analysis.

“We produced CNTs, we are characterising them and we integrate them into functional devices,” Haluška said. “These devices could be, for example, resonators or gas sensors.”

For Haluška, the ultimate goal is practical technology that improves daily life.

“Already from childhood, I was trying to improve the life of humans, especially to make it easier and better,” he said. “This motivated me to pursue research to help people to have healthier and safer lives.”

How Raman spectroscopy helps scientists “see” carbon nanotubes

One can imagine CNTs as seamlessly rolled graphene sheets forming cylinders of carbon atoms with diameters only nanometres wide. Their tiny size gives them extraordinary physical and chemical properties, making them highly attractive for sensors. But that same small size also makes them difficult to locate and analyse.

Haluška’s work demonstrates that Raman spectroscopy, a technique based on how light scatters after interacting with matter, can do much more than simply confirm a nanotube is present.

Raman spectra reveal key nanotube properties, including diameter, structural quality and whether a nanotube behaves like a metal or semiconductor. Different Raman “bands” act almost like fingerprints for nanotubes. By combining information from several Raman peaks rather than relying on only one, his group dramatically improved nanotube detection rates. Using two laser wavelengths, in this work 488 nm and 514 nm excitation lasers, the team achieved nanotube detection yields approaching 96% compared with scanning electron microscopy (SEM) measurements. Using properly selected third laser wavelengths, the total Raman detection yield additionally increases. This makes Raman spectroscopy an increasingly powerful alternative for locating suspended nanotubes during device fabrication.

The technique is especially important because nanotube-based sensors often require carefully selected individual nanotubes rather than random collections of material. The MNS group, in collaboration with three other groups from ETH, has also explored automated approaches for rapidly selecting and integrating nanotubes into devices, potentially enabling large-scale manufacturing in the future.

Carbon nanotube gas sensors could change everyday health monitoring

The most compelling part of Haluška’s interview was not the spectroscopy itself, but what these sensors may eventually do for ordinary people.

CNT gas sensors based on individual single-walled CNTs consume extremely little power while remaining highly sensitive to tiny amounts of gases. Haluška highlighted nitrogen dioxide (NO₂), a pollutant linked to vehicle emissions and respiratory disease, as one important target.

“This pollutant is more or less everywhere,” he said. “Even relatively low levels are dangerous for humans. And, with CNT gas sensors, we can detect it.”

He imagines a future in which sensors are embedded directly into devices people already carry everywhere.

“We hope that one day you would have your environmental dangerous gas sensor directly in your mobile phone or your smart watches,” he said.

The idea extends beyond environmental pollution. Researchers worldwide are increasingly interested in “breath analysis,” where disease-related chemicals in exhaled air could provide early warning signs of illness. Haluška sees nanotube sensors as a natural fit for that emerging field.

“Illnesses could be detected early if human breath contains some specific and abnormal gases that can be recognised,” he explained. “They can tell you ‘go to the doctor’, maybe you need another check because you have potentially started to develop some disease.”

Unlike traditional medical testing, breath analysis could happen continuously and non-invasively. Haluška noted that people already use smartphones constantly, making them ideal platforms for passive health monitoring.

“You don't need extra devices, extra time,” he said. “Just use your call with your family, and it can detect and record while you talk. That means you could be monitored every day, so that every change could be saved.”

Raman lasers can also modify nanotubes

One of the most intriguing aspects of Haluška’s lecture was the “dual role” of lasers in Raman spectroscopy. The Raman laser is not only a diagnostic tool, it can also alter nanotubes and the sensor device directly.

By carefully adjusting laser power and exposure time, researchers can remove contamination, induce defects or even oxidise and peel nanotubes. These changes may improve sensor performance or help tailor nanotube properties for specific applications.

Haluška presented examples showing how controlled laser treatments affected nanotube Raman signals, sometimes enhancing desirable features while preserving structural integrity. In other cases, excessive exposure damaged nanotubes partly or even entirely. Understanding these limits is crucial if nanotube manufacturing is ever to become reliable at industrial scale.

The approach highlights a broader trend in nanotechnology: characterisation tools increasingly double as fabrication tools. Instead of simply observing and characterising materials, scientists can now manipulate them with extraordinary precision.

The challenge of turning nanoscience into real products

Despite decades of excitement surrounding CNTs, widespread commercial applications remain relatively limited. Haluška is realistic about the obstacles.

“One doesn’t know if such approaches will be accepted with companies,” he admitted.

He also spoke candidly about the pressures of academic science itself. After completing a PhD, many researchers move through temporary contracts and short-term positions, often balancing heavy workloads with family life.

“It’s a problem in science that often there are not permanent position for people who are not professors,” he said.

Yet he remains optimistic because he has already seen promising technologies emerge from his research environment. He described startup companies connected with the MNS group that successfully developed wearable monitoring systems, including devices that estimate core body temperature in athletes.

“They started with just PhD students,” he said. “And now there are like 50 people and they’ve got investors.”

That success gives him hope that nanotube-based sensing technologies may eventually follow a similar path.

Building foundations for the next generation

Haluška, who joined ETH Zurich in 2009 after research positions across Europe and the United States, does not expect to personally see every vision fully realised.

“I cannot say, okay, I would already like to have our sensor in my cell phone, this is probably not realistic,” he said.

But he hopes the next generation of scientists and engineers will continue building on the work.

“I hope that maybe my daughter will be able to have a cell phone and there will be a sensor to measure, to monitor her health,” he said.

That quiet optimism perhaps captures the true spirit of nanotechnology research. Progress is often slow, incremental and technically demanding. Yet behind the spectroscopy graphs and nanotube spectra lies a much larger ambition: technology small enough to disappear into everyday life while helping people live safer and healthier lives.

About the interviewee

Miro Haluška received his diploma from the Slovak University of Technology in Bratislava and earned his degree in physics from the University of Vienna. He subsequently worked as a postdoctoral and visiting researcher at several institutions, including the Max Planck Institute in Stuttgart, the Laboratory for Nanotechnology at Clemson University, the Department of Physics at Wake Forest University and the Eindhoven University of Technology in the Nano- and Micro-Scale Engineering group. In May 2009, he joined Professor Ch. Hierold’s Micro- and Nanosystems group at ETH Zurich. His research focuses on the targeted growth of single-walled carbon nanotubes, their integration into gas sensor devices, and the use of Raman spectroscopy for the investigation and treatment of carbon nanomaterials.

By Dr Karen Steward