Figure 1. Schematic overview of a selection round using Bead Surface Display (BeSD).

(1) The DNA template, a streptavidin-coated magnetic bead, benzyl guanine (BG)-conjugated primers and biotin (BB)-conjugated primers are encapsulated in water-in-oil droplets, in such a way that the Poisson distribution dictates that there is no more than one DNA template per bead; (2) DNA is amplified by emulsion PCR (ePCR) to give >10⁶ copies, of which ~100–1,000 copies are captured on-bead; (3) the droplet contents are de-emulsified and the beads are washed; (4) BG-BB DNA anchors are added (as additional valencies for display); (5) compartmentalisation of single beads together with IVTT (in vitro transcription/translation) mix in water-in-oil droplets; (6) protein is expressed from the bead-immobilised templates (4 hour expression at 25 °C); (7) de-emulsification liberates beads that are now displaying the protein of interest (e.g., SNAP-scFv-HA), followed by washes to remove the IVTT mixture and unbound excess of expressed protein; (8) incubation with the target (FasR-Fc) followed by washes to remove unbound target; (9) incubation with secondary antibody (anti-Fc DyLight^®488); (10) washes to remove excess detection antibody; (11) beads that bind (and show fluorescence above a chosen threshold) are sorted by flow cytometry (FACS) at a rate of ~10⁶ per hour; (12) recovery of the DNA that encoded clones identified as binders. The Figure was adapted from Diamante et al.³¹ which is available under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/).