Biomedical Engineering Reference
In-Depth Information
blood.cells.are.counted.by.an.automatic.hematology.analyzer.with.or.without.depleting.
CD4
+
.cells.by.MT4.MAb,.and.the.CD4
+
.cell.count.is.obtained.by.the.difference.between.
the.two.values.
6.3 AdvancesinMicrofluidicsandImaging
TechnologiesforPOCCD4
+
Testing
Although.efforts.have.been.put.into.simpliied.and.affordable.low.cytometers,.they.remain.
too. complex. for. district. hospitals. or. POC. use. in. developing. countries,. as. they. require.
expensive.reagents,. multiple.sample. preparation.steps,.and.costly.maintenance..Current.
manual.CD4
+
.cell.counting.methods.are.restricted.by.the.high.cost.for.a.single.assay.(despite.
the.reduced.cost.for.instrumentation),.intensive.labor,.and.low.throughput..Thus,.on-chip.
CD4
+
.cell.counting.methods.have.recently.been.developed.to.facilitate.expanding.ART.in.
developing. countries.
18,23,24
. This. is. mainly. because. microchip. fabrication. is. inexpensive.
and. can. be. easily. scaled. up. with. recent. advances. in. microelectromechanical. systems.
41
.
CD4
+
.cell.counting.can.be.realized.on-chip.with.ingerprick.whole.blood,.eliminating.the.
need.for.sample.processing.and.transport..Furthermore,.the.actual.detection.and.counting.
have.been.made.easier,.as.counting.can.be.performed.using.a.lensless.imaging.system,.in.
contrast.to.low.cytometry.and.manual.counting.under.a.microscope.
18
.These.instruments.
have. the. potential. to. be. portable,. user-friendly,. and. do. not. require. costly. maintenance..
Based.on.microluidic.chips,.other.detection.methods,.such.as.chemiluminescence,
42
.quan-
tum.dot-based.luorescence,
17,43
.and.impedance.spectroscopy,
44
.are.also.utilized.for.on-chip.
HIV.monitoring.applications,.including.CD4
+.
cell.counting..These.technologies.represent.
the.latest.advances.in.POC.CD4
+
.cell.counting.
6.3.1 Design of CD4 Microfluidic Chips
To.facilitate.CD4
+
.cell.detection.from.whole.blood,.CD4
+
.cells.need.to.be.effectively.sep-
arated. from. red. blood. cells. (RBCs),. monocytes. and. other. lymphocytes.. A. circular. low.
cell. containing. a. 3. µm. Nuclepore. polycarbonate. ilter
23
. was. built. in. a. metal. case. with. a.
poly(methyl. methacrylate). (PMMA). top. and. bottom.. There. is. an. inlet. and. outlet. on. the.
PMMA.top,.allowing.low-through.of.blood.samples..The.PMMA.bottom.serves.as.a.sup-
port.for.the.ilter,.which.permits.passage.of.RBCs.and.retention.of.lymphocytes,.thus.elim-
inating. the. need. for. lysis. of. RBCs.. The. device. only. uses. microliters. of. a. blood. sample;.
this. signiicantly. reduces. reagent. consumption. and. biohazardous. waste.. This. device. is.
not. disposable. and. still. represents. a. macroscale. device,. which. requires. a. technician. to.
operate. properly.. Later,. straight. microchambers. made. of. polydimethylsiloxane. (PDMS).
were.used.to.maintain.a.constant.shear.stress.
24,45
.In.addition.to.surface.chemistry.(anti-
CD4
+
.antibody),.shear.stress.helped.to.differentiate.monocytes.from.CD4
+
.cells..Due.to.the.
differences.in.cell.size.and.density.of.CD4
+
.molecules.on.the.cell.surface,.the.adhesion.of.
monocytes.to.the.chamber.surface.is.kept.at.a.low.level.(<5.cells/mm
2
).
45
.Recently,.Cheng.
et. al.. designed. a. double-stage. cascaded. microchip.. It. includes. four. monocyte. depletion.
chambers,.which.are.coated.with.anti-CD14
+
.MAb,.to.remove.monocytes.before.CD4
+
.cell.
capture.
46
Moon.et.al.
used.a.combination.strategy.of.surface.chemistry.and.shear.stress.to.selec-
tively. capture. CD4
+
. cells. in. a. straight. microchannel.
18
. To. facilitate. lensless. imaging,.
