Fig 1. Outline of the experimental concept.

(a) SEIRAS optical cell with a droplet of the cell-free expression system to produce bacteriorhodopsin (bR) after addition of the encoding DNA. (b) Nanodisc as biomimetic membrane comprising a phospholipid bilayer (DMPC) wrapped by two amphiphilic membrane scaffold proteins. Each of the latter carry an N-terminal His-tag to bind the nanodiscs to a Ni-NTA modified surface. (c) In vitro transcription and translation system synthesizing the polypeptides, which insert into the surface-tethered monolayer of nanodiscs. As the surface enhancement decays exponentially with the distance with an effective length of about 10 nm, processes are exclusively probed by SEIRAS that occur at and within the nanodisc monolayer.