Optical Observation of Ultrasound Phenomena in Nano-Sized Spot by Using Spatiotemporal Analysis of Radial Fluorescence Fluctuation

We propose a method to observe ultrasound phenomena in the nano-sized area by transferring to the hydrogel network occurring around supersaturated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{CO}_{2}$</tex> liposomes. The image analysis method increased the resolution from 270 nm to several tens of nm. The pore size of the hydrogel network around the supersaturated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{CO}_{2}$</tex> liposomes tended to increase with the irradiation of MHz-band ultrasound. In particular, at 2.5MPa, the pore size increased by about 20 nm from that before ultrasound irradiation. This is indicated to be due to the expansion of the nano-vibrating nucleus or the amplitude of the vibration of supersaturated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{CO}_{2}$</tex> liposomes.