Covering the bases: Quantum effect may hold promise for low-cost DNA sequencing, sensor ap...(base pairs through techniques like optic...)

Lindsay believes there may be a radical solution.

Dr. Lindsay's technique for observing DNA sequences relies on devices known as scanning tunneling- (STM) and atomic force- (ATM) microscopes. He exploits these sensitive instruments to identify complementary DNA base pairs, evaluating the hydrogen bonds formed between them. Base pairing rules for DNA dictate that the hydrogen bonds work to join up appropriate nucleotide pairs like jigsaw piecesadenine with thymine and cytosine with guanine.

The scanning tunneling microscope used in the present study features a delicate electrode tip held very close to the DNA sample. When this tip is fitted with a particular nucleotide and brought in contact with its complementary mateembedded in the substrate, the hydrogen bonds stick the bases together and they attach, like tiny magnets (see fig. 1). As Lindsay describes the method, " you have sensing chemicals attached to one electrode and the target you want to sense attached to another one. When the junction spontaneously self-assembles, you get a signal. It's a new way of doing recognition at the atomic scale."

Crucial to the new technique is the fact that the strength of the glue fastening complementary bases differs for A-T and C-G pairs. While two hydrogen bonds hold A-T bases together, C-G pairs use three hydrogen bonds. For this reason, it's physically harder to break C-G bonds. By measuring the current drop in the electrical circuit formed between the microscope probe and the substrate as the hydrogen bonds are gently pulled apart, a positive identification of the base being read can be made. The new method, as Lindsay explains, combines chemical recognitionthe hydrogen bo
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