This video explains Roche's innovative Sequencing by Expansion (SBX) technology, a method designed to overcome the physical limitations of resolving closely spaced DNA bases. The technology synthesizes a surrogate molecule, called an "expander," which is over 50 times longer than the original DNA template. This is achieved using novel nucleotides (xNTPs), each carrying a large, high-signal "reporter" that corresponds to one of the four DNA bases. After synthesis, the expander is threaded through a biological nanopore. A Translocation Control Element (TCE) within each reporter momentarily holds it in the pore, generating a distinct electrical signal that identifies the base. A voltage pulse then advances the expander to the next reporter. This process is massively parallelized on a CMOS sensor, enabling extremely high, real-time sequencing rates.
Roche's Sequencing by Expansion (SBX): A Nanopore-Based Approach
0:00:06 The Fundamental Challenge: DNA bases are separated by only 3.4 angstroms, a distance too small for many sequencing methods to resolve easily.
0:00:16 The SBX Solution: Sequencing by Expansion (SBX) technology creates a physically expanded surrogate molecule, the "expander," which is over 50 times longer than the target DNA, making it much easier to read.
0:00:38 Novel Building Blocks (xNTPs): The expander is built from four types of novel nucleotides called xNTPs (A, C, G, and T).
0:00:46 Expander Synthesis: Using a modified DNA replication process, xNTPs are linked sequentially along the target DNA template, creating a new molecule that encodes the original DNA sequence information into its structure.
0:01:04 High-Signal Reporters: Each xNTP contains a large, high signal-to-noise "reporter" molecule attached via a tether. The identity of the reporter mirrors the identity of the DNA base it represents.
0:01:20 Translocation Control Element (TCE): Located in the center of each reporter, the TCE is a key component that precisely modulates the expander's movement through the nanopore during the sequencing phase.
0:01:55 Creating the Expander: After synthesis, a reagent degrades the original DNA template and cleaves a bond in the xNTP backbone, allowing the molecule to physically expand.
0:02:11 Electrical Reading via Nanopore: The expander is threaded through a biological nanopore. The TCE holds each reporter in the pore, altering the electrical resistance to generate one of four unique signals that identifies the corresponding DNA base.
0:02:37 Step-Wise Advancement: After a base is read, a short, high-voltage pulse is applied to reliably advance the expander to the next reporter for measurement.
0:02:46 Massive Parallelization and Speed: This process is performed simultaneously across millions of wells on a single CMOS-based sensor, achieving remarkable real-time sequencing rates of hundreds of millions of bases per second.