Detection of toxic gases

Color change sensors detect toxic gases in very low concentrations

Danger often lurks unnoticed: many toxic gases such as carbon monoxide are colorless and odorless, but have a damaging effect on health even at low concentrations or through chronic exposure. Sensors that can reliably measure toxic gases even at low concentrations provide the only protection against health hazards.

Fraunhofer IPM develops gas sensors based on the color change principle: a dye changes color upon contact with a target gas. The reaction is comparable to the key-lock principle, i.e. there is no interaction with other gases. A few molecules of the target gas are sufficient to trigger the color change.

Visual detection or optical detection depending on the application  

Fraunhofer IPM synthesizes and modifies gas-specific dyes for specific applications. The analysis of the color change ranges from a simple label to complex optical measuring systems with independent evaluation. To produce a gas-sensitive label, the dye is applied to e.g. paper or foil using a printing method. The sensitive surface is thus flexible in terms of size and shape. After reaction with the target gas, the color change can be detected and evaluated either by color matching with the bare eye or with a smartphone app, for example. In the independent optical measuring system, the color change can principally be detected via transmitted light (transmission) or top view (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