The invention relates to core-shell particles comprising a shell which forms a matrix, and a core which is essentially solid and has an essentially monodisperse size distribution, the refractive index of the core material being different from that of the shell material. The invention especially relates to the use of said particles for producing sensors for detecting mechanical forces and sensors having an optical effect, essentially consisting of core-shell particles comprising a shell which forms a matrix and a core which is essentially solid and has an essentially monodisperse size distribution, the refractive index of the core material being different from that of the shell material. The inventive particles are characterised in that at least one contrast material is stored in the matrix.