Nanoparticle Photoacoustic Imaging Agents

The invention described herein relates to colloidal particles useful for photoacoustic imaging. The particles comprise a photoacoustic imaging agent with an absorbance maximum or plateau in the range of wavelengths 700-1100 nm. The imaging agent also displays low optical absorbance at some wavelength in the range 700-1100 nm. This combination of high and low optical absorbance enables background subtraction in photoacoustic imaging applications. The imaging agent is an organic compound having low aqueous solubility so that it is stably encapsulated in the hydrophobic core of the particle. The particle is stabilized by a polymeric surface coating, and the polymeric stabilizing layer on the surface of the particle may contain targeting ligands for targeted diagnostics or therapeutic delivery. The particle core may also contain therapeutic agents or other imaging agents.