DNA Stabilizes Eight-Electron Superatom Silver Nanoclusters with Broadband Downconversion and Microsecond-Lived Luminescence

Abstract

DNA oligomers are known to serve as stabilizing ligands for silver nanoclusters (Ag N -DNAs) with rod-like nanocluster geometries and nanosecond-lived fluorescence. Here, we report two Ag N -DNAs that possess distinctly different structural properties and are the first to exhibit only microsecond-lived luminescence. These emitters are characterized by significant broadband downconversion from the ultraviolet/visible to the near-infrared region. Circular dichroism spectroscopy shows that the structures of these two Ag N -DNAs differ significantly from previously reported Ag N -DNAs. We find that these nanoclusters contain eight valence electrons, making them the first reported DNA-stabilized luminescent quasi-spherical superatoms. This work demonstrates the important role that nanocluster composition and geometry play in dictating luminescence properties of Ag N -DNAs and significantly expands the space of structure–property relations that can be achieved for Ag N -DNAs.

Chloride ligands on DNA-stabilized silver nanoclusters

“…These peaks also do not correspond to higher mass adducts of AgN-DNA species with Na + or NH4 + , which are commonly observed in ESI-MS for AgN-DNAs and other DNA complexes. 9,32 Instead, the experimental mass spectrum matches the predicted isotopic distribution for a product composed of two DNA strands, 16 Ag atoms, and two Cl atoms, with a total nanocluster charge of q = 8: (DNA)2[Ag16Cl2] 8+ . This corresponds to a nanocluster with N0 = 6 effective valence electrons.…”

“…DNA-stabilized silver nanoclusters (AgN-DNAs) are a diverse class of emitters that hold promise for bioimaging and biosensing. [1][2][3] AgN-DNAs have been reported with wide-ranging emission wavelengths from 400 nm to 1,200 nm, 4,5 emission lifetimes from nanoseconds to microseconds, [6][7][8][9] and favorably high quantum yields and extinction coefficients. [10][11][12] The combinatorial nature of DNA ligand sequence is responsible for the diversity of AgN-DNA emitters, with nucleobase sequence selecting AgN composition and photophysical properties.…”

Mapping H+ in the Nanoscale (A2C4)2-Ag8 Fluorophore

“…Neutral silver atoms bind weakly with DNA with little charge redistribution, so we suggest that Ag + adducts could acidify the C6-NH 2 and C4-NH 2 groups . Our calorimetry studies suggest that 5 of the 8 silvers in (A 2 C 4 ) 2 -Ag 8 may be Ag + , consistent with other oxidized clusters such as Ag 6 4+ , Ag 10 6+ , Ag 17 9+ , and Ag 30 18+ . ,− Thus, we expect Ag + in a partially oxidized Ag 8 cluster could acidify the adenines and cytosines.…”

“…This sub-duplex shares key structural features with other DNA complexes with oxidized silvers: Ag + –DNA bond lengths of 2.1–2.2 Å, N–Ag + –N bond angles of 164°–176°, and base pairs twisted by 30°–60°. − Here, we consider thermodynamic similarities by reacting Ag + with a A 2 C 4 duplex and measuring the Ag + stoichiometry and affinity using isothermal titration calorimetry. This reaction was considered because silver cluster chromophores, such as the green emitting Ag 10 6+ and the near-infrared emitting Ag 30 18+ , can be significantly oxidized. ,− We consider that the Ag + and Ag 0 may be distinct components within a DNA–cluster complex . To mimic the (A 2 C 4 ) 2 duplex observed in the crystal structure, two A 2 C 4 strands were covalently linked via an inert triethylene glycol (see the inset in Figure ).…”

Chloride Ligands on DNA-Stabilized Silver Nanoclusters

“…13,14,29 A newly reported class of Ag N -DNAs with a spherical superatomic magic number N 0 = 8 exhibits distinct UV−vis spectra and microsecond-lived luminescence rather than fluorescence. 12 Thus, it is clear that N 0 plays an important role in the Ag N -DNA electronic structure. The first X-ray crystal structures of Ag N -DNAs were recently published, 7,31−34 providing the exciting possibility of theoretically solving the electronic structure of Ag N -DNAs for the first time.…”