This proposal describes the development of a simple, rapid and cost effective 'spot and read' detection platform for single nucleotide polymorphisms (SNP's) based on gold nanoparticle probes. In phase I, it was demonstrated that the highly selective gold nanoparticle probes could be used for rapid and reliable SNP genotyping of PCR-amplified APC gene sequences containing the I1307K mutation. The colorimetric change generated by the probes when bound to DNA target was recorded by spotting onto a membrane and visualized using a simple flatbed scanner or the naked eye. In phase II, Nanosphere seeks to extend this new assay to large scale analysis of SNP's. This will be accomplished by developing a new spotting methodology and simple colorimetric reader/software package that enables multiple PCR samples to be spotted rapidly and analyzed for the presence of specific DNA sequences with minimal user intervention. These developments will then be used to rapidly extend the assay to other SNP's and mutations (e.g. insertions and deletions) related to colorectal cancer, breast cancer, and cardiovascular disease. The development of this technology will ultimately fill the void of a cost effective and reliable SNP detection platform that is both rapid and simple.