A novel, homogeneous and sensitive assay for the detection of single nucleotide polymorphisms (SNPs) by integration of rolling circle amplification (RCA) and cationic conjugated polymer (CCP) has been developed and tested. Mutant DNA serves as the template for specifically circularizing a padlock probe (PLP) with a sequence that is complementary to the mutant DNA. Afterwards, the mutant DNA directly acts as the primer to initiate the RCA reaction in the presence of phi29 DNA polymerase that generates a long, tandem single-strand DNA product. During the RCA reaction, fluorescein-labeled dUTPs are incorporated into the RCA products. When the CCP is introduced, efficient FRET from CCP to fluorescein occurs as a result of the strong electrostatic interactions between the CCP and the DNA produced by RCA. The wild-type DNA contains a single base mismatch with PLP with the result that the PLP is not circularized, RCA is not triggered and inefficient FRET results. By measuring the change of the emission intensities of CCP and fluorescein, it was possible to detect the SNP in a homogeneous manner. The method is sensitive and specific enough to detect 0.1 pmol/L mutant DNA and to determine a mutant allele frequency as low as 2.0%. Single-nucleotide polymorphisms (SNPs) are the most common type of genetic variation. Cationic conjugated polymers (CCPs) with a large number of repeated absorbing units can transfer the excitation energy along the whole CCP backbone to the chromophore reporter [12]. Because of their unique light-harvesting properties, CCPs provide an effective platform for homogeneous SNP detection based on the formation of polyelectrolyte complexes stabilized by electrostatic interactions between the CCPs and negatively charged DNA. When a fluorophore-labeled nucleotide is incorporated into the DNA chain during the primer extension reaction at an SNP