Electrochemical coding of single-nucleotide polymorphisms by monobase-modified gold nanoparticles.

Rapidly increasing information about the human genome requires a fast and simple method for the detection of single-nucleotide polymorphisms (SNPs). To date, the conventional SNP detection technologies have been unable to identify all possible SNPs and needed further development in cost, speed, and sensitivity. Here we describe a novel method to discriminate and code all possible combinations. SNPs were coded by monitoring the changes in the electrochemical signal of the monobase-modified colloidal gold (Au) nanoparticles. First, a chitosan layer was formed on the alkanethiol self-assembled monolayer-modified Au nanoparticle. The monobases were then attached onto the chitosan-coated Au nanoparticles through their 5' phosphate group via the formation of a phosphoramidate bond with the free amino groups of chitosan. The size of the surface-modified Au nanoparticle was found to be 8.46 +/- 1.53 nm by using atomic force microscopy. If there is a SNP in DNA and the mismatched bases are complementary to the monobase, Au nanoparticles accumulate on the electrode surface in the presence of DNA polymerase I (Klenow fragment), thus resulting in a significant change in the Au oxide wave. In this report, monobase-modified Au nanoparticles show not only the presence of a SNP, but also identify which bases are involved within the pair. Especially, the identification of a transversion SNP, which contains a couple of the same pyrimidine or purine bases, is greatly simplified. A model study was performed by using a synthetic 21-base DNA probe related to tumor necrosis factor (TNF-alpha) along with its all possible mutant combinations. This versatile nanoparticle-based electrochemical protocol is a promising candidate for coding all mutational changes.