In most tissues, collagen is present in the form of fibrils, large supramolecular assemblies of fundamental
structural units of polypeptide chains. In this contribution we report a clear correlation between the
intensity profile of the Raman spectrum of collagen and the orientation of a collagen fiber, depending on
the laser polarization. More specifically, fiber orientation is shown to affect the relative intensity ratio
between the bands at 1245 and 1268cm−1 (amide III doublet). In view of this finding based on the analysis
of a collagen fiber, the customary use of this parameter as an exclusive marker for collagen secondary structure in tissues has to be reconsidered, taking into account fibrils orientation. Moreover, in Raman microspectroscopy of tissues this effect could be exploited to yield information, which could be relevant for diagnostic purposes or fundamental research, about the orientation of collagen fibrils.
