Biomedical Engineering Reference
In-Depth Information
tweezers. system.. The. basic. criteria. for. the. trapping. laser. include. excellent. pointing.
stability. (to. avoid. trap. position. displacement). and. low. power. luctuation. (to. attain. good.
trap. stiffness).. Common. laser. sources. like. argon. ion,. helium-neon,. and. diode-pumped.
solid. state. (DPSS). laser. beams. can. satisfy. most. general. optical. trap. applications.. But. if.
photodamage.or.photoheating.effects.from.light.absorption.become.serious,.for.example,.
in.live.biological.systems.trapping.applications,.a.neodymium:yttrium-aluminum-garnet.
(Nd:YAG),. neodymium:yttrium-lithium-luoride. (Nd:YLF),. or. neodymium:yttrium-
orthovanadate. (Nd:YVO 4 ). laser. source. is. often. chosen.. These. laser. sources. have. a. near.
infrared. wavelength. (e.g.,. 1047,. 1053,. 1064.nm). and. relatively. low. optical. damage. to.
biological.samples..With. E. coli .cells.and.Chinese.hamster.ovary.(CHO).cells,.researchers.
found.that.the.minimum.laser.damage.occurs.at.a.wavelength.of.970.and.830.nm.from.a.
Ti-sapphire. laser. with. available. power. of.∼100.mW. (Figure. 19.4).. To. accomplish. eficient.
trapping,.the.incident.laser.usually.has.a.Gaussian.TEM 00 .mode.single.output.with.a.small.
beam.waist.
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100
1200
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(a)
Wavelength (nm)
10 min
30 s
(b)
Figure 19.4
The.photodamage.of.optical.tweezers.to.cells..(a).The.photodamage.of. E. coli .and.Chinese.hamster.ovary.(CHO).
cells.under.various.laser.wavelengths..The.solid.circle.is.the.half.lethal.dose.time.(LD50).for. E. coli .(using.the.
left.axis,.samples.were.exposed.to.a.laser.power.of.100.mW,.data.from.Neuman.et.al..1999).and.the.open.circles.
are.the.cloning.eficiency.of.CHO.cells.(using.the.right.axis,.samples.were.exposed.to.a.laser.power.of.88.mW.
for.5.min,.data.from.Liang.et.al..1996)..(Reprinted.from. Biophys. J .,.70,.Liang,.H.,.Vu,.K..T.,.Krishnan,.P.,.Trang,.
T..C.,.Shin,.D.,.Kimel,.S.,.and.Berns,.M.W.,.Wavelength.dependence.of.cell.cloning.eficiency.after.optical.trap-
ping,.1529-1533,.1996..Copyright.1996,.with.permission.from.Elsevier;. Biophys. J .,.77,.Neuman,.K.C.,.Chadd,.E.H.,.
Liou,. G.F.,. Bergman,. K.,. and. Block,. S.M.,. Characterization. of. photodamage. to. Escherichia coli . in. optical. traps,.
2856-2863,.1999..Copyright.1999,.with.permission.from.Elsevier.).(b).Comparison.on.a.K562.cell.after.a.short.term.
(30.s).and.a.long.term.(10.min).trapping.period.by.optical.tweezers.in.culturing.medium.
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