Developments of combined scanning near-field optical microscopy and atomic force microscopy applied to biological system

Innovative nanotechnologies for selective measurement of biological parameters can be helpful to reduce environmental impact, to prevent food contamination and poisoning and to assess the biocompatibility of nano-materials. In particular, Atomic Force Microscopy (AFM) produces high-resolution topographical pictures of biological samples and it allows measurements of physical properties such as elasticity, viscoelasticity and electrostatic interaction. Scanning Near-field Optical Microscopy (SNOM) delivers information both on topography and optical properties with sub-wavelength resolution. Then it combines the high resolution of scanning probe microscopy with the contrast of optical microscopy. We applied SNOM and AFM to a model system constituted by dormant spores of C. tyrobutyricum. Detailed topographic study of the spore external layers was performed with AFM, providing information about the morphology of spores, of their vegetative cells and flagellae structures at nano-scale level. AFM used both in lateral force mode and spectroscopy mode give us a qualitative picture of the elastic and viscoelastic properties of the spore coat. SNOM was used in illumination-mode and allows to take optical images in transmission and reflection simultaneously with topography, revealing the presence of structures inside the C. tyrobutyricum spores. Therefore, we show how combined use of the AFM and the SNOM technique provides not only to image but also to obtain information about mechanical and local optical properties of a biological sample. The perspective is to develop the SNOM – AFM technique in order to study mechanical and optical properties of biological systems (s-layers, cell membranes, …)