Biomedical Engineering Reference
In-Depth Information
tweezers.based.FACS.has.been.successfully.used.to.separate.cells.carrying.green.luorescent.
proteins.(GFP).from.their.parental.cells.without.GFP..It.achieved.a.high.recovery.rate.(>85%).
and.a.high.throughput.(∼.at.10
6
.cells/s).at.various.mixing.ratios.(0.01-0.52).
19.4.2.3 Assembling and Surgery
Besides.trapping.and.relocating,.optical.tweezers.can.also.be.used.to.grab.multiple.cells.
and. to. create. well-deined,. 3D. cell. arrays. (Figure. 19.10).. Such. assembly. capability. is.
generally.accomplished.when.equipped.with.computer-controlled.SLMs,.such.as.a.SLM/
AOD.module..The.irst.optical.assembly.was.demonstrated.with.silica/glass.particles,.in.
which.a.diamond.lattice.was.created.with.a.unit.cell.length.within.several.micrometers.
(Ozkan.et.al..2003a,b)..Similar.assembly.conigurations.were.later.achieved.with.bacteria.
(e.g.,.
E. coli
.cells,.Leach.et.al..2004).and.mammalian.cells.(e.g.,.3T3.ibroblast,.Akselrod.et.al..
2006)..If.the.laser.beams.are.switched.off.upon.the.ixing.of.cells,.the.optically.assembled.
cells. can. survive. for. many. days.. With. its. potential. to. create. 3D. complex. architecture,.
optical.cell.assembly.has.stimulated.biologists'.interest.to.use.it.for.mimicking.real.tissue.
and. understanding. how. neighbor. cells. (their. relative. position,. proximity,. number,. and.
cell-cell.interactions).affect.the.proliferation.and.differentiation.of.the.target.cells.at.the.
center.. For. example,. an. optical. cell. assembly. pattern. was. created. to. study. the. bacterial.
infection.of.mammalian.cells.(Akselrod.et.al..2006)..In.this.experiment,.nine.2.mW.beams.
were.used.to.trap.a.3T3.ibroblast.cell.at.the.center.and.another.16.beams.(2.mW.for.each.
beam). to. position. 16. bacteria. surrounding. the. 3T3. cell.. Each. bacterium. was. ixed. with.
one.of.these.16.beams.and.their.trapping.positions.were.predeined.to.create.a.cell.array.
in. which. the. distance. between. the. cells. was. maintained. (<400.nm).. Similar. strategies.
have. also. been. used. to. create. various. model. systems. to. investigate. cell. differentiation,.
infusion,.and.cell-cell.interactions.(Titushkin.and.Cho.2006)..Such.optical.assembly.may.
help. reveal. many. fundamental. questions. in. tissue. engineering,. stem. cell. engineering,.
and.synthetic.biology.
As.the.laser.beams.used.in.optical.tweezers.have.high.power,.they.might.also.be.used.
as.scalpels.or.scissors.to.precisely.cut.cells.from.cell.clusters.or.components.inside.cells.
with. a. submicrometer. resolution. (Figure. 19.10c).. A. short-time. laser. irradiation. may. also.
help. make. a. cell. membrane. temporarily. permeable,. which. allows. cell. membranes. to. be.
fused.together.(Figure.19.10d).or.may.beneit.molecular.probe.delivery.into.cells.(so-called.
optoinjection).. Individual. sperms. have. been. successfully. transported. into. oocytes. with.
such. an. optoinjection. approach. to. generate. hybrid. cells. (Steubing. et. al.. 1991).. Small.
molecules. were. also. speciically. delivered. into. the. cytosol. and. nucleus. of. Neuro-2A.
mouse. neuroblastoma. cells. in. a. similar. way. (Schopper. et. al.. 1999).. In. these. cell. surgery.
applications,.Nd:YAG.laser.beams.are.often.favored.
19.5 Concluding Remarks, Improvements, and Perspectives
Optical. tweezers. allow. remote. capturing. of. individual. molecules. and. precise. measure-
ment. of. the. forces. and. the. displacement. of. their. molecular. chains. with. focused. laser.
beams..Since.its.invention,.it.has.drawn.great.attention.from.various.scientiic.communi-
ties.including.physics,.engineering,.and.biology..Its.great.success.attributes.to.its.invasive.
trapping. nature,. concise. force. measurement. at. the. single. molecule. level,. and. lexibility.
