Excellent choice! Aptamer Screening is the core process for discovering these synthetic, single-stranded DNA or RNA molecules that bind to a specific target with high affinity and specificity. It's often called SELEX (Systematic Evolution of Ligands by EXponential enrichment). Here’s a comprehensive breakdown of aptamer screening, from concept to modern advancements. 1. The Core Principle: SELEX The traditional screening method is an in vitro Darwinian evolutionary process. The basic cycle is repeated until a pool of high-affinity aptamers is obtained. Key Steps: Library Design: Start with a vast random-sequence oligonucleotide library (10^13 - 10^15 different molecules). Each molecule has a central random region (20-60 nucleotides) flanked by constant primer regions for PCR amplification. Incubation: The library is incubated with the target molecule (e.g., a protein, small molecule, cell). Partitioning: Unbound sequences are washed away. Bound sequences (potential aptamers) are retained. This is the most critical step, dictating the success of the entire screen. Elution: The bound sequences are recovered (e.g., by heating, denaturing agents, or target digestion). Amplification: The recovered sequences are amplified by PCR (for DNA) or RT-PCR (for RNA) to create an enriched pool for the next round. Iteration: Steps 2-5 are repeated (typically 5-15 rounds) under increasingly stringent conditions (e.g., shorter incubation time, more washes, competitive agents) to select…
