Polymer photonic crystal sensors for food packaging

The objective of this Thesis is the design of a simple optical method for the detection of biogenic amines in food packaging. These compounds are indeed typical of the degradation of protein-based food. In particular, it targets colorimetric sensors based on distributed Bragg reflectors (DBRs), that are periodic multilayered lattices, made of the alternation of two media with different refractive index. Owing to the periodic index modulation, DBRs are characterized by a photonic band structure that defines spectral regions for which photons cannot propagate through the structure and are refracted generating vibrant colours. These regions are often referred to as photonic bandgaps (PBGs). As, the PBGs spectral properties depend on the refractive index and thickness of the DBR components, it is intuitive that a variation of these parameters induces modifications of their spectral features, and hence of the displayed color. This Thesis exploited this property to design and develop DBRs sensitive to food degradation byproducts, fostering irreversible colorimetric response, also detectable by the naked eye, thus providing antitampering optical sensors for smart packaging applications. The target is to monitor the actual state of conservation of food in situ and in real time. This Thesis presents two different approaches that exploits a chemical receptor for the detection of amines, and the use of a sensitive polymer as the DBR building block. Both the systems are tested in presence of vapors of amines and upon degradation of real food samples, representing a promising tool for smart packaging.