The IMB-CNM develops an innovative color-changing sensor for the detection of pollutants in the environment

A color-changing sensor could revolutionize the detection of pollutants and volatile organic compounds (VOCs). A team from the CSIC's Institute of Microelectronics of Barcelona (IMB-CNM-CSIC) has developed a polymer-based device that bends and changes color when it comes into contact with different substances, providing an immediate visual reading without the need for complex electronic systems. This is an initial development, recently published in Advanced Optical Materials, which provides a way to simplify air quality control and opens the door to applications in environmental control, medical diagnosis, and industrial safety.

"This technology allows for the rapid detection and identification of volatile compounds and pollutants in the environment," says Mar Álvarez, a scientist at IMB-CNM who is leading the research.

A mechanochromic sensor relies on mechanical stimuli, such as tension or pressure, to change color. In this case, the team has manufactured a cantilever-shaped sensor using layers of two different polymers, repeating chain molecules: polydimethylsiloxane (PDMS) and non-stoichiometric thiol-ene-epoxy (OSTE+). The combination of the two polymers allows for a different response from the sensor due to the change in volume of each polymer when exposed to different pollutants. In addition, one of the cantilever surfaces contains photonic nanostructures, which break down light and give the sensor a specific color. Thus, when the device comes into contact with one of the compounds and the polymers swell, the cantilever curves, changing from a single color (such as blue) to a color gradient along the length of the cantilever. The greater the curvature, the greater the color gradient, making it possible to observe the entire color spectrum on the cantilever.

"We are talking about a very small sensor (cantilever), less than 1 square millimeter in area, which has been completely microfabricated at the IMB-CNM and would be integrated into the analysis control equipment or device," Álvarez continues.

The device responds to the differential volume change of the two polymers that form it when absorbing a volatile compound, which generates a curvature and, consequently, a color change. "It is a passive system that does not need its own electronics to function," adds the researcher. To quantify the sensor's response and identify the compound based on the color pattern in real time, all that is needed is a white light and a camera. This detection can be done easily, for example, with a smartphone.

Innovative manufacturing

Currently, there are highly sensitive commercial systems capable of detecting volatile organic compounds in the air. However, they are not able to discriminate between different types of compounds; they only detect the total concentration of VOCs in the environment. In addition, these devices are bulky and expensive. The advance proposed by the IMB-CNM simplifies the detection and discrimination of VOCs, which normally requires complex matrices with multiple sensors that are unable to discriminate between different vapors.

"Discrimination is possible thanks to the different solubility of the two polymers in different organic compounds," explains Ferran Pujol, postdoctoral researcher at IMB-CNM and first author of the publication. In this study, he adds, "it has been possible to identify which solubility parameters, known as Hansen parameters (dispersion, H-bonds, and polarity), govern the sensor's response direction depending on each type of compound."

This allows the sensor to respond differently depending on the type of compound, without the need to add complex or specific biochemical matrices to each compound. 

The next steps in the research include expanding the range of volatile organic compounds that can be detected and integrating artificial intelligence techniques, which, due to their ability to discriminate between very similar patterns, would enable robust operation outside the laboratory. They also plan to test the device in the detection of volatile organic compounds present in human breath, where some of these compounds act as biomarkers of disease and could facilitate early diagnosis or monitoring of chemical exposures.

_{Ref. article: F. Pujol-Vila, E. Casas-Aguilera, and M. Alvarez, “Competitive Bidirectional Response in Bi-Polymeric Mechanochromic Cantilevers Toward Color Imaging-Based VOC Discrimination.” Adv. Optical Mater. 13, no. 32 (2025): e02088. https://doi.org/10.1002/adom.202502088}