Microfluidics - Introduction to BioMEMS - page 201

E

σ + σ - σ + σ -

400 µm

E

σ + σ - 100 µm

FIGURE 3.103 Homogenization.induced.by.surface.charge.patterns..The.patterned.electro-osmotic.
low.is.shown.schematically.with.arrows.on.the.top.diagram..The.bottom.is.a.micrograph.that.shows.
the.trajectories.of.luorescent.beads.in.a.vertical.plane.through.the.channel..The.micrograph.was.
compiled.from.multiple.series.of.images.that.were.taken.at.intervals.of.0.2.seconds..The.direction.of.
motion.is.indicated.by.the.arrows..The.applied.electric.ield.was. E .=.95.V/cm..The.globular.objects.
at.the.bottom.of.the.image.are.beads.that.have.stuck.to.the.surface.at.the.stagnation.point.in.the.
low.at.the.transition.between.positively.and.negatively.charged.regions..(From.A..D..Stroock,.M..
Weck,.D..T..Chiu,.W..T..S..Huck,.P..J..A..Kenis,.R..F..Ismagilov,.and.G..M..Whitesides,.“Patterning.
electro-osmotic.low.with.patterned.surface.charge,”. Phys. Rev. Lett. .84,.3314-3317,.2000;.and.
A.. D.. Stroock. and. G.. M.. Whitesides,. “Controlling. lows. in. microchannels. with. patterned. surface.
charge.and.topography,”. Acc. Chem. Res. .36,.597-604,.2003..Reprinted.with.permission.from.the.
American.Chemical.Society.)

Fluidigm, who sells the chips for high-throughput screening of protein crystals. If implemented
in the doormat microvalve design, as shown in Figure 3.106 , the volumes of the chambers
are fully predicted by photolithography and they do not distort transmitted-light microscopy
modes (such as phase-contrast microscopy). he titrations are determined simply by the ratios
of the volumes of the chambers.

Piezo transducer

a Fluid A

Off

Fluid B

b

Wave propagation

Flow

Bubble trapped in
horseshoe

Mixed fluid On

c

On
100 µm

Microfluidic channel Microstreaming

FIGURE 3.104 Bubble-based.on-off.millisecond.homogenizer..(From.Daniel.Ahmed,.Xiaole.Mao,.
Jinjie.Shi,.Bala.Krishna.Juluri,.and.Tony.Jun.Huang,.“A.millisecond.micromixer.via.single-bubble-
based.acoustic.streaming,”. Lab Chip .9,.2738-2741,.2009..Reproduced.with.permission.from.The.
Royal.Society.of.Chemistry.)