Probing Local Folding Allows Robust Metal Sensing Based on a Na⁺ -Specific DNAzyme

Area of Science:

• Biochemistry
• Molecular Biology
• Chemical Sensing

Background:

• Fluorescent DNA-based metal sensors face challenges with specificity due to non-specific metal-DNA interactions.
• Existing methods often rely on distance changes or local fluorophore environments, which can be confounded by various binding mechanisms.

Purpose of the Study:

• To compare two signaling strategies for a sodium ion (Na+)-specific DNAzyme sensor.
• To investigate the impact of systematically shortening DNAzyme duplex regions on sensor performance.
• To design a more robust and specific metal ion sensor.

Main Methods:

• Utilized a 2-aminopurine (2AP)-labeled substrate strand to monitor Na+ binding effects on local fluorescence.
• Systematically varied the length of duplex regions in the DNAzyme.
• Designed a Förster Resonance Energy Transfer (FRET)-based sensor by labeling opposite ends of the DNAzyme.

Main Results:

• Na+ binding enhanced 2AP fluorescence, indicating a change in its local environment.
• A synergistic effect between Na+ binding and duplex formation at the 5'-end was observed, with optimal binding at a five base-pair stem.
• The 3'-end showed a more continuous response, requiring stem formation before Na+ binding.
• The FRET-based sensor could not distinguish Na+ from Li+ or K+, suggesting local environment probing is superior for specificity.

Conclusions:

• Probing local environmental changes near a fluorophore provides more robust and specific metal ion sensing compared to FRET-based distance measurements.
• Optimizing the DNAzyme structure, particularly the stem length and substrate binding arm, is crucial for effective Na+ sensing.
• The findings offer insights into designing highly specific DNA-based sensors for various metal ions.