Colorimetric detection of DNA by using target catalyzed DNA nanostructure assembly and unmodified gold nanoparticles

The authors describe a strategy for colorimetric detection of DNA. It is making use of a target catalyzed DNA nanostructure assembly and gold nanoparticles. The assay comprises the following steps: (a) A programmed DNA nanostructure is assembled from three auxiliary hairpin structure DNAs and the single stranded DNA (ssDNA; the target/analyte); (b) in the presence of target DNA, these three hairpin DNAs are opened, thereby activating a catalytic self-assembly process via a target assisted toe-hold strand displacement reaction; (c) The formed DNA nanostructures are mixed with gold nanoparticles. As the DNA nanostructure is less stabilized without ssDNA sticky ends, it cannot prevent the gold nanoparticles (AuNPs) to undergo salt-induced aggregation which is accompanied by a color change from purple to blue; (d) The color change of the colloid solution can be read out with bare eyes or instrumentally. The detection limit by using UV–vis spectrometry is 0.6 pM of target DNA. This is comparable to previously AuNP-based methods. Thus, this assay provides free modification detection based on DNA nanostructure without sophisticated procedures. Conceivably, the method can be applied to numerous other DNA targets.