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3.4 Applications of Optical Tweezers 115
(a) (e)

After 10 seconds
(f)

Befor trapping
(b)

After 1 minute
(g)

Trapping and contacting
(c)

After 5 minutes
(h)
Laser radiation
(d)

After 15 minutes
After 1 second
Fig. 3.40. Living cell fusion by violet light exposure at contact area between two
cells trapped independently [3.20]. Courtesy of S. Sato, Tohoku University, Japan

Displacement and force due to actin–myosin interactions were determined
by measuringbead displacement with nanometer accuracy by a quadrant
photodiode. Individual ATPase reactions were monitored by an SIT camera as
changes in fluorescence intensity due to association–(hydrolysis)–dissociation
events of a fluorescent ATP (analoglabeled with Cy3-ATP) with the myosin
head. As a result, it was found that the myosin head produces several hun-
dred of milliseconds after a bound nucleotide is released. This suggests that
myosin has hysteresis or memory state, and stores chemical energy from ATP
hydrolysis [3.26].

Chemistry

Optical tweezers are used in the field of chemistry. Figure 3.43 shows a mi-
crochemical conversion system [3.6] for the studies of reaction kinetics that
allows the selective excitation of optically manipulated particles in reaction en-
vironments, which was prepared by micromachining. Continuous wave YAG