A method for detecting an ingredient in a food product or detecting a disease includes allowing a food sample solution obtained from a food product or a body fluid from an individual to come to contact with a nano-scale surface structure in a sensor, wherein the nano-scale surface structure comprises a plurality of columns over a substrate or a plurality of holes in a substrate. The method includes illuminating the food sample solution or the body fluid on the nano-scale surface structure on the sensor by a laser beam; obtaining a Raman spectrum from the scattered light using a spectral analyzer; and identifying the spectral signature in the Raman spectrum to determine the existence of the chemical substance in the food product or identifying a disease in the individual.