Fragmentation patterns of DNA-stabilized silver nanoclusters under mass spectrometry.

DNA-stabilized silver nanoclusters (Ag-DNAs) are emitters with tuneable structures and photophysical properties. While understanding of the sequence-structure-property relationships of Ag-DNAs has advanced significantly, their chemical transformations and degradation pathways are far less understood. To advance understanding of these pathways, we analysed the fragmentation products of 21 different red and NIR Ag-DNAs using negative ion mode electrospray ionization mass spectrometry (ESI-MS). Ag-DNAs were found to lose Ag under ESI-MS conditions, and sufficient loss of silver atoms can lead to a transition to a lesser number of effective valence electrons, . Of more than 400 mass spectral peaks analysed, only even values of were identified, suggesting that solution-phase Ag-DNAs with odd values of are unlikely to be stable. Ag-DNAs stabilized by three DNA strands were found to fragment significantly more than Ag-DNAs stabilized by two DNA strands. Moreover, the fragmentation behaviour depends strongly on the DNA template sequence, with diverse fragmentation patterns even for Ag-DNAs with similar molecular formulae. Molecular dynamics simulations, with forces calculated from density functional theory, of the fragmentation of (DNA)(AgCl) with a known crystal structure show that the 6-electron AgCl core fragments into a 4-electron Ag and a 2-electron Ag, preserving electron-pairing rules even at early stages of the fragmentation process, in agreement with experimental observation. These findings provide new insights into the mechanisms by which Ag-DNAs degrade and transform, with relevance for their applications in sensing and biomedical applications.