Nanoscale Chemical and Topology Imaging of Collagen with Photo-Induced Force Microscopy

Abstract

Collagen is the major structural protein of bone, dentine and the extracellular matrix and can template the nucleation and growth of numerous mineral phases. Collagen meso-scale architecture on surfaces, which is critical for its function, is controlled by the relative magnitude of collagen-substrate (C-S) and collagen-collagen (C-C) interactions. Thus, understanding the nature of these interactions and the mechanisms of assembly on surfaces may enable us to manufacture complex 2D protein assemblies for tissue engineering.Infrared Photo-induced Force Microscopy (IR PiFM) is based on an atomic force microscopy (AFM) platform that is coupled to a widely tunable mid-IR laser. PiFM measures the sample's polarizability by detecting the dipole-dipole force that exists between the light induced dipole in the sample and the mirror image dipole in the metallic AFM tip. This interaction is strongly affected by the IR absorption of the sample. Due to its AFM heritage, PiFM acquires both the topography and spectral images concurrently and provides information on the relationship between local chemistry and topology with spatial resolution of ∼ 10nm.PiFM studies on various stages of fibril formation of collagen molecules deposited onto muscovite mica will be presented. The results consist of PiFM spectral images associated with Amide I absorption band. Hyperspectral images, where each pixel consists of PiFM spectrum centered about the Amide I band, are used to study C-C and C-S interactions by tracking the peak shape and position. By enabling imaging at the nm-scale with chemical specificity, PiFM provides a powerful new analytical method for deepening our understanding of bio-materials and facilitating technological applications of such materials.