DNA and RNA aptamers
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DNA and RNA aptamers

Date：2026-01-04

What Are Aptamers?

Aptamers (from the Latin aptus = “to fit,” and Greek meros = “part”) are short, single-stranded oligonucleotides (DNA or RNA) that fold into specific 3D shapes, allowing them to bind to a target molecule with high affinity and specificity. They are often called “chemical antibodies” due to their similar function, but they are made of nucleic acids, not proteins.

DNA Aptamers

  • Composition: Deoxyribonucleic acid.

  • Structure: Typically more rigid and stable than RNA due to the absence of the 2′-hydroxyl group, which makes it less prone to hydrolysis.

  • Key Features:

    • High Stability: Very resistant to degradation, especially compared to RNA. They are the more robust choice for diagnostic applications outside of controlled environments.

    • Ease of Synthesis: DNA is chemically simpler and cheaper to synthesize and modify at large scales.

    • Simpler Folding: DNA libraries can have less structural diversity than RNA, which may limit the complexity of binding pockets they can form.

  • Common Applications: Biosensors, diagnostic assays, as inhibitors in therapeutics.

RNA Aptamers

  • Composition: Ribonucleic acid.

  • Structure: The presence of the 2′-hydroxyl group allows for greater structural diversity and more complex folding (e.g., pseudoknots, tight loops). This often enables higher-affinity binding.

  • Key Features:

    • Structural Complexity: Can form a wider variety of intricate 3D shapes, leading to potentially higher specificity and affinity for challenging targets.

    • Lower Innate Stability: Highly susceptible to degradation by ubiquitous RNase enzymes. This is a major hurdle for therapeutic use in vivo.

    • Chemical Modifications: To overcome instability, RNA aptamers are almost always chemically modified (e.g., 2′-fluoro, 2′-O-methyl) during or after synthesis to resist nucleases.

  • Common Applications: Therapeutics (where high affinity is critical), research tools to study protein function, despite the need for stabilization.

How Are They Made? The SELEX Process

Both DNA and RNA aptamers are discovered through an in vitro evolutionary process called SELEX (Systematic Evolution of Ligands by EXponential enrichment).

  1. Library Creation: A vast, random synthetic library of ~10^14 different DNA or RNA sequences is generated.

  2. Incubation: The library is incubated with the target molecule (e.g., a protein, small molecule, or even a whole cell).

  3. Partitioning: Sequences that bind the target are separated from those that do not.

  4. Amplification: The bound sequences are amplified by PCR (for DNA) or Reverse Transcription-PCR (for RNA).

  5. Iteration: This cycle of binding, selection, and amplification is repeated 8-15 times, enriching the pool for the tightest-binding sequences.

  6. Cloning & Sequencing: The final pool is sequenced to identify the individual aptamer sequences.

Key Difference in SELEX: RNA SELEX requires an extra reverse transcription step to convert the selected RNA back into DNA for amplification, and then re-transcription back into RNA for the next round.

Comparison Table: DNA vs. RNA Aptamers

Feature DNA Aptamers RNA Aptamers
Chemical Stability High (resistant to hydrolysis) Low (susceptible to RNase degradation)
Structural Diversity Lower (simpler folds) Higher (complex folds, more functional groups)
Typical Affinity Good to High Often Very High (nM to pM range)
Cost & Synthesis Simpler, Cheaper More Complex, More Expensive
Therapeutic Use Easier to stabilize Requires heavy chemical modification
Key Advantage Robustness for diagnostics Binding performance & versatility

Key Applications

  1. Therapeutics: As antagonists to block pathogenic proteins (e.g., Pegaptanib/Macugen®, an anti-VEGF RNA aptamer for age-related macular degeneration, now discontinued but a landmark drug).

  2. Diagnostics: As capture/detection agents in biosensors (e.g., electrochemical, optical) for point-of-care testing.

  3. Targeted Drug Delivery: Aptamers can be conjugated to drugs, toxins, or nanoparticles to direct them to specific cells (e.g., cancer cells).

  4. Research Tools: To inhibit, localize, or detect specific proteins in cellular studies.

  5. Analytical Chemistry: As stationary phases in “aptamer-affinity chromatography” for protein purification.

Advantages Over Antibodies

  • In vitro selection (no animals needed).

  • Target molecules that are toxic or non-immunogenic.

  • Reversible denaturation: Can be heated and refolded reliably.

  • Easier modification: Chemical tagging is straightforward.

  • Smaller size: Better tissue penetration.

  • Low batch-to-batch variability.

Challenges

  • Susceptibility to Nuclease Degradation (especially RNA): Requires modification.

  • Rapid Renal Clearance (small size): Often need to be PEGylated or sized up.

  • Limited Commercial Availability: The toolkit is not yet as vast as for antibodies.

  • Potential for Non-Specific Binding: Due to the polyanionic sugar-phosphate backbone.

In summary, DNA aptamers are the workhorses for stable, cost-effective applications like diagnostics and sensors, while RNA aptamers, with their superior structural sophistication, are powerful candidates for high-performance therapeutics, albeit with greater stability challenges. The field continues to evolve with new modifications (e.g., XNA, or xeno-nucleic acids) and innovative SELEX methods to unlock their full potential.