Interaction between bacterial cell membranes and nano-TiO₂ revealed by two-dimensional FTIR correlation spectroscopy using bacterial ghost as a model cell envelope

The interaction between microorganisms and nanoparticles is a crucial step towards understanding the subsequent biological effect. In this study, the interaction between TiO₂ nanoparticles and bacterial cell membrane was investigated by Two-dimensional Correlation Fourier Transformation Infrared spectroscopy (2D-FTIR-COS) using bacterial ghosts (BGs), which are non-living bacterial cell envelopes devoid of cytoplasm. The synchronous map of 2D-FTIR-COS results indicated that the functionalities in proteins of BGs preferentially interacted with TiO₂ nanoparticles; whereas the interaction of TiO₂ nanoparticles with characteristic functionality in polysaccharides (C[sbnd]OH) and phospholipids (P[dbnd]O) were very weak or insensitive. This conclusion was further corroborated by settling of TiO₂ nanoparticles in the presence of pure protein, polysaccharide and phospholipid represented by bovine serum albumin (BSA), alginate and phosphatidylethanolamine (PE). Additionally, the asynchronous map of 2D-FTIR-COS indicated a sequential order of functionalities bonded to TiO₂ nanoparticles with the order of: COO⁻ > aromatic C[dbnd]C stretching > N[sbnd]H, amide II > C[dbnd]O, ketone. These findings contribute to deeper understanding of the interaction between TiO₂ nanoparticles and bacterial cell membrane in aquatic systems.