Silk fibroin (SF)-based flexible electronic/photonic materials have gained great attention in wearable devices and soft sensors. However, it remains challenging to understand the molecular interaction mechanisms and subsequently fabricate SF-based flexible materials that exhibit fluorescence, humidity sensitivity, and conductivity properties. In this study, by incorporating lanthanide europium ion (Eu3+), the design and fabrication of a flexible, fluorescent, and conductive SF membrane was proposed. The coordination and cation-π interactions between amino acid residues (i.e., tyrosine, tryptophan, and phenylalanine) of SF and Eu3+ established ion-conductive pathways by plasticizing and capturing water. The SF/Eu3+ membranes (Eu3+ content of 20%) displayed high stretchability, with strain reaching 700% at a relative humidity (RH) of 85%. Furthermore, the SF/Eu3+ membranes showed outstanding performance in real-time monitoring of physiological movement signals and resistance-humidity-related signal extraction and conversion output. Besides, the energy transfer between SF and Eu3+ improved the energy conversion efficiency, allowing fluorescence emission performance of the SF/Eu3+ membrane under UV light. The SF/Eu3+membranes displayed fluorescence emission intensity at the characteristic emission peak of 593 nm, which was linearly dependent on a Eu3+ content of 5–20 and 20–80% RH. This study offers a facile way for preparing flexible, fluorescent, and conductive SF materials for applications in wearable sensors and flexible and implantable electronic/photonic devices.
Chen et al. (Mon,) studied this question.