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Nano Science and Technology Institute 2005 NSTI Nanotechnology Conference & Trade Show
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Rapid DNA Sequence Identification based on Electrostatic Interactions with Unmodified Gold Nanoparticles

H.X. Li and L.J. Rothberg
University of Rochester, US

DNA, gold nanoparticle, detection, Au nanoparticles

Sequence-specific detection of DNA play more and more important role in clinical diagnosis and molecular biology research. Most assays identify specific sequence through hybridization of an immobilized probe to the target analyte after the latter has been modified with a covalently linked label such as a fluorescent or radioactive tag. Oligonucleotide detection schemes that avoid analyte tagging such as surface plasmon resonance, imaging ellipsometry and sandwich assays using chemically functionalized gold nanoparticles have been invented. These approaches use complex surface functionalization chemistry and/or expensive measurement instrumentation. The detection is slow. Recently we have developed very simple, fast assays without need of expensive instruments and complex procedures. Our assays are based on a new observation of the differential interaction between single-stranded and double-stranded oligonucleotides (ss-DNA and ds-DNA) with unmodified gold nanoparticles. We found that ss-DNAs adsorb to gold nanoparticles and can protect the gold nanoparticles from salt-induced aggregation, While ds-DNAs do not adsorb to gold nanoparticles and can not prevent the salt-induced aggregation. Our assay including colorimetric and fluorescence methods, in which hybridization is completely separate from detection so that it can be done under optimal conditions without steric constraints of surface bound probes that slow hybridization and make it less efficient. The assay is complete within five minutes. Single base pair mismatches are easily detected. Colorimetric detection can detect less than 100 fm target without instrumentation. Fluorescence method can detect 0.1 fm target under un-optimized condition.

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