Prashant Jain, from Dr. Mostafa El-Sayed's research group, won the best graduate research poster given by the Physical Chemistry Division of the American
Chemical Society at the 231st ACS National Meeting in Atlanta, March 26-30, 2006. This award also included a $300 prize.

The title of his poster was "Ultrafast spectroscopy of the femtosecond pulse-initiated Au-S bond
dissociation in gold nanoparticle-thiolated DNA conjugates," by Prashant K. Jain, Wei Qian and Mostafa A. El-Sayed.

Using UV-Visible extinction spectroscopy and femtosecond pump-probe transient absorption spectroscopy, we have studied the effect of femtosecond laser heating of gold nanoparticles attached to DNA ligands via thiol groups. It is found that femtosecond pulse excitation of the DNA-modified nanoparticles at a wavelength of 400 nm leads to desorption of the thiolated DNA strands from the nanoparticle surface by the dissociation of the gold-sulfur bond. The laser initiated gold-sulfur bond breaking process is a new pathway for the nonradiative relaxation of the optically excited electrons within the DNA-modified nanoparticles, as manifested by a faster decay rate of the excited electronic distribution at progressively higher laser pulse energies. Kinetic and thermodynamic considerations favor the role of hot electron-initiated surface phonons of the nanoparticles as a source for the bond dissociation process, over the conventional phonon-phonon thermal heating processes. The latter processes have been observed previously by our group to be effective in the selective photothermal destruction of cancer cells bound to anti-EGFR-conjugated gold nanoparticles.

Congratulations, Prashant!