Molecular separation in the lipid bilayer medium: electrophoretic and self-spreading approaches

Molecular separation in a microchannel is a key technology for future miniature devices. Because of growing advances in microfabrication techniques, we now have various choices of microscopic molecular separation systems. Recent progress in this field is reviewed in this manuscript. In particular, the use of the lipid bilayer as a separation medium is highlighted, because of its possible application to the manipulation of relatively small biomaterials such as membrane proteins and lipids. In this context, an approach based on electrophoresis is reviewed for molecular separation in the bilayer. Although the methods based on electrophoresis are effective, we will also focus on their limitation, i.e., only charged molecules can be manipulated. To solve this dilemma, we review new techniques based on the self-spreading nature of the lipid bilayer. In this method, there is no need to input an external field, such as an electric field, to achieve molecular separation. Phenomenological insights into the self-spreading nature and newly proposed molecular separation effects are shown in detail. This novel concept enables us to establish a completely unbiased molecular separation system in future microscopic and nanoscopic devices.