Methods and kits for the detection of DNA

A method for detecting a target deoxyribonucleic acid (DNA) in a sample, the method comprising:

• a) contacting the sample with a plurality of metal nanoparticles functionalised with one or more ribonucleic acid (RNA) probes;
• b) forming a heteroduplex between the target DNA and RNA probe on an RNA-functionalised metal nanoparticle;
• c) contacting the heteroduplex of target DNA and RNA probe on the RNA-functionalised metal nanoparticle with an enzyme that cleaves RNA in a DNA-RNA heteroduplex thereby releasing the target DNA;
• d) repeating steps (b) and (c) until all, or substantially all, of the RNA probes on the plurality of RNA-functionalised metal nanoparticles have been cleaved from the metal nanoparticles;
• and
• e) aggregating the metal nanoparticles from which all, or substantially all, of the RNA probes have been cleaved,
• wherein the aggregating is performed in the presence of a salt in a final concentration of from about 0.5 to 10M, thereby indicating the presence of the target DNA, and wherein limit of the detection of said method is about ≤1 pM.