Abstract
DNA-stabilized silver clusters (Ag-DNA) show excellent promise as a multi-functional nanoagent for molecular investigations in living cells. The unique properties of these fluorescent nanomaterials allow for intracellular optical sensors with tunable cytotoxicity based on simple modifications of the DNA sequences. Three Ag-DNA nanoagent designs are investigated, exhibiting optical responses to the intracellular environments and sensing-capability of ions, functional inside living cells. Their sequence-dependent fluorescence responses inside living cells include (1) a strong splitting of the fluorescence peak for a DNA hairpin construct, (2) an excitation and emission shift of up to 120 nm for a single-stranded DNA construct, and (3) a sequence robust in fluorescence properties. Additionally, the cytotoxicity of these Ag-DNA constructs is tunable, ranging from highly cytotoxic to biocompatible Ag-DNA, independent of their optical sensing capability. Thus, Ag-DNA represents a versatile live-cell nanoagent addressable towards anti-cancer, patient-specific and anti-bacterial applications.
Highlights
DNA-encapsulated silver nanoclusters (Ag-DNA) have recently attracted much attention, as they exhibit numerous unique fluorescence properties, like high photostability, fluorescence quantum yields of up to 90% and tunable excitation and emission spectra[1,2,3,4,5,6]
The DNA template, consisting of 28 single bases, yields an Ag-DNA construct (Ag-28b in Fig. 1b) with strong and stable fluorescence properties[35], which we show are retained upon insertion into living cells
We demonstrate that a simple modification of Ag-28b produces an Ag-DNA construct which shows optical sensor functionality inside living cells: shortening the 28b sequence by nine bases produces the Ag-19b construct[44] (Fig. 1c), which exhibits an optical response to the intracellular environment
Summary
DNA-encapsulated silver nanoclusters (Ag-DNA) have recently attracted much attention, as they exhibit numerous unique fluorescence properties, like high photostability, fluorescence quantum yields of up to 90% and tunable excitation and emission spectra[1,2,3,4,5,6]. As nano-sized silver is highly bioactive, its broad utilization bears a potential risk for humans[28,29,30], making a more controlled and tunable way of its application appealing These fluorescent Ag-DNA nanomaterials are compatible with DNA nanotechnology and DNA origami, and provide an easy attachment site for specific addition of desired targets and recognition elements. Fluorescent Ag-DNA are synthesized upon reduction of silver ions by sodium borohydride (NaBH4) in the presence of DNA (Fig. 1a), resulting in rod-shaped silver cores comprised of 4–12 neutral Ag atoms[35,36] These nanomaterials can exhibit peak emission wavelengths across the visible and near-IR spectrum[37]. DNA sequences color code are displayed for (b) Ag-28b, (c) Ag-19b and (d) Ag-HP by Cytosine =yellow, Guanine =green, Thymine =blue, Adenine =red
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