The steps in cell-SELEX technology resemble SELEX procedure. The DNA library, which is composed of 30-40 bases flanked by primer sequences, is being incubated with target cells in specific conditions. The unbound DNA probes are washed out and the bound ones are collected with heat denaturing. The eluant is then amplified by PCR or used for counter selection. Counter selection represents a step in cell-SELEX, where apatamer probes are incubated with negative (control) cells. This time the unbound probes are collected and amplified. The final step is composed of dsDNA amplification treated with streptavidin beads resulting in antisens strands with biotin retaining on the beads and sens strand elution with sodium hydroxide solution. At the end, eluted ssDNA represents the enriched library for the next round of cell- SELEX. To prove that high affinity ligands are being enriched, flow cytometry or fluorescence microscopy is used. The pool is usually composed of high affinity ligands after 15-25 cycles of the cell-SELEX procedure. In the last step the pool is cloned and sequenced to determine the sequence of enriched DNA pools.
