16:00 〜 18:00
▲ [16p-P10-5] Femtosecond Laser Trapping and Ejection Dynamics of Hydrophobic and Hydrophilic Nanoparticles
キーワード：laser trapping, femtosecond laser pulses, nanoparticles
Laser trapping of a tightly focused continuous wave laser has been a powerful tool to manipulate micrometer and sub-micrometer sized objects suspended in solution. Compared to the continuous wave laser, ultrashort laser pulses can be utilized to achieve more efficient trapping of nano-sized objects in solution. Furthermore, it has been reported that there are unique and interesting phenomena of femtosecond laser trapping. Recently, our group found the unconventional ejection behavior when the femtosecond laser pulses were irradiated in the solution of 50 nm polystyrene (PS) nanoparticles (NPs). The NPs were ejected from the laser focus perpendicularly to linearly polarized light, and the ejected direction was alternatively switched from one direction to opposite direction. It has been systematically examined that enough laser power, short pulse width, and high particle density are necessary condition to induce this interesting behavior.
As light field is always symmetrical, this directional ejection can be ascribed to the property of NP. We consider that hydrophobic/hydrophilic surface is critical. Therefore, we substituted the PS NPs with bare silica NPs, and then the ejection was not observed. When the silica surface is modified to be hydrophobic by silane surface treatment, the ejection appeared. We consider that the formation of transient assembly is necessary to generate this directional ejection behavior and this hydrophobic surface possibly enhances the association of the NPs. In addition to the silane surface treatment, we prepare perylene diimide (PDI)-coated silica NPs to examine the ejection phenomenon. PDI is widely used because of its high photostability and large absorption coefficient. We will analyze femtosecond laser trapping dynamics of these NPs by light scattering and fluorescence spectroscopic measurements.
As light field is always symmetrical, this directional ejection can be ascribed to the property of NP. We consider that hydrophobic/hydrophilic surface is critical. Therefore, we substituted the PS NPs with bare silica NPs, and then the ejection was not observed. When the silica surface is modified to be hydrophobic by silane surface treatment, the ejection appeared. We consider that the formation of transient assembly is necessary to generate this directional ejection behavior and this hydrophobic surface possibly enhances the association of the NPs. In addition to the silane surface treatment, we prepare perylene diimide (PDI)-coated silica NPs to examine the ejection phenomenon. PDI is widely used because of its high photostability and large absorption coefficient. We will analyze femtosecond laser trapping dynamics of these NPs by light scattering and fluorescence spectroscopic measurements.