A label-free two-dimensional colorimetric DNA sensor is reported. This sensor is based on the 2D aggregation of oligonucleotide-modified gold nanoparticle probes induced by the molecular hybridization of single-stranded oligonucleotide probes and their complementary single-stranded DNA targets. To detect the aggregation, we have developed a new detection method based on the selective desorption of nonaggregated nanoparticles. We will show here that this detection method is highly specific and allows the quantification of the DNA targets.