Microfluidics for Biosensor Chips - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 152

surrounding liquid known as the thermal lens effect, which can be
probed with the other wavelength. The resulting refraction index
change can focus or de-focus the probed light beam co-axially as
aligned with the irradiation heating beam using the same microscope
objective.
Individual gold nanoparticles absorb a continuous light at
532 nm under one microscope objective to station simultaneously.
The light-absorbing nanoparticles release heat to change the
refraction index around them. Probing light at 670 nm is directed via
the same objective to interrogate the refraction index variability. 45
Alternatively, gold nanoparticles pass through the detection area of
a microchannel to be probed under a thermal lens microscope. 46,47
Detection has been found to be more eficient in a narrow channel
(~1 micron in width) than in the channel of 100 microns.
7.7 Conclusion
When incident light directly interacts with free electrons on the
surfaces of noble nanoparticles, the scattering wavelength and
intensity dependence of relectivity is determined by particle surface
dielectrics. This phenomenon can be used for PPR spectroscopic
detections because the scattering indicates the speciic docking of
immobilized probes, such as antigens, with targeted bio-molecules
(for example, antibodies).
Noble metal nanoparticles for PPR detection can be designed as
colorimetric assays or coated on a stripped optical iber to monitor
the intensity attenuation of propagating light along the iber. Either
colorimetric PPR or FO-PPR can be conducted in microchannels.
However, due to slow diffusivity of detected bio-molecules, developing
micro-mixing units are required to accelerate detection response. In
addition, electrospray ionization can occur at the microchannel outlet
to determine the desorbed bio-molecules with mass spectrometry
via applying high voltage at the channel tip. Alternatively, using the
strong light absorbance of noble nanoparticles, upon laser irradiation
the docked molecules are desorbed and ionize to determine with
mass spectrometry via MALDI processes.
Noble metal nanoparticles, which have a strong afinity for
thiol groups, can immobilize a variety of bio-molecular probes,
including proteins and nucleic acids. These functionalized particles