Can photoacoustic imaging quantify surface-localized J-aggregating nanoparticles?

We investigate the feasibility of photoacoustic (PA) imaging to quantify the concentration of surface-localized nanoparticles, using tissue-mimicking phantoms and imaging with a commercial PA instrument at 815 nm and a linear-array transducer at a center frequency of 40 MHz. The nanoparticles were J-aggregating porphysomes (JNP) comprising self-assembling, all-organic porphyrin-lipid micelles with a molar absorption coefficient of 8.7 x 10(8) cm(-1) M-1 at this wavelength. The PA signal intensity versus JNP areal concentration followed a sigmoidal curve with a reproducible linear range of similar to 17 fmol/mm(2) to 11 pmol/mm(2), i.e., similar to 3 orders of magnitude with +/- 34% error. For physiologically-relevant conditions (i.e., optical scattering-dominated tissues: transport albedo >0.8) and JNP concentrations above similar to 330 fmol/mm(2), the PA signal depends only on the nanoparticle concentration. Otherwise, independent measurement of the optical absorption and scattering properties of the underlying tissue is required for accurate quantification. The implications for surface PA imaging, such as in the use of targeted nanoparticles applied topically to tissue as in endoscopic diagnosis, are considered. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)