Nanomechanical measurement of bacterial adhesion force using soft nanopillars

Bacteria adherent to the surface are implicated with biofilm formation and infection. Elastic polymer with tunable mechanical properties, such as PDMS (polydimethyl siloxane), has been used as a substrate for measuring traction force generated by animal cells. In this study, soft pillars (diameter: 900 nm, height: 2 m, stiffness: 24.1 μN/m) made of PDMS were used to measure adhesion force between Staphylococcus aureus and PDMS surface. The retraction of soft pillars upon S. aureus binding serves as a means for force estimation and is measured by change of the center-to-center (c-t-c) distance between pillars. Surprisingly, the c-t-c distance between two neighbouring pillars was decreased by 2.2% from its original distance upon bacterial adhesion onto the pillars. Based on the result, the average adhesion force of bacterial binding to pillars was calculated to 0.9 ± 2 nN, which is much higher than expected. This suggests that the soft pillars can be used as a nanomechanical sensor for detecting various bacteria and could be a tool for sensing bacterial adhesion force in nano-newton range.