Electronic noses, or e-noses, are devices that can detect hazardous chemical vapors. But their electronic components are often expensive and vulnerable to humid conditions. Optoelectronic noses offer an alternative, using dye molecules in place of electronic components to indicate the detection of hazardous chemicals.
When developing these optoelectronic noses, it can be difficult to produce colourimetric sensor arrays (CSAs) that can handle multiple analytes quickly and reliably. Existing methods are often complex and costly, which limits their practical use.
A new study in ACS Sensors describes a cost-effective, straightforward approach to CSA fabrication. Their research could make a huge difference to on-the-spot detection.
A Simple Embossing Method
The researchers developed a one-step embossing process that applied mesoporous silica microparticles loaded with dyes to self-adhesive paper. They created 36 sensor units by loading sensitive dyes onto mesoporous silica microparticles and embossing them onto self-adhesive paper using a 384-well plate.
Each unit works as a sensor: when exposed to a gas, the embedded dyes react by shifting colour and intensity. A thin metal backing gives the array stability, while the paper format keeps costs low and fabrication simple. The colorimetric units consisted of different combinations of dyes, such as bromophenol blue, lead(II) acetate, and mercuric chloride.
Tested Against Chemical Threat Agents
The embossed CSA was tested against 12 chemical threat agents, including the toxic gas chlorosarin, at concentrations below their Immediately Dangerous to Life and Health (IDLH) limits. Within just five minutes, each gas produced a distinct colour pattern across the 36 sensor units.
By photographing the sensors before and after exposure, researchers generated unique fingerprints for each gas. Machine learning analysis with a support vector machine achieved 99 % accuracy for qualitative identification and 96 % accuracy for concentration analysis.
Importantly, the sensors maintained accuracy even at 100 % relative humidity, with detection limits below permissible exposure levels. Variability was kept low, with a relative standard deviation under 9 %.
Low Cost, High Potential
Each array costs only 20 cents (USD) to produce, making it both affordable and scalable. The method is compatible with a wide range of dyes and particle types, offering flexibility in array size, shape, and design.
This new sensor technology's ability to perform even under extreme humidity makes it extremely useful outside of the lab, from monitoring industrial leaks to portable devices for emergency response. The pastel-hued “sniffing paper” could even be adapted for outdoor detection of chemical warfare agents.
Toward Portable Optoelectronic Noses
The next step is developing a handheld optoelectronic nose that can instantly read the array’s colour patterns in the field. Researchers envision compact devices for environmental monitoring, workplace safety, and rapid threat detection.
Along with their low cost, the sensors combine simplicity and accuracy to move optoelectronic noses closer to practical use. Once confined to labs, these tools are edging toward everyday use for keeping people safe.
Journal Reference
Shrivas, R. et al. (2025). Simple and Cost-Effective Fabrication of Embossed Colorimetric Sensor Array for an Optoelectronic Nose via Integration of a Self-Adhesive Paper and Mesoporous Colorimetric Silica Microparticles. ACS Sensors. DOI: 10.1021/acssensors.5c01026, https://pubs.acs.org/doi/10.1021/acssensors.5c01026
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