Exploring collagen fibrillogenesis at the nanoscale: Tip‐enhanced Raman imaging of protofibrils

Collagen, a key structural component of the extracellular matrix, assembles through a hierarchical process of fibrillogenesis. Despite extensive studies on mature collagen fibrils, intermediates such as protofibrils remain underexplored, particularly at the nanoscale. This study presents hyperspectral tip-enhanced Raman spectroscopy (TERS) imaging of collagen protofibrils, offering chemical and structural insights into early fibrillogenesis by acquiring nanoscale molecular profiles of collagen intermediates. TERS spectra, complemented by atomic force microscopy (AFM) images, reveal characteristic molecular vibrational modes, including the phenylalanine ring breathing mode, amide II and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>CH</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:annotation>${\rm CH}_2$</mml:annotation></mml:semantics> </mml:math> / <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>CH</mml:mi> <mml:mn>3</mml:mn></mml:msub> <mml:annotation>${\rm CH}_3$</mml:annotation></mml:semantics> </mml:math> stretching vibrations, with distinct spectral signatures compared to mature fibrils.