Amyloid-like staining property of RADA16-I nanofibers and its potential application in detecting and imaging the nanomaterial

BACKGROUND: Designer self-assembling peptide nanofibers (SAPNFs) as a novel kind of emerging nanomaterial have received more and more attention in the field of nanomedicine in recent years. However, a simple method to monitor and image SAPNFs is still currently absent. METHODS: RADA16-I, a well-studied ionic complementary peptide was used as a model to check potential amyloid-like staining properties of SAPNFs. Thioflavin-T (ThT) and Congo red (CR) as specific dyes for amyloid-like fibrils were used to stain RADA16-I nanofibers in solution, combined with drugs or cells, or injected in vivo as hydrogels. Fluorescent spectrometry and fluorescent microscopy were used to check ThT-binding property, and polarized light microscopy was used to check CR-staining property. RESULTS: ThT binding with the nanofibers showed enhanced and blue-shifted fluorescence, and specific apple-green birefringence could be observed after the nanofibers were stained with CR. Based on these properties we further showed that ThT-binding fluorescence intensity could be used to monitor the forming and changing of nanofibers in solution, while fluorescent microscopy and polarized light microscopy could be used to image the nanofibers as material for drug delivery, 3D cell culture, and tissue regeneration. CONCLUSION: Our results may provide convenient and reliable tools for detecting SAPNFs, which would be helpful for understanding their self-assembling process and exploring their applications.