One example of a sensor for moisture content, shown in Fig. 12, is based upon carbon-coated copper nanoparticles dispersed in a tenside film
In humid environments, swelling of the polymer matrix results in larger degrees of inter-nanoparticle separation; these changes cause sensor strips to reflect or absorb different colors of light which can be monitored easily for quick and accurate determination of package moisture levels without invasive sampling.
A noninvasive method of measuring carbon dioxide content in MAPs has also been devised, and is based upon lifetime analysis of luminescent dyes standardized by fluorophore-encapsulated polymer nanobeads ; notably, this CO2 sensor has a detection range of 0.8–100%, a resolution of 1%, and only 0.6% cross-sensitivity with molecular oxygen.