Visual detection of sub-femtomole DNA by a gold nanoparticle seeded homogeneous reduction assay: toward a generalized sensitivity-enhancing strategy.

Gold nanoparticles (AuNPs) have been employed to design colorimetric visual sensing assays toward the detections of various targets including DNA, based on the aggregation induced color transitions of AuNPs. However, the relatively high detection limit (LOD 10nM) in the case of DNA detection has become a stumbling block on the road of the further development and applications of these assays. This research aims at overcoming this limit by virtue of a seeded gold reduction strategy. Typically, low concentrations of 13 nm AuNPs modified with suitable DNA probes are allowed to hybridize with a DNA target to form aggregates, which are then transferred into a gold-enhancing cocktail for further depositions of more gold on the initial AuNP seeds. The color of the assay thus sensitively reflects the initial aggregation status of the 13 nm AuNPs, which can be related to the concentrations of the DNA target. This assay has a sensitivity that is at least 25-50 times improved. Under still not fully optimized conditions, 0.4 fmol DNA in a 2 microL sample can be confidently detected with the ability of distinguishing a single base mutation. It does not require isolations of the 13 nm AuNP aggregates during analyses and shares the advantages of a homogeneous assay, including simplicity, adaptability, convenience, and being free of interferences due to non-specific surface adsorptions.