Biomimetic sensor chip monitoring real-time food degradation: correlating chemical deterioration with microbiological status

Conventional tests currently in use for the detection and identification of food-borne pathogens and also of microbial food deterioration are time-consuming as they are based on conventional culturing techniques or monitoring environmental conditions like the increase of temperature or change in pH. These parameters do not reflect the real quality of the meat to be tested. The aim of our approach was to create a simple and cheap sensor providing reasonable sensitivity and selectivity to indicate the bacterial infection in real-time monitoring combined with a memory effect that cannot easily be corrupted. Thus, an optical thin film sensor chip was developed able to detect bacterial decay of food through a specific colour change. 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 nanoparticle layer 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 distance layer. This setup represents a special kind of reflection interference filter. In such a sensor setup a biomimetic polymer is integrated, which is degradable by lytic enzymes excreted by microorganisms in food decay. Meat deterioration under controlled conditions is correlated to the amount of enzymes secreted by microorganisms and the bacterial count. Thus, after incubation of the sensor setup with standard meat preparations, the enzymes released from decaying cell material change the thickness of the polymer layer and generate an easily visible colour change. This setup would be useful for integration into meat packaging.