Colorimetric sensors

Low-power gas sensoren

Fraunhofer IPM is developing new types of low-power gas sensors based on the colorchange principle. A dye in combination with a matrix reacts when it comes into contact with the target gas and changes its color. This color change correlates with the concentration of the gas and has no interaction with other gases. Just a few molecules of the target gas are sufficient to trigger the color change. The reaction takes place at room temperature thus meaning that no heating power is required. The power consumption is in the range of a few milliwatts.  Depending on the measurement cycle, the system can therefore manage without battery  replacement for several years.

Realization of various sensor concepts

Fraunhofer IPM synthesizes and modifies gas-specific dyes with regard to their subsequent field of application. The analyis of the color change ranges from a simple paper-based gas sensor label to complex optical measuring systems with independent evaluation.

To produce a gas sensor label, the dye is applied to e.g. paper or foil using a printing method. The color change caused by the reaction with the target gas can be evaluated by color matching with the bare eye or e.g. via smartphone app with automated color matching.

In the independent optical measuring system, the color change can be detected via transmission or reflection.  For transmission-based approaches, the dye is embedded in a transparent polymer-based matrix and deposited on an optical carrier (plastic or glass).  In reflection-based measurement systems, colored inorganic particles are used. The decisive factor is the integration of a light source (e.g. LED) in the wavelength range of the maximum color change. The color change can be measured indirectly, e.g. by the attenuation or increase of the light.  

Application areas for color change based gas sensors are:

• Environmental monitoring
  
• Protection of people
  
• Occupational safety
  
• Early fire gas detection
  
• Food monitoring