Microfluidics for Biosensor Chips - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 139

lasers, X-rays, or synchrotron radiation, have also been used to
ablate microchannels with high aspect ratios on plastic substrates. 10
Techniques such as injection molding and micro-milling have also
been used to fabricate microchannels on thermoplastic chips. 11 After
the microchannels have been patterned, the structured plastic chip
and the cover chip are sealed using thermal bonding techniques.
This step usually involves organic solvents, which enhance the fusion
strength of plastics at the gap between the two chips.
Elastomers such as polydimethylsiloxane (PDMS) are commonly
used to fabricate microluidic devices. 12 A typical procedure is to
irst develop a silicon master molds with a positive surface relief
pattern. Next, a PDMS precursor solution is poured into the mold
to start polymerizing when cured at approximately 65°C. When
the polymerization processes are accomplished, patterned PDMS
substrates can be peeled from the mold. The resulting structured
chip can be sealed with either a PDMS chip or a glass chip. When the
cover chips are nearly perfectly lat, the sealing can be accomplished
by merely pressing the structured chip against the cover. Otherwise,
ozone plasma is used to activate the silane surface of the PDMS or
glass chip prior to the chip bonding step, which fuses the two chips
using water or methanol smeared on the plasma-activated surfaces.

7.3 Particle Plasmon Resonance Detection

in Microfluidic Devices Using Noble
Metal Nanoparticles

When incident light impinges into the thin ilm surface of bulk
dielectric materials such as noble metals, and is relected, partial
light absorption occurs. This is due to the interactions between the
evanescent wave ield of incoming light (penetrating the ilm) and the
dielectrics, which only occur at certain angle ranges of incident light
resulting in relectance minima. The wave vector component parallel
to the free electron dipole of the dielectric surface is almost absorbed.
As a result, the relectance intensity decreases dramatically. This
phenomenon is known as surface plasmon resonance (SPR). 13 The
electric permittivity of a dielectric ilm can be altered by immobilized
molecules on the reverse side; therefore, the angle of relectance
minima is shifted when the planted probes are docked with detected
molecules. Several commercial spectroscopic biosensors reviewed