Light-Activated Carbon Nanotube Sensor for Oxygen Detection

Researchers at ETH have developed a low-cost carbon nanotube sensor capable of accurately, efficiently, and selectively measuring trace amounts of oxygen in gas mixtures when exposed to light. This sensor has potential applications in environmental monitoring, industry, and medicine.

Oxygen is involved in many chemical processes. As such, methods to accurately measure oxygen are important for a variety of industrial and medical applications. These include analyzing exhaust gases from combustion, enabling oxygen-free food and medicine processing, monitoring air oxygen content, and measuring blood oxygen saturation.

Oxygen analysis is also becoming increasingly important in environmental monitoring. "However, such measurements usually require bulky, power-hungry, and expensive devices that are hardly suitable for mobile applications or continuous outdoor use," said Máté Bezdek, Professor of Functional Coordination Chemistry at ETH Zurich. His group applies molecular design techniques to develop new sensors for environmental gases.

Bezdek's group has successfully developed a solution for oxygen detection. In a study published in Advanced Science, the researchers introduced a light-activated, high-performance sensor capable of precisely detecting oxygen in complex gas mixtures, with the necessary properties for field use.

An Uncompromising All-Rounder

Conventional measurement methods often compromise high sensitivity at the expense of other criteria.

Lionel Wettstein, Ph.D. Student and Study First Author, ETH Zurich

Some sensors, for instance, are extremely sensitive to oxygen, but they also use a lot of power and are impacted by ambient variables like humidity. Others are less sensitive and quickly consumed, but they can tolerate interfering gasses.

Stationary devices, complex samples, and high costs also limit the possible applications.

Lionel Wettstein, Ph.D. Student and Study First Author, ETH Zurich

In contrast, the new sensor offers several advantages. It is highly sensitive, capable of accurately detecting oxygen molecules even among a million gas particles, and can do so at higher concentrations. The sensor has a long service life and is selective, able to withstand moisture and other interfering gases. It also consumes very little power, is compact and affordable, and easy to use.

These features make the miniaturized sensor particularly suitable for portable devices and mobile real-time measurements in the field, such as analyzing vehicle exhaust or detecting early signs of food spoilage. Additionally, it can be integrated into distributed sensor networks for continuous monitoring of environments like soils, rivers, and lakes.

“The oxygen content in these ecosystems is an important indicator of ecological health,” said Wettstein.

Sensing Molecules with Nanotubes

Bezdek's group designed the sensor by combining molecular components to achieve the desired features. It belongs to a class of small electrical circuits called chemiresistors, which have an active sensor material that interacts with the target molecule to alter its electrical resistance.

“The big advantage is that this signal can be measured very easily,” said Bezdek.  

The researchers chose to base the sensor material on a combination of carbon nanotubes and titanium dioxide. However, titanium dioxide typically only functions as a chemical resistor at very high temperatures.

“For this reason, we have incorporated carbon nanotubes into the composite material,” continued Bezdek.

The energy-efficient platform consists of nanotubes that ensure the sensor reaction occurs at room temperature, eliminating the need for heating. Inspired by dye-sensitized solar cells, which use specialized dye molecules called photosensitizers to convert light energy into electrical current, the team ensured the sensor material could reliably differentiate oxygen from other gases.

This functional concept was applied to the sensor. When exposed to green light, the photosensitizer transfers electrons to the titanium dioxide and nanotube composite, activating the material and making it highly sensitive to oxygen.

“In contrast to other gases, oxygen hinders this charge transfer in the activated sensor, which changes its resistance,” said Wettstein, summarizing the basis of the sensor reaction.

From the Lab to Field Application

The researchers are actively seeking industrial partners to further develop the sensor, having already submitted a patent application. The market for reliable sensors that can accurately measure oxygen in gas mixtures is estimated to be around 1.4 billion US dollars annually.

The team is now focusing on adapting their sensor concept to detect additional ambient chemicals that are vital to ecology, alongside oxygen.

“Our sensor material has a modular structure, and we want to explore how changing its chemical composition can enable the detection of other target molecules,” said Bezdek.

One of the group's key focuses is identifying nitrogen-based contaminants that affect soil and water, leading to over-fertilization in agriculture.

“To reduce the ecological footprint of the agricultural sector, we need sensors that enable precise fertilization of fields,” said Bezdek.

Journal Reference:

Wettstein, L., et al. (2025) A Dye-Sensitized Sensor for Oxygen Detection under Visible Light. Advanced Science. doi.org/10.1002/advs.202405694