What are Aptamers?

What are Aptamers?

Aptamers are single-stranded DNA or RNA molecules obtained through in vitro selection techniques (such as SELEX) from synthetic, randomized nucleic acid libraries. They can bind to target molecules (such as proteins, small molecules, cells, etc.) with high affinity and specificity through unique three-dimensional structures, earning them the titles “chemical antibodies” or “nucleic acid antibodies.”

Key Characteristics

1. Chemical Nature
   Mostly single-stranded DNA or RNA, producible via chemical synthesis, offering good stability and ease of modification or labeling.

2. Binding Mechanism
   Form hydrogen bonds, electrostatic interactions, etc., through spatial conformations (e.g., hairpins, pockets, bulges) to recognize targets with atomic-level precision.

3. High Affinity & Specificity
   Capable of distinguishing structurally similar molecules (e.g., caffeine vs. theophylline), with dissociation constants (Kd) reaching nanomolar (nM) or even picomolar (pM) levels.

4. Strong Stability
   Resistant to high temperatures, reversible denaturation, and less susceptible to damage in acidic/basic environments (especially DNA aptamers), making them suitable for complex applications.

Advantages Compared to Antibodies

Applications

1. Disease Diagnosis

   • Serve as recognition elements in biosensors (e.g., electrochemical, fluorescent sensors) to detect disease biomarkers (e.g., cancer proteins, viral antigens).

   • Used in point-of-care testing (POCT) devices, such as COVID-19 test strips.

2. Targeted Therapy

   • As drug carriers: Conjugated with chemotherapy drugs or nucleic acid therapeutics for precise delivery (e.g., the approved drug Macugen for age-related macular degeneration).

   • Direct inhibitors: Block pathogen proteins or cancer cell signaling pathways.

3. Cellular Imaging

   • Fluorescently labeled aptamers for in vivo or cellular imaging to track target distribution.

4. Food Safety & Environmental Monitoring

   • Detect toxins (e.g., aflatoxins), antibiotic residues, or pollutants.

5. Basic Research Tools

   • Used in protein function studies, cell sorting, etc.

Selection Technology: SELEX

SELEX (Systematic Evolution of Ligands by Exponential Enrichment) is the core method for aptamer selection:

1. Construct a nucleic acid library with 10¹³–10¹⁵ random sequences;

2. Incubate with the target and wash away unbound sequences;

3. Recover specifically bound sequences and amplify them via PCR;

4. Repeat for multiple rounds (typically 8–15) to enrich high-affinity sequences.
   Modern SELEX variants include cell-SELEX, automated microfluidic SELEX, etc.

Challenges and Prospects

• Challenges:
  Susceptibility to nuclease degradation (especially RNA aptamers; improvable via chemical modifications);
  Complex in vivo environments may affect conformation; high costs for large-scale production.

• Future Directions:
  Developing more stable locked nucleic acid (LNA) or peptide nucleic acid (PNA) aptamers;
  AI-assisted design to shorten selection cycles;
  Integrating nanotechnology for multifunctional diagnostic/therapeutic platforms.

As molecular recognition tools, aptamers are increasingly demonstrating potential to replace or complement traditional antibodies in fields like precision medicine and detection technology, making them a research hotspot at the intersection of chemical biology and nanomedicine.