Ionic Strength-Dependent Attachment of Pseudomonas aeruginosa PAO1 on Graphene Oxide Surfaces

Graphene oxide (GO) is a widely used antimicrobial and antibiofouling material in surface modification. Although the antibacterial mechanisms of GO have been thoroughly elucidated, the dynamics of bacterial attachment on GO surfaces under environmentally relevant conditions remain largely unknown. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to examine the dynamic attachment processes of a model organism Pseudomonas aeruginosa PAO1 onto GO surface under different ionic strengths (1–600 mM NaCl). Our results show the highest bacterial attachment at moderate ionic strengths (200–400 mM). The quantitative model of QCM-D reveals that the enhanced bacterial attachment is attributed to the higher contact area between bacterial cells and GO surface. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and atomic force microscopy (AFM) analysis were employed to reveal the mechanisms of the bacteria–GO interactions under different ionic strengths. The strong electrostatic and steric repulsion at low ionic strengths (1–100 mM) was found to hinder the bacteria–GO interaction, while the limited polymer bridging caused by the collapse of biopolymer layers reduced cell attachment at a high ionic strength (600 mM). These findings advance our understanding of the ionic strength-dependent bacteria–GO interaction and provide implications to further improve the antibiofouling performance of GO-modified surfaces.