Fig. 2.

Demonstration of optical trapping of nanoparticles. (A) Fluorescence time trace of 120-nm polystyrene nanoparticles doped by fluorescent label (Spherotech Inc., light yellow) under 785-nm continuous-wave (CW) laser irradiation. The 785-nm laser works as an optical trapping beam and two-photon excitation beam. The number of trapped nanoparticles increases, and fluorescence intensity increases. Fluorescence microscope images also confirm that the laser spot becomes brighter due to the increased number of trapped nanoparticles. (Scale: 10 × 10 µm.) The arrows indicate the focused laser spot. Similar experiments were originally reported in ref. 8. (B) Bright-field microscope images of 60-nm polystyrene nanoparticles (Spherotech Inc.) under optical trapping by a 532-nm CW laser. (Scale: 10 × 10 µm.) The arrows indicate the laser spot. The size of particles is smaller than the diffraction limit of optical microscope; therefore, images appear blurry. The blurry objects at the center, however, gradually become more evident over the course of trapping as the number of trapped nanoparticles increases. Similar experiments were originally reported in ref. 9.