Active transport: a new chemical separation method?

The biological world offers continuous inspiration for investigators in the field of lab-on-a-chip and especially in nanofluidics where the old adage ‘Natura Artis Magistra’ (nature teaches the art) certainly seems to hold true. An active area of exploration is for example the use of motor proteins, that perform functions on chip fuelled by ATP. In this focus paper we want to draw the attention of the lab-on-a-chip community to a biochemical phenomenon that also involves the consumption of ATP but that to our knowledge has not yet been applied in analytical chemistry or lab-ona-chip, namely active transport. We will use this expression here in its common specialized sense, namely the active transport that takes place across the lipid bilayer membranes of biological organisms. Both primary and secondary active transport will be considered, that are performed by special families of proteins called, respectively, pumps and transporters. Living organisms operate these transporters and pumps amongst others to separate and concentrate ions and nutrients at locations where they benefit their survival. In this paper we propose to apply the same proteins for separation and concentration in chemical analysis. It will be argued that the properties of these molecules carry quite some promise for analysis, if we are able to contain them in a suitable environment. First we will introduce the proteins and their general characteristics, and show some applications that have already been demonstrated especially in conversion of photonic to chemical energy. Subsequently we will discuss some possible applications for chemical analysis. The considerable technological challenges and hurdles will in this context be considered.