Unraveling the binding microprocess of individual

The initial microprocess of a major cariogenic bacterium Streptococcus mutans forming biofilm at a single-cell level via sucrose-dependent adhesion has not been observed because the cells' high moisture content caused measurement challenges. To develop a high-sensitivity biosensor chip and a real-time, label-free method to observe bioactive molecule interactions with single cells from oral biofilms. We made the chips of immobilized bacteria by micronano-processing. A surface plasmon resonance imaging (SPRI) system was used to detect and record the association and dissociation microprocess of S. mutans with sucrose/dextran solutions of various concentrations, and the calculus model was adopted to treat the data. At the location of S. mutans, a unique 'comet-tail' SPRI signal was observed. The binding patterns of S. mutans differed between individual cells exposed to the same solution as well as between sucrose and dextran. The different cells exhibited different affinities with dissociation constants for sucrose being 5.697 × 10-3 to 3.689 M and for dextran 1.235 × 10-3 to 1.282 M, indicating cell-to-cell heterogeneity. Our SPRI detection method is effective in investigating microbial binding, initial biofilm formation, and oral microecology. It offers new possibilities for studying oral microorganism characteristics and development of oral diseases.