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A novel spectroscopic technique based on single-particle plasmon resonance is developed and used to study the metal-insulator phase transition of vanadium dioxide (VO₂) - a prototypical correlated insulator. Two characteristics responsible for the Mott transition are observed indirectly by monitoring the plasmon response variation of individual Au nanoparticles deposited on a thin VO₂ film when thermally cycling through the metal-to-insulator transition of VO₂. This nanospectroscopy technique opens promising possibilities for studying the phase transition in a general class of correlated electron materials with simultaneous nanoscale spatial resolution and ultrasensitive spectroscopic characterization.

single-particle plasmon resonance nanospectroscopy; Mott transition; vanadium dioxide