Biomedical Engineering Reference
In-Depth Information
load. for. different. molecular. motors. varies. largely,. from. a. few. pN. to. several. tens. pN..
For.example,.it.is.∼25.pN.for.RNAP.molecular.motors.from.
E. coli
.(Wang.et.al..1998),.while.
∼60.pN. for. phage's. DNA-translocating. ATPase. used. in. viral. packaging,. respectively.
(Smith.et.al..2001).
19.4.2 Cell related Study
Unlike.the.single.biomolecule.trap.by.optical.tweezers,.cells.can.be.easily.trapped.in.still.
luid.or.low.without.anchoring.to.dielectric.objects..To.date.optical.tweezers.technology.has.
been.widely.applied.to.trap,.position,.manipulate,.sort,.and.assemble.different.types.of.cells.
19.4.2.1 Trapping and Positioning
The.basic.use.of.optical.tweezers.in.cell.related.research.is.to.trap.cells.and.position.them.
at. desired. locations.. As. such,. grabbing. and. relocating. does. not. require. contact. with. a.
solid.surface.or.other.cells,.it.is.convenient.to.create.appropriate.model.systems.for.some.
fundamental. studies.. For. example,. a. single. kidney. cell. was. optically. trapped. to. reveal.
the. water. transport. across. the. cell. membrane. and. correspondingly. the. volume. change.
dynamics.under.osmotic.shock.(Lucio.et.al..2003)..Single.K562.cells. (a.chronic. leukemia.
cell.line).had.been.positioned.at.various.locations.between.two.electrodes.to.study.the.cell.
membrane.permeability.change.during.and.after.an.electric.pulse.to.help.understand.the.
cell.electroporation.mechanism.(Figure.19.8).
Upon.the.occurrence.of.an.optical.trap,.cells.can.also.be.transported.to.desired.locations.
for. further. study.. For. example,. placing. a. trapped. cell. among. many. ligand-anchored.
microparticles.is.often.used.to.investigate.the.ligand-cell.interactions.(Fallman.et.al..2004)..
When.unattached.cells.are.trapped.and.transported.near.a.group.of.cells.growing.on.the.
common.culture.substrate,.cell-cell.interactions.can.also.be.conveniently.investigated..It.
was.reported.that.when.a.trapped.rod.cell.was.positioned.to.a.cone.cell.and.a.multipolar.
neuron,.optical.trapping.did.not.change.the.cell.adhesion.to.the.culture.substrate.or.cell.
structure.. However,. the. growth. of. the. neuron. could. be. inhibited. because. of. cell-cell.
interactions.(Townes-Anderson.et.al..1998)..If.a.trapped.cell.is.positioned.in.a.predeined.
microenvironment,.it.can.reveal.how.cells.respond.to.chemical.or.physical.stimuli.from.
extracellular. environments.. It. has. been. reported. that. a. few. optically. trapped. yeast. cells.
were.relocated.in.a.programmed.manner.between.two.different.media.to.ind.out.the.in.
situ.response.of.these.cells.to.various.glucose.concentrations.(Eriksson.et.al..2007)..Similar.
strategies.may.also.be.adopted.for.in.vitro.monitoring.of.the.response.of.cells.to.drugs.by.
feeding.them.with.a.speciic.pharmaceutical.solution.
Cells,. when. optically. trapped. by. a. single. beam,. could. still. rotate. along. the. trapping.
axis. (Grover. et. al.. 2000).. This. fact. sometimes. interferes. with. the. real-time. study. of. the.
biochemical.activity/response.of.the.trapped.cell..By.applying.multiple.traps.around.the.
periphery. of. the. cell,. more. stable. trap. can. be. established.. If. scanning. across. the. entire.
conined.cell,.the.spectra.of.various.components.inside.(e.g.,.cell.membrane,.cytoplasm,.and.
the.nucleus).could.also.be.attained.with.optical.tweezers.(Creely.et.al..2005;.Jess.et.al..2006).
19.4.2.2 Sorting and Separation
Upon.capture,.the.intensity.of.light.scattering.on.the.cell.varies.with.its.viability,.morphology.
(e.g.,. size. and. shape),. and. intracellular. contents. related. to. their. dielectric. properties..
Following. this. rationale,. cells. may. be. identiied,. sorted,. or. even. separated. with. optical.
