Selective transportation of charged ZnO nanoparticles and microorganism dialysis through silicon nanoporous membranes

It is well known that, besides the membrane pore size and the charge on the pore walls, transport of biomolecues through nanoporous membranes is strongly dependent on the size as well as the charge on the biomolecules. In this paper we do a systematic study to understand this transport using zinc oxide (ZnO) nanoparticles as the analogues for the biomolecules. The batch fabricated nanoporous membranes, with average pore size of 9 nm, were used for diffusion experiments on ZnO nanoparticles grouped as S1 (1-4 nm) and S2 (20-25 nm). The nanoparticles, S1 passed through the pores while the S2 did not due to the larger size. The charge on the S1 particles was varied, keeping the size constant by adding selective capping agents. The membrane and the pore walls develop a net negative charge in alcohol medium which facilitate the transport of neutral nanoparticles while impeding both the positively and negatively charged particles. Interestingly, both the neutral and slightly negative charged particles diffuse at more or less equal rates, while slightly positive charged material shows much less diffusion. This may be due to the enhanced blocking of the pores resulting from the electrostatic interaction between the particles and the pore walls. Transport of four different microorganisms of size 30 nm to 3 pm was also investigated and were found to be blocked by the membranes. (C) 2016 Elsevier B.V. All rights reserved.