As a model system, we have taken a therapeutically relevant aptamer (MinE07) which binds to the epidermal growth factor receptor (EGFR), a transmembrane receptor tyrosine kinase and a validated extracellular target in the treatment of cancer. Our approach was to create a one-bead-onecompound library of modified aptamers which could then be sorted using a flow cytometer which would provide accurate control of selection gating and in-line analytical data, followed by sequencing by mass spectrometry, and validation. We identified six key steps necessary for the SOLFABS process: