Colorimetric genotyping of single nucleotide polymorphism based on selective aggregation of unmodified gold nanoparticles.

We have developed a colorimetric method for genotyping of single nucleotide polymorphism (rs2131877) in 15 human DNA samples using selective aggregation of unmodified gold nanoparticles. First, we designed two different types of oligonucleotide probes with either thymine or cytosine at the end that are perfect complementary to the target allele sequence. After hybridization of the probe and target DNAs, the double-stranded DNA was added to the unmodified gold nanoparticle suspensions. By adjusting the salt concentration, we could induce aggregation of gold nanoparticles exclusively for the samples with the perfectly matched double-stranded DNAs, which resulted in a distinct color change of the suspension. This enabled us to discern samples with three different genotypes of the target sequences by naked eye: (i) the genotype with only T (thymine) alleles; (ii) that with only C (cytosine) alleles; (iii) that with both T and C alleles. We also confirmed these results by an independent direct sequencing method. These results suggest that the selective aggregation of unmodified gold nanoparticles can successfully be used to discern genotypes of single nucleotide polymorphisms.