Disclosed herein are multifunctional nanoparticles, comprising: polymer nanoparticles formed by loading a drug into a polymer; a gold thin film deposited on a portion of the surface of the polymer nanoparticles; and an antibody to a substance expressed on the surface of a cell to which the drug is to be delivered, the antibody being conjugated to the gold thin film. Also disclosed is a method for preparing multifunctional nanoparticles, the method comprising the steps of: loading a drug into a polymer to prepare polymer nanoparticles; depositing a portion of the surface of the polymer nanoparticles with a gold thin film; conjugating to the gold thin film an antibody to a substance expressed on the surface of a cell to which the drug is to be delivered; and separating from the resulting nanoparticles those in which a portion of the surface of the polymer nanoparticles is deposited with the gold thin film and conjugated with the antibody. Furthermore, disclosed are a composition containing the multifunctional nanoparticles and a method for diagnosing and treating disease using the composition.