Biomedical Engineering Reference
In-Depth Information
whole. blood.
23
. In. contrast,. a. colorimetric. method. has. been. developed. to. facilitate. dif-
ferentiation.of.CD4
+
.T.lymphocytes.from.monocytes.and.other.immune.cells..However,.
luorescence. microscopy-based. detection. is. not. practical. for. resource-limited. settings,.
as.luorescence.microscopes.are.expensive.and.require.skilled.operation.and.dedicated.
laboratory.space.
To.simplify.detection,.Cheng.et.al..used.a.combination.strategy.of.surface.chemistry.and.
shear.stress.to.selectively.capture.CD4
+
.cells.from.whole.blood,.which.enabled.CD4
+
.cell.
counting.under.a.light.microscope.
24,45
.This.offers.a.great.advantage.for.resource-limited.
settings. since. a. light. microscope. is. affordable. and. accessible. in. most. district. hospitals..
However,. these. devices. still. take. a. long. time. per. test. to. count. manually. thousands. of.
captured.cells.under.a.microscope..Although.this.microchip.method.is.less.accurate.than.
low.cytometry.for.the.range.where.CD4
+
.cells.are.more.than.800.cells/µl,.it.can.effectively.
identify.clinically.relevant.thresholds.of.200,.350,.and.500.cells/µl.
24
6.3.3 Impedance Sensing
Another.label-free.CD4
+
.counting.method.can.be.achieved.electrically,.as.opposed.to.opti-
cal. counting.
44,46
. In. this. method,. patterned. surface. electrodes. were. used. to. measure. the.
change.of.conductivity.in.the.microchannel,.which.is.proportional.to.the.number.of.cap-
tured.CD4
+
.cell.count.after.cell.lysis..As.with.the.previous.design,.CD4
+
.cells.are.captured.
from. whole. blood. in. a. microluidic. channel. functionalized. with. anti-CD4
+
. MAb.. In. an.
ion-free.media,.CD4
+
.cells.are.passed.through.the.channel.and.captured..After.injecting.a.
low-conductivity.cell.lysis.buffer,.intracellular.ions.are.released,.increasing.the.conductiv-
ity..The.bulk.conductance.is.detected.by.built-in.electrodes.and.measured.by.an.external.
impedance. spectroscope.. As. reported,. concentrations. as. low. as. 20. CD4
+
. cells/µl. can. be.
detected..This.method.successfully.eliminates.the.need.for.cell.labeling.and.luorescence.
detection.in.the.previous.CD4
+
.cell.counting.system..In.addition,.the.lengthy.optical.count-
ing. process. under. microscopy. is. transformed. to. reading. electrical. signals,. signiicantly.
shortening.the.sample-to-answer.time..However,.this.method.assumes.identical.ion.con-
centration.for.all.cells,.which.needs.to.be.validated.using.clinical.samples..Also,.cells.can.
release.ions.without.lysis.and.may.contribute.to.measurement.errors,.which.necessitates.
stringent.storage.of.blood.samples.
6.3.4 Lensless Imaging
To. further. simplify. CD4
+
. cell. counting,. a. lensless,. ultra-wide-ield. cell. array. based. on.
shadow.imaging.(LUCAS).has.been.developed.
47
.LUCAS.is.designed.to.provide.shadow.
images. for. cell. counting
over. an. ultra-wide. ield. of. view,. e.g.,. a. few. square. centimeters,.
rather.than.images.with.a.high.spatial.resolution.(Figure 6.2)..LUCAS.signiicantly.increases.
the.imaging.speed.to.a.few.seconds.of.the.whole.microchip,.in.comparison.to.other.imag-
ing.technologies.
48,49
.In.addition.to.this.sensor,.an.algorithm.has.also.been.developed.to.
simultaneously. count. cells. within. a. few. seconds.
51
. This. automatic. counting. allows. the.
counting.of.CD4
+
.cells.100.times.more.eficiently.than.manual.methods.under.a.conven-
tional.light.microscope..Furthermore,.LUCAS.uses.a.charged-coupled.device.(CCD).as.a.
light.source.due.to.the.high.signal-to-noise.ratio..This.device.can.be.powered.by.recharge-
able.batteries.and.increases.portability..Therefore,.the.simpliied.design.permits.CD4
+
.cell.
capturing.and.label-free.counting.in.such.a.portable.system,.which.is.suitable.for.resource-
limited.settings.
