According to an example, methods for forming three-dimensional (3-D) nano-particle assemblies may include depositing surface-enhanced spectroscopy (SES) elements onto respective tips of nano-fingers, in which the nano-fingers are arranged in sufficiently close proximities to each other to enable the tips of groups of adjacent ones of the nano-fingers to come into sufficiently close proximities to each other to enable the SES elements on the tips to be bonded together when the nano-fingers are partially collapsed. The methods also include causing the nano-fingers to partially collapse toward adjacent ones of the nano-fingers to cause a plurality of SES elements on respective groups of the nano-fingers to be in relatively close proximities to each other and form respective clusters of SES elements, introducing additional particles that are to attach onto the clusters of SES elements, and causing the clusters of SES elements to detach from the nano-fingers.