Photoluminescence of Gold Nanoparticles and Their Applications to Sensing and Cell Imaging - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 199

absorption band at ca. 375 nm (Fig. 9.7A) and emitted luminescence
at wavelengths centered in the region 525-550 nm (Fig. 9.7B). The
corresponding TEM images (Fig. 9.7C) indicate that the Man-Au NPs
prepared at Man-RSH concentrations of 0, 1, 2.5, 5, and 10 mM are
well dispersed, having average diameters of 2.9 (±0.5), 2.1 (±0.2),
1.8 (±0.3), 1.7 (±0.2), and 1.5 (±0.1) nm, respectively. The decreasing
size of these Au NPs upon increasing the concentration of Man-RSH
results from signiicant fragmentation caused by strong Au-S
interactions. No Au NPs were present in the solution when the
concentration of Man-RSH was greater than 20 mM, revealing that
the Au NPs had all dissociated into Au-thiolate complexes under
these conditions. As a result, the as-prepared solution did not absorb
light at 375 nm and did not luminesce (cf. spectra f in Fig. 9.7A,B).
Figure 9.7 (A) UV-Vis absorption spectra, (B) luminescence spectra, and
(C) TEM images of the 2.9 nm Au NP solutions after treatment
with Man-RSH solutions having concentrations of (a) 0, (b) 1,
(c) 2.5, (d) 5, (e) 10, and (f) 20 mM. Inset to (B): Photograph
displaying the luminescence of the various Man-Au ND
solutions upon excitation under a hand-held UV lamp (365 nm).
Reprinted with permission from Ref. 25. See also Color Insert.
9.5 Applications
Luminescent, water-soluble Au NCs and Au NPs offer several
features that make them attractive for use in bioassays, including
large Stokes-shifted and long luminescence lifetimes, sizes
comparable to those of biopolymers, and good water-solubility.