PH-responsive discoloration silk fibroin films based on prodigiosin from microbial fermentation

Abstract

Smart color-changing films are emerging as promising functional materials having multiple applications. pH-responsive discoloration film can present optical response to outer pH value, which has diverse functions like indicating, packaging and monitoring, etc. Prodigiosin possesses biodegradability and biocompatibility, which is a natural red pigment derived primarily from secondary metabolites of microorganisms. Based on these properties, an effective approach to develop pH-responsive discoloration film with biodegradability is proposed. Prodigiosins from microbial fermentation were evenly dispersed in silk fibroin solution to form a well-developed composite film via the casting method, exhibiting switchable pH-responsive color-changing performance. The film showed reddish-purple (λ max = 530 nm) at pH below 8, and turned to orange and yellow (λ max = 480 nm) as the pH increased from 8 to 10. The glycerol and 1-(3-Dimethylaminopropyl)-3-ethyl carbodiimide hydro (EDC) were incorporated as plasticizing and cross-linking agents, respectively. Glycerol and EDC significantly reduced the water contact angle from 83.4° to 4.7°and improved the mechanical properties of pH-responsive silk fibroin film. In addition, this pH-responsive silk fibroin-based film is biodegradable and can be attached to the skin for long-term colorimetric indicating. The design of color-changing silk fibroin film presented here provides a new direction of thinking for the preparation of substrate materials for stimulation-responsive biosensors. Smart color-changing films are emerging as promising functional materials having multiple applications. pH-responsive discoloration film can present optical response to outer pH value, which has diverse functions like indicating, packaging and monitoring, etc. Prodigiosin possesses not only pH-responsive discoloration property but biodegradability and biocompatibility. Based on these properties, an effective approach to develop pH-responsive discoloration film with biodegradability is proposed. Prodigiosins from microbial fermentation were evenly dispersed in silk fibroin solution to form a well-developed composite film via the casting method, exhibiting switchable pH-responsive color-changing performance. The film showed reddish-purple (λ max = 535 nm) at pH below 8, and turned orange and yellow (λ max = 480 nm) as the pH increased from 8 to 10. The glycerol and 1-(3-Dimethylaminopropyl)-3-ethyl carbodiimide hydro (EDC) were incorporated as plasticizing and cross-linking agents, respectively. Glycerol and EDC significantly reduced the water contact angle from 83.4° to 4.7°and improved the mechanical properties of pH-responsive silk fibroin film. In addition, this pH-responsive silk fibroin-based film is biodegradable and can be attached to the skin for long-term colorimetric indicating. The design of color-changing silk fibroin film presented here provides a new direction of thinking for the preparation of substrate materials for stimulation-responsive biosensors.