Sensor for real-time monitoring of food degradation

We have developed a simple and cheap optical thin film sensor chip able to detect the decay of food through a specific colour change providing reasonable sensitivity and selectivity to indicate "best use before" period. The design of the sensor relates to the phenomenon of "anomalous absorption", which can best be described as a thin film enhanced absorption. A metal cluster film positioned at a well defined distance to a smooth metal surface shows that the minimum of spectral reflectivity strongly depends on the thickness of the interlayer: This setup represents a special kind of reflection interference filter. In such a sensor setup we have integrated a biodegradable polymer which is degraded by the same enzymes and at the same rate as food decay will happen. The degradation of the polymer results in reduction of the film thickness and thus in a specific change of the color.