A single nucleotide potymorphism (SNP) base on the target is displayed at a gap in a ternary duplex carrying B-cyclodextrin-modified DNA. A stable tandem duplex forms regardless of the type of SNP base. A nucleobase-specific ligand is then added to this system. The dansyl moiety in the ligand is expected to form a luminous inclusion complex with nearby B-CyD, only when the ligand recognizes the specific base displayed in the gap.