A new type of contrast agent is described, which comprises matrix particles with a plurality of metal nanoparticles as well as the method of imaging therewith. A plurality of metal nanoparticles are encapsulated in a non-proteinaceous biocompatible or biodegradable matrix particle and/or attached to a non-proteinaceous biocompatible or biodegradable matrix particle, the matrix of the matrix particles being selected from the group consisting of a carbohydrate, a lipid, a synthetic polymer, an aqueous liquid, a surfactant and an organic liquid, or a mixture thereof. The matrix particles are biocompatible and/or biodegradable and can be coupled to targeting molecules for targeted visualization.
