1. What is SELEX? SELEX stands for Systematic Evolution of Ligands by EXponential enrichment. It is a laboratory technique used to identify aptamers—short single-stranded DNA or RNA sequences that can bind specifically to a target molecule (proteins, small molecules, cells, or even viruses). Aptamers act similarly to antibodies but are synthetic, highly stable, and can be chemically modified. 2. Principle of SELEX The SELEX process is based on iterative rounds of selection and amplification: Library Preparation Start with a large randomized pool of oligonucleotides (typically 10^13–10^15 unique sequences). Each sequence is a potential aptamer candidate. Binding (Target Incubation) Incubate the library with the target molecule. Only sequences that can bind the target will stay attached; non-binders are washed away. Partitioning (Separation of Binders and Non-binders) Physically separate bound sequences from unbound sequences. Techniques depend on the target (magnetic beads, affinity columns, etc.). Elution Bound sequences are eluted (released) from the target. Amplification The eluted sequences are amplified using PCR (for DNA aptamers) or RT-PCR (for RNA aptamers). This generates an enriched pool for the next round. Iterative Rounds Steps 2–5 are repeated for 8–15 rounds to gradually enrich sequences with high affinity and specificity for the target. Sequence Identification After…
