Photoclickable Biopolymer for Soft, Spectrally-tunable and Reconfigurable Fluorescent Optical Patterning

Patterned fluorescence has many applications in cell-tracking, fiducial markers and cryptography. Incorporating fluorescent patterning into soft and non-planar optics can be challenging with current rigid optical materials and planar fabrication techniques. Silk fibroin is a soft biomaterial that is highly transparent in the visible range with fair transmission in the near-UV and near-IR, and as such has been a proven optical material for waveguides, diffractive and refractive optics, photonic crystals and more¹. To make a patterned fluorescent material silk can be functionalized with methacrylate groups that allow it to participate in 2,5-diaryl tetrazole photoclick reactions. These photoclick reactions are catalyst-free, light-mediated, “click” reactions that produce highly fluorescent pyrazoline adducts from non-fluorescent reactants². In this work we have synthesized a library of photoclick-able tetrazoles with varying emission characteristics and environmental responses and integrated them into soft silk-based materials including films, hydrogels and nanoparticles. These materials display intense fluorescence and can be both implanted and patterned within biological media. The tunable secondary structure conformations of silk provide further control of the patterning, with selective wettability enabling diffusion restriction of the tetrazoles which act as a physical masking process. Alternatively, the intentional formation of di-tyrosine crosslinks acts in an auto-masking function to create soft and conformal photomasks well-tuned to the tetrazole excitation wavelength. The interplay of these mechanisms allows us to achieve complex multispectral patterns in multiple material formats of broad utility.<br/><br/>1. G. Guidetti, L. d’Amone, T. Kim, G. Matzeu, L. Mogas-Soldevila, B. Napier, N. Ostrovsky-Snider, J. Roshko, E. Ruggeri, F. G. Omenetto, <i>Applied Physics Reviews</i>. <b>9</b>, 011302 (2022).<br/>2. V. Pirota, A. Benassi, F. Doria, <i>Photochem Photobiol Sci</i>. <b>21</b>, 879–898 (2022).