DNA Scaffolded Silver Clusters: A Critical Study

Abstract

Fluorescent silver nanoclusters (Ag-NCs) are in prominence as novel sensing materials due to their biocompatibility, photostability, and molecule-like optical properties. The present work is carried out on an array (17 sequences) of 16 bases long cytosine rich, single stranded DNA templates 5′-C3XiC3XiiC3XiiiC3Xiv-3′ where i, ii, iii, iv correspond to T/G/C deoxynucleobases (with default base A). Among all the oligonucleotides, a sequence C3AC3AC3TC3G (3T4G) has been identified, which grows three different near-infrared-emitting NC species with absorption/emission maxima at ~620/700 (species I), 730/800 (species II), and 830 (Species III) nm, respectively. The nature of the spectral profiles, along with relevant parameters namely absorption maximum (\(\lambda_{abs}^{max}\)), emission maximum (\(\lambda_{em}^{max}\)), anisotropy (r), lifetime (\(\tau\)), circular dichroism spectral data are used to understand the microenvironments of the fluorescent NC species I, II, and III. DNA:Ag stiochiometric, pH and solvent dependent studies proved that i-motif scaffolds with different folding topologies are associated with the growth of these three species and a certain concentration of silver and H+ favor the growth of species III. Size exclusion chromatographic measurements provided similar indications that a folded, more compact, classic i-motif template is associated with the formation of the longer NIR (~830 nm) absorbing species. This study provides a more definitive approach to design and obtain a targeted DNA templated Ag-NC with required emission properties for biophysical and cellular applications.

Keywords

• i-motif
• microenvironment
• circular dichroism
• fluorescence
• size exclusion chromatography