Few-Atom Silver Clusters as Fluorescent Reporters - Advanced Fluorescence Reporters in Chemistry and Biology - page 327

Fig. 14 Use of two different DNA duplexes with inserted cytosine loops working as synthetic
scaffolds to generate fluorescent silver clusters for the identification of the sickle cell anemia gene
mutation ( black dots represent hydrogen bonds formed in base pairing and black dashed lines the
sugar-phosphate backbone) [ 74 ]
The duplex with the normal HBB gene has one hydrogen-bonded base pair more
than the duplex with the mutated HBB gene, and therefore the first duplex has more
double-helical region. The single-nucleotide mismatch has a significant effect on
the structure of the duplexes, which in turn strongly influences the local environ-
ment where the clusters could form.
5.3 Wavelength-Shifting
Silver clusters change color while sensing their surroundings [ 20 , 75 ]. Ras et al.
have demonstrated that the absorption and emission bands of silver clusters are
tunable by changing the chemical environment, such as solvent (Fig. 15 ) or the
relative amount of silver ions (Fig. 12 )[ 20 ]. In Fig. 15b is shown a photograph of
the clusters in a series of water-methanol mixtures. Figure 15c shows the fluores-
cence of the same samples under UV illumination. The absorption and emission
spectra clearly demonstrate a large solvatochromic shift without significant broad-
ening of the spectral bands (Fig. 15d , e). The principles behind the wavelength shift
are not yet known. The wavelength-shifting of plasmonic metal nanoparticles forms
the basis of localized surface plasmon resonance sensing, a technology which is
useful in detecting single molecules of chemical and biological relevance [ 76 ].
Analogously, we expect that wavelength-shifting of the fluorescent silver clusters
may lead to applications for molecular sensing.