PCR is normally needed to amplify the quantity of natural DNA samples for visual detection before they can be detected. For point-of-care applications in particular, the need for a PCR machine is cumbersome. In this communication, the researchers demonstrate a method for specific visual detection of a DNA sample without the need for PCR.
Gold nanoparticles are often coated with ligands for target specific detection. The different inter-particle distances provide a visual output when the target is added. Well-dispersed gold nanoparticles appear read and as the distance decreases this colour changes down the spectrum to purple and then to blue. Aggregation of the nanoparticles causes them to precipitate as black or grey sediments. It has been shown before that synthetic DNA sequences can be detected in this way using thiolated ligands. This study uses double stranded DNA samples at room temperature – surprising as single stranded DNA is optimal for adsorbing to the gold nanoparticle surface.
The researchers test their simple assay on genomic DNA extracts from Salmonella enterica. The sensitivity of the system leaves much to be desired compared to when PCR is used, however this easy protocol at room temperature with readily available agents and no need for electricity has some great advantages. The lack of PCR in detection of genomic DNA is a positive step forward for point-of-care diagnostics.
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Direct visual detection of Salmonella genomic DNA using gold nanoparticles
Kamaladasan Kalidasan, Jia Ling Neo and Mahesh Uttamchandani
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