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.

Despite successful clinical application of non-equilibrium atmospheric pressure plasma (APP), the details of the molecular mechanisms underlying APP-inducible biological responses remain ill-defined. We previously reported that exposure of 3T3L1 cells to APP-irradiated buffer raised the cytoplasmic free Ca 2+ ([Ca 2+ ] i) concentration by eliciting Ca 2+ influx in a manner sensitive to transient receptor potential (TRP) channel inhibitors. However, the precise identity of the APP-responsive channel molecule(s) remains unclear. In the present study, we aimed to clarify channel molecule(s) responsible for indirect APP-responsive [Ca 2+ ] i rises. siRNA-mediated silencing experiments revealed that TRPA1 and TRPV1 serve as the major APP-responsive Ca 2+ channels in 3T3L1 cells. Conversely, ectopic expression of either TRPA1 or TRPV1 in APP-unresponsive C2C12 cells actually triggered [Ca 2+ ] i elevation in response to indirect APP exposure. Desensitization experiments using 3T3L1 cells revealed APP responsiveness to be markedly suppressed after pretreatment with allyl isothiocyanate or capsaicin, TRPA1 and TRPV1 agonists, respectively. APP exposure also desensitized the cells to these chemical agonists, indicating the existence of a bi-directional heterologous desensitization property of APP-responsive [Ca 2+ ] i transients mediated through these TRP channels. Mutational analyses of key cysteine residues in TRPA1 (Cys421, Cys621, Cys641, and Cys665) and in TRPV1 (Cys258, Cys363, and Cys742) have suggested that multiple reactive oxygen and nitrogen species are intricately involved in activation of the channels via a broad range of modifications involving these cysteine residues. Taken together, these observations allow us to conclude that both TRPA1 and TRPV1 channels play a pivotal role in evoking indirect APPdependent [Ca 2+ ] i responses. Recent innovative plasma technologies allow us to generate non-equilibrium atmospheric pressure plasma (APP), and have thus garnered a great deal of attention due to their biomedical and biotechnical applications. Indeed, direct or indirect application of APP to clinical targets has been successfully employed for wound healing, blood coagulation, the sterilization of surfaces, cancer therapy, and so on 1,2 , though the precise molecular mechanisms underlying these APP-mediated benefits have yet to be elucidated. While direct application of APP generates charged particles, ultraviolet radiation, electromagnetic fields, and shockwaves 3 , APP also has the capability to produce a variety of reactive oxygen and nitrogen species (RONS), including superoxide radical (O 2 •−), peroxynitrite anion (ONOO −) and nitric oxide radical (• NO) from oxygen (O 2), nitrogen (N 2), and water (H 2 O) in ambient air, which can be efficiently delivered into an aqueous biological medium 4. Given the physiological and pathophysiological importance of RONS in regulating a wide array of biological functions 5,6 , these reactive species generated in the medium via gas-liquid interfacial APPs are regarded a...