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Thermophoretic forces on DNA measured with a single-molecule spring balance
Jonas N Pedersen1, Christopher J Lüscher1, Rodolphe Marie1
1Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Lyngby, Denmark.
Physical Review Letters
|January 24, 2015
Summary
Researchers measured DNA molecule thermophoresis using the molecule as an entropic spring. This novel method revealed forces 11x stronger than bulk measurements, offering precise Soret coefficient data.
Area of Science:
- Biophysics
- Physical Chemistry
- Materials Science
Background:
- Thermophoresis, the movement of molecules in response to a temperature gradient, is crucial for understanding DNA behavior in solution.
- Previous studies on DNA thermophoresis often used indirect methods or were limited by the molecule's ability to shield itself in bulk solutions.
- Measuring forces at the single-molecule level provides direct insights into these complex interactions.
Purpose of the Study:
- To directly measure the thermophoretic forces acting on a single DNA molecule.
- To investigate how confinement in a nanochannel affects DNA thermophoresis compared to bulk conditions.
- To determine the Soret coefficient of DNA with high precision across various ionic strengths.
Main Methods:
- Utilizing a single DNA molecule as an entropic spring to measure thermophoretic forces.
- Calibrating the entropic spring by analyzing the molecule's Brownian motion within a nanochannel.
- Employing a static configuration to measure forces up to 130 fN.
Main Results:
- Observed thermophoretic forces up to 130 fN, which is eleven times stronger than forces in bulk solution.
- Demonstrated that confinement in a nanochannel significantly enhances thermophoretic forces on DNA.
- Stretched the DNA molecule up to 80% of its contour length due to the measured forces.
- Determined the Soret coefficient per unit length of DNA at various ionic strengths with high precision.
Conclusions:
- Direct single-molecule force measurements provide unprecedented accuracy for studying DNA thermophoresis.
- Confinement effects in nanochannels dramatically amplify thermophoretic forces, challenging previous assumptions.
- The obtained Soret coefficient data align with existing thermodynamic models and bulk measurements for short DNA fragments.
