Force measurements between bacteria and poly(ethylene glycol)-coated surfaces

The atomic force microscope (AFM) was used to directly measure the forces o f interaction between E. coli D21 bacteria and hydrophilic glass or hydroph obic N-octadecyltrichlorosilane (OTS)-treated glass substrates coated with the block copolymers, poly(ethylene glycol) (PEG)-lysine dendron or Pluroni c F127 surfactant, respectively. Short-range repulsive interactions between bacterial cells and substrates coated with the block copolymers were detec ted by the AFM over distances of separation comparable to the extended leng th of the PEG polymer chains. In contrast, glass and OTS-treated glass devo id of PEG-lysine dendron or Pluronic F127 exerted long-range attractive for ces on E. coli D21 bacteria. Thus, polymeric brush layers appear to not onl y block the long-range attractive forces of interaction between bacteria an d substrates but also introduce repulsive steric effects.