DNA sequencing through nanopores typically requires a motor protein to ratchet the strand through the pore one base at a time. The protein controls the translocation speed — without it, the strand zips through too fast to read. But the protein adds complexity, limits throughput, and requires biological reagents.
Cressiot, Greive, and Bhatt demonstrate protein-free sequencing by electrostatic unzipping. Double-stranded DNA approaches the pore; the electric field peels one strand away, forcing the remaining strand through base by base. Each base blocks the ionic current differently, producing a characteristic signal. The unzipping itself provides the ratcheting — each base-pair separation is a discrete mechanical step that advances the strand by exactly one nucleotide.
The error rate is below 5% per base, achieved purely through the electrostatic mechanics of unzipping — no enzyme, no chemical modification, no feedback control. The signal-to-noise comes from the discrete nature of base-pair breaking: each unzipping event produces a measurable dwell-time step whose duration depends on the base identity and the local sequence context.
The method works with solid-state nanopores — fabricated holes in synthetic membranes — rather than biological nanopores. Solid-state pores are more robust, more reproducible, and more scalable than their biological counterparts, but they lacked the single-base resolution that motor proteins provided in biological systems. The unzipping mechanism restores single-base resolution without the motor.
DNA sequencing reduced to physics: an electric field, a hole, and the mechanics of peeling apart a double helix one base at a time.