How Oligonucleotide Synthesizers Work (And What You Need to Run Them)

Introduction

Oligonucleotide synthesizers automate a complex chemical process into a reliable, repeatable workflow. Understanding how they work — and what they require — is essential before bringing synthesis in-house.

How Oligonucleotide Synthesis Works

Most synthesizers use solid-phase phosphoramidite chemistry, building oligos in the 3′ → 5′ direction through a repeating four-step cycle:

1. Deblocking (Detritylation)
   Removes the DMT protecting group to expose a reactive hydroxyl group.
2. Activation & Coupling
   An activated phosphoramidite binds to the growing oligo chain.
3. Capping
   Unreacted sites are blocked to prevent truncated sequences from extending.
4. Oxidation (or Sulfurization)
   Stabilizes the newly formed linkage.

This cycle repeats until the full sequence is complete. The oligo is then cleaved from the solid support and deprotected before purification.

Essential Raw Materials

Running a synthesizer requires:

• Solid supports (typically CPG)
• DNA, RNA, or modified phosphoramidites
• Anhydrous acetonitrile
• Deblocking acids (DCA or TCA)
• Activators (e.g., ETT)
• Capping reagents
• Oxidizers or sulfurizing reagents
• Deprotection solutions 
• Dry inert gas (argon or nitrogen)
• Application-specific consumables

Some reagents — such as methylamine — may require special permits.

Why Reagent Quality Matters

Even small amounts of moisture or degraded reagents can dramatically reduce coupling efficiency and final yield. Proper storage, handling, and bottle configuration are critical for consistent success.

👉 Next up: How to choose the right oligonucleotide synthesizer for your throughput and application needs.