Vibrational mode-specific interference imaging for collagen in tumors

We introduce vibrational sum-frequency generation (VSFG) microscopy as a label-free chemical imaging technique for tumor identification. This method combines the chemical specificity of vibrational spectroscopy with the coherent interference properties of nonlinear optics. We obtained hyperspectral images of collagen I in metastatic and tumor-free lung tissues, revealing distinct spectral differences. Tumor tissues showed higher NH stretch (NHS) and CH stretch (CHS) signals relative to the CH2 symmetric stretch (CH2,Ss) compared to healthy controls. Two key spectral markers—NHS/CH2,Ss and CHS/CH2,Ss intensity ratios—were identified for distinguishing tumors from normal tissues, with strong accuracy in both mouse and human lung samples. Theoretical modeling revealed these contrasts arise from variations in interfibrillar distances, which alter interference among spectral peaks and modify their intensity ratios. This suggests denser collagen fibril packing in tumors, consistent with their enhanced stiffness. VSFG microscopy provides high-sensitivity, label-free imaging while maintaining sample integrity, offering significant potential for oncology, pathology, and biophysical research