There is provided a metal-based particle assembly comprising 30 or more metal-based particles separated from each other and disposed in two dimensions, the metal-based particles having an average particle diameter in a range of from 200 to 1600 nm, an average height in a range of from 55 to 500 nm, and an aspect ratio, as defined by a ratio of the average particle diameter to the average height, in a range of from 1 to 8, wherein the metal-based particles are disposed such that an average distance between adjacent metal-based particles may be in a range of from 1 to 150 nm. This metal-based particle assembly presents significantly intense plasmon resonance and also allows plasmon resonance to have an effect over a range extended to a significantly large distance.