Switching-type fluorescent nanoparticle probe, and fluorescent molecular imaging method using same

A fluorescent nanoparticle probe comprising:

• a molecular assembly composed of an amphiphilic block polymer having a hydrophilic block chain and a hydrophobic block chain;
• and
• a fluorescent dye encapsulated in the molecular assembly, wherein
• (a) an essential hydrophilic structural unit is defined as a unit selected from a sarcosine unit and an alkylene oxide unit, and the hydrophilic block chain has 20 or more essential hydrophilic structural units,
• (b) an essential hydrophobic structural unit is defined as a unit selected from the group consisting of an amino acid unit and a hydroxylic acid unit, and the hydrophobic block chain has 15 or more essential hydrophobic structural units, and
• (c) the fluorescent dye is a polylactic acid-bound cyanine compound comprising:
• a fluorescent group represented by the following structural formula (I):
• wherein R1 is a hydrocarbon group which may be substituted, and R2 is a bivalent hydrocarbon group which may be substituted;
• A′ is an anion and m is 0 or 1;
• a ring B and a ring D may be the same or different from each other and each is a nitrogen-containing heterocycle;
• and L is a linking group that constitutes a polymethine chain, which may include a ring structure, and which may be substituted;
• and
• a polylactic acid group having 5 to 50 lactic acid units, and
• two or more molecules of the fluorescent dye are encapsulated in a self-quenching state by association in the single molecular assembly,
• wherein the fluorescent dye is encapsulated in the molecular assembly in an amount of 5 to 20 mol % with respect to a total amount of the amphiphilic block polymer and the fluorescent dye so that the fluorescent nanoparticle remains self-quenching state by contact with a blood component.