Few-Atom Silver Clusters as Fluorescent Reporters - Advanced Fluorescence Reporters in Chemistry and Biology - page 325

Fig. 12 (a) Image of PMAA-protected fluorescent silver clusters prepared with increasing initial
ratio Ag + :MAA from 0.5:1 to 12:1 and equal irradiation time. (b) Absorption spectra of the same
samples as in (a). (c) Variation of absorption maxima of some of the samples in (a) with molar
ratio. Black arrows indicate how the absorption band shifts to the blue with the addition of extra
polymer to a fluorescent cluster solution explaining the transfer effect of silver clusters among
PMAA chains [ 20 ]
5 Silver Clusters as Fluorescent Probes for Molecular Sensors
The silver clusters can be applied as fluorescent probes to retrieve information
about the chemical environment. There are reported three classes of sensors based
on silver clusters. First, we discuss silver cluster sensors of which the fluorescence
quenches in the presence of the analyte. Second, we discuss a sensor in which
fluorescent clusters are formed only in presence of the analyte. Finally, we discuss
the shift in the absorption and fluorescence bands of silver clusters while sensing the
chemical environment.
5.1 Quenching
Quenching of silver cluster fluorescence is suitable to detect the presence of small
analytes such as cysteine [ 70 ] and metal ions [ 71 - 73 ]. Sensing is possible with a
low detection limit and high selectivity. Interestingly, Guo et al. show selectivity
for Hg 2+ , not for Cu 2+ [ 72 ], whereas Lan et al. show the selectivity for Cu 2+ , not for
Hg 2+ [ 73 ]. This may seem at first sight a discrepancy; however, both papers use a
different DNA sequence leading to a different type of emitter. It shows that the
properties of a specific type of silver cluster cannot always be generalized to all
silver clusters. Figure 13 shows the case of cysteine detection, in which the silver