Biomedical Engineering Reference
In-Depth Information
Table 14.1.
A comparison of optical spring constants measured by different
methods
Method
Analysis
k
OT
(
x
)
k
OT
(
y
)
(pN
µ
m
−
1
)
(pN
µ
m
−
1
)
Brownian motion
Displacement variance
7.07
6.31
Potential well
7.28
6.84
Power spectrum
7.21
6.88
Optical forced oscillation
Amplitude
7.69
Phase
7.61
optical force field
E
(
x, y
) can be simultaneously mapped, and the associated
spring constants
k
x
and
k
y
conveniently measured in stationary optical tweez-
ers via the Brownian motion method. The optical spring constants
k
x
and
k
y
on the transverse plane obtained from the Brownian motion analysis agree
with each other to within approximately
6%, which is consistent with the
earlier theoretical and experimental results [46, 51, 52] and also with those
reported previously for the case of a fiber-optical dual-beam trap [14, 45].
As an example, transverse optical spring constants,
k
x
±
and
k
y
,fora
polystyrene particle (diameter = 1
.
5
m) suspended in deionized water and
trapped in optical tweezers (characterized by
λ
= 1064 nm, NA = 1
.
0, trap-
ping optical power = 2 mW) obtained by different methods are compared and
summarized in Table 14.1.
µ
14.4 Potential Biomedical Applications
Potential biomedical applications of optical trapping and manipulation in-
clude (1) trapping and stretching a cell to measure its visco-elastic property
and to correlate with its physiological condition, (2) trapping two cells to mea-
sure cell-cell interaction, (3) trapping two protein-coated microparticles to
measure protein-protein interaction, (4) trapping one protein-coated particle
to interact with membrane proteins on a cell to measure the protein-protein
interaction at the cellular membrane, (5) trapping two beads with a segment
of DNA molecule stretched in between to measure the interaction dynamics
of the DNA with proteins injected into the sample chamber. Selected video
demonstrations of some of the features listed above can be viewed at the
website of the authors' lab (http://photoms.ym.edu.tw).
In general, optical trapping and manipulation promise to provide one or
more of the following unique features in biomedical applications:
1.
Micropositioning
: One can guide cell-cell, cell-molecule, or molecule-
molecule interactions in terms of where and when the interactions
take place. The interaction can therefore be measured within a time
point on the order of “second” after the initiation of the molecular
interaction.
