Microfluidics for Biosensor Chips - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 146

phase when the particles are illuminated. For instance, absorbed
peptides on the self-assembled monolayer of Au nanoparticles can
be imaged with mass spectrometer via ionizing these peptide with
precise laser focusing to spatially control desorption spots. 34

7.5 Fluorescence Spectroscopic Detection

in Microfluidic Devices Using Noble
Metal Nanoparticles

Like other types of nanoparticles, noble metal nanoparticles have
been used as supporting substrates to immobilize molecular probes
and luorophores. This facilitates biosensing with luorescence
detection in microluidic chips. Various luorescence detection
schemes employing the interactions between luorophore and
noble metal particles have been developed. Examples include using
gold nanoparticles as quenching acceptors for FRET detection and
using silver nanoparticles for surface plasmon coupled luorescence
detection. In addition, molecular beacons can be immobilized on
noble metal nanoparticles to determine metal species.

7.5.1 Applying Gold Nanoparticles as Quenching

Acceptors to Förster Resonance Energy Transfer
(FRET) Detections

Förster resonance energy transfer is a non-radiative process of
dissipating the energy of electrons populated in the excited state. 35
This energy transfer process occurs when the transition dipoles
of one pair of luorophores, the donor and acceptor, have strong
interactions. When the transition dipole of the donor luorophore
is excited enough to pump electrons from the ground state to an
excited state, some of the extra energy of stimulated electrons on the
donor luorophore, presumably to emit luorescence, is transferred
to excite the transition dipole of an acceptor luorophore. Finally, the
detected luorescence emission comes partially from the acceptor
luorophore. Alternatively, extra energies are absorbed by the
acceptor, resulting in the disappearance of luorescence emission.
Figure 7.2 shows the mechanism of the FRET process.
The resonance frequencies of donor and acceptor transition
dipoles must overlap to a certain degree to ensure the eficient