Chitosan and gold nanoparticles-based thermal history indicators and frozen indicators for perishable and temperature-sensitive products

Nanocomposite of chitosan and gold nanoparticles (AuNPs) was used to develop sensors that can indicate the frozen state and thermal history of foods and other temperature-sensitive products based on the visual color change that accompanies the growth and aggregation or agglomeration of AuNPs due to their localized surface plasmon resonance. The synthesis parameters of the chitosan/AuNPs nanocomposites were optimized and the synthesis mechanisms were carefully investigated by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible spectroscopy. Optimally synthesized chitosan/AuNPs nanocomposite was used as a frozen detector, indicated by pink to dark grey color change upon freezing for one day. This sharp color change can be used to help ensure the quality of products such as seafood, meats etc. that may be affected by frozen storage. Chitosan/AuNPs nanocomposites synthesized under different set of parameters could serve as thermal history indicators (THIs) to reflect the temperature abuse of perishable foods and other temperature-sensitive biomaterials. The color of the THIs becomes more intense with the duration they suffer temperature abuse at room or higher temperature. The color change is irreversible and the THIs can be customized to fulfill different time-temperature storage requirements. These frozen detectors and THIs offer novel, cost-effective and environmentally benign alternatives to track and indicate product thermal history by visible color change, without the need of additional read-out devices. These sensors can potentially be integrated with existing packaging to help track and ensure the quality and safety of perishable food, pharmaceuticals and biomaterials.