Photoacoustic probes and methods of imaging

A photoacoustic probe comprising:

• a targeting moiety, a non-fluorescent absorber compound, an enzyme cleavable linker, and a fluorescent compound, wherein the targeting moiety is linked to the non-fluorescent absorber compound and the enzyme cleavable linker, while the enzyme cleavable linker is linked to the fluorescent compound such that the fluorescent compound is separated from the targeting moiety and the non-fluorescent absorber compound by the enzyme cleavable linker, wherein the fluorescent compound has the characteristic of being able to absorb an optical energy and being able to generate a fluorescent signal, wherein the non-fluorescent absorber compound has the characteristic of being able to absorb the optical energy and being able to convert the absorbed energy to thermal energy to produce an acoustic signal, wherein the fluorescent compound more efficiently absorbs the optical energy relative to the non-fluorescent absorber compound, wherein the enzyme cleavable linker is capable of being cleaved by an enzyme so that the fluorescent compound is not attached to the photoacoustic probe, wherein the photoacoustic probe is configured to only significantly generate the fluorescent signal when the fluorescent compound is attached to the photoacoustic probe, and wherein the photoacoustic probe is configured to generate the acoustic signal when the fluorescent compound is not attached to the photoacoustic probe, and wherein the fluorescent absorber compound is a near infrared (NIR) dye.