Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 235

of the intensity. Similar results are also found in luorescein over-
labeled human serum albumin deposited on the two surfaces. 88
Variable shapes of nanomaterials such as Ag nanorods and
triangular Ag NPs are also useful for SEF. The absorption spectra for
Ag nanorods are somewhat different than their spherical Ag NPs,
similarly showing a ~420 nm transverse absorption band with an
additional ~580 nm longitudinal absorption. Ag nanorod-coated
surfaces show density dependent luorescence enhancements
when coated with monolayers of human serum albumin labeled
with indocyanine green with greater than 11-fold luorescence
enhancements. 89 The absorption spectra of Ag triangles differ from
Ag nanorods and spherical Ag NPs, showing two SPR bands at about
450 and 550 nm. Ag triangle-coated surfaces also show density
dependence of the luorescence but provide greater enhancements
of the monolayer of human serum albumin labeled with indocyanine
green for similar surface optical densities. 90
In addition to Ag NPs, Au and Cu NPs are also useful materials for
SEF. 14-16 Au NPs with 40 and 200 nm diameters that are deposited
onto glass substrates have been used to observe angular dependent
luorescence emission of luorescein-human serum albumin. 14 The
emission intensity of luorescein-human serum albumin is 2.5-fold
brighter than the emission on bare glass substrates at an angle of 270°
due to factors explained by the Radiating Plasmon Model wherein
the mixing system of the luorophore and Au NPs emits following the
photophysical characteristics of the luorophore after the excitation.
In addition, partial radiationless energy transfer occurs between
the excited states of the luorophore and the surface plasmons of
the Au NPs. The luorescence enhancement of 200 nm Au NPs is
greater than that of 40 nm Au NPs due to the increased contribution
of the scattering portion. When compared to Ag NPs, Au NPs offer
more stable surfaces for applications requiring longer term storage
and use. Cu NPs also provide similar SEF effects. Although surfaces
coated with Cu NPs are not as stable as those coated with Au, they
are cheaper. 16
10.3.2 DNAAnalysis
Completion of the human genome sequence is driving development
of a wide variety of approaches to DNA analysis, including DNA arrays
or gene chips, PCR-based assays, and hybridization assays. 91-94 Many