This study proposes a stretchable photonic crystal (PC) film for visible detection of spoilage milk. Thermoplastic polyurethane (TPU) was used as the substrate for the PC structure. The back-barrier layer of an AAO film was used as the template to form a nickel mold through electroforming. The back-barrier array was then transferred onto the TPU substrate through nanoimprinting. Experimental results confirmed that that the structural color change of the fabricated PC TPU film can be easily achieved by a relatively small stretch force. Further experiments on spoiled milk detection demonstrated that the proposed PC TPU film is a highly smartcost-effective biosensor for the detection of spoiled foods in a container.

Food storability is a modern problem where unmarkedunlabeled food can expire without the user＇s knowledge. A method that can visually indicate the food has gone bad is a new area of research for food industriallife sciences. In this study, we propose a novel stretchable thermoplastic polyurethane (TPU) film with photonic crystals (PC) that enables the simultaneous change of PC periodicityincident angles with small strain. The spoiled milk detection results demonstrated that the proposed PC TPU film is a highly smartcost-effective biosensor for the detection of spoiled foods in a container. The developed PC TPU film can be used to replace the currently used aluminum foil seal.

"The United Nations FoodAgriculture Organization estimated that about 1/3 of all food produced, manufactured, and/or sold for around the globe is wastedlost. Dairy products account for nearly 17 of this waste. Using a chemical-freelow-cost method to detect spoiled food would be a great advantage.
 
 We successfully designedfabricated novel stretchable photonic crystal (PC) films that enable change of PC structure colors with small stretchpressure strain. The spoiled milk detection results demonstrated that the proposed stretchable PC film is a highly feasible smart biosensor for the detection of spoiled foods in a container. The developed stretchable PC film can be used to replace the currently used aluminum foil sea