Algal polysaccharides on lipid Langmuir–Blodgett films and molecular effects upon metal ion contact

The capability of extracellular polysaccharides released from microorganisms to bind to metal ions is a potential molecular biotechnological tool to produce biosorbents as an alternative for the removal of heavy metals from aquatic environments. In this paper, we exploit the ability of polysaccharides from extracellular polymeric substances produced by phytoplankton adsorbed on lipid monolayers as Langmuir–Blodgett films to interact with silver ions in aqueous environments. The properties of the biomacromolecules after the interaction were investigated with polarisation modulation infrared reflection-absorption spectroscopy and atomic force microscopy. The vibrational spectroscopy technique applied to the Langmuir–Blodgett films before and after contact with silver ions indicated significant changes for the bands related to the chemical groups present in polypeptides and polysaccharides. These changes point to the influence of the metal interaction on the molecular organisation and on the structure of the Langmuir–Blodgett film. Therefore, the behaviour of these biomacromolecules adsorbed at bioinspired interfaces is better understood in terms of properties at the molecular level. This understanding leads to a model in which metal incorporation affects the molecular structure of the ultrathin film.

► Extracellular material released from algae was adsorbed at a lipid monolayer.
► Monolayer changes its rheological properties with material incorporation.
► Changes in proteins and polysaccharides are identified with PM-IRRAS.
► Langmuir–Blodgett films of this composite are sensitive to metal ions in water.