A conventional silicon naphthalocyanine-containing liposome is required to incorporate a dye dispersed therein for use in photodynamic therapy, and is thus low in dye content and also low in photoacoustic signal. According to a lipid particle containing a silicon naphthalocyanine analog, in which the ratio A/B of an absorption coefficient A at a first absorption local maximum to an absorption coefficient B at a second absorption local maximum in a range from 700 nm to 800 nm is 5.0 or less, the dye content in the lipid particle can be increased and the photoacoustic signal intensity can be improved.
