Fig. 1. (a) Structure of DiD dye molecule with its dipole orientation indicated by a red arrow; (b) schematic of single-molecule sample manipulated by applying a perpendicular or parallel electric field to the surface of single-molecule sample, respectively.(a) DiD分子的结构式, 红色箭头表示其固有偶极取向; (b)垂直于单分子样品表面电场和平行于样品表面电场操控单分子示意图

Fig. 2. Fluorescence measurement of single DiD molecules: (a) Fluorescence image of single DiD molecules in 18 μm × 18 μm area; (b) schematic view of the S-polarized and P-polarized fluorescence of arbitrary dipole moment for single-molecule (Obj, objective; PBS, polarized beam splitter); (c) fluorescence trajectories of single DiD molecule indicated by the red circle in panel (a) in S and P polarization; (d) the relationship between fluorescence polarization and time; (e) the statistics of fluorescence polarization with the most probable value being 48.8°.DiD单分子的偶极取向与偏振测量　(a)在18 μm × 18 μm区域内DiD单分子的荧光成像; (b)任意偶极取向的DiD单分子的S偏振及P偏振方向荧光探测示意图, 其中Obj是物镜, PBS是偏振分束棱镜; (c)成像图(a)中红色圆圈标记的DiD分子的S和P偏振方向的荧光强度轨迹图; (d)荧光偏振方向α随时间的变化; (e) DiD分子光漂白前荧光偏振方向的统计, 最可几值为48.8°

Fig. 3. Polarized orientation for single DiD molecules under the different conditions: (a) Non-electric field; (b) perpendicular and (c) parallel electric field of 3500 V/mm. The peaks of α are (a) 41.0° ± 21.9°, (b) 44.2° ± 26.3°, (c) 32.0° ± 13.5° and 55.5°±21.6°, respectively. DiD单分子在不同情况下取向极化的效果　(a)未加电场; 3500 V/mm的(b)垂直电场取向极化和(c)平行电场取向极化; 荧光的偏振方向α的统计峰值分别是 (a) 41.0° ± 21.9°, (b) 44.2° ± 26.3°, (c) 32.0° ± 13.5°和55.5° ± 21.6°

Fig. 4. Simplified scheme of the polarization of the dipole orientation of single-molecule under the influence of external electric field. The directions of the electric field are parallel (a), perpendicular (b), and arbitrary (c) to the dipole orientation of single-molecule, respectively.单分子偶极取向在外电场作用下的极化示意图 (a) 电场方向与分子偶极取向同向; (b) 电场方向垂直于单分子偶极取向; (c)电场作用于任意取向单分子