A novel method for point mutation detection was developed. This approach combined the optical properties of gold nanoparticles with the specificity of allele-specific amplification (ASA). K-ras oncogene was studied for its possible point mutation at codon 12. In ASA, only the mutant K-ras gene can be amplified using the mutant-specific primers. Thus, the mutant amplification products were made of mostly double-stranded DNA, while the wild-type products were made of mostly unconsumed single-stranded DNA. Unmodified gold nanoparticles were used as reported groups. The amplification products were mixed with the gold colloid, followed by addition of salt solution. Because single- and double-stranded DNA have different electrostatic interactions with gold nanoparticles, only the gold nanoparticles in the wild-type mixtures did not aggregate due to the adsorption of ss-strand DNA. Therefore, the two kinds of genotype mixtures gave different absorption spectra and colors were observed easily by naked eyes. This new method is rapid, simple, low cost, and will offer a broad application for point mutation detection.

Key words: gold nanoparticle, surface plasmon peak, allele-specific amplification, point mutation