Sequence programmed DNA three-way junctions for templated assembly of fluorescent silver nanoclusters

Area of Science:

• Nanotechnology
• Biochemistry
• Materials Science

Background:

• DNA-templated silver nanoclusters (AgNCs) are promising label-free fluorophores.
• Existing DNA-nanocluster designs often use overhangs or loops on duplex strands.
• A need exists for novel DNA structures to template stable and tunable AgNCs.

Purpose of the Study:

• To report a new design strategy for sequence-programmed DNA three-way junctions (DNA-3WJ) for AgNC formation.
• To investigate the role of unhybridized cytosine nucleobases in the DNA-3WJ center for AgNC stabilization.
• To explore how DNA-3WJ structure influences AgNC optical properties and metal ion sensing capabilities.

Main Methods:

• Synthesis of DNA three-way junctions with varying central cytosine base content.
• Formation and characterization of silver nanoclusters using spectroscopic (e.g., fluorescence spectroscopy) and microscopic techniques.
• Evaluation of fluorescence quantum yield, emission maxima, and metal ion selectivity (specifically Hg2+).

Main Results:

• DNA-3WJs with central unhybridized cytosine bases successfully templated fluorescent AgNCs.
• A specific construct (3WJ20-C12) showed an emission maximum around 630 nm and a 12% quantum yield.
• Control DNA-3WJs lacking sufficient central cytosines did not form fluorescent AgNCs, confirming cytosine's role.
• The duplex arms of the DNA-3WJs modulated the fluorescent properties of the AgNCs.
• The 3WJ20-C12/AgNCs demonstrated selective and sensitive detection of Hg2+ in the nanomolar range.

Conclusions:

• Sequence-programmed DNA three-way junctions provide a robust platform for creating stable, fluorescent silver nanoclusters.
• Unhybridized central cytosine bases are critical for the formation and stabilization of these AgNCs.
• This DNA-3WJ-templated AgNC system offers potential for label-free fluorophore applications and selective metal ion sensing.