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A molecular ruler based on plasmon coupling of single gold and silver nanoparticles


Förster Resonance Energy Transfer has served as a molecular ruler that reports conformational changes and intramolecular distances of single biomolecules1,2,3,4. However, such rulers suffer from low and fluctuating signal intensities, limited observation time due to photobleaching, and an upper distance limit of 10 nm. Noble metal nanoparticles have plasmon resonances in the visible range and do not blink or bleach. They have been employed as alternative probes to overcome the limitations of organic fluorophores5,6, and the coupling of plasmons in nearby particles has been exploited to detect particle aggregation by a distinct color change in bulk experiments7,8,9. Here we demonstrate that plasmon coupling can be used to monitor distances between single pairs of gold and silver nanoparticles. We followed the directed assembly of gold and silver nanoparticle dimers in real time and studied the kinetics of single DNA hybridization events. These 'plasmon rulers' allowed us to continuously monitor separations of up to 70 nm for >3,000 s.

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We acknowledge financial support through the Alexander von Humboldt Foundation (C.S.), the Otto A. Wipprecht Foundation (B.M.R.), Deutsche Forschungsgemeinschaft (B.M.R.), US Department of Energy contracts DE-AC03-76SF00098 and W-7405-ENG-36.

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Competing interests

The authors declare no competing financial interests.

Correspondence to Jan Liphardt or A Paul Alivisatos.

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Supplementary Fig. 1

Control experiments (PDF 413 kb)

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Figure 1: Color effect on directed assembly of DNA-functionalized gold and silver nanoparticles.
Figure 2: Effect of buffer exchange.
Figure 3: Spectral shift upon DNA hybridization.