Combined information from AFM imaging and SHG signal analysis of collagen thin films

Collagen being the most abundant protein in mammals is important for a variety of functions and its structure, concentration and orientation disturbance is associated with different pathological states. The use of the optical second harmonic generation (SHG) is emerging as a powerful non-invasive tool for assessing collagen modification in a variety of pathological conditions. The properties of second harmonic light from collagen structures have not yet been fully clarified due to a number of limitations, such as the difficulty to prepare collagen samples with well-known characteristics and optical properties, at a nanoscale resolution. The results of this paper suggest that some of these limitations can be overcome by using thin collagen films with pre-determined characteristics (PDC), which maintain or/and enhance their NLO properties capacities, as they have been checked by using atomic force microscopy (AFM). The collagen fiber structure and orientation was systematically altered by using thermal denaturation or different preparation methodologies (spin coating procedure, use of collagen solution hydrodynamic flow). These films can be used as prototypes and the combined information from AFM imaging and the one included in SHG signal, delivered from them, can significantly contribute to further understanding of the NLO properties of collagen and in the long term to take advantage as a non-invasive tool.