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| - Ultrafast Cooling of Photoexcited Electrons in GoldNanoparticle−Thiolated DNA Conjugates Involves theDissociation of the Gold−Thiol Bond
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| - Using UV−visible extinction spectroscopy and femtosecond pump−probe transient absorptionspectroscopy, we have studied the effect of femtosecond laser heating on gold nanoparticles attached toDNA ligands via thiol groups. It is found that femtosecond pulse excitation of the DNA-modified nanoparticlesat a wavelength of 400 nm leads to desorption of the thiolated DNA strands from the nanoparticle surfaceby the dissociation of the gold−sulfur bond. The laser-initiated gold−sulfur bond-breaking process is anew pathway for nonradiative relaxation of the optically excited electrons within the DNA-modified goldnanoparticles, as manifested by a faster decay rate of the excited electronic distribution at progressivelyhigher laser pulse energies. The experimental results favor a bond dissociation mechanism involving thecoupling between the photoexcited electrons of the nanoparticles and the gold−sulfur bond vibrations overone involving the conventional phonon−phonon thermal heating processes. The latter processes havebeen observed previously by our group to be effective in the selective photothermal destruction of cancercells bound to anti-epidermal growth factor receptor-conjugated gold nanoparticles.
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