The reader is able to distinguish the individual chemical bases of DNA

Tiny DNA reader could herald personalised medicine

A semiconductor DNA reader just nanometres across could make whole genome profiling for personalised medicine an everyday practice.

Using advanced semiconductor technology, known as atomic layer deposition, scientists have built a tiny device sensitive enough to distinguish the individual chemical bases of DNA – known by their abbreviated letters of A, C, T or G – when they are pumped past the reading head.

The team from Arizona State University (ASU) and IBM's T.J. Watson Research Center hope the technology could eventually be used to personalise medicine, by using patients’ DNA profiles to design treatments specific to their individual makeup.

"Our goal is to put cheap, simple and powerful DNA and protein diagnostic devices into every single doctor's office," said Professor Stuart Lindsay, director of the Center for Single Molecule Biophysics at ASU’s Biodesign Institute.

In a paper published in the journal ACS Nano, the team demonstrated proof-of-concept using solutions of the individual DNA bases, which gave clear signals sensitive enough to detect tiny amounts of DNA at levels better than today's state-of-the-art DNA sequencers.

The device consists of two metal electrodes separated by a two-nanometer-thick insulating layer, created using the atomic layer deposition process, before a hole known as a nanopore is cut through the entire structure.

When a current is passed through the nanopore, a spike in the current unique to each base in the DNA molecule is created as they pass the gap between the metal layers.

"The technology we've developed might just be the first big step in building a single-molecule sequencing device based on ordinary computer chip technology," said Prof Lindsay.

"Previous attempts to make tunnel junctions for reading DNA had one electrode facing another across a small gap between the electrodes, and the gaps had to be adjusted by hand. This made it impossible to use computer chip manufacturing methods to make devices.

"Our approach of defining the gap using a thin layer of dielectric (insulating) material between the electrodes and exposing this gap by drilling a hole through the layers is much easier.

"What is more, the recognition tunnelling technology we have developed allows us to make a relatively large gap compared to the much smaller gaps required previously for tunnel current read-out (which were less than a single nanometre wide).

“The ability to use larger gaps for tunnelling makes the manufacture of the device much easier and gives DNA molecules room to pass the electrodes."

The team encountered considerable device-to-device variation, so calibration will be needed to make the technology more robust and the final big step of reducing the diameter of the hole through the device to that of a single DNA molecule has yet to be taken.

The research team is also working on modifying the technique to read other single molecules, which could be used in an important technology for drug development.

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