Biomedical Engineering Reference
In-Depth Information
Table 4.1
Materials Used as Substrates for PCR Chips
Material
Advantages
Disadvantages
Silicon
Thermal.conductivity.(rapid.heating.and.
cooling.for.rapid.cycling)
Microfab.processes.available
Bare.Si.inhibits.PCR.(adsorption.of.
DNA?)
Thermal.conductivity.(thermal.
insulation)
Opaque.(limits.luorescence.readouts)
Expensive.processing
Micropumps.dificult
Glass
Transparent.(optical.readout)
Allows.for.EOF.for.integration.with.CE.
(DNA.separation)
Etching.dificult,.expensive.processing
No.micropumps
Adsorbs.PCR.sample
PDMS
Inexpensive
Transparent
Molded.
⇒
.fab.inexpensive
Flexible.
⇒
.micropumps.and.valves
Less.adsorption.than.glass
Permeability.to.water.(concentration.
changes.
→
.can.be.avoided.by.
presoaking.or.“priming”.PDMS.for.
24 hours)
Permeability.to.air.(air.bubbles.when.
cycling.
→
.can.be.avoided.by.
pressurization,.by.degassing.the.PCR.
sample,.and.by.adding.a.solvent.such.
as.glycerol.that.increases.the.boiling.
point)
PC
Inexpensive.fab.(hot.embossing)
Inexpensive.material
High.glass.transition.temperature.
(150°C)
Some.autoluorescence
PMMA
Inexpensive.fab.(CO
2
.laser)
Inexpensive.material
Little.adsorption.of.DNA.or.protein
Little.autoluorescence
Glass.transition.temperature.105°C.
(close.to.95°C.for.strand.separation).
limits.heat.treatments
dominate the input copy number. he trends have followed the general trends in microluidics:
the irst devices were fabricated in silicon and glass (mostly due to convenience, as fabrication
was performed in MEMS facilities) and slowly, as the advantages of new polymeric materials
such as PDMS, polycarbonate (PC), and poly(methyl methacrylate) (PMMA) have been unveiled
and characterized, designs in these materials have become available. Fluidigm sells a reusable
PDMS PCR chip (for digital PCR) that can process 36,960 reactions simultaneously from up to
48 samples.
Table 4.1
summarizes the advantages and disadvantages of the materials commonly
used in the fabrication of PCR chips.
4.6.5.2 PCR Chip Architectures
PCR chip architecture can be classiied as stationary (chamber-based) PCR chip or dynamic
(continuous low-based) PCR chip. Chamber-based architectures, which were the irst to be
developed, are the result of shrinking down the traditional macroscopic PCR reactors—a strat-
egy that does not scale well because of the importance of the surface-to-volume ratio in such
critical biochemical reactions as PCR (or the devices and the solutions must be kept propor-
tionately cleaner of nucleic acid contaminants, which increases processing costs). One of the
leading laboratories in this area is Richard Mathies' laboratory at the University of California
