A general answer ist difficult, clearly. One important propertie of nano particles are that their can pass the blood-brain barrier. Searching with the key words "blood-brain barriere" plus "nano particles" will give you a lot of literature.
Various tissues in the body allow the various substances enter to the cells but some of them is limited to permeability just allow those substances in very small size especially blood brain barrier of brain tissues for example , nano particle I may affect on brain cells