The present disclosure relates to a metal nanoparticle sensor and fabrication method thereof. The metal nanoparticle sensor includes a SERS substrate, comprising a substrate, metal oxide nanostructures formed on the substrate, and metal nanoparticles grown on the metal oxide nanostructures. The metal oxide nanostructures include crystal facets. The metal nanoparticles substantially cover the crystal facets and the metal nanoparticles are grown in a vacuum chamber at an elevated substrate temperature.