A kit for detecting a nucleic acid target comprising a container holding an aggregate probe, the aggregate probe comprising at least two types of nanoparticles having oligonucleotides attached thereto, the nanoparticles of the aggregate probe being bound to each other as a result of the hybridization of some of the oligonucleotides attached to them, at least one of the types of nanoparticles of the aggregate probe having oligonucleotides attached thereto which have a sequence complementary to a portion of the sequence of a nucleic acid target, wherein in the presence of said nucleic acid target and under hybridization conditions, the nanoparticles having oligonucleotides bound thereto form a complex with said nucleic acid target, the resulting nanoparticle-nucleic acid target complex having a sharp melting profile and an increased melting temperature, relative to a melting profile and a melting temperature of an analogous complex formed with said nucleic acid target and an unlabeled or fluorophore-labeled oligonucleotides having a sequence identical to the oligonucleotides bound to the nanoparticles, to allow for selective discrimination of a single nucleotide insertion, deletion, or mismatch in said nucleic acid target under stringent hybridization conditions, whereby the stringency of said hybridization conditions are higher than those possible for said analogous complex.