Multiallelic DNA sensors for molecular traceability of olive oil varietal origin

Olive oil, besides its nutritional value and unique organoleptic characteristics, offers multiple health benefits due to the abundance of bioactive compounds. Identification of cultivar origin is an important and challenging task. Methods based on metabolite profile changes between olive cultivars require advanced spectroscopy and chromatography instrumentation along with powerful chemometric tools. Molecular methods are the most accurate, because DNA is unaffected by environmental conditions, soil composition and harvest period, but also require advanced instrumentation, e.g., sequencing, capillary electrophoresis, and flow cytometry with laserinduced fluorescence detection. Contrary to all the methods reported, we have developed DNA sensing devices for olive oil cultivar verification, which are disposable, multianalyte sensors enabling simultaneous nakedeye detection of variety-specific combinations of multiple alleles. The method comprises PCR amplification, DNA polymerase-driven allele discrimination and application on the devices in which the fragments are captured via hybridization and visualized by antibody-functionalized gold nanoparticles generating an 8-spot color string for 8 alleles. The accuracy of the method was evaluated with 7 olive cultivars and the results were in full concordance with sequencing data. The proposed strategy may find broader applications to cultivar origin traceability of important agri-food products.