Emission modulation of DNA-templated fluorescent silver nanoclusters by divalent magnesium ion

DNA-templated fluorescent silver nanoclusters (Ag NCs) composed of several or tens of atoms are gaining much interest because of their unique properties and convenient emission tunability by DNA sequence and length. However, the modulation by other factors other than DNA is also dependent on the special DNA secondary structure formation such as i-motif or G-quadruplex that is stimulated by pH or K+. One main observation considered in this work is emission modulation of Ag NCs by divalent Mg2+ during or after the clusters' creation. Tuning the emitting intensities and band positions can be realized by Mg2+ addition for the examined single-stranded DNA (ss-DNA) templates, which is dependent on the addition moment of Mg2+, while only intensity modulation should be achieved for the used double-stranded DNA (ds-DNA). Despite of this discrepancy, Mg2+ addition always induces a lifetime-varied emission state of Ag NCs. The modulated emission still follows the common nature of the previously used DNA sequence- and length-dependent emitting. Efficient screening the negative charges of DNA backbone upon addition of the divalent ion is responsible for the modulation by adaptively accommodating the formed Ag NCs. This strategy could be more advantageous over the emission modulation by DNA sequence and length because a desired emitting could be achieved only by alteration of the electrolyte conditions during or after the Ag NCs' creation.