Acoustic fingerprints of photoacoustic contrast agents for molecular imaging

Protein nanospheres capable of frequency controlled oscillation in response to laser stimulation are presented as contrast agents for photoacoustic imaging. Incident laser energy absorbed by dye-labeled protein nanospheres causes thermoelastically generated sound production. Plotted A-line graphs reveal a distinctive morphology and greater than 2 orders of magnitude increase in signal amplitude subsequent to converting labeled proteins into nanospheres. Evidence of nonlinearity and enhancement of ultrasound backscatter indicate a potential use in contrast-enhanced harmonic imaging. Photoacoustic and ultrasound imaging of protein nanospheres in phantom vessels show enhanced contrast at low concentration and clear delineation of the phantom vessel wall.