The safety of food and other consumables has caught intensive attention worldwide for better quality of life. Raman spectroscopy is one of the most powerful methods in testing applications such as food, beverages, drugs, pollutants and explosives. We invented a new type of substrates for dramatically amplifying Raman signals and pushing the molecular detection limit down to the unprecedented level. The substrates are based on colloidal noble metal nanoparticles that are flexible in applications, diverse, upgradable and at low cost.