Few-Atom Silver Clusters as Fluorescent Reporters - Advanced Fluorescence Reporters in Chemistry and Biology - page 315

a 1.00 b c

1.00

1.0

0.75 0.75 0.8

0.6

0.50 0.50

0.4

0.25 0.25

0.2

0.00 0.00 0.00

300 350 400 450 500 550 600 650 700 750 800

350 400 450 500 550 600 650 700 750

300 350 400 450 500 550 600 650 700

Wavelength (nm) Wavelength (nm) Wavelength (nm)

d e f

1.00 1.00

0.75 0.75

0.50 0.50

0.25 0.25

0.00 0.00

500 550 600 650 700 750 800 850 900

450 500 550 600 650 700 750 800 850

Wavelength (nm) Wavelength (nm)

Fig. 4 Steady-state excitation and emission spectra for five distinct ssDNA encapsulated Ag
clusters. (a) Blue emitters created in 5 0 -CCCTTTAACCCC-3 0 ,(b) green emitters created in 5 0 -
CCCTCTTAACCC-3 0 ,(c) yellow emitters created in 5 0 -CCCTTAATCCCC-3 0 ,(d) red emitters
created in 5 0 -CCTCCTTCCTCC-3 0 , and (e) near-IR emitters created in 5 0 -CCCTAACTCCCC-3 0 .
(f) Pictures of emissive solutions in (a)-(d)[ 46 ]

Fig. 5 (a) Image of single IR-emitting dC 12 -Ag n molecules in a poly(vinyl alcohol) (PVA) film.
(b) Image of single Cy5.29 molecules in a PVA film. The image dimensions are 40 40 m, and

m

imaging conditions of (a) and (b) are identical [ 19 ]

Recently it was shown that optical modulation of the silver cluster fluorescence
could allow extracting weak signals from extremely fluorescing backgrounds. The
method consists in coillumination with an intensity-modulated secondary laser
(excitation

800 nm) and produces a photobrightening of higher energy cluster
emissions by depopulation of the dark state without increasing the background
(Fig. 6a ,b)[ 27 ]. In this way, silver clusters with emission at 710 nm (upon

excitation at 633 nm) can be distinguished from background signals created by
autofluorescence (Fig. 6c , d) or dyes (Cy5) (Fig. 6e ,f)[ 27 ].