Composite hydrogel-loaded alumina membranes for nanofluidic molecular filtration

highlights
• Homogeneous nanoporous alginate hydrogels obtained by one-step crosslinking.
• Facile preparation of composite nanoporous membranes.
• Excellent electrostatic exclusion properties for negatively charged molecules.
• Good selectivity for separation of similar sized proteins in PBS solution.

In this paper a nanofluidic molecular filtration system based on soft alginate hydrogel fillings and a solid-state alumina support membrane is presented. The electrostatically controlled diffusion is characterized by partition coefficient of the hydrogel and the flux through the composite membrane for positively and negatively charged dye molecules. The partition coefficient of negatively charged fluorescein sodium molecules into the gel is 2 orders of magnitude lower in 1 mM KCl solution than that in 1 M KCl solution. The molecular transport properties through the hydrogel loaded alumina membrane are solely dominated by the soft nanoporous hydrogel. Such a composite membrane with alginate hydrogel of only 6 wt% shows a selectivity of 5 for the separation of bovine serum albumin (BSA) and bovine hemoglobin (BHb) in high ionic strength solution of phosphate-buffered saline (PBS).