Bis(dipicolylamine) derivatized cellulose microspheres for the sequestration of negatively charged biomembrane bearing species

Spherical materials capable of binding to negatively charged biomembrane bearing species like bacterial cells in still or flowing liquids can have a number of important applications. For example, they could be used to remove bacterial cells from blood facilitating the diagnosis and treatment of bacteremia (i.e., bacterial infection of blood). Other applications involve removal of such species from aqueous foodstuffs, pharmaceutical formulations, and wastewater discharges. Here we report of the preparation of bis(dipicolylamine) (BDPA) bearing nonporous cellulose microspheres (CMs) for the sequestration of negatively charged biomembrane bearing species. When complexed with Zn 2+ ions, BDPA ligands are capable of binding to biomembranes that display negatively charged phosphate amphiphiles on their outer surfaces. Three different chemical ligation strategies (amide bond formation, reductive amination, and epoxide opening) were employed to obtain BDPA derivatized CMs. Using fluorescence microscopy and spectroscopy it was demonstrated that these BDPA-CMs were capable of binding to negatively charged liposomes, but not to neutral liposomes. Fluorescence microscopy also revealed that all the BDPA-CMs were capable of binding to green fluorescent protein-expressing Escherichia coli (K12). Quantification of bacterial binding of one of these BDPA-CMs revealed binding capacities of 1.01 × 10 8 colony forming units (CFU)/g for E. coli (K12) through fluorescence spectroscopy, and ≥ 8.96 × 10 7 and 5.93 × 10 7 CFU/g respectively for E. coli (ATCC 35049) and Staphylococcus aureus (ATCC 25923) using optical density measurements at 600 nm (OD 600 ). Such high binding capacities make these materials good candidates for future applications where sequestration of bacterial cells and other species with similar membrane properties from liquids is desired. Graphical abstract