Biomedical Engineering Reference
In-Depth Information
chamber containing microparticles suspended in water [13,14], (2) the counter-
propagating dual-beam trap can not only trap a red blood cell (RBC), osmot-
ically swollen into spherical shape, but also stretch the spherical RBC to
deform into an ellipsoid [15-17]. This technique has since been investigated
for the measurement of the visco-elastic properties of various cells to correlate
with their physiological conditions, including the feasibility of identifying a
cancer cell against a normal cell [18].
Although a self-aligned counter-propagating dual-beam trap can be imple-
mented, in principle, with a single input beam in conjunction with a nonlinear
optical phase-conjugate mirror [19], it has not been further developed due to
some practical limitation in the nonlinear optical properties of the materi-
als available for optical phase-conjugation. More recently, three-dimensional
stable trapping of a microparticle from a single laser beam emitting from a
single-mode fiber with different structure fabricated at the tip of the fiber and
without any external lens has also been successfully demonstrated [20, 21].
Another critical factor that further expands the potential biomedical ap-
plications of optical trapping is its capability to measure forces on the order of
tens of femto-Newton to hundreds of pico-Newton. This topic will be discussed
in greater details in Sect. 14.3 along with potential biomedical applications in
Sect. 14.4, which together form the core of this chapter.
Other ramifications of optical trapping involve the integration of opti-
cal trap with one or more other optical techniques, such as near-field mi-
croscopy [22,23], Raman spectroscopy [24,25], and second and third harmonic
generation microscopy [26], as well as with microfluidics for a wide range of
particles or cells sorting [27-29].
In this chapter, we focus mainly on the measurement of optical forces in op-
tical traps and potential applications of optical trapping as a force transducer
for the measurement of biomolecular forces in the range of sub-pico-Newton
to hundreds of pico-Newton. Partly because of the limited size of this chap-
ter, and partly because of our lack of experiences with some ramifications of
the subjects, several important topics such as those dealing with integrated
photo-voltaic optical tweezers [30, 31] and optically driven rotation [32-34] of
micronsized samples in optical traps are left out. Interested readers are en-
couraged to consult excellent accounts of these topics in the references cited
above.
For those who want to learn the subject in greater depth and in more
details, two excellent review papers [35, 36] each with an impressive list
of references can be consulted. In addition, many leading research groups
all over the world have posted incredible amount of information with very
entertaining and informative video demonstrations of a wide range of fea-
tures of optical trapping and manipulation. A few selected video demonstra-
tions of various forms of optical trapping can also be viewed at our website
(http://photoms.ym.edu.tw).
