Base-Directed Formation of Fluorescent Silver Clusters

Abstract

Small silver clusters that form with short oligonucleotides are distinguished by their strong fluorescence. Previous work showed that red and blue/green emitting species form with the cytosine oligonucleotide dC12. To understand how the bases and base sequence influence cluster formation, the blue/green emitting clusters that form with the thymine-containing oligonucleotides dT12, dT4C4T4, and dC4T4C4 are discussed. With dT12 and dT4C4T4, variations in the solution pH establish that the clusters associate with the N3 of thymine. The small clusters are bound to the larger DNA template, as demonstrated by fluorescence anisotropy, circular dichroism, and fluorescence correlation spectroscopy (FCS) studies. For dT4C4T4, FCS studies showed that approximately 50% of the strands are labeled with the fluorescent clusters. Absorption spectra and the gas dependence of the fluorescence show that nonfluorescent clusters also form following the reduction of the silver cation – oligonucleotide conjugates. Fluorescent cluster formation is favored by oxygen, thus indicating that the DNA-bound clusters are partially oxidized. To elaborate the sequence dependence of cluster formation, dC4T4C4 was studied. Cluster formation depends on the oligonucleotide concentration, and higher concentrations favor a red emitting species. A blue/green emissive species dominates at lower concentrations of dC4T4C4, and it has spectroscopic, physical, and chemical properties that are similar to those of the clusters that form with dT12 and dT4C4T4. These results suggest that cytosine- and thymine-containing oligonucleotides stabilize a preferred emissive silver cluster.

DNA-stabilized, fluorescent, metal nanoclusters for biosensor development

“…For this reason, poly-T DNA templated synthesis was reported only at pH 11 [40]. The N7 position in A and G are high affinity metal binding sites, where other nitrogens in the purine rings can also contribute to metal coordination [41,42].…”

“…It needs to be noted that partial oxidation is often needed for luminescence. In an experiment where oxygen was completely removed, the resulting AgNC was non-fluorescent [40].…”

Research Update: Density functional theory investigation of the interactions of silver nanoclusters with guanine

“…[1][2][3] Small sized metal nanoclusters (with diameters up to around 2 nm) are considered to be brighter and more photostable fluorophores [4][5][6][7][8][9][10][11] compared to existing organic dyes as well as smaller and less toxic compared to quantum dots. 12 In particular, silver nanoclusters (AgNCs) are of interest, and these systems involve stabilizing ligands to prevent them from oxidation and aggregation.…”

Correlation of photobleaching, oxidation and metal induced fluorescence quenching of DNA-templated silver nanoclusters

“…[44][45][46] In some cases, oxygen was identified as a requirement to produce fluorescent AgNCs; in an oxygen-free condition, only non-fluorescent species was produced. 47 Finally, 3 many AgNCs have relatively low photostability. 44,48,49 In this work, we take the advantage that AgNCs of different emission colors can be produced using different DNA sequences and prepared a total of eight AgNCs.…”