Preparation and humidity response performance of chitosan / heparin sodium-based nanofilm

To explore an eco-friendly and straightforward anti-counterfeiting strategy, this study constructed a multi-layer composite film was constructed on a silicon substrate surface using unmodified natural cationic polysaccharide chitosan (CHI) and anionic polysaccharide heparin sodium (HS), through layer by layer self-assembly technology (LBL). The morphology and structure of the multi-layer films, and their responsibility towards humidity, were investigated. The results showed that the film exhibited significant color changes as the number of polymer layers increased. In addition, the film exhibits reversible color conversion in the visible light range (430-600 nm) under environmental humidity variation: from purple (430 nm) to yellow (600 nm) when exposed to moisture, and can be recovered to its initial color within 2 seconds after removing the stimulus. After selective ultraviolet irradiation, controlled display and disappear of the set pattern have been achieved. The prepared films are entirely based on natural polymers, providing a new way for the development of green and intelligent anti-counterfeiting materials.