A tightly focused laser beam exerts optical force on nanoparticles dispersed in an aqueous solution, leading to an optical trapping of them at the focal point. Recently, we have developed plasmonic optical tweezers for soft nano-matters such as DNA, thermoresponsive polymer chains, and dye aggregates. We observed the interested trapping behaviors of the soft nanomaterials on such liquid-solid interfaces. Our attention is paid to such optical trapping of them on interfaces because optical force strongly depends on the dielectric constant of the surrounding medium. In the present study, we demonstrated that optical trapping of quantum dots and octahedral gold nanocrystals at water-oil interface. Dark-field microscopy was a powerful tool to observe the trapping behaviors of the gold nanoparticles, while fluorescence microscopy was used for the observations of the quantum dots.
We present a novel manipulation technique for living cyanobacteria on a plasmonic substrate. Upon plasmon excitation,
a local temperature around the excitation area was elevated, leading to a microbubble formation in water. Subsequently,
living cyanobacteria were transported to the microbubble by a thermal convection. The cyanobacteria were permanently
fixed on the area even after switching off the plasmon excitation. We found that about a half of the fixed cyanobacteria
were alive. We succeeded in a micro-ring pattern of living cyanobacteria by the technique.