Biomedical Engineering Reference
In-Depth Information
modeling, template imprinting, and laser ablation. Various detection
technologies, such as optical spectroscopy, mass spectrometry, and
electrochemical methods have been successfully integrated with
microluidic chips.
In addition to briely reviewing microchip fabrication processes,
this chapter discusses detection technologies that employ noble
metal nanoparticles in microluidic chips. These technologies include
PPR spectroscopy, including hybrid instrumentation of PPR with
mass spectrometry, luorescence spectroscopy, and other detection
techniques, such as surface-enhanced Raman scattering and thermal
lens detections.
7.2
Fabrication of Microfluidic Devices
Most of the fabrication technologies discussed in this section have
been reviewed in Chapter 6. Therefore, this section only outlines
the major substrate materials used to make microluidic chips, and
briely describes their fabrication procedures.
5
Table 7.1 illustrates the substrate materials and fabrication
technologies discussed in this chapter. Since fused silica capillary
has been the most popular conduit for capillary electrophoresis (CE),
SiO
2
-based materials such as glass and quartz have been also used
to fabricate microchip CE devices. Wet chemical etching processes
with highly erosive reagents such as hydroluoric acid can be used to
create microchannels on these materials.
6
Before chemical etching
with strong acidic and alkaline reagents, such as hydroluoric acid
and concentrated potassium hydroxide, glass or quartz substrate
chips are coated with a layer of photoresist material. Covered with
this mask, the chip is then exposed to UV light, which etches along
the mask edges to create microchannels. The photoresist layer is
further developed after UV light exposure. Etching reagents are then
poured on the photoresist layer to erode the light exposed areas
and the substrate underneath the areas to complete microchannel
fabrication in approximately 30 min. The etching time depends on
reagent concentrations. An alternative technique is to use Al
2
O
3
powder blasting to craft a microchannel measuring 100 microns
in depth and width; this process takes only minutes.
7
However, the
channel roughness of using blasting technique is usually less than
ideal, about 1 micron.
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