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114 3 Optical Tweezers
3.0
Metal oxide
Relative refractive index 2.0 (l = 0.63 mm) Living cell
2.5
n = 1.16 - 2.2
Semiconductor
k < 0.002
1.5
Dielectric
1.0
Organic
Metal
0.5
k = 7.5
0 (3D) n = 0.28 (2D)
0.001 0.01 0.1 1.0 10 100 1000
Particle diameter (mm)
Fig. 3.38. Reported materials and sizes possible for optical trapping by YAG laser
beam. Various particles ranging from 20 nm to tens micrometer in size including
biological, dielectric, polymer and metal particles are included

L X, Y, Z mount

VC
BF
BS
BF
E

BS

Objective F
SL
Sample
cell
X, Y, Z stage
Bacteria
CL

I

Fig. 3.39. Example of bacterial manipulation and measurement of swimming speed
of mitocondria by optical tweezers [3.23]

Figure 3.42 shows the simultaneous measurement of individual ATPase and
mechanical reactions of single one-headed myosin molecules [3.26]. A single
actin filament with beads attached to both ends was suspended in a solution
by YAG laser trapping. The fluorescence was excited by the evanescent wave
generated by the total reflection of the green laser shown in the figure. The
local illumination by the evanescent light greatly reduced the background
luminescence.