Professor Lewis Rothberg of the University of Rochester Chemistry Department received a NYSTAR grant in August 2006 to continue working on a recent discovery by Huixiang Li, a research associate in his group: how to rapidly test DNA to improve our health and make sure we're drinking clean water and eating uncontaminated food. In fact, his new method can be used to help forensics labs identify criminals, test ponds and pools before children swim in them, and identify harmful genetic sequences in medical research, to name only a few applications. Rothberg's innovative procedure quickly and inexpensively identifies genetic sequences in any sample of DNA.

The technology is a novel fluorescent DNA screening assay, which rapidly determines whether specific DNA target sequences are present in an analyte. In simple terms, the analyte contains the DNA target sequences as well as other DNA sequences, and the assay filters out only the targets. Professor Rothberg's assay is based on the electrostatic properties of DNA.

The principle underlying the method is that single-stranded DNA and double-stranded DNA have significantly different affinities for attaching to ionically charged gold nanoparticles. Because ions have electric charges, having gained or lost electrons, they attract their opposites. An anion with a negative electric charge will attract positive charges, a cation with a positive charge will attract negative charges. Single-stranded DNA adsorbs on negatively charged citrate ions on the gold nanoparticles while double-stranded DNA does not. Given that both single-stranded and double-stranded DNA are (nominally) negatively charged, this proven phenomenon intrigues the research group.

The new assay determines whether a fluorescently-tagged short probe sequence of single-stranded DNA matches a sequence in the target analyte. When it does not, the fluorescently tagged probe adsorbs on a gold nanoparticle and its fluorescence is quenched. If the probe sequence is able to hybridize to the target, it will not adsorb on the gold and its fluorescence persists.


Posted by: Beverly    Source

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