Aptamer Development Service: Introduction to Aptamer Screening – SELEX

Date：2025-12-18

Key Strengths of Your Description:

Scale of Diversity: Highlighting the library size (up to 10^15 unique sequences) is crucial. This immense diversity is the starting pool from which “winners” are found.
Structure of Library: You correctly note the design: a central random region (for binding diversity) flanked by fixed primer regions (for PCR amplification).
Iterative Cycles: The heart of SELEX is the repeated cycle of Binding -> Partitioning (Washing) -> Elution -> Amplification. Each round increases the proportion of high-affinity binders.
Importance of Conditions: Emphasizing the control of buffer, pH, temperature, etc., is key. These counter-selection or negative selection steps are vital to ensure the resulting aptamers bind specifically to the target (e.g., a protein’s active site) and not to the container or other irrelevant components.

A Slightly Expanded Framework for Clarity:

To complement your text, here’s a visual summary of the classic SELEX cycle:

The Classic SELEX Cycle (Visualizing Your Description):

[Step 1: INCUBATION]
Combinatorial Library (10^15 sequences) + Target Molecule
|
[Step 2: PARTITIONING]
|-> Bound Sequences (to target) --[ELUTION]--> Recovered Aptamer Candidates
|-> Unbound Sequences (washed away)
|
[Step 3: AMPLIFICATION]
Recovered Candidates --[PCR (DNA) / RT-PCR (RNA)]--> Enriched Library
|
[Step 4: REPETITION]
New Enriched Library ---(Return to Step 1 for next round, 8-15 rounds typical)--->
|
[Final Step: CLONING & SEQUENCING]
Highly Enriched Pool -> Individual Sequences -> Identify Conserved Motifs -> Synthesize & Characterize

Evolution Beyond the “Classic Way”:

Your introduction correctly labels this as the conventional method. Modern aptamer development services now employ advanced SELEX variants to address challenges of the classic protocol:

Increased Efficiency & Reduced Bias:
- Capillary Electrophoresis SELEX (CE-SELEX): Uses charge-to-mass ratio for separation, enabling fewer rounds and very high affinity.
- High-Throughput Sequencing (HTS): Used after each round to monitor enrichment in real-time, preventing the loss of good candidates and allowing earlier stopping.
- Microfluidic SELEX: Automates and miniaturizes the process on a chip, reducing reagent use and time.
Expanding Target Range & Stability:
- Cell-SELEX: Uses whole living cells as targets to find aptamers for unknown surface biomarkers (e.g., for cancer cells).
- Toggle SELEX: Alternates targets between two related species (e.g., human and mouse protein) to find cross-reactive aptamers.
- Modified Nucleotide SELEX: Incorporates chemically modified nucleotides (e.g., 2′-F, 2′-OMe) during library synthesis to enhance nuclease resistance for therapeutic use.