Evaluation of Sericin Protein Photoluminescence: Contribution Attribution of Amino Acid Units and Insight into the Emission Mechanism and Application Exploration

Abstract

Amorphous biomaterials with photoluminescence (PL) and persistent room-temperature phosphorescence (p-RTP), such as proteins, are rarely reported, so their emission mechanism and characteristics are still in the preliminary research stage. In particular, the relationship between the PL property and the amino acid units of these proteins has not been elucidated in detail, and elucidating the above connections is the key to clarifying the emission mechanism of proteins. Herein, we found that both solutions and solids of sericin (SR) possess aggregation-induced emission (AIE) behavior and prominent excitation-dependent p-RTP emission. Through in-depth comparison and analysis of the emission behavior of SR with its main amino acid units, it is found that there is every probability that the PL of SR solution is mainly contributed by aspartic acid and l-lysine, while the main PL (especially, p-RTP) contribution of SR powder is from l-alanine to l-lysine. The above inference is further supported by theoretical calculation and single-crystal analysis. The overall emission behavior of SR can be preliminarily explained by a clustering-triggered emission (CTE) mechanism. Moreover, the PL is greatly enhanced after compressing the powder into a tablet, which can be explained by packing density-promoted emission (PDE). Furthermore, SR has been successfully applied to the fields of multiple anti-counterfeiting encryption, ion detection, biological imaging, and screen printing. Therefore, the above results suggest a way to clarify the protein PL through a detailed comparative analysis of the contribution of major amino acid units of proteins to their emission.