2 The abbreviations used are: RabGAP, Rab GTPase-activating protein; AS160, Akt substrate of 160 kDa; CBD, calmodulin-binding domain; [Ca 2ϩ ] i , intracellular Ca 2ϩ concentrations; MSD, mean square displacement; PTB, phosphotyrosine-binding; QD, quantum dot; AMPK, AMP-activated protein kinase; EGFP, enhanced green fluorescent protein; ECFP, enhanced cyan fluorescent protein; NPE, nitrophenyl-EGTA.

Photoacoustic (PA) imaging is a hybrid imaging technique with light-dependent contrast and ultrasound-dependent depth. In previous studies, the interest of PA imaging was mainly clinical research. However, in recent years, PA imaging that targets cells also has attracted attention. Cells are the smallest unit in our body, and cell abnormalities cause various diseases. Therefore, PA imaging of cells is important for elucidating the relationship between diseases and PA properties and linking the results to the clinical application of PA imaging. For PA imaging of cells and its internal structures, sub-micron lateral resolution is required. In this study, we have developed an optical resolution photoacoustic microscopy (OR-PAM) system using a high NA objective lens and a single-mode fiber to achieve sub-micron lateral resolution. With the OR-PAM, it was confirmed that the lateral resolution was better than 700 nm, and the characteristic shapes of red blood cells and melanoma cells could be visualized.