Probing visible light induced photochemical stabilization of collagen in green solvent medium.

Crosslinking of proteins such as collagen for enhanced stability and mechanical properties is an intriguing area in the context of both biomedical and industrial applications. Herein, we have shown the crosslinking of collagen fibers using visible light in a green solvent, ethanol, in the presence of photosensitizers such as methylene blue (Mb) and erythrosine B (Eb). The visible light induced crosslinking increases the shrinkage temperature of collagen fibers from 67 to 100 °C in a concentration dependent manner (1.0 mM Mb/Eb) as revealed by differential scanning calorimetry. Such manifestation was possible only in the presence of ammonium persulphate, a photo-initiator, which has been corroborated through enzymatic degradation, fluorescence and Raman spectroscopic studies. We have also demonstrated that the photoexcited tyrosine moiety of collagen fibers form di-tyrosine during the crosslinking between the peptide chains through steady-state and time-resolved fluorescence measurements. The results suggest a new and efficient photocrosslinking technique to stabilize proteins for diverse applications.