Colorimetric Polymer Sensors for Smart Packaging

Abstract

Nowadays, consumers can estimate the condition of packaged foods only by checking the expiration date on the label. However, this approach is inefficient when it comes to assessing the actual edibility of fresh products, since the events that accelerate the onset of degradation phenomena, such as a rise in temperature, cannot be continuously assessed. In this context, the detection of a different parameter, such as low concentration of amines, can reveal the onset of degradation processes. Here, a colorimetric photonic multilayer sensor is reported for detecting low amine concentrations suitable for sealed packages. The sensor consists of alternating layers of poly(N-vinylcarbazole) and polyacrylic acid, and its response is based on the selective interaction between the latter and amines. This interaction causes the polymer layers to swell and introduce disorder into the photon structure, resulting in fading its bright color. Since the reaction of these systems is usually reversible, manipulation or false readings are possible due to inapt sealing of the package. It is shown that the activation of carboxylic acid residues of the sensitive polymer with N-hydroxysuccinimide produces an irreversible response to amine vapor concentrations as low as 3 parts per billion.