Development of Nontoxic Carbon Quantum Dot-Based Fluorescent Silk as Biomaterial for Biosensing

Fluorescent silk fibroin, produced by incorporating fluorescent materials into the diet of silkworms, has recently emerged as a promising biomaterial for biosensing applications. However, most fluorescent materials used in this approach are toxic, limiting their suitability for biomedical applications. This study aims to develop a novel, nontoxic fluorescent material capable of generating bright fluorescent silk, with the goal of advancing its application in safe and effective biosensing technologies. Three types of nontoxic carbon quantum dots (CQDs) were synthesized from Rhodamine B using the hydrothermal method. Transmission Electron Microscopy (TEM) imaging confirmed the successful synthesis of CQDs, which measured 2-3 nm in diameter and exhibited bright fluorescence under UV light. Six types of fluorescent materials, B-CQD, G-CQD, O-CQD, Rh B, Rh 101, and Rh 110, were utilized in this study. The rhodamine dyes served as a comparison to evaluate the performance of the newly synthesized nontoxic CQDs. Each material was incorporated into silkworm chow at a concentration of 0.1 wt% to produce fluorescent silk through natural feeding. Silk produced through CQD feeding demonstrated improved mechanical strength and enhanced optical properties. Scanning Electron Microscopy (SEM) imaging revealed that silk produced with CQDs was approximately 3.48 nm thicker than silk produced with Rhodamine derivatives. In addition, the fluorescent silk was fabricated into silk fibroin scaffolds, enabling its use in biomedical applications. Mesenchymal stem cell growth on nontoxic silk fibroin scaffolds was conducted. It was observed that cells covered approximately 9% of the scaffold by day 3, increasing to 37.5% by day 6. For the first time, nontoxic fluorescent silk enabled noninvasive real-time tracking without causing damage or harm to the cells.