Lipids distribution imaging of lipid vesicles by multi-focus excitation CARS microscope

We demonstrated high-speed imaging of the distribution of DPPC (dipalmitoylphosphatidylcholine), d62-DPPC (deuterated DPPC), and DOPC (dioleoylphosphatidylcholine) lipids in a lipid vesicle with a multi-focus excitation CARS (coherent anti-Stokes Raman scattering) microscope using a microlens array scanner. By the multi-focus excitation, the dwell time is increased in proportion to the number of focal spots compared with a single beam scanning, and high-speed and high-quality CARS imaging is possible without increasing the peak power of each spot. We demonstrated the selectively visualization of DPPC and d62-DPPC lipid vesicles, in which the vesicles contain a type of lipid, by observing at 2840 cm-1 and 2090 cm-1. We also visualized the DOPC and DPPC lipids distribution in a lipid mixture vesicle observed at 1440 cm-1 and 1655 cm-1. The image acquisition time of 10 s/image at each Raman shift was realized. The signal ratio of 1440 cm-1 and 1655 cm-1 was locally intense on the lipid vesicle. It must be because the gel phase domain of DPPC lipids was exists in the DOPC lipids which were liquid-crystalline phase at room temperature.