Visualization of Cells at the Solid-microbe Interface Using Confocal Reflection Microscopy With Index-matching Materials

Herein, we demonstrated that the use of index-matching materials (IMM) allows direct visualization of microbial cells maintained at a solid-liquid interface through confocal reflection microscopy (CRM). The RI mismatch induces a background reflection at the solid-liquid interface, which dwarfs the reflection signals from the cells and results in low-contrast images. We found that the IMM sufficiently suppressed the background reflection at the solid-liquid interface, facilitating the imaging of microbes at the solid surface using CRM. Further, we succeeded in temporal imaging of initial biofilms directly colonizing the IMM with CRM in a tag free fashion, and thus, it is highly advantageous for probing the dynamics of biofilm formation, along with visualization of environmental organisms and newly isolated bacteria, for which transformation methods are difficult to establish.