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Joan van der Waals colloquium - online

Friday 15 January 2021

Optical Microspectroscopy of single Molecules and Nanoparticles

I shall discuss various optical signals from single molecules and single gold nanoparticles. The latter objects interact strongly with light through their plasmon resonance, and are chemically and photochemically very stable. For example, the anti-Stokes photoluminescence spectrum of single gold nanorods is enhanced by pIasmonic effects and depends on the absolute temperature of the particles. This spectrum can be used as an absolute thermometer, providing the actual temperature of single particles under the optical microscope.
The sensitivity of photothermal contrast can be pushed to the detection of photosensitive individual molecules such as organic conjugated polymers. We recently used a circularly polarized heating beam to probe the circular dichroism and the chirality of single nanoparticles.
The strong optical near field close to the tips of gold nanorods enhances coupling to optical waves, both for excitation and for emission, and make the surface plasmon resonance sensitive to refractive index changes in the environment. Non-absorbing protein molecules can thus be detected individually by their polarizability only, without need for fluorescent or absorbing labeling.
Finally, plasmonic field enhancement in the near field of gold nanoparticles makes it possible to detect the fluorescence signals of weakly emitting absorbers such as dyes with low quantum yields for fluorescence. We have shown that the redox activity of single molecules can be monitored in real time, exhibiting the redox cycles of individual dye molecules or of single protein molecules.

LION Physics Image Award

Before Michel Orrit's talk, the winner of LION Image Award, carefully selected by a professional jury, will be announced.

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