Waveguide Evanescent Field Scattering (WEFS) Microscopy of Bacterial Biofilms

Waveguide Evanescent Field Scattering (WEFS) Microscopy was introduced in 1997 with examples on technical structures such as thin SiO2 and photoresist pattern. The evanescent field of a slab waveguide mode was used to illuminate ultrathin structures located on the waveguide. The scattered photons were collected under 90° geometry in a microscope. This technology had been expanded in recent years to Waveguide Evanescent Field Fluorescence (WEFF) microscopy for the investigation of cell-substratum interactions. Here the plasma membranes of the cells were stained. We now demonstrate WEFS microscopy of living bacteria forming biofilms. WEFS allowed investigation of the adhesion of bacteria onto a waveguide surface via close junctions. We were able to distinguish between bacterial colonies, single bacteria and dividing bacteria. The big advantage of WEFS over WEFF microscopy is the label-free approach. It is now possible to image living bacteria adhered to a surface without the addition of chemical treatment such as staining. This is of great relevance for the development of anti-bacterial surfaces and for sensor applications, e.g. in monitoring drinking water.